Course Material for Unit - I

Name of the Course : Manufacturing Technology

Name of the Unit : Theory of Metal Cutting

Name of the Topic : Introduction, mechanics of metal cutting –Chip

formation, Types of Chips, Cutting force
calculations.

 Objectives: To understand the concepts of metal cutting.

1. Outcomes: Upon successful completion, the student should be able to

Understand the mechanics of metal cutting process

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. The following parameters determine the model of continuous chip formation:
1. True feed 2. Cutting velocity 3. Chip thickness
4. Rake angle of the cutting tool.
The parameters which govern the value of shear angle would include
(a) 1,2 and 3
(b) 1,3 and 4
(c) 1,2 and 4
(d) 2,3 and 4.

2. Plain milling of mild steel plate produces

(a) irregular shaped discontinuous chips
(b) regular shaped discontinuous chip
(c) continuous chips without built up edge
(d) joined chips
3. During machining, excess metal is removed in the form of chip as in the case of turning on
a lathe. Which of the following are correct?
Continuous ribbon like chip is formed when turning
a. at a higher cutting speed 3. a brittle material
b. at a lower cutting speed 4. a ductile material
Select the correct answer using the code given below:
(a) 1 and 3
(b) 1 and 4
(c) 2 and 3
(d) 2 and 4

4. Friction at the tool-chip interface can be reduced by

(a) decreasing the rake angle
(b) increasing the depth of cut
(c) decreasing the cutting speed
(d) increasing the cutting speed

5. In orthogonal cutting, shear angle is the angle between

(a) shear plane and the cutting velocity
(b) shear plane and the rake plane
(c) shear plane and the vertical direction
(d) shear plane and the direction of elongation of crystals in the chip

6. In a machining operation chip thickness ratio is 0.3 and the back rake angle of the tool is
10°. What is the value of the shear strain?
(a) 0.31
(b) 0.13
(c) 3.00
(d) 3.34
7. The rake angle of a cutting tool is 15°, shear angle 45° and cutting velocity 35 m/min.
What is the velocity of chip along the tool face?
(a) 28.5 m/min
(b) 27.3 m/min
(c) 25.3 m/min
(d) 23.5 m/min

8. In orthogonal cutting, the depth of cut is 0.5 mm at a cutting speed of 2 m/s. If the chip
thickness is 0.75 mm, the chip velocity is
(a) 1.33 m/s
(b) 2 m/s
(c) 2.5 m/s
(d) 3 m/s

9. The cutting velocity in m/sec, for turning a work piece of diameter 100 mm at the spindle
speed of 480 RPM is
(a) 1.26
(b) 2.51
(c) 48
(d) 151

10. In orthogonal turning of a low carbon steel bar of diameter 150 mm with uncoated
carbide tool, the cutting velocity is 90 m/min. The feed is 0.24 mm/rev and the depth of cut is
2 mm. The chip thickness obtained is 0.48 mm. If the orthogonal rake angle is zero and the
principal cutting edge angle is 90°, the shear angle is degree is
(a) 20.56
(b) 26.56
(c) 30.56
(d) 36.56
Machining: Term applied to all material-removal processes
Metal cutting: The process in which a thin layer of excess metal (chip) is removed by a
wedge-shaped single-point or multipoint cutting tool with defined geometry from a work
piece, through a process of extensive plastic deformation.
3. MECHANICS OF CHIP FORMATION
The cutting itself is a process of extensive plastic deformation to form a chip that is removed
afterward. The basic mechanism of chip formation is essentially the same for all machining
operations. Assuming that the cutting action is continuous, we can develop so-called
continuous model of cutting process.

4. Forces in machining
If you make a free body analysis of the chip, forces acting on the chip would be as follows.

At cutting tool side due to motion of chip against tool there will be a frictional force and a
normal force to support that. At material side thickness of the metal increases while it flows
from uncut to cut portion. This thickness increase is due to inter planar slip between different
metal layers. There should be a shear force (Fs) to support this phenomenon. According to
shear plane theory this metal layer slip happens at single plane called shear plane. So shear
force acts on shear plane. Angle of shear plane can approximately be determined using shear
plane theory analysis. It is as follows
 Forces acting on the chip on tool side and shear plane side
Shear force on shear plane can be determined using shear strain rate and properties of
material. A normal force (Fn) is also present perpendicular to shear plane. The resultant
force(R) at cutting tool side and metal side should balance each other in order to make the
chip in equilibrium. Direction of resultant force, R is determined as shown in Figure.

5. Types of chip
There are three types of chips that are commonly produced in cutting,
Discontinuous chips
Continuous chips
Continuous chips with built up edge
A discontinuous chip comes off as small chunks or particles. When we get this chip it may
indicate,
Brittle work material
Small or negative rake angles Coarse feeds and low speeds
A continuous chip looks like a long ribbon with a smooth shining surface. This chip type may
indicate,
Ductile work materials
Large positive rake angles
Fine feeds and high speeds
Continuous chips with a built up edge still look like a long ribbon, but the surface is no
longer smooth and shining. Under some circumstances (low cutting speeds of ~0.5 m/s, small
or negative rake angles),
Work materials like mild steel, aluminium, cast iron, etc., tend to develop so-called built-up
edge, a very hardened layer of work material attached to the tool face, which tends to act as a
cutting edge itself replacing the real cutting tool edge. The built-up edge tends to grow until it
reaches a critical size (~0.3 mm) and then passes off with the chip, leaving small fragments
on the machining surface. Chip will break free and cutting forces are smaller, but the effects
is a rough machined surface. The built-up edge disappears at high cutting speeds.

5.1 Chip control

Discontinuous chips are generally desired because They are less dangerous for the operator
Do not cause damage to workpiece surface and machine tool Can be easily removed from the
work zone
Can be easily handled and disposed after machining.

There are three principle methods to produce the favourable discontinuous chip: Proper
selection of cutting conditions
Use of chip breakers
Change in the work material properties

5.2 Chip breaker

Chip break and chip curl may be promoted by use of a so-called chip breaker. There are two
types of chip breakers
External type, an inclined obstruction clamped to the tool face
Integral type, a groove ground into the tool face or bulges formed onto the tool face

Test after completion

1. The effect of rake angle on the mean friction angle in machining can be explained by
(a) sliding (coulomb) model of friction
(b) sticking and then siding model of friction
(c) sticking friction
(d) sliding and then sticking model of friction
2. During orthogonal cutting of mild steel with a 10° rake angle tool, the chip thickness ratio
was obtained as 0.4. The shear angle (in degrees) evaluated from this data is
(a) 6.53
(b) 20.22
(c) 22.94
(d) 50.00

3. In an orthogonal machining operation, the chip thickness and the uncut thickness are equal
to 0.45 mm. If the tool rake angle is 0°, the shear plane angle is
(a) 45°
(b) 30°
(c) 18°
(d) 60°

4. Thrust force will increase with the increase in

(a) side cutting edge angle
(b) tool nose radius
(c) rake angle
(d) end cutting edge angle.

5. In orthogonal cutting test, the cutting force = 900 N, the thrust force = 600 N and chip
shear angle is 30o. Then the chip shear force is
(a) 1079.4 N
(b) 969.6 N
(c) 479.4 N
(d) 69.6 N
 Conclusion
 The geometry of the chips being formed at the cutting zone follow a particular pattern
especially in machining ductile materials.
 The major sections of the engineering materials being machined are ductile in nature;
even some semi-ductile or semi-brittle materials behave ductile under the compressive
forces at the cutting zone during machining.
 The pattern and degree of deformation during chip formation are quantitatively
assessed and expressed by some factors, the values of which indicate about the forces
and energy required for a particular machining work.
 When the cutting tool moves towards the work piece, there occurs a plastic
deformation of the work piece and the metal is separated without any discontinuity
and it moves like a ribbon.
 Ductile chips usually become curled or tend to curl (like clock spring) even in
machining by tools with flat rake surface due to unequal speed of flow of the chip at
its free and generated (rubbed) surfaces and unequal temperature and cooling rate at
those two surfaces.
 Despite advent of several modern cutting tool materials, HSS is still used for its
excellent TRS (transverse rupture strength) and toughness, formability, grindability
and low cost.

Demo Videos
http://youtube.com/watch?v=N2HBxu_zA8E

References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.
 Answers to the assignments with full explanation
Assignment 1
1. Ductile chips usually become curled or tend to curl (like clock spring) even in
machining by tools with flat rake surface due to unequal speed of flow of the chip at
its free and generated (rubbed) surfaces and unequal temperature and cooling rate at
those two surfaces. With the increase in cutting velocity and rake angle (positive) the
radius of curvature increases, which is more dangerous.
2. This is also called as segmental chips. This mostly occurs while cutting brittle
material such as cast iron or low ductile materials. Instead of shearing the metal as it
happens in the previous process, the metal is being fractured like segments of
fragments and they pass over the tool faces.
3. When the cutting tool moves towards the work piece, there occurs a plastic
deformation of the work piece and the metal is separated without any discontinuity
and it moves like a ribbon. The chip moves along the face of the tool. This mostly
occurs while cutting a ductile material. It is desirable to have smaller chip thickness
and higher cutting speed in order to get continuous chips. Lesser power is consumed
while continuous chips are produced. Total life is also mortised in this process.
4. Under such high stress and temperature in between two clean surfaces of metals,
strong bonding may locally take place due to adhesion similar to welding. Such
bonding will be encouraged and accelerated if the chip tool materials have mutual
affinity or solubility.
5. When the cutting tool moves towards the work piece, there occurs a plastic
deformation of the work piece and the metal is separated without any discontinuity
and it moves like a ribbon. The chip moves along the face of the tool. This mostly
occurs while cutting a ductile material. It is desirable to have smaller chip thickness
and higher cutting speed in order to get continuous chips. Lesser power is consumed
while continuous chips are produced. Total life is also mortised in this process.
 Course Material for Unit - I
Name of the Course : Manufacturing Technology

Name of the Unit : Theory of Metal Cutting

Name of the Topic : Torque and Power Calculations in Machining,

nomenclature of single point cutting tool.

 Objectives: To understand the concepts of metal cutting.

1. Outcomes: Upon successful completion, the student should be able to

Understand the mechanics of metal cutting process

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Chip equivalent is increased by

(a) an increases in side-cutting edge angle of tool

(b) an increase in nose radius and side cutting edge angle of tool

(c) increasing the plant area of cut

(d) Increasing the depth of cut.

2. Which of the following is a single point cutting tool?

(a) Hacksaw blade

(b) Milling cutter

(c) Grinding wheel

(d) Parting tool

3. For cutting of brass with single-point cutting tool on a lathe, tool should have

(a) negative rake angle

(b) positive rake angle

(c) zero rake angle

(d) zero side relief angle

4. The angle between the face and the flank of the single point cutting tool is
known as

(a) rake angle

(b) clearance angle

(c) lip angle

(d) point angle.

5. Single point thread cutting tool should ideally have

(a) zero rake

(b) positive rake

(c) negative rake

(d) normal rake.

6. The following tool signature is specified for a single-point cutting tool in

American system:

10, 12, 8, 6, 15, 20, 3

What does the angle 12 represent?

(a) Side cutting-edge angle

(b) Side rake angle

(c) Back rake angle

(d) Side clearance angle

7. Consider the following statements with respect to the effects of a large nose
radius on the tool:

1. It deteriorates surface finish.

2. It increases the possibility of chatter.

3. It improves tool life.

Which of the above statements is/are correct?

(a) 2 only
(b) 3 only

(c) 2 and 3 only

(d) 1, 2 and 3

8. Consider the following machining conditions:

(a) Ductile material.

(b) High cutting speed.

(c) Small rake angle.

(d) Small uncut chip thickness.

9. Consider the following statements:

1. A large rake angle means lower strength of the cutting edge.

2. Cutting torque decreases with rake angle.

Which of the statements given above is/are correct?

(a) Only 1

(b) Only 2

(c) Both 1 and 2

(d) Neither 1 nor 2

10. The angle of inclination of the rake face with respect to the tool base
measured in a plane perpendicular to the base and parallel to the width of the
tool is called

(a) Back rake angle

(b) Side rake angle

(c) Side cutting edge angle

(d) End cutting edge angle

3. Single-point cutting tool
As distinguished from other cutting tools such as a The cutting edge is ground to suit a
particular machining operation and may be re sharpened or reshaped as needed. The
ground tool bit is held rigidly by a tool holder while it is cutting.

Back Rake is to help control the direction of the chip, which naturally curves into the
work due to the difference in length from the outer and inner parts of the cut. It also helps
counteract the pressure against the tool from the work by pulling the tool into the work.
Side Rake along with back rake controls the chip flow and partly counteracts the
resistance of the work to the movement of the cutter and can be optimized to suit the
particular material being cut. Brass for example requires a back and side rake of 0 degrees
while aluminum uses a back rake of 35 degrees and a side rake of 15 degrees. Nose
Radius makes the finish of the cut smoother as it can overlap the previous cut and

eliminate the peaks and valleys that a pointed tool produces. Having a radius also
strengthens the tip, a sharp point being quite fragile.
All the other angles are for clearance in order that no part of the tool besides the actual
cutting edge can touch the work. The front clearance angle is usually 8 degrees while the
side clearance angle is 10-15 degrees and partly depends on the rate of feed expected.
Minimum angles which do the job required are advisable because the tool gets weaker as
the edge gets keener due to the lessening support behind the edge and the reduced ability
to absorb heat generated by cutting.
The Rake angles on the top of the tool need not be precise in order to cut but to cut
efficiently there will be an optimum angle for back and side rake.
4. Cutting tool nomenclature

Back Rake is to help control the direction of the chip, which naturally curves into the
work due to the difference in length from the outer and inner parts of the cut. It also helps
counteract the pressure against the tool from the work by pulling the tool into the work.
Side Rake along with back rake controls the chip flow and partly counteracts the
resistance of the work to the movement of the cutter and can be optimized to suit the
particular material being cut. Brass for example requires a back and side rake of 0 degrees
while aluminum uses a back rake of 35 degrees and a side rake of 15 degrees.
Nose Radius makes the finish of the cut smoother as it can overlap the previous cut and
eliminate the peaks and valleys that a pointed tool produces. Having a radius also
strengthens the tip, a sharp point being quite fragile.
All the other angles are for clearance in order that no part of the tool besides the actual
cutting edge can touch the work. The front clearance angle is usually 8 degrees while the
side clearance angle is 10-15 degrees and partly depends on the rate of feed expected.
Minimum angles which do the job required are advisable because the tool gets weaker as
the edge gets keener due to the lessening support behind the edge and the reduced ability
to absorb heat generated by cutting.
The Rake angles on the top of the tool need not be precise in order to cut but to cut
efficiently there will be an optimum angle for back and side rake.
6. Orthogonal metal cutting

Orthogonal metal cutting Oblique metal cutting

Cutting edge of the tool is The cutting edge is inclined

perpendicular to the direction at an angle less than 90o to
of tool travel. the direction of tool travel.
The direction of chip flow is The chip flows on the tool
perpendicular to the cutting face making an angle.
edge.
The chip coils in a tight flat The chip flows side ways in
spiral a long curl.

For same feed and depth of The cutting force acts on

cut the force which shears larger area and so tool life is
the metal acts on smaller more.
areas. So the life of the tool
is less.
Produces sharp corners. Produces a chamfer at the
end of the cut

Smaller length of cutting For the same depth of cut

edge is in contact with the greater length of cutting edge
work. is in contact with the work.
Generally parting off in This method of cutting is
lathe, broaching and slotting used in almost all machining
operations are done in this operations.
method.

Depending on whether the stress and deformation in cutting occur in a plane (two-
dimensional case) or in the space (three-dimensional case), we consider two principle
types of cutting:
Orthogonal cutting the cutting edge is straight and is set in a position that is perpendicular
to the direction of primary motion. This allows us to deal with stresses and strains that act
in a plane.
Oblique cutting the cutting edge is set at an angle.
According to the number of active cutting edges engaged in cutting, we distinguish again
two types of cutting:
Single-point cutting the cutting tool has only one major cutting edge Examples: turning,
shaping, boring
Multipoint cutting the cutting tool has more than one major cutting edge
Examples: drilling, milling, broaching, reaming. Abrasive machining is by definition a
process of multipoint cutting.
6.1 Cutting conditions
Each machining operation is characterized by cutting conditions, which comprises a set of
three elements:
Cutting velocity: The traveling velocity of the tool relative to the work piece. It is
measured in m/s or m/min.
Depth of cut: The axial projection of the length of the active cutting tool edge, measured
in mm. In orthogonal cutting it is equal to the actual width of cut.
Feed: The relative movement of the tool in order to process the entire surface of the work
piece. In orthogonal cutting it is equal to the thickness of cut and is measured in mm.

7. Evaluation of cutting power consumption and specific energy requirement

Cutting power consumption is a quite important issue and it should always be tried to be
reduced but without sacrificing MRR.
Cutting power consumption (PC) can be determined from, PC = PZ.VC + PX.Vf
where, Vf = feed velocity = Nf / 1000 m/min [N = rpm]
Since both PX and Vf, specially Vf are very small, PX.Vf can be neglected and then PC ≅
PZ.VC
Specific energy requirement (Us) which means amount of energy required to remove unit
volume of material, is an important machinability characteristics of the work material.
Specific energy requirement, Us, which should be tried to be reduced as far as possible,
depends not only on the work material but also the process of the machining, such as
turning, drilling, grinding etc. and the machining condition, i.e., VC, f, tool material and
geometry and cutting fluid application.
Compared to turning, drilling requires higher specific energy for the same work-tool
materials and grinding requires very large amount of specific energy for adverse cutting
edge geometry (large negative rake). Specific energy, Us, is determined from,
Us = PZ.VC / MRR = PZ/ t.f

Test after completion

1. In a machining process, the percentage of heat carried away by the chips is typically
(a) 5%
(b) 25%
(c) 50%
(d) 75%

2. In metal cutting operation, the approximate ratio of heat distributed among chip, tool
and work, in that order is
(a) 80: 10: 10
(b) 33: 33: 33
(c) 20: 60: 10
(d) 10: 10: 80

3. As the cutting speed increases

(a) more heat is transmitted to the workpiece and less heat is transmitted to the tool
(b) more heat is carried away by the chip and less heat is transmitted to the tool
(c) more heat is transmitted to both the chip and the tool
(d) more heat is transmitted to both the workpiece and the tool

4. The heat generated in metal cutting can conveniently be determined by

(a) installing thermocouple on the job
(b) installing thermocouple on the tool
(c) calorimetric set-up
(d) using radiation pyrometer
 5. The primary tool force used in calculating the total power consumption in machining is
the
(a) radial force
(b) tangential force
(c) axial force
(d) frictional force.

Conclusion
 Large rake angle reduces the tool cross section. Hence the amount of heat
absorbed by the tool is also reduced.
 In orthogonal cutting, the tool approaches the workpiece with its cutting edge
parallel to the uncut surface and at right angles to the direction of cutting. Thus
tool approach angle and cutting edge inclination are Zero. This type of cutting is
also known as Two-dimensional Cutting.
 In oblique cutting, the cutting edge of the tool is inclined at an acute angle with
the direction of tool feed or work feed, the chip begin disposed of at a certain
angle. This type of cutting is also called Three-dimensional cutting.
 This system is also called as ASA system; ASA stands for American Standards
Association. Geometry of a cutting tool refers mainly to its several angles or
slopes of its salient working surfaces and cutting edges. Those angles are
expressed with respect to some planes of reference.
 The word tool geometry is basically referred to some specific angles or slope of
the salient faces and edges of the tools at their cutting point. Rake angle and
clearance angle are the most significant for all the cutting tools.

Demo Videos
http://youtube.com/watch?v=iaOqlDuSoNs
References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.
 Answers to the assignments with full explanation
Assignment 2

1. Orthogonal cutting process (Two - dimensional cutting) - The cutting edge or

face of the tool is 900 to the line of action or path of the tool or to the cutting
velocity vector. This cutting involves only two forces and this makes the analysis
simpler.

2. Oblique cutting process (Three - dimensional cutting) - The

cutting edge or face of the tool velocity vector. Its analysis is more difficult of its
three dimensions.
3. The optimum side cutting angle lies between 30 degree to 25
degree. Increase in nose radius improves the tool life since the stress
concentration is lesser for greater nose radius.
4. Relief angle:
- Angle b/w side flank and line perpendicular to base of tool
- If angle is large, cutting edge will break- lack of support
- If angle is small, tool cannot be fed into job- rubbing-
overheating-affect surface finish.

5. Side Cutting Edge angle:

- angle between side cutting edge and side of the tool shank
- controls the chip flow
- Distributing the cutting force.
 Course Material for Unit - I
Name of the Course : Manufacturing Technology

Name of the Unit : Theory of Metal Cutting

Name of the Topic : Tool materials, Influence of tool Geometry, Tool

Life, machining time calculation.

 Objectives: To understand the concepts of metal cutting.

1. Outcomes: Upon successful completion, the student should be able to

Understand the mechanics of metal cutting process

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Tool life in generally specified by

(a) number of pieces machined
(b) volume of metal removed
(c) actual cutting time
(d) any of the above

2. For increasing the material removal rate in turning, without any constraints, what is the
right sequence to adjust the cutting parameters?
1. Speed 2. Feed 3. Depth of cut
Select the correct answer using the code given below
(a) 1- 2- 3
(b) 2- 3- 1
(c) 3- 2- 1
(d) 1- 3- 2
3. Consider the following elements:
1. Nose radius 2. Cutting speed 3. Depth of cut4. Feed
The correct sequence of these elements in DECREASING order of their influence on tool
life is
(a) 2, 4, 3, 1
(b) 4, 2, 3, 1
(c) 2, 4, 1, 3
(d) 4, 2, I, 3

4. In a single-point turning operation of steel with a cemented carbide tool, Taylor's tool
life exponent is 0.25. If the cutting speed is halved, the tool life will increase by
(a) two times
(b) four times
(c) eight times
(d) sixteen times

5. In an orthogonal cutting, the depth of cut is halved and the feed rate is double. If the
chip thickness ratio is unaffected with the changed cutting conditions, the actual chip
thickness will be
(a) doubled
(b) halved
(c) quadrupled
(d) unchanged.

6. Using the Taylor equation VTn = c, calculate the percentage increase in tool life when
the cutting speed is reduced by 50% (n = 0•5 and c = 400)
(a) 300%
(b) 400%
(c) 100%
(d) 50%
7. The approximately variation of the tool life exponent 'n' of cemented carbide tools is
(a) 0.03 to 0.08
(b) 0.08 to 0.20
(c) 0.20 to 0.48
(d) 0.48 to 0.70

8. Which of the following values of index n is associated with carbide tools when
Taylor's tool life equation, V.Tn = constant is applied?
(a) 0.1 to 0.15
(b) 0.2 to 0.4
(c) 0.045 to 0.6
(d) 0.65 to 0.9

9. The tool life increases with the

(a) increase in side cutting edge angle
(b) decrease in side rake angle
(c) decrease in nose radius
(d) decrease in back rake angle.

10. Tool life of 10 hours is obtained when cutting with single point tool at 63 m/min. If
Taylor's constant C = 257.35, tool life on doubling the velocity will be
(a) 5 hours
(b) 25.7 min
(c) 38.3 min
(d) unchanged
3. Cutting tool materials
Requirements
The cutting tool materials must possess a number of important properties to avoid
excessive wear, fracture failure and high temperatures in cutting, the following
characteristics are essential for cutting materials to withstand the heavy conditions of the
cutting process and to produce high quality and economical parts:
Hardness at elevated temperatures (so-called hot hardness) so that hardness and strength
of the tool edge are maintained in high cutting temperatures:
Toughness: ability of the material to absorb energy without failing. Cutting if often
accompanied by impact forces especially if cutting is interrupted, and cutting tool may
fail very soon if it is not strong enough.
Wear resistance: although there is a strong correlation between hot hardness and wear
resistance, later depends on more than just hot hardness. Other important characteristics
include surface finish on the tool, chemical inertness of the tool material with respect to
the work material, and thermal conductivity of the tool material, which affects the
maximum value of the cutting temperature at tool-chip interface.
Cutting tool materials
Carbon Steels
It is the oldest of tool material. The carbon content is 0.6~1.5% with small quantities of
silicon, Chromium, manganese, and vanadium to refine grain size. Maximum hardness is
about HRC 62. This material has low wear resistance and low hot hardness. The use of
these materials now is very limited.
High-speed steel (HSS)
First produced in 1900s. They are highly alloyed with vanadium, cobalt, molybdenum,
tungsten and Chromium added to increase hot hardness and wear resistance. Can be
hardened to various depths by appropriate heat treating up to cold hardness in the range of
HRC 63-65. The cobalt component give the material a hot hardness value much greater
than carbon steels. The high toughness and good wear resistance make HSS suitable for
all type of cutting tools with complex shapes for relatively low to medium cutting speeds.
The most widely used tool material today for taps, drills, reamers, gear tools, end cutters,
slitting, broaches, etc.
Cemented Carbides
Introduced in the 1930s. These are the most important tool materials today because of
their high hot hardness and wear resistance. The main disadvantage of cemented carbides
is their low toughness. These materials are produced by powder metallurgy methods,
sintering grains of tungsten carbide (WC) in a cobalt (Co) matrix (it provides toughness).
There may be other carbides in the mixture, such as titanium carbide (TiC) and/or
tantalum carbide (TaC) in addition to WC.
Ceramics
Ceramic materials are composed primarily of fine-grained, high-purity aluminum oxide
(Al2O3), pressed and sintered with no binder. Two types are available:
White, or cold-pressed ceramics, which consists of only Al2O3 cold pressed into inserts
and sintered at high temperature.
Black, or hot-pressed ceramics, commonly known as cermets (from ceramics and metal).
This material consists of 70% Al2O3 and 30% TiC. Both materials have very high wear
resistance but low toughness; therefore they are suitable only for continuous operations
such as finishing turning of cast iron and steel at very high speeds. There is no occurrence
of built- up edge, and coolants are not required.
Cubic boron nitride (CBN) and synthetic diamonds
Diamond is the hardest substance ever known of all materials. It is used as a coating
material in its polycrystalline form, or as a single-crystal diamond tool for special
applications, such as mirror finishing of non-ferrous materials. Next to diamond, CBN is
the hardest tool material. CBN is used mainly as coating material because it is very
brittle. In spite of diamond, CBN is suitable for cutting ferrous materials.
4. Tool wear and tool life
The life of a cutting tool can be terminated by a number of means, although they fall
broadly into two main categories:
Gradual wearing of certain regions of the face and flank of the cutting tool, and abrupt
tool failure. Considering the more desirable case Πthe life of a cutting tool is therefore
determined by the amount of wear that has occurred on the tool profile and which reduces
the efficiency of cutting to an unacceptable level, or eventually causes tool failure. When
the tool wear reaches an initially accepted amount, there are two options,
To resharpen the tool on a tool grinder, or to replace the tool with a new one.
This second possibility applies in two cases,
When the resource for tool resharpening is exhausted. or
The tool does not allow for resharpening, e.g. in case of the indexable carbide inserts
Wear zones
Gradual wear occurs at three principal locations on a cutting tool. Accordingly, three
main types of tool wear can be distinguished,
Crater wear
Flank wear
Corner wear
Crater wear: consists of a concave section on the tool face formed by the action of the
chip sliding on the surface. Crater wear affects the mechanics of the process increasing
the actual rake angle of the cutting tool and consequently, making cutting easier. At the
same time, the crater wear weakens the tool wedge and increases the possibility for tool
breakage. In general, crater wear is of a relatively small concern.
Flank wear: occurs on the tool flank as a result of friction between the machined surface
of the workpiece and the tool flank. Flank wear appears in the form of so-called wear land
and is measured by the width of this wear land, VB, Flank wear affects to the great extend
the mechanics of cutting. Cutting forces increase significantly with flank wear. If the
amount of flank wear exceeds some critical value (VB > 0.5~0.6 mm), the excessive
cutting force may cause tool failure.
Corner wear: occurs on the tool corner. Can be considered as a part of the wear land and
respectively flank wear since there is no distinguished boundary between the corner wear
and flank wear land. We consider corner wear as a separate wear type because of its
importance for the precision of machining. Corner wear actually shortens the cutting tool
thus increasing gradually the dimension of machined surface and introducing a significant
dimensional error in machining, which can reach values of about 0.03~0.05 mm.
Tool life
Tool wear is a time dependent process. As cutting proceeds, the amount of tool wear
increases gradually. But tool wear must not be allowed to go beyond a certain limit in
order to avoid tool failure. The most important wear type from the process point of view
is the flank wear, therefore the parameter which has to be controlled is the width of flank
wear land, VB. This parameter must not exceed an initially set safe limit, which is about
0.4 mm for carbide cutting tools. The safe limit is referred to as allowable wear land
(wear criterion).
The cutting time required for the cutting tool to develop a flank wear land of width is
called tool life, T, a fundamental parameter in machining. The general relationship of VB
versus cutting time is shown in the figure (so-called wear curve). Although the wear
curve shown is for flank wear, a similar relationship occurs for other wear types. The
figure shows also how to define the tool life T for a given wear criterion VBk
Parameters, which affect the rate of tool wear, are
Cutting conditions (cutting speed V, feed f, depth of cut d)
Cutting tool geometry (tool orthogonal rake angle)
Properties of work material

5. Designation of tool geometry

The geometry of a single point tool is designated or specified by a series of values of the
salient angles and nose radius arranged in a definite sequence as follows:
Designation (Signature) of tool geometry in ASA System - γy, γx, αy, αx, φe, φs, r (in inch)
Example: A tool having 7, 8, 6, 7, 5, 6, 0.1 as designation (Signature) in ASA system will
have the following angles and nose radius.
Back rack angle = 7o
Side rake angle = 8o
Back clearance angle = 6o
Side clearance angle = 7o
End cutting edge angle = 5o
Side cutting edge angle = 6o
Nose radius = 0.1 inch

Test after completion

1. Power consumption in metal cutting is mainly due to
(a) tangential component of the force
(b) longitudinal component of the force
(c) normal component of the force
(d) friction at the metal-tool interface

2. Cutting power consumption in turning can be significantly reduced by

(a) increasing rake angle of the tool
(b) increasing the cutting angles of the tool
(c) widening the nose radius of the tool
(d) increasing the clearance angle

3. Consider the following statements about nose radius

1. It improves tool life 2. It reduces the cutting force 3. It improves the surface finish.
Select the correct answer using the codes given below:
(a) 1 and 2
(b) 2 and 3
(c) 1 and 3
(d) 1, 2 and 3

4. Ease of machining is primarily judged by

(a) life of cutting tool between sharpening
(b) rigidity of work -piece
(c) microstructure of tool material
(d) shape and dimensions of work
 5. Which of the following can be used in dynamometer for measures cutting forces?
1. Strain gauge 2. Piezoelectric transducer
3. Pneumatic transducer 4. Hydraulic transducer
(a) 1 and 2
(b) 1, 3 and 4
(c) 2, 3 and 4
(d) 1, 2, 3 and 4

Conclusion
 The cutting tools need to be capable to meet the growing demands for higher
productivity and economy as well as to machine the exotic materials which are
coming up with the rapid progress in science and technology.
 Advent of HSS in around 1905 made a break through at that time in the history of
cutting tool materials though got later superseded by many other novel tool
materials like cemented carbides and ceramics which could machine much faster
than the HSS tools.
 The basic composition of HSS is 18% W, 4% Cr, 1% V, 0.7% C and rest Fe. Such
HSS tool could machine (turn) mild steel jobs at speed only up to 20 ~ 30 m/min
(which was quite substantial those days).
 It is already mentioned earlier that the properties and performance of HSS tools
could have been sizably improved by refinement of microstructure, powder
metallurgical process of making and surface coating. Recently a unique tool
material, namely Coronite has been developed for making the tools like small and
medium size drills and milling cutters etc. which were earlier essentially made of
HSS.
 In Taylor’s tool life equation, only the effect of variation of cutting velocity, V C
on tool life has been considered.

Demo Videos
http://youtube.com/watch?v=6idqtnSjxLw
References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.
4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 3

1. The enhanced strength, TRS and toughness have made these ZTAs more widely
applicable and more productive than plain ceramics and cermets in machining steels
and cast irons. Fine powder of partially stabilized zirconia (PSZ) is mixed in
proportion of ten to twenty volume percentage with pure alumina, then either cold
pressed and sintered at 16000 C - 17000 C or hot isostatically pressed (HIP) under
suitable temperature and pressure.
2. The properties, performances and application range of alumina based ceramic tools
have been improved spectacularly through drastic increase in fracture toughness (2.5
times), TRS and bulk thermal conductivity, without sacrificing hardness and wear
resistance by mechanically reinforcing the brittle alumina matrix with extremely
strong and stiff silicon carbide whiskers. The randomly oriented, strong and thermally
conductive whiskers enhance the strength and toughness mainly by crack deflection
and crack-bridging and also by reducing the temperature gradient within the tool.
3. Next to diamond, cubic boron nitride is the hardest material presently available. Only
in 1970 and onward CBN in the form of compacts has been introduced as cutting
tools. It is made by bonding a 0.5 - 1 mm layer of polycrystalline cubic boron nitride
to cobalt based carbide substrate at very high temperature and pressure.
4. Wear and hence tool life of any tool for any work material is governed mainly by the
level of the machining parameters i.e., cutting velocity (VC), feed (f) and depth of cut
(t). Cutting velocity affects maximum and depth of cut minimum.
5. Factors affecting tool life
The life of the cutting tool is affected by the following factors:
 Cutting speed.
 Feed and depth of cut.
 Tool geometry.
 Tool material.
 Cutting fluid.
 Work piece material.
 Rigidity of work, tool and machine.
 Course Material for Unit - I
Name of the Course : Manufacturing Technology

Name of the Unit : Theory of Metal Cutting

Name of the Topic : Machinability – evaluating and rating, metal

cutting economics, problems in Merchant’s circle,
tool life, and machining time.

 Objectives: To understand the concepts of metal cutting.

1. Outcomes: Upon successful completion, the student should be able to

Understand the mechanics of metal cutting process

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Consider the following:

1. Tool life
2. Cutting forces
3. Surface finish
Which of the above is/are the machinability criterion/criteria?
(a) 1, 2 and 3
(b) 1 and 3 only
(c) 2 and 3 only
(d) 2 only

2. Which of the following are the machinability criteria?

1. Tool life2. Cutting forces 3. Surface finish
Select the correct answer using the code given below:
(a) 1, 2 and 3
(b) 1 and 2 only
(c) 1 and 3 only
(d) 2 and 3 only
3. Primary object of fuel annealing is to
(a) Increase toughness and yield point
(b) Reduce ductility and resilience
(c) Remove foreign impurities and improve surface finish
(d) Increase ductility and machinability

4. Consider the following criteria in evaluating machinability:

1. Surface finish 2. Type of chips 3. Tool life 4. Power consumption.
In modern high speed CNC machining with coated carbide tools, the correct sequence of
these criteria in DECREASING order of their importance is
(a) 1, 2, 4, 3
(b) 2, 1, 4, 3
(c) 1, 2, 3, 4
(d) 2, 1, 3, 4

5. Which of the following indicate better machinability?

1. Smaller shear angle 2. Higher cutting forces
3. Longer tool life 4. Better surface finish.
(a) 1 and 3
(b) 2 and 4
(c) 1 and 2
(d) 3 and 4

6. Small amounts of which one of the following elements/pairs of elements is added to

steel to increase its machinability?
(a) Nickel
(b) Sulphur and phosphorus
(c) Silicon
(d) Manganese and copper
7. Which of the following pairs regarding the effect of alloying elements in steel are
correctly matched?
1. Molybdenum: Forms abrasion resisting particles.
2. Phosphorus: Improves machinability in free cutting steels.
3. Cobalt: Contributes to red hardness by hardening ferrite.
Select the correct answer using the codes given below:
(a) 2, 3 and 4
(b) 1, 3 and 4
(c) 1, 2 and 4
(d) 1, 2 and 3

8. In low carbon steels, presence of small quantities sulphur improves

(a) weldability
(b) formability
(c) machinability
(d) hardenability

9. The main purpose of spheroidising treatment is to improve

(a) Hardenability of low carbon steel
(b) machinability of low carbon steels
(c) hardenability of high carbon steels
(d) machinability of high carbon steels

10. Consider the following approaches normally applied for the economic analysis of
machining:
1. Maximum production rate 2. Maximum profit criterion 3. Minimum cost criterion
The correct sequence in ascending order of optimum cutting speed obtained by these
approaches is
(a) 1, 2, 3
(b) 1, 3, 2
(c) 3, 2, 1
(d) 3, 1, 2
3. Machinability
Machinability is a term indicating how the work material responds to the cutting process.
In the most general case good machinability means that material is cut with good surface
finish, long tool life, low force and power requirements, and low cost.
Machinability of different materials
Steels Leaded steels: lead acts as a solid lubricant in cutting to improve considerably
machinability.
Resulphurized steels: sulphur forms inclusions that act as stress raisers in the chip
formation zone thus increasing machinability.
Difficult-to-cut steels: a group of steels of low machinability, such as stainless steels, high
manganese steels, precipitation-hardening steels.
Other metals
Aluminium: easy-to-cut material except for some cast aluminium alloys with silicon
content that may be abrasive.
Cast iron: gray cast iron is generally easy-to-cut material, but some modifications and
alloys are abrasive or very hard and may cause various problems in cutting.
Cooper-based alloys: easy to machine metals. Bronzes are more difficult to machine than
brass.
Selection of cutting conditions
For each machining operation, a proper set of cutting conditions must be selected during
the process planning. Decision must be made about all three elements of cutting
conditions,
Depth of cut Feed
Cutting speed
There are two types of machining operations:
Roughing operations: the primary objective of any roughing operation is to remove as
much as possible material from the work piece for as short as possible machining time. In
roughing operation, quality of machining is of a minor concern.

Finishing operations: the purpose of a finishing operation is to achieve the final shape,
dimensional precision, and surface finish of the machined part. Here, the quality is of
major importance. Selection of cutting conditions is made with respect to the type of
machining operation. Cutting conditions should be decided in the order depth of cut - feed
- cutting speed.
4. Merchant’s Circle Diagram and its use
In orthogonal cutting when the chip flows along the orthogonal plane, π0, the cutting force
(resultant) and its components PZ and PXY remain in the orthogonal plane. Fig. 1.39 is
schematically showing the forces acting on a piece of continuous chip coming out from
the shear zone at a constant speed. That chip is apparently in a state of equilibrium.

Fig 1.39 Development of Merchant’s circle diagram

Fig. 1.40 Merchant’s Circle Diagram with cutting forces

 The forces in the chip segment are:
 From job-side:
 Ps - Shear force.
 Pn - force normal to the shear force.
 From the tool side:
 R1 = R (in state of equilibrium)
where, R1 = F + N
N - Force normal to rake face.
F - Friction force at chip tool interface.
The resulting cutting force R or R1 can be resolved further as,
R1 = PZ + PXY
where, PZ - Force along the velocity vector.
PXY - force along orthogonal plane.

The circle(s) drawn taking R or R1 as diameter is called Merchant’s circle which contains all
the force components concerned as intercepts. The two circles with their forces are combined
into one circle having all the forces contained in that as shown by the diagram called
Merchant’s Circle Diagram (MCD) in Fig. 1.40.
The significance of the forces displayed in the Merchant’s Circle Diagram is:
Ps - The shear force essentially required to produce or separate the chip from the parent body
by shear.

The magnitude of PS provides the yield shear strength of the work material under the cutting
action. The values of F and the ratio of F and N indicate the nature and degree of interaction
like friction at the chip tool interface. The force components PX, PY, PZ are generally
obtained by direct measurement. Again PZ helps in determining cutting power and specific
energy requirement. The force components are also required to design the cutting tool and the
machine tool.
1.6.4 Advantageous use of Merchant’s circle diagram
Proper use of MCD enables the followings:
o Easy, quick and reasonably accurate determination of several other forces
from a few known forces involved in machining.

o Friction at chip tool interface and dynamic yield shear strength can be easily
determined.
 o Equations relating the different forces are easily developed.

Some limitations of use of MCD:

o Merchant’s circle diagram (MCD) is only valid for orthogonal cutting.
o By the ratio, F/N, the MCD gives apparent (not actual) coefficient of friction.
o It is based on single shear plane theory.

Test after completion

1. The magnitude of the cutting speed for maximum profit rate must be
(a) in between the speeds for minimum cost and maximum production rate
(b) higher than the speed for maximum production rate
(c) below the speed for minimum cost
(d) equal to the speed for minimum cost

2. In turning, the ratio of the optimum cutting speed for minimum cost and optimum cutting
speed for maximum rate of production is always
(a) equal to 1
(b) in the range of 0.6 to 1
(c) in the range of 0.1 to 0.6
(d) greater than 1

3. In economics of machining, which one of the following costs remains constant?

(a) Machining cost per piece
(b) Tool changing cost per piece
(c) Tool handling cost per piece
(d) Tool cost per piece

4. Consider the following characteristics

1. The cutting edge is normal to the cutting velocity.
2. The cutting forces occur in two directions only.
3. The cutting edge is wider than the depth of cut.
The characteristics applicable to orthogonal cutting would include
(a) 1 and 2
(b) 1 and 3
(c) 2 and 3
(d) 1, 2 and 3

5. In orthogonal turning of medium carbon steel. The specific machining energy is 2.0
J/mm3. The cutting velocity 5 m/min. The main cutting force in N is
(a) 40
(b) 80
(c) 400
(d) 800

Conclusion
 People tried to describe “Machinability” in several ways such as:
o It is generally applied to the machining properties of work material.
o It refers to material (work) response to machining.
o It is the ability of the work material to be machined.
o It indicates how easily and fast a material can be machined.
 Therefore, higher cutting speeds, fine feeds and low depth of cuts or applied to ensure
good surface finish. Usually, it is done in finishing cuts. But, lower cutting speeds,
coarse feeds and heavier depth of cuts are applied in rough cutting operations.
 For R & D purposes, tool life is always assessed or expressed by span of machining
time in minutes, whereas, in industries besides machining time in minutes some other
means are also used to assess tool life, depending upon the situation, such as:
 Number of pieces of work machined.
 Total volume of material removed.
 Total length of cut.
 Tool life generally indicates the amount of satisfactory performance or service
rendered by a fresh tool or a cutting point till it is declared failed.
 Flank wear is a flat portion worn behind the cutting edge which eliminates some
clearance or relief. It takes place when machining brittle materials.
 Demo Videos
http://youtube.com/watch?v=1Y6cShP77-Q
References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 4
1. But it has been agreed, in general, that it is difficult to clearly define and quantify
Machinability. For instance, saying ‘material A is more machinable than material B’
may mean that compared to ‘B’:
 ‘A’ causes lesser tool wear or longer tool life.
 ‘A’ requires lesser cutting forces and power.
 ‘A’ provides better surface finish.
2. Attempts were made to measure or quantify machinability and it was done mostly in
terms of:
o Tool life which substantially influences productivity and economy in
machining.

o Magnitude of cutting forces which affects power consumption and

dimensional accuracy.

o Surface finish which plays role on performance and service life of the
product.

3. The work material properties that generally govern machinability in varying extent
are:
 The basic nature - brittleness or ductility etc.
 Microstructure.
 Mechanical strength - fracture or yield.
 Hardness and hot hardness, hot strength.
 Work hardenability.
 Thermal conductivity
4. Machinability will be considered desirably high when cutting forces, temperature,
surface roughness and tool wear are less, tool life is long and chips are ideally
uniform and short enabling short chip-tool contact length and less friction.
5. Such ease of machining or machinability characteristics of any tool-work pair is to be
judged by:
 Magnitude of the cutting forces.
 Tool wear or tool life.
 Surface finish.
 Magnitude of cutting temperature.
 Chip forms.
 Course Material for Unit - II
Name of the Course : Manufacturing Technology

Name of the Unit : Lathe

Name of the Topic : Centre lathe, constructional features, cutting tool

geometry, various operations, taper turning
methods.

 Objectives: To provide knowledge on various types of lathes used.

1. Outcomes: Upon successful completion, the student should be able to

understand the various types of lathe machines.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. What is the number of jaws in self-centred chuck?

(a) Eight
(b) six
(c) Four
(d) Three

2. The spindle speed range in a general purpose lathe is divided into steps which
approximately follow
(a) arithmetic progression
(b) geometric progression
(c) harmonic progression
(d) logarithmic progression

3. Feed gear box for a screw cutting lathe is designed on the basis of
(a) geometric progression
(b) arithmetic progression
(c) harmonic progression
(d) none.
4. Which one of the following sets of forces are encountered by a lathe parting tool while
groove cutting?
(a) Tangential, radial and axial
(b) Tangential and radial
(c) Tangential and axial
(d) Radial and axial

5. Which one of the following methods should be used for turning internal taper only?
(a) Tailstock offset
(b) Taper attachment
(c) Form tool
(d) Compound rest

6. A 400 mm long shaft has a 100 mm tapered step at the middle with 4° included angle.
The tailstock offset required to produce this taper on a lathe would be
(a) 400 sin 4°
(b) 400 sin 2°
(c) 100 sin 4°
(d) 100 sin 2°

7. A single short thread of pitch 2 mm is to be produced on a lathe having a lead screw

with a double start thread of pitch 4 mm. The ratio of speeds between the spindle and
lead screw for this operation is
(a) 1 : 2
(b) 2: 1
(c) 1: 4
(d) 4: 1
8. It is required to cut screw threads of 2 mm pitch on a lathe. The lead screw has a pitch
of 6 mm. If the spindle speed is 60 rpm, then the speed of the lead screw will be
(a) 10 rpm
(b) 20 rpm
(c) 120 rpm
(d) 180 rpm

9. Which of the following statement is incorrect with reference of lathe cutting tools?
(a) The flank of the tool is the surface below and adjacent to the cutting edges
(b) The nose is the corner, or chamfer joining the side cutting and the end cutting edges
(c) The heel is that part of the which is shaped to produce the cutting edges and face
(d) The base is that surface of the shank which against the support and takes tangent

10. It is required to cut screw threads with double start and 2 mm pitch on a lathe having
lead screw pitch of 6 mm. What is the speed ratio between lathe spindle and lead
screw?
(a) 1 : 3
(b) 3: 1
(c) 2 : 3
(d) 3: 2

3. Center Lathes
A lathe is a machine tool that rotates the work piece against a tool whose position it
controls. The spindle is the part of the lathe that rotates. Various work holding
attachments such as three jaw chucks, collets, and centers can be held in the spindle. The
spindle is driven by an electric motor through a system of belt drives and gear trains.
Spindle rotational speed is controlled by varying the geometry of the drive train.
The tailstock can be used to support the end of the work piece with a center, or to hold
tools for drilling, reaming, threading, or cutting tapers. It can be adjusted in position along
the ways to accommodate different length work pieces. The tailstock barrel can be fed
along the axis of rotation with the tailstock hand wheel.
The carriage controls and supports the cutting tool. It consists of:
A saddle that slides along the ways;
An apron that controls the feed mechanisms;
A cross slide that controls transverse motion of the tool (toward or away from the
operator);
A tool compound that adjusts to permit angular tool movement; v a tool post that holds
the cutting tools.
There are a number of different lathe designs, and some of the most popular are discussed
here.
Centre lathe
The basic, simplest and most versatile lathe.
This machine tool is manually operated that is why it requires skilled operators. Suitable
for low and medium production and for repair works.
There are two tool feed mechanism in the engine lathes. These cause the cutting tool to
move when engaged.
The lead screw will cause the apron and cutting tool to advance quickly. This is used for
cutting threads, and for moving the tool quickly.
The feed rod will move the apron and cutting tool slowly forward. This is largely used for
most of the turning operations.
Work is held in the lathe with a number of methods.
Between two centers. The work piece is driven by a device called a dog; the method is
suitable for parts with high length-to-diameter ratio.
A 3 jaw self-centering chuck is used for most operations on cylindrical work parts. For
parts with high length-to-diameter ratio the part is supported by center on the other end.
Collet consists of tubular bushing with longitudinal slits. Collets are used to grasp and
hold bar stock. A collet of exact diameter is required to match any bar stock diameter.
A face plate is a device used to grasp parts with irregular shapes.
4. Taper turning methods

A taper is a conical shape. Tapers can be cut with lathes quite easily. There are some
common methods for turning tapers on a center lathe,
Using a form tool: This type of tool is specifically designed for one cut, at a certain taper
angle. The tool is plunged at one location, and never moved along the lathe slides.
Compound Slide:
Method: The compound slide is set to travel at half of the taper angle. The tool is then fed
across the work by hand, cutting the taper as it goes.
Off-Set Tail Stock: In this method the normal rotating part of the lathe still drives the
work piece (mounted between centres), but the centre at the tailstock is offset
towards/away from the cutting tool. Then, as the cutting tool passes over, the part is cut in
a conical shape. This method is limited to small tapers over long lengths. The tailstock
offset h is defined by
h = Lsinα, where L is the length of work piece, and α is the half of the taper angle.

5. Various operations
The machining operations generally carried out in centre lathe are:
  Rough and finish turning - The operation of producing cylindrical surface.

 Facing - Machining the end of the work piece to produce flat surface.

 Centering - The operation of producing conical holes on both ends of the work
piece.

 Chamfering - The operation of beveling or turning a slope at the end of the work
piece.

 Shouldering - The operation of turning the shoulders of the stepped diameter work
piece.

 Grooving - The operation of reducing the diameter of the work piece over a
narrow surface. It is also called as recessing, undercutting or necking.

 Axial drilling and reaming by holding the cutting tool in the tailstock barrel.

 Taper turning by
- Offsetting the tailstock.
- Swiveling the compound slide.
- Using form tool with taper over short length.
- Using taper turning attachment if available.
- Combining longitudinal feed and cross feed, if feasible.

 Boring (internal turning); straight and taper – The operation of enlarging the
diameter of a hole.

 Forming; external and internal.

 Cutting helical threads; external and internal.

 Parting off - The operation of cutting the work piece into two halves.

 Knurling - The operation of producing a diamond shaped pattern or impression on

the surface.

In addition to the aforesaid regular machining operations, some more operations are also
occasionally done, if desired, in centre lathes by mounting suitable attachments available
in the market. Some of those common operations carried out in centre lathe are shown in
Fig. 2.30.
 Fig. 2.30 Some common machining operations carried out in a centre lathe

Test after completion

1. A lead-screw with half nuts in a lathe, free to rotate in both directions has
(a) V-threads
(b) Whitworth threads
(c) Buttress threads
(d) Acme threads
2. For taper turning on centre lathes, the method of swiveling the compound rest is
preferred for:
(a) long jobs with small taper angles
(b) long jobs with steep taper angles
(c) short jobs with small taper angles
(d) short jobs with steep taper angles
3. Consider the following operations:
1. Under cutting 2. Plain turning 3. Taper turning 4. Thread cutting
The correct sequence of these operations in machining a product is
(a) 2, 3, 4, 1
(b) 3, 2, 4, 1
(c) 2, 3, 1, 4
(d) 3, 2, 1, 4

4. The amount of offset of tail stock for turning taper on full length of a job 300 mm long
which is to have its two diameters at 50 mm and 38 mm ultimately is
(a) 6 mm
(b) 12 mm
(c) 25 mm
(d) 44 mm

5. Assertion (A): For thread cutting, the spindle speed selected on a lathe, is very low.
Reason (R): The required feed rate is low in threading operation.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R arc true but R is NOT the correct explanation of A
(c) A is true hut R is false
(d) A is false but R is true

Conclusion
 Lathe is the oldest machine tool invented, starting with the Egyptian tree lathes. It
is the father of all machine tools. Its main function is to remove material from a
work piece to produce the required shape and size.
 This is accomplished by holding the work piece securely and rigidly on the
machine and then turning it against the cutting tool which will remove material
from the work piece in the form of chips.
 It is used to machine cylindrical parts. Generally single point cutting tool is used.
In the year 1797 Henry Maudslay, an Englishman, designed the first screw cutting
lathe which is the forerunner of the present day high speed, heavy duty production
lathe.
  Headstock: It holds the spindle and through that power and rotation are
transmitted to the job at different speeds. Various work holding attachments such
as three jaw chucks, collets, and centres can be held in the spindle. The spindle is
driven by an electric motor through a system of belt drives and gear trains.
Spindle rotational speed is controlled by varying the geometry of the drive train.
 The movement of the tool relative to the work piece is termed as “feed”. The lathe
tool can be given three types of feed, namely, longitudinal, cross and angular.

Demo Videos
http://youtube.com/watch?v=yVqhjzlaNFg

References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 1
1. The feed rod is a long shaft, used to move the carriage or cross-slide for turning,
facing, boring and all other operations except thread cutting. Power is transmitted
from the lathe spindle to the apron gears through the feed rod via a large number of
gears.
2. The lead screw is long threaded shaft used as a master screw and brought into
operation only when threads have to cut. In all other times the lead screw is
disengaged from the gear box and remains stationary. The rotation of the lead screw is
used to traverse the tool along the work to produce screw. The half nut makes the
carriage to engage or disengage the lead screw.
3. The tumbler gear mechanism being a non-rigid construction cannot be used in a
modern heavy duty lathe. The clutch operated bevel gear feed reversing mechanism
incorporated below the head stock or in apron provides sufficient rigidity in
construction.
4. A tool bit is a small piece of cutting material having a very short shank which is
inserted in a forged carbon steel tool holder and clamped in position by bolt or screw.
A tool bit may be of solid type or tipped one according to the type of the cutting tool
material. Tool holders are made of different designs according to the shape and
purpose of the cutting tool.
5. To ensure rigidity that a brazed tool does not offer, tips are sometimes clamped at the
end of a tool shank by means of a clamp and bolt. Ceramic tips which are difficult to
braze are clamped at the end of a shank.
 Course Material for Unit - II
Name of the Course : Manufacturing Technology

Name of the Unit : Lathe

Name of the Topic : Thread cutting methods, special attachments,

machining time and power estimation.

 Objectives: To provide knowledge on various types of lathes used.

1. Outcomes: Upon successful completion, the student should be able to

understand the various types of lathe machines.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. For machining a casting on a lathe, it should be held in __________.
A. Collect chuck
B. Magnetic chuck
C. Three-jaw chuck
D. Four-jaw chuck

2. In a capstan lathe, the turret is mounted on ____________

A. A short slide of ram sliding on the saddle
B. The saddle sliding on the bed
C. Compound rest
D. Back tool post

3. The purpose of tumbler gears in lathe is to.........

A. Cut gears
B. Cut threads
C. Reduce spindle speed
D. Give desired direction of movement to the lathe carriage
4. On bar type barrel lathes, work to be machined is gripped in __________.
A. Three-jaw chucks
B. Four-jaw chucks
C. Pneumatic chucks
D. Collet

5. Lathe bed is usually made of ______________.

A. Structural steel
B. Stainless steel
C. Cast iron
D. Mild steel

6. Lathe spindle has got __________.

A. Internal threads
B. External threads
C. Taper threads
D. No threads

7. Lathe centres are provided with the following standard taper _____________.
A. Morse
B. British
C. Metric
D. Sharpe

8. Internal or external tapers on a turret lathe can be turned by _____________.

A. Face turning attachment
B. Taper turning attachment
C. Sliding attachment
D. Morse taper attachment
9. Which of the following lathe operations requires that the cutting edge of a tool bit
be placed exactly on the work center line _______________.
A. Boring
B. Drilling
C. Facing
D. Turning

10. In lathe, the carriage and tail stock are guided on _____________.
A. Same guide ways
B. Different guide ways
C. Any of the above
D. Not guided on guide ways

3. Thread cutting methods

Different possibilities are available to produce a thread on a lathe. Threads are cut
using lathes by advancing the cutting tool at a feed exactly equal to the thread pitch.
The single- point cutting tool cuts in a helical band, which is actually a thread. The
procedure calls for correct settings of the machine, and also that the helix be restarted
at the same location each time if multiple passes are required to cut the entire depth of
thread. The tool point must be ground so that it has the same profile as the thread to
be cut.
Another possibility is to cut threads by means of a thread die (external threads), or a
tap (internal threads). These operations are generally performed manually for small
thread diameters.
4. Special Attachments
Unless a work piece has a taper machined onto it which perfectly matches the internal
taper in the spindle, or has threads which perfectly match the external threads on the
spindle (two conditions which rarely exist), an accessory must be used to mount a
work piece to the spindle.
A work piece may be bolted or screwed to a faceplate, a large, flat disk that mounts to
the spindle. In the alternative, faceplate dogs may be used to secure the work to the
faceplate.
A work piece may be mounted on a mandrel, or circular work clamped in a three- or
four-jaw chuck. For irregular shaped work pieces it is usual to use a four jaw
(independent moving jaws) chuck. These holding devices mount directly to the Lathe
headstock spindle.
In precision work, and in some classes of repetition work, cylindrical work pieces are
usually held in a collet inserted into the spindle and secured either by a draw-bar, or
by a collet closing cap on the spindle. Suitable collets may also be used to mount
square or hexagonal work pieces. In precision tool making work such collets are
usually of the draw-in variety, where, as the collet is tightened, the work piece moves
slightly back into the headstock, whereas for most repetition work the dead length
variety is preferred, as this ensures that the position of the work piece does not move
as the collet is tightened.
A soft work piece (e.g., wood) may be pinched between centers by using a spur drive
at the headstock, which bites into the wood and imparts torque to it.

5. Machining time
Machining time is the time when a machine is actually processing something.
Generally, machining time is the term used when there is a reduction in material or
removing some undesirable parts of a material. For example, in a drill press,
machining time is when the cutting edge is actually moving forward and making a
hole. Machine time is used in other situations, such as when a machine installs screws
in a case automatically.
One of the important aspects in manufacturing calculation is how to find and calculate
the machining time in a machining operation. Generally, machining is family of
processes or operations in which excess material is removed from a starting work
piece by a sharp cutting tool so the remaining part has the desired geometry and the
required shape. The most common machining operations can be
classified into four types: turning, milling, drilling and lathe work.

Calculate Time for Turning

6. Power estimation

Power is the product of cutting force and velocity. In machining process, force
component is nothing but the force in the direction of cutting speed. This only considered.
Forces in the direction of feed and depth are too small when compared to the force in the
direction of cutting speed. So, these two are insignificant. Force involved in orthogonal
cutting is the force component in the direction of cutting

Power required (WC) = FC × V

Due to shear and friction, the total power is divided into two components. They are;

1. Power due to shear.

2. Power due to friction.
So, Total power = Power due to shear + Power due to friction

WC = Ws + Wf = [Fs x Vs] + [Ff x Vf]

where, Fs – Force due to shear.

Vs – Velocity of shear.
Ff – Force due to friction.
Vf – Velocity of friction.

7. Design requirements for Tool force Dynamometers

For consistently accurate and reliable measurement, the following requirements are
considered during design and construction of any tool force dynamometers:
 Sensitivity: The dynamometer should be reasonably sensitive for precision
measurement.
 Rigidity: The dynamometer need to be quite rigid to withstand the forces without
causing much deflection which may affect the machining condition.
 Cross Sensitivity: The dynamometer should be free from cross sensitivity such
that one force (say PZ) does not affect measurement of the other forces (say PX
and PY).
 Stability against humidity and temperature.
 Quick time response.
 High frequency response such that the readings are not affected by vibration
within a reasonably high range of frequency.
 Consistency: The dynamometer should work desirably over a long period.

The dynamometers being commonly used nowadays for measuring machining forces
accurately and precisely (both static and dynamic characteristics) are either strain
gauge type or piezoelectric type. Strain gauge type dynamometers are inexpensive but
less accurate and consistent, whereas, the piezoelectric type are highly accurate,
reliable and consistent but very expensive for high material cost and rigid
construction.
Fig. 2.59 (a and b) Construction of a strain gauge type 2D turning dynamometer

Fig. 2.59 (c) Photographic view of a strain gauge type 2D turning dynamometer
Fig. 2.59 (d) Photographic view of a piezoelectric type 3D turning dynamometer

Test after completion

1. A 150 mm long, 12 mm diameter 304 stainless steel rod is being reduced in
diameter to 11.5 mm by turning on a lathe. The spindle rotates at N = 400 rpm and the
tool is travelling at an axial speed of 200 mm/min. The time taken for cutting is given
by
(a) 30 s
(b) 36 s
(c) 1 minute
(d) 45 s

2. A medium carbon steel work piece is turned on a lathe at 50 m/min. cutting speed
0.8 mm/rev feed and 1.5 mm depth of cut. What is the rate of metal removal?
(a) 1000 rnm3/min
(b) 60,000 mm3/min
(c) 20,000 mm3/min
(d) Cannot be calculated with the given data
3. The time taken to face a work piece of 72 mm diameter, if the spindle speed is 80
r.p.m. and cross-feed is 0.8 mm/rev, is
(a) 1.5 minutes
(b) 3.0 minutes
(c) 5.4 minutes
(d) 8.5 minutes

4. Match List I (Cutting tools) with List II (Features) and select the correct answer
using the codes given below the Lists:
List I List II
A. Turning tool 1. Chisel edge
B. Reamer 2. Flutes
C. Milling cutter 3 Axial relief
4. Side relief
AB C
(a) 1 2 3
(b) 4 3 2
(c) 4 2 3
(d) 1 3 2

5. In turning of slender rods, it is necessary to keep the transverse force minimum

mainly to
(a) improve the surface finish
(b) increase productivity
(c) improve cutting efficiency
(d) reduce vibrations and chatter

Conclusion
 Thread cutting is one of the most important operations performed in a centre
lathe. It is possible to cut both external and internal threads with the help of
threading tools.
 There are a large number of thread forms that can be machined in a centre
lathe such as Whitworth, ACME, ISO metric, etc.
 The principle of thread cutting is to produce a helical groove on a cylindrical
or conical surface by feeding the tool longitudinally when the job is revolved
between centres or by a chuck (for external threads) and by a chuck (for
internal threads). The longitudinal feed should be equal to the pitch of the
thread to be cut per revolution of the work piece.
 The change gear ratio may result either in a ‘Simple gear train’ or ‘Compound
gear train’. In modern lathes using quick change gears, the correct gear ratio
for cutting a particular thread is quickly obtained by simply shifting the levers
in different positions which are given in the charts or instruction plates
supplied with the machine.
 The depth of first cut is usually 0.2 to 0.4 mm. This is gradually decreased for
the successive cuts until for the final finishing cut; it is usually 0.025 to 0.075
mm.
 Demo Videos
http://youtube.com/watch?v=wvYQdi68074
References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 2

1. Often it becomes necessary to machine large threads on one or very few pieces of heavy
blanks of irregular size and shape like heavy castings or forgings. In such cases, the blank
is mounted on face plate in a centre lathe with proper alignment. The deep and wide
threads are produced by intermittent cutting action by a rotating tool. A separate
attachment carrying the rotating tool is mounted on the saddle and fed as usual by the lead
screw of the centre lathe.
2. With the rapid and vast advancement of science and technology, the manufacturing
systems including machine tools are becoming more and more versatile and productive on
one hand for large lot or mass production and also having flexible automation and high
precision on the other hand required for production of more critical components in pieces
or small batches.
3. Grinding attachment is very similar to milling attachment. It has a bracket. It is mounted on
the cross slide. A grinding wheel attached to the bracket is driven by a separate motor. The
work piece may be held between centres or in a chuck. The grinding wheel is fed against
the work piece. In this operation both work piece and grinding wheel rotate. By using this
attachment both the external and internal grinding operation can be done.
4. To estimate power required for machining operations, the force has to be measured by a
suitable measuring instruments. Generally, cutting forces in cutting tool are measured in
different ways such as: Dynamometer, Ammeter, Wattmeter, Calorimeter, Thermocouple,
etc. Among these, dynamometers are generally used for measuring cutting forces.
Especially, strain gauge dynamometers are used. In this case, spring deflection is measured
which is proportional to the cutting forces.
5. Internal thread cutting: It is similar to that of an external thread, the only difference being
in the tool used. The tool is similar to a boring tool with cutting edges ground to the shape
conforming to the type of the thread to be cut. The hole is first bored to the root diameter of
the thread. For cutting metric thread, the compound slide is swiveled 300 towards the
headstock. The tool is fixed on the tool post or on the boring bar after setting it at right
angles to the lathe axis, using a thread gauge.
 Course Material for Unit - II
Name of the Course : Manufacturing Technology

Name of the Unit : Lathe

Name of the Topic : Capstan and turret lathes – automats – single

spindle, Swiss type, automatic screw type.

 Objectives: To provide knowledge on various types of lathes used.

1. Outcomes: Upon successful completion, the student should be able to

understand the various types of lathe machines.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. A capstan lathe is used to mass-produce, in batches of 200, a particular component.

The direct material cost is Rs 4 per piece, the direct labour cost is Rs 3 per piece and the
overhead costs are 400% of the labour costs. What is the production cost per piece?
(a) Rs 19
(b) Rs 23
(c) Rs 16
(d) Rs 15

2. Which one of the following is the characteristic for capstan lathe?

(a) Rate of production is low
(b) Labour cost is high
(c) Used for handling jobs of varying shapes and sizes
(d) Capstan head is mounted on a slide

3. Consider the following statements related to Turret lathe:

1. Turret is mounted directly on the saddle.
2. Turret is mounted on an auxiliary slide.
3. Much heavier and larger jobs than Capstan lathe can be produced.
Which of the above statements is/are correct?
(a) 1 and 3
(b) 2 and 3
(c) 1 only
(d) 2 only
4. Apart from hexagonal turret, the elements (s) in a turret lathe include (s)
(a) cross-slide tool post
(b) cross-slide tool post and rear tool post
(c) cross-slide tool post and tail stock
(d) real tool post and tail stock

5. Swiss type screw machines have

(a) turrets
(b) radial slides
(c) spindle carriers
(d) tool posts

6. Consider the following characteristics:

1. Multiple operations can be performed
2. Operator's fatigue is greatly reduced.
3. Ideally suited for batch production
4. A break-down in one machine does not affect the flow of products.
5. Can accommodate modifications in design of components, within certain limits.
The characteristics which can be attributed to special purpose machines would include
(a) 1, 3 and 4
(b) 1, 2 and 4
(c) 2, 3 and 5
(d) 1, 2 and 5

7. Consider the following operations and time required on a multispindle automatic

machine to produce a particular job
1. Turning …1.2 minutes
2. Drilling …1.6 minutes
3. Forming …0.2 minute
4. Parting …0.6 minute
The time required to make one piece (cycle time) will be
(a) 0.6 minutes
(b) 1.6 minutes
(c) 3.6 minutes
(d) 0.9 minute

8. Assertion (A): In a multispindle automatic lathe, the turret tool holder is indexed to
engage the cutting tools one by one for successive machining operations.
Reason (R): Turret is a multiple tool holder so that for successive machining operation,
the tools need not be changed.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R arc true but R is NOT the correct explanation of A
(c) A is true hut R is false
(d) A is false but R is true
9. Which one of the following mechanisms is employed for indexing of turret in an
automatic lathe?
(a) Whitworth
(b) Rack and pinion
(c) Ratchet and pawl
(d) Geneva wheel

10. For the manufacture of screw fasteners on a mass scale, which is the most suitable
machine tool?
(a) Capstan lathe
(b) Single-spindle automatic lathe
(c) CNC turning centre (lathe)
(d) CNC machining centre

3. Capstan versus turret

Capstan Lathe

Turret Lathe

The term "capstan lathe" overlaps in sense with the term "turret lathe" to a large extent. In
many times and places, it has been understood to be synonymous with "turret lathe". In
other times and places it has been held in technical contradistinction to "turret lathe", with
the difference being in whether the turret's slide is fixed to the bed (ram-type turret) or
slides on the bed's ways (saddle-type turret). The difference in terminology is mostly a
matter of United Kingdom and Common wealth usage versus United States usage.
American usage tends to call them all "turret lathes".
The word "capstan" could logically seem to refer to the turret itself, and to have been
inspired by the nautical capstan. A lathe turret with tools mounted in it can very much
resemble a nautical capstan full of handspikes. This interpretation would lead Americans
to treat "capstan" as a synonym of "turret" and "capstan lathe" as a synonym of "turret
lathe". However, the multi-spoked handles that the operator uses to advance the slide are
also called capstans, and they themselves also resemble the nautical capstan.

No distinction between "turret lathe" and "capstan lathe" persists upon translation from
English into other languages. Most translations involve the term "revolver", and serve to
translate either of the English terms.

The words "turret" and "tower", the former being a diminutive of the latter, come
ultimately from the Latin "turris", which means "tower", and the use of "turret" both to
refer to lathe turrets and to refer to gun turrets seems certainly to have been inspired by its
earlier connection to the turrets of fortified buildings and to siege towers. The history of
the rook in chess is connected to the same history, with the French word for rook, tour,
meaning "tower".

It is an interesting coincidence that the word "tour" in French can mean both "lathe" and
"tower", with the first sense coming ultimately from Latin "tornus", "lathe", and the
second sense coming ultimately from Latin "turris", "tower". "Tour revolver", "tour
tourelle", and "tour tourelle revolver" are various ways to say "turret lathe" in French.

4. Semi-automatic
Sometimes machines similar to those above, but with power feeds and automatic turret-
indexing at the end of the return stroke, are called "semi-automatic turret lathes". This
nomenclature distinction is blurry and not consistently observed. The term "turret lathe"
encompasses them all. During the 1860s, when semi-automatic turret lathes were
developed, they were sometimes called "automatic". What we today would call
"automatics", that is, fully automatic machines, had not been developed yet. During that
era both manual and semi-automatic turret lathes were sometimes called "screw
machines", although we today reserve that term for fully automatic machines.

5. Automatic
During the 1870s through 1890s, the mechanically automated "automatic" turret lathe was
developed and disseminated. These machines can execute many part-cutting cycles
without human intervention. Thus the duties of the operator, which were already greatly
reduced by the manual turret lathe, were even further reduced, and productivity increased.
These machines use cams to automate the sliding and indexing of the turret and the
opening and closing of the chuck. Thus, they execute the part-cutting cycle somewhat
analogously to the way in which an elaborate cuckoo clock performs an automated theater
show. Small- to medium-sized automatic turret lathes are usually called "screw machines"
or "automatic screw machines", while larger ones are usually called "automatic chucking
lathes", "automatic chuckers", or "chuckers".
 5.1 SINGLE SPINDLE AUTOMATIC CUTTING OFF MACHINE

Fig. 2.82 Arrangement of tool slide

Fig. 2.83 Simple parts produced on cutting off machine

Working principle :
Typical arrangement of tool slide in an automatic cutting off machine is illustrated in Fig.
2.82. The required length of work piece (stock) is fed out with a cam mechanism, up to
the stock stop which is automatically advanced in line with the spindle axis, at the end of
each cycle. The stock is held in the collect chuck of the rotating spindle. The machining is
done by tools held in cross slides operating only in the crosswise direction. The form tool
held in the front tool slide produces the required shape of the component. The parting off
tool in the rear tool slide is used to cut off the component after machining. Special
attachments can be employed if holes or threads are required on the simple parts.
This machine has a single cam shaft which controls the working and idle motions of the
tools. The cam shaft runs at constant speed. Therefore working motions and idle motions
takes place at the same speed. Hence the cycle time is more. Typical simple parts (from 3
mm to 20 mm in diameter) produced on this machine are shown in Fig. 2.83.

5.2 SWISS TYPE AUTOMATIC SCREW MACHINE

This machine was designed and developed in Switzerland. So it is often called as Swiss
auto lathe. This machine is also known as ‘Sliding head screw machine’, or ‘Movable
headstock machine’, because the head stock is movable and the tools are fixed. This
machine is used for machining long accurate parts of small diameter (2 mm to 25 mm).
Fig. 2.84 Swiss type automatic screw machine

The cutting action is confined close to the support bushing reducing the overhang to a
minimum. As a result, the work can be machined to very close limits. All tools can work
at a time. After the work piece is machined, the head stock slides back to the original
position. One revolution of the cam shaft produces one component.
A wide variety of formed surfaces may be obtained on the work piece by synchronized
alternating or simultaneous travel of the headstock (longitudinal feed) and the cross slide
(approach to the depth of cut). The bar stock used in these machines has to be highly
accurate and is first ground on centre less grinding machines to ensure high accuracy.

Advantages
 It is used to precision turning of small parts.
 Wide range of speeds is available.
 It is rigid in construction.
 Micrometre tool setting is possible.
 Interchangeability of cams is possible.
 Tolerance of 0.005 mm to 0.0125 mm is obtained.

5.3 SINGLE SPINDLE AUTOMATIC SCREW TYPE MACHINE

This is essentially wholly automatic bar type turret lathe. This is very similar to capstan
and turret lathes with reference to tool layout, but all the tool movements are cam
controlled, such that full automation in manufacturing is achieved. This is designed for
machining complex external and internal surfaces on parts made of bar stock or of
separate blanks. These machines are made in several sizes for bar work from 12.7 mm to
60 mm diameter.

Working principle :
The bar stock is held in a collet chuck and advanced by a feed finger after each piece is
finished and cut off. All movements of the machine units are actuated by cams mounted
on the camshaft. The bar stock is pushed through stock tube in a bracket and its leading
end is clamped in rotating spindle by means of a collet chuck. The bar is then fed out for
the next part by stock feeding mechanism. Longitudinal turning and machining of the
central hole are performed by tools mounted on turret slide. The cut off and form tools are
mounted on the cross-slides. At the end of each cut, turret slide is withdrawn
automatically and indexed to bring the next tool into position. One revolution of camshaft
produces one component. It is used for producing small jobs, screws, stepped pins, taper
pins, bolts, etc.

Fig. 2.88 Single spindle automatic screw cutting machine

Test after completion

1. The indexing of the turret in a single-spindle automatic lathe is done using
(a) Geneva mechanism
(b) Ratchet and Pawl mechanism
(c) Rack and pinion mechanism
(d) Whitworth mechanism

2. Assertion (A): In a Swiss - type automatic lathe, the turret is given longitudinal feed for
each tool in a specific order with suitable indexing.
Reason (R): A turret is a multiple tool holder to facilitate machining with each tool by
indexing without the need to change the tools.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R arc true but R is NOT the correct explanation of A
(c) A is true hut R is false
(d) A is false but R is true

3. Maximum production of small and slender parts is done by

(a) Watch maker's lathe
(b) Sliding head stock automatic lathe
(c) Multi-spindle automatic lathe
(d) Capstan lathe
4. A multi-spindle automat performs four operations with times 50. 60. 65 and 75 seconds
at each of its work centers. The cycle time (time required to manufacture one work piece)
in seconds will be
(a) 50 + 60 + 65 + 75
(b) (50 + 60 + 65 + 75) /4
(c) 75/4
(d) 75

5. Screw threads are produced on solid rods by using which of the following?
(a) Dies
(b) Punch
(c) Mandrel
(d) Boring bar

Conclusion
 Capstan and turret lathes are production lathes used to manufacture any number of
identical pieces in the minimum time. These lathes are development of centre
lathes. The capstan lathe was first developed in the year 1860 by Pratt and
Whitney of USA.
 The bed is a long box like casting provided with accurate guide ways upon which
the carriage and turret saddle are mounted. The bed is designed to ensure strength,
rigidity and permanency of alignment under heavy duty services.
 Electric motor driven headstock: In this type of headstock the spindle of the
machine and the armature shaft of the motor are one and the same. Any speed
variation or reversal is effected by simply controlling the motor. Three of four
speeds are available and the machine is suitable for smaller diameter of work
pieces rotated at high speeds.
 Pre-optive or pre-selective headstock: It is an all geared headstock with
provisions for rapid stopping, starting and speed changing for different operations
by simply pushing a button or pulling a lever. The required speed for next
operation is selected beforehand and the speed changing lever is placed at the
selected position. After the first operation is complete, a button or a lever is
simply actuated and the spindle starts rotating at the selected speed required for
the second operation without stopping the machine. This novel mechanism is
effect by the friction clutches.
 In a capstan lathe, the ram saddle bridges the gap between two bed ways, and the
top face is accurately machined to provide bearing surface for the ram or auxiliary
slide. The saddle may be adjusted on lathe bed ways and clamped at the desired
position. The hexagonal turret is mounted on the ram or auxiliary slide.

Demo Videos
http://youtube.com/watch?v=FIS6BhSv6XA
 References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 3
1. The work pieces are held in collets or chucks. In turret lathes, large work pieces are held by
means of jaw chucks. These chucks may be hydraulically or pneumatically operated. In a
capstan lathe, bar stock is held in collet chucks. A bar feeding mechanism is used for
automatic feeding of bar stock. At least eleven tools can be set at a time in turret and
capstan lathes.
2. Six tools are held on the turret faces, four tools in front square tool post and one parting off
tool at the rear tool post. While machining, the turret head moves forward towards the job.
After each operation, the turret head goes back. The turret head is indexed automatically
and the next tool comes into machining position. The indexing is done by an indexing
mechanism. The longitudinal movement of the turret corresponding to each of the turret
position can be controlled independently.
3. By holding different tools in the turret faces, the operations like drilling, boring, reaming,
counter boring, turning and threading can be done on the component. Four tools held on
the front tool post are used for different operations like necking, chamfering, form turning
and knurling. The parting off tool in the rear tool post is used for cutting off the work
piece. The cross wise movements of the rear and front tool posts are controlled by pre-
stops.
4. Centre type: In this type, the work piece is held between centres, for which a head stock
and a tail stock are mounted on the bed of the machine. Usually, external stepped or
formed surfaces are machined on this machine. The work is machined by two groups of
cutting tools. The front tool slide holds the cutting tools which require a longitudinal feed
motion to turn the steps of a shaft, while the rear tool slide carries the tools that require a
transverse feed motion to perform operations such as facing, shouldering, necking,
chamfering etc.
5. Chucking type: In this type, the work piece is held in a chuck. Such a machine may be
equipped with various tool slide arrangements. In addition to longitudinal and transverse
feed tool slides, these machines may also be equipped with a central end working tool slide
or a turret if internal surfaces are also to be machined in addition to the external surfaces.
 Course Material for Unit - II
Name of the Course : Manufacturing Technology

Name of the Unit : Lathe

Name of the Topic : Multi spindle - Turret Indexing mechanism, bar

feed mechanism.

 Objectives: To provide knowledge on various types of lathes used.

1. Outcomes: Upon successful completion, the student should be able to

understand the various types of lathe machines.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Quality screw threads are produced by

(a) thread milling
(b) thread chasing
(c) thread cutting with single point tool
(d) thread casting

2. Tail stock set over method of taper turning is preferred for

(a) internal tapers
(b) small tapers
(c) long slender tapers
(d) steep tapers

3. Half nut is connected with __________________.

A. Milling machine
B. Locking device
C. Jigs and fixture
D. Thread cutting on lathe

4. A good lubricant for thread-cutting operation is ________________.

A. Graphite
B. White lead
C. Mineral lard oil
D. Water soluble oil
5. The power is transmitted by lead screw to the carriage through ____________.
A. Gear box
B. Worm and gear
C. Rack and pinion
D. Half nut

6. The tail stock set over method of taper turning is preferred for
A. Internal tapers
B. Small tapers
C. Long slender tapers
D. Steep tapers

7. The angle between the lathe centres is

A. 30oC
B. 45oC
C. 60oC
D. 90oC

8. The taper on the lathe spindle is

A. 1 in 10
B. 1 in 15
C. 1 in 20
D. 1 in 30

9. The size of a lathe is specified by the

A. Length between centers
B. Swing diameter over the bed
C. Swing diameter over the carriage
D. All of the above

10. The lead screw of a lathe has ________________ threads.

A. Single start
B. Double start
C. Multi-start
D. Any one of these

3. MULTI SPINDLE AUTOMATS

The multi spindle automats are the fastest type of production machines and are made
in a variety of models with 2, 4, 5, 6 or 8 spindles. Each of the spindles is provided
with its own set of tools for operation. As a result, more than one work piece can be
machined simultaneously in these machines. In contrast to the single spindle automat,
where one turret face at a time is working on one spindle, the multi spindle automat
has all turret faces working on all spindles at the same time. The production rate of a
multi spindle automat, however, is less than that of the corresponding number of
single spindle automats. E.g. the production rate of a 4 spindle automat is not four
times but only 2½ to 3 times more than that of a single spindle automat.

3.1 PARALLEL ACTION MULTI SPINDLE AUTOMAT

These machines are usually automatic cutting off bar type machines. This is also
called as ‘multiple-flow’ machine. In this machine, the same operation is performed
on each spindle and a work piece is finished in each spindle in one working cycle.
The rate of production is very high, but the machine can be employed to machine
simple parts only since all the machining processes are done at one position. Fig. 2.90
shows the basic configuration of a parallel action multi spindle automat.

They are used to perform the same work as single spindle automatic cutting off
machines. Centering or a single drilling operation can also be performed on certain
models. The machine consists of a frame with a head stock. The horizontal work
spindles which are arranged in a line, one above the other, are housed in this
headstock. Cross slides are located at the right and left hand sides of the spindles and
carry the cross feeding tools. All the working and the auxiliary motions of the
machine units are obtained from the cam mounted on the cam shaft.

Fig. 2.90 Parallel action multi spindle automat

3.2 PROGRESSIVE ACTION MULTI SPINDLE AUTOMAT

In this machine the blanks clamped in each spindle are machined progressively in
station after station.
Construction: Fig. 2.91 shows the basic configuration of a six-spindle progressive
action automat. The headstock is mounted at the left end of the base of the machine. It
contains a spindle carrier which periodically indexes through a definite angle (3600
divided by the number of spindles) about a horizontal axis through the centre of the
machine at each tool retraction.
The working spindles are mounted in this spindle carrier. The working spindles carry
the collets on which the work pieces are held. The bar stock is fed to the working
spindle from the rear.
Cross slides which carry tools for operations such as cut off, turning, facing, forming,
chamfering etc. are mounted in a frame above the face of the spindle carrier. These
cross slides travel radially inward for cutting operation. The number of cross slides is
equal to the number of spindles. The feed of each tool, both cross slide tools and end
slide tools, is controlled by its own individual cam.

Fig. 2.91 Six-spindle progressive action automat

Working principle:
The spindle carrier indexes on its own axis by 600 (3600/6) at each tool retraction. As
the spindle carrier indexes, it carries the work from station to station, where various
tools operate on it. The stock moves around the circle in counter clockwise direction
and comes to the station number 6 for cutting off. A finished component is obtained
for one full revolution of the spindle carrier.

4. Turret indexing mechanism

Fig. 2.65 Turret indexing mechanism

Construction: Fig. 2.65 shows the schematic view of the turret indexing mechanism.
It illustrates an inverted plan of the turret assembly. This mechanism is also called as
Geneva mechanism. There is a small vertical spindle fixed on the turret saddle. At the
top of the spindle, the turret head is mounted. Just below the turret head on the same
spindle, a circular index plate having six slots, a bevel gear and a ratchet are mounted.
There is a spring actuated plunger mounted on the saddle which locks the index plate
this prevents the rotation of turret during the machining operation.
Working principle:

When the turret reaches the backward position (after machining) the projecting pin of
the plunger rides over the sloping surface of the cam. So the plunger is released from
the groove of the index plate. Now the spring loaded pawl engages the ratchet groove
and rotates it. The index plate and the turret spindle rotate through 1/6 of a revolution.
The pin and the plunger drop out of the cam and hence the plunger locks the index
plate at the next groove. The turret is thus indexed and again locked into the new
position automatically. The turret holding the next tool is now fed forward and the
pawl is released from the ratchet plate by the spring pressure.

The corresponding movement of the stop rods with the indexing of the turret can also
be understood from the Fig. 2.65. The pinion shaft has a bevel pinion at one end. The
bevel pinion meshes with the bevel gear mounted on the turret spindle. At its other
end, a circular plate is connected. Six adjustable stop rods are fitted to this circular
plate. When the turret rotates, the bevel pinion will also rotate. And hence the circular
stop plate is also indexed by 1/6 of a revolution. The ratio of the teeth between the
pinion and the gear is chosen according to this rotation.

5. Bar feeding mechanisms

The capstan and turret lathes while working on bar work require some mechanism for
bar feeding. The long bars which protrude out of the headstock spindle require to be
fed through the spindle up to the bar stop after the first piece is completed and the
collet chuck is opened. In simple cases, the bar may be pushed by hand. But this
process unnecessarily increases the total production time by stopping, setting, and
starting the machine. Therefore, various types of bar feeding mechanisms have been
designed which push the bar forward immediately after the collet releases the work
without stopping the machine, enabling the setting time to be reduced to the
minimum.

Fig. 2.63 Bar feeding mechanism

 Type 1: This mechanism is shown in Fig. 2.63. After the work piece is complete and
part off, the collet is opened by moving the lever manually in the rightward direction.
Further movement of the lever in the same direction causes forward push of the bar
with the help of ratchet - pawl system.

Fig. 2.64 Bar feeding mechanism

Type 2: This mechanism is shown in Fig. 2.64. The bar is passed through the bar
chuck, spindle of the machine and then through the collet chuck. The bar chuck
rotates in the sliding bracket body which is mounted on a long sliding bar. The bar
chuck grips the bar centrally by two set screws and rotates with the bar in the sliding
bracket body. One end of the chain is connected to the pin fitted on the sliding bracket
and the other end supports a weight. The chain running over two fixed pulleys
mounted on the sliding bar. The weight constantly exerts end thrust on the bar chuck
while it revolves on the sliding bracket and forces the bar through the spindle at the
moment the collet chuck is released. Thus bar feeding may be accomplished without
stopping the machine.
In this way the bar is fed without stopping the machine. After a number of such
feedings, the bar chuck will approach the rear end of the head stock. Now the bar
chuck is released from the bar and brought to the left extreme position. Then it is
screwed on to the bar.

Test after completion

1. The swing diameter over the bed is ______________ the height of the centre measured
from the bed of the lathe.

A. Equal to

B. Twice

C. Thrice

D. One-half
2. Slow speed of the spindle is necessary in

A. Thread cutting

B. Turning a work of larger diameter

C. Turning a hard or tough material

D. All of these

3. The chuck used for setting up of heavy and irregular shaped work should be

A. Four jaw independent chuck

B. Three jaw universal chuck

C. Magnetic chuck

D. Drill chuck

4. It is required to cut screw threads of 2 mm pitch on a lathe. The lead screw has a pitch of 6
mm. If the spindle speed is 60 r.p.m., then the speed of lead screw will be

A. 10 r.p.m.

B. 20 r.p.m.

C. 120 r.p.m.

D. 180 r.p.m.

5. Consider the following statements associated with the lathe accessories:

1. Steady rest is used for supporting a long job in between head stock and tail stock.

2. Mandrel is used for turning small cylindrical job.

3. Collects are used for turning disc-shaped job.

Of these statements:

(a) 1 and 2 are correct

(b) 2 and 3 are correct

(c) 3 alone is correct

(d) 1 alone is correct

 Conclusion
 In a capstan lathe, the ram saddle bridges the gap between two bed ways, and the top
face is accurately machined to provide bearing surface for the ram or auxiliary slide.

 The saddle may be adjusted on lathe bed ways and clamped at the desired position.
The hexagonal turret is mounted on the ram or auxiliary slide.

 The standard practice of holding the work piece between two centres in a centre lathe
finds no place in a capstan lathe or turret lathe as there is no dead centre to support the
work piece at the other end. Therefore, the work piece is held at the spindle end by the
help of chucks and fixtures.

 A combination chuck may be used both as a self-centering and an independent chuck

to take advantage of both the types.

 The jaws may be operated individually by separate screws or simultaneously by the

scroll disc. The screws mounted on the frame have teeth cut on its underside which
meshes with the scroll and all the jaws together with the screws move radially when
the scroll is made to rotate by a pinion.

Demo Videos
http://youtube.com/watch?v=2fvqRCHywJA
References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 4

1) Heavy duty turret lathes and capstan lathes engaged in mass production work are
equipped with air operated chucks for certain distinct advantages. The chuck grips the
work piece quickly and is capable of taking powerful grip with least manual exertion.
The chucks are operated by air at a pressure of 5.5 kg/cm2 to 7 kg/cm2.
2) The mechanism incorporates an air cylinder mounted at the back end of the headstock
spindle and rotates with it. Fluid pressure may be communicated to the cylinder by
operating a valve with a lever and the piston will slide within the cylinder. The
movement of the piston is transmitted to the jaws by means of connecting rod and
links. A guide is provided for the movement of the connecting rod.
3) Collet chucks or collets are used mainly to hold bar stock, especially in the smaller
sizes. A collet is a circular steel shell having three or four equally spaced slits
extending the greater part of its length. These slits impart springing action to the collet.
That is why, collets are also known as “spring collets”. The collet nose is made thicker
to form the jaws. The outside surface of the nose fits in the taper hole of the hood. The
inside of the collet is made according to the shape of the work to be held.
4) Plain or adjustable angle cutter holder: It is similar as that of a straight cutter holder
but having an angular slot. The tool is fitted in this slot by means of setscrews. The
inclination of the tool helps in turning or boring operations close to the chuck jaws or
up to the shoulder of the work piece without any interference. In plain type of holder,
the setting of the cutting edge relative to the work is effect by opening the set screws
and then adjusting the tool by hand. In adjustable type of holder, the accurate setting of
the tool can be effect by rotating a micrometer screw. Fig.2.70 illustrates an adjustable
angle cutter holder.
5) Two sets of form tool holders have been designed for holding straight and circular form
cutters. The usual procedure of holding a form tool holder is on the cross-slide. In the
straight form tool holder, the tool is mounted on a dovetail slide and the height of the
cutting edge may be adjusted by moving the tool within the slide. The height of the
circular form tool may be adjusted by rotating the circular cutter.
 Course Material for Unit - III
Name of the Course : Manufacturing Technology

Name of the Unit : Shaper, Planer and Milling processes

Name of the Topic : Shaper, Planer and Slotter: Introduction, types,

specification, mechanism - holding devices,
hydraulic drives in shaper.

 Objectives: To understand the difference between shaper planner and slotter

in manufacturing domain.

1. Outcomes: Upon successful completion, the student should be able to

understand the shaper, planer and slotter machines.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Which of the following is used for machining larger jobs?

a) shaper
b) planer
c) can’t say anything
d) none of the mentioned

2. Which of the following is used for machining smaller jobs?

a) shaper
b) planer
c) can’t say anything
d) none of the mentioned
3. Which of the following machine is primarily intended for producing flat surfaces?
a) shaper
b) drilling
c) lathe
d) none of the mentioned

4. Which of the following operation can be performed in shaper?

a) gear cutting
b) keyways cutting
c) curvilinear contours
d) all of the mentioned

5. In shaper, the job is kept_____

a) stationary
b) rotating
c) reciprocating
d) none of the mentioned

6. Which stroke is cutting stroke in shaper?

a) forward
b) return
c) can’t say anything
d) none of the mentioned

7. Which stroke is idle stroke in shaper?

a) forward
b) return
c) can’t say anything
d) none of the mentioned
8. At the end of one cycle, job is given a feed motion______ to the direction of tool
movement.
a) parallel
b) perpendicular
c) anti-parallel
d) none of the mentioned

9. In shaper, the tool head consists of_______

a) tool post
b) tool slide
c) clamper box
d) all of the mentioned

10. The main parts of shaper are _______

a) base and body
b) ram and tool head
c) cross rail and body
d) all of the mentioned
3. RECIPROCATING MACHINE TOOLS
In lathes the work piece is rotated while the cutting tool is moved axially to produce
cylindrical surfaces. But in reciprocating machine tools the single point cutting tool is
reciprocates and produces flat surfaces. The flat surfaces produced may be horizontal,
vertical or inclined at an angle. These machine tools can also be arranged for machining
contoured surfaces, slots, grooves and other recesses. The major machine tools that fall in
this type are: Shaper, Planer and Slotter. The main characteristic of this type of machine
tools is that they are simple in construction and are thus economical in operation.
3.1 SHAPER
The main function of the shaper is to produce flat surfaces in different planes. In general
the shaper can produce any surface composed of straight line elements. Modern shapers
can generate contoured surface. The shaper was first developed in the year 1836 by James
Nasmyth, an Englishman. Because of the poor productivity and process capability the
shapers are not widely used nowadays for production. The shaper is a low cost machine
tool and is used for initial rough machining of the blanks.
3.2 Classification of shapers
Shapers are broadly classified as follows:
According to the type of mechanism used:
 Crank shaper.
 Geared shaper.
 Hydraulic shaper.
According to the position and travel of ram:
 Horizontal shaper.
 Vertical shaper.
 Traveling head shaper.
According to the type of design of the table:
 Standard or plain shaper.
 Universal shaper.
According to the type of cutting stroke:
 Push type shaper.
 Draw type shaper.
3.3 Standard or plain shaper
A shaper is termed as standard or plain when the table has only two movements,
vertical and horizontal, to give the feed. The table may or may not be supported at the
outer end.

Fig. 3.1 Schematic view of a standard shaper

3.4 Ram drive mechanism of a shaper
In a shaper, rotary movement of the drive is converted into reciprocating movement of
the ram by the mechanism contained within the column of the machine. In a standard
shaper metal is removed in the forward cutting stroke and during the return stroke no
metal is removed. To reduce the total machining time it is necessary to reduce the
time taken by the return stroke. Thus the shaper mechanism should be so designed
that it can allow the ram to move at a comparatively slower speed during the forward
cutting stroke and during the return stoke it can allow the ram to move at a faster rate
to reduce the idle return time. This mechanism is known as quick return mechanism.
3.4.1 Hydraulic drive quick return mechanism

Fig. 3.8 Hydraulic drive for horizontal shaper

A typical hydraulic drive for horizontal shaper is shown in Fig. 3.8. A constant speed
motor drives a hydraulic pump which delivers oil at a constant pressure to the line.
The piston is pushed by the oil and, being connected to the ram by the piston rod,
pushes the ram carrying the tool. The admission of oil to each end of the piston,
alternately, is accomplished with the help of trip dogs and pilot valve. As the ram
moves and completes its stroke (forward or return) a trip dog will trip the pilot valve
which operates the regulating valve. The regulating valve will admit the oil to the
other side of the piston and the motion of the ram will get reversed. It is clear that the
length of the ram stroke will depend upon the position of the trip dogs. The length of
the ram stroke can be changed by unclamping and moving the trip dogs to the desired
positions.
The above system is a constant pressure system. The velocity of the ram travel will be
directly proportional to the oil pressure and the piston area to which it is applied. The
return stroke is quicker, since the piston area on which the oil pressure acts is greater
as compared to the other end for which it gets reduced because of the piston rod.
Another oil line is connected to a smaller feed cylinder to change the hydraulic power
to mechanical power for feeding the work past the tool.
 Advantages of Hydraulic drive
o Does not make any noise and operates very quietly.

o Ability to stall against an obstruction without damage to the tool or the

machine.

o Ability to change length and position of stroke or speed while the

machine is running.

o The cutting and return speeds are practically constant throughout the
stroke.

o This permits the cutting tool to work uniformly during cutting stroke.

o The reversal of the ram is obtained quickly without any shock as the
oil on the other end of the cylinder provides cushioning effect.

o Offers great flexibility of speed and feed and the control is easier.

4. Work holding devices used in a shaper:

The work piece may be supported on the shaper table by using any one of the
following work holding devices depending upon the geometry of the work piece and nature
of the operation to be performed.
o Machine vice.
o Clamping work on the table.
o Angle plate.
o V-blocks.
o Shaper centre.
4.1 Machine vice

Fig. 3.12 Machine vice (a) Plain vice (b) Swivel vice and (c) Universal vice
A vice is a quick method of holding and locating small and regular shaped work pieces. It
consists of a base, screw, fixed jaw and movable jaw. The work piece is clamped between
fixed and movable jaws by rotating the screw. Types of machine vise are plain vise, swivel
vie and universal vice.

A plain vice is the most simple of all the types. The vice may have a single screw or double
screws for actuating the movable jaw. The double screws add gripping strength while taking
deeper cuts or handling heavier jobs. Fig. 3.12 (a) illustrates a plain vice.

In a swivel vice the base is graduated in degrees, and the body of the vice may be swivelled at
any desired angle on a horizontal plane. The swivelling arrangement is useful in bevelling the
end of work piece. Fig. 3.12 (b) illustrates a swivel vice.

A universal vice may be swivelled like a swivel vice. In addition to that, the body may be
tilted in a vertical plane up to 90 degrees from the horizontal. An inclined surface may be
machined by a universal vice. Fig. 3.12 (c) illustrates a universal vice.

5. PLANER
Like shapers, planers are also basically used for producing flat surfaces. But planers are very
large and massive compared to the shapers. Planers are generally used for machining large
work pieces which cannot be held in a shaper. The planers are capable of taking heavier cuts.
The planer was first developed in the year 1817 by Richard Roberts, an Englishman.

5.1 Types of planer

The different types of planer which are most commonly used are:
o Standard or double housing planer.
o Open side planer.
o Pit planer.
o Edge or plate planer.
o Divided or latching table planer.

Fig. 3.30 Schematic view of a double housing planer Fig. 3.31 Schematic view of an
open side planer
5.2 Standard or double housing planer

It is most widely used in workshops. It has a long heavy base on which a table reciprocates
on accurate guide ways. It has one drawback. Because of the two housings, one on each side
of the bed, it limits the width of the work that can be machined. Fig. 3.30 shows a double
housing planer.

5.3 Open side planer

It has a housing only on one side of the base and the cross rail is suspended from the housing
as a cantilever. This feature of the machine allows large and wide jobs to be clamped on the
table. As the single housing has to take up the entire load, it is made extra-massive to resist
the forces. Only three tool heads are mounted on this machine. The constructional and driving
features of the machine are same as that of a double housing planer. Fig. 3.31 shows an open
side planer.

6. Work holding devices used in a planer

A planer table is used to hold very large, heavy and intricate work pieces, and in many cases,
large number of identical work pieces together. Setting up of the work pieces on a planer
table requires sufficient amount of skill. The work piece may be held on a planer table by the
following methods:
o By standard clamping.
o By special fixtures.
6.1 Standard clamping devices
The standard clamping devices are used for holding most of the work pieces on a planer
table.
The standard clamping devices are as follows:
o Heavy duty vices.
o T-bolts, step blocks and clamps.
o Stop pins and toe dogs.
o Angle plates.
o Planer jacks.
o Planer centres (similar to shaper centre).
o V-blocks.

Fig. 3.40 Clamping a large work piece on a planer table

 Fig. 3.41 Use of planer jack

7. SLOTTER
Slotter can simply be considered as vertical shaper where the single point (straight or formed)
cutting tool reciprocates vertically and the work piece, being mounted on the table, is given
slow longitudinal and / or rotary feed. The slotter is used for cutting grooves, keyways,
internal and external gears and slots of various shapes. The slotter was first developed in the
year 1800 by Brunel.

7.1 Types of slotter

The different types of slotter which are most commonly used are:
o Puncher slotter.
o Precision slotter.

Fig. 3.46 Schematic view of a slotter

Puncher slotter
It is a heavy, rigid machine designed for removal of a large amount of metal from large
forging or castings. The length of a puncher slotter is sufficiently large. It may be as long as
1800 to 2000 mm. The ram is usually driven by a spiral pinion meshing with the rack teeth
cut on the underside of the ram. The pinion is driven by a variable speed reversible electric
motor similar to that of a planer. The feed is also controlled by electrical gears.
7.2 Work holding devices used in a slotter
The work is held on a slotter table by a vice, T-bolts and clamps or by special fixtures. T-
bolts and clamps are used for holding most of the work on the table. Before clamping,
parallels are placed below the work piece so as to allow the tool to complete the cut without
touching the table. Special fixtures are used for holding repetitive work. Fig. 3.49 shows a
typical slotting fixture.

Fig. 3.49 Slotting fixture

7.3 Slotter operations

o Internal flat surfaces.
o Enlargement and / or finishing non-circular holes bounded by a number of flat
surfaces as shown in Fig. 3.51 (a).
o Blind geometrical holes like hexagonal socket as shown in Fig. 3.51 (b).
o Internal grooves and slots of rectangular and curved sections.
o Internal keyways and splines, straight tooth of internal spur gears, internal
curved surfaces, and internal oil grooves etc as shown in Fig. 3.51 (c), which
are not possible in shaper.

(a) Through rectangular hole (b) Hexagonal socket and (c) Internal keyway
Fig. 3.51 Typical machining operations performed in a slotter
7.4 Specifications of a slotter
The slotter is specified by the following parameters:
 The maximum stroke length.
 Diameter of rotary table.
 Maximum travel of saddle and cross slide.
 Type of drive used.
 Power of the motor.
 Net weight of machine.
 Number and amount of feeds.
 Floor area required.
 Test after completion
1. The body of the shaper comprises of ________
a) pillar
b) column
c) frame
d) all of the mentioned

2. Which of the following part of shaper supports the entire load of the machine?
a) base
b) crossrail
c) frame
d) none of the mentioned

3. Drive mechanism consists of ________

a) main drives
b) the gear box
c) quick return mechanism
d) all of the mentioned

4. The top of the body provides guide ways for______

a) ram
b) cross rail
c) can’t say anything
d) none of the mentioned

5. The front of the body provides guide ways for _______

a) ram
b) cross rail
c) can’t say anything
d) none of the mentioned

Conclusion
 A stop pin is a one-leg screw clamp. Stop pins are used to prevent the work piece
from coming out of position during the cutting stroke. The body of the stop pin is
fitted in the slot on the table and the screw is tightened till it forces against the work.
 For holding “L” shaped work piece, angle plate is used. Angle plate is made of cast
iron and is accurately planed on two sides at right angles. One of the sides is clamped
to the table by T-bolts while the other side holds the work by clamps.
 V-blocks are used for holding round rods. Work piece may be supported on two V-
blocks at its two ends and is clamped to the table by T-bolts and clamps. V-blocks are
made of cast iron or steel and are accurately machined.
  The cutting tool used in a shaper is a single point cutting tool having rake, clearance
and other tool angles similar to a lathe tool. It differs from a lathe tool in tool angles.
 The design of a plate or edge planer is totally unlike that of an ordinary planer. It is
specially intended for squaring and bevelling the edges of steel plates used for
different pressure vessels and ship- building works.
 The hydraulic drive is quite similar to that used for a horizontal shaper. More than one
hydraulic cylinder may be used to give a wide range of speeds.

Demo Videos
http://youtube.com/watch?v=1_eULWhRKKk

References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 1

1. In a planer the feed is provided intermittently and at the end of the return stroke
similar to a shaper. The feed of a planer, both down feed and cross feed, is given by
the tool head. The down feed is applied while machining a vertical or angular surface
by rotating the down feed screw of the tool head.
2. The cross feed is given while machining horizontal surface by rotating the cross feed
screw passes through a nut in the tool head. Both the down feed and cross feed may
be provided either by hand or power by rotating two feed screws, contained within the
cross rail. If the two feed screws are rotated manually by a handle, then it called hand
feed. If the two feed screws are rotated by power, then it is called automatic feed.
3. The cutting tools used on planers are all single point cutting tools. They are in general
similar in shapes and tool angles to those used on a lathe and shaper. As a planer tool
has to take up heavy cut and coarse feed during a long cutting stroke, the tools are
made heavier and larger in cross-section. Planer tools may be solid, forged type or bit
type. Bits are made of HSS, stellite or cemented carbide and they may be brazed,
welded or clamped on a mild steel shank. Cemented carbide tipped tool is used for
production work.
4. The vertical ram holding the cutting tool is reciprocated by a ram drive mechanism.
The work piece, to be machined, is mounted directly or in a vice on the work table.
Like shaper, in slotter also the fast cutting motion is imparted to the tool and the feed
motions to the work piece. In slotter, in addition to the longitudinal and cross feeds, a
rotary feed motion is also provided in the work table.
5. A slotter removes metal during downward cutting stroke only whereas during upward
return stroke no metal is removed. To reduce the idle return time, quick return
mechanism is incorporated in the machine.
 Course Material for Unit - III
Name of the Course : Manufacturing Technology

Name of the Unit : Shaper, Planer and Milling processes

Name of the Topic : Difference between shaper and planer.

Introduction, types and specifications of milling
machines.

 Objectives: To understand the difference between shaper planner and slotter

in manufacturing domain.

3. Outcomes: Upon successful completion, the student should be able to

understand the shaper, planer and slotter machines.

4. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. The cross rail is mounted on the______ of the body frame.
a) front
b) back
c) can’t say anything
d) none of the mentioned

2. The _______ movements of cross rail permit the jobs of different heights to be
accommodated below the tool.
a) horizontal
b) vertical
c) can’t say anything
d) none of the mentioned

3. Shaper can produce contours of ______

a) concave
b) convex
c) both concave and convex
d) none of the mentioned
4. According to the type of mechanism used for giving reciprocating motion to the ram,
shaper can be classified as______
a) crank type
b) geared type
c) both crank type and geared type
d) none of the mentioned

5. According to the type of design of the table, lathe can be classified as_____
a) standard shaper
b) universal shape
c) both standard shaper and universal shaper
d) none of the mentioned

6. Push type shaper is type of shaper according to______

a) design of the table
b) position and travel of the ram
c) type of cutting stroke
d) none of the mentioned

7. Draw type shaper is type of shaper according to______

a) design of the table
b) position and travel of the ram
c) type of cutting stroke
d) none of the mentioned

8. A shaper is termed as standard when the table has _____ movements.

a) only one
b) only two
c) only three
d) none of the mentioned

9. Which type of movements of table can be given to the feed?

a) horizontal
b) vertical
c) horizontal or vertical
d) none of the mentioned

10. The base of the standard shaper is able to_____

a) resist vibration
b) take up high compressive
c) both resist vibration and take up high compressive
d) none of the mentioned
 3. Difference between shaper and planer

Sl. No. Shaper Planer

The tool reciprocates and the work is The work reciprocates and the tool is
1
stationary. stationary.
Feed is given to the work during the idle Feed is given to the tool during the idle
2
stroke of the ram. stroke of the work table.
It gives more accuracy as the tool is rigidly Less accuracy due to the over hanging of the
3
supported during cutting. ram.
4 Suitable for machining small work pieces. Suitable for machining large work pieces.
5 Only light cuts can be applied. Heavy cuts can be applied.
Only one tool can be used at a time. So Vertical and side tool heads can be used at a
6
machining takes longer time. time. So machining is quicker.
7 Setting the work piece is easy. Setting the work piece is difficult.
Only one work piece can be machined at a Several work pieces can be machined at a
8
time. time.
9 Tools are smaller in size. They are larger in size.
10 Shapers are lighter and smaller. Planers are heavier and larger.

4. MILLING MACHINE

This is a machine tool that removes material as the work is fed against a rotating cutter.
The cutter rotates at a high speed and because of the multiple cutting edges it removes
material at a very fast rate. The machine can also hold two or more number of cutters at a
time. That is why a milling machine finds wide application in machine shop. The first
milling machine came into existence in about 1770 and was of French origin. The milling
cutter was developed by Jacques de Vaucanson in the year 1782.

4.1 Types of Milling Machine

Milling machines are broadly classified as follows:

Column and knee type
 Hand milling machine.
 Plain or horizontal milling machine.
 Universal milling machine.
 Omniversal milling machine.
 Vertical milling machine.
Manufacturing or bed type
 Simplex milling machine.
 Duplex milling machine.
 Triplex milling machine.
Planer type Special type
 Drum milling machine.
 Rotary table milling machine.
 Profile milling machine.
 Pantograph milling machine.
 Planetary milling machine.
4.2 Column and knee type milling machines
This is the most commonly used machine in view of its flexibility and easier setup. In
such small and medium duty machines the table with work travels above the saddle in
horizontal direction (X axis) (left and right). The saddle with table moves on the slide
ways provided on the knee in transverse direction (Y axis) (front and back). The knee
with saddle and table moves on a dovetail guide ways provided on the column in vertical
direction (Z axis) (up and down).

4.2.1 Plain or Horizontal Milling Machine

The work table can be linearly fed along three axes (X, Y, and Z) only. The table may be
fed by hand or power. These machines are most widely used for piece or batch production
of jobs of relatively simple design and geometry. Fig. 3.53 schematically shows the basic
configuration of a horizontal milling machine.

Fig. 3.53 Plain or horizontal milling machine

4.2.2 Vertical Milling Machine

Fig. 3.56 Vertical milling machine

The work table may or may not have swivelling features. The spindle head may be
swivelled at an angle, permitting the milling cutter to work on angular surfaces. In some
machines, the spindle can also be adjusted up or down relative to the work piece. This
machine works using end milling and face milling cutters. This machine is adapted for
machining grooves, slots and flat surfaces. Fig. 3.56 schematically shows the basic
configuration of a vertical milling machine.

4.3 Major parts of a column and knee type milling machine

The general configuration of a column and knee type conventional milling machine with
horizontal arbor is shown in Fig. 3.53. The major parts are:

Base:
It is accurately machined on its top and bottom surface and serves as a foundation
member for all other parts. It carries the column at its one end. In some machines, the
base is hollow and serves as a reservoir for cutting fluid.

Column:
It is the main supporting frame mounted vertically on the base. The column is box
shaped, heavily ribbed inside and houses all the driving mechanisms for the spindle and
table feed.

Knee:
The knee houses the feed mechanism of the table, and different controls to operate it. The
top face of the knee forms a slide way for the saddle to provide cross travel of the table.

Table
The table rests on ways on the saddle and travels longitudinally. The top of the table is
accurately finished and T-slots are provided for clamping the work and other fixtures on
it. A lead screw under the table engages a nut on the saddle to move the table horizontally
by hand or power. The longitudinal travel of the table may be limited by fixing trip dogs
on the side of the table. In universal machines, the table may also be swivelled
horizontally.

Overhanging arm:
The overhanging arm that is mounted on the top of the column extends beyond the
column face and serves as a bearing support for the other end of the arbor. The arm is
adjustable so that the bearing support may be provided nearest to the cutter.

Front brace:
The front brace is and extra support that is fitted between the knee and the over arm to
ensure further rigidity to the arbor and the knee. The front brace is slotted to allow for the
adjustment of the height of the knee relative to the over arm.
 Spindle:
The spindle of the machine is located in the upper part of the column and receives power
from the motor through belts, gears, clutches and transmits it to the arbor. The front end
of the spindle just projects from the column face and is provided with a tapered hole into
which various cutting tools and arbors may be inserted. The accuracy in metal machining
by the cutter depends primarily on the accuracy, strength, and rigidity of the spindle

Arbor:
It may be considered as an extension of the machine spindle on which milling cutters are
securely mounted and rotated. The arbors are made with taper shanks for proper
alignment with the machine spindles having taper holes at their nose. The arbor may be
supported at the farthest end from the overhanging arm or may be of cantilever type
which is called stub arbor. The arbor shanks are properly gripped against the spindle taper
by a draw bolt which extends throughout the length of the hollow spindle. The threaded
end of the draw bolt is fastened to the tapped hole of the arbor shank and then the lock nut
is tightened against the spindle. The spindle has also two keys for imparting positive drive
to the arbor in addition to the friction developed in the taper surfaces. The cutter is set at
the required position on the arbor by spacing collars or spacers of various lengths but of
equal diameter. The entire assembly of the milling cutter and the spacers are fastened to
the arbor by a long key. The end spacer on the arbor is slightly larger in diameter and acts
as a bearing bush for bearing support which extends from the over arm. Fig. 3.62
illustrates an arbor assembly used in a milling machine.

Fig. 3.62 Arbor assembly Fig. 3.63 Principle of operation

4.4 Working principle of a Column and Knee type milling machine

The kinematic system comprising of several mechanisms enables transmission of motion

and power from the motor to the cutting tool for its rotation at varying speeds and to the
work table for its slow feed motions along X, Y and Z directions. The milling cutter
mounted on the horizontal milling arbor, receives its rotary motion at different speeds
from the main motor through the speed gear box. The feeds of the work piece can be
given by manually or automatically by rotating the respective wheels by hand or by
power. The work piece is clamped on the work table by a work holding device. Then the
work piece is fed against the rotating multipoint cutter to remove the excess material at a
very fast rate.

Test after completion

1. Milling machine can hold______ cutters at a time.
a) only one
b) only two
c) only three
d) none of the mentioned

2. Which of the following machine is superior to other machines as regards accuracy and
better surface finish?
a) lathe
b) drill
c) shaper
d) milling

3. Which type of machining can be done by milling machine?

a) cutting keyways
b) slots and grooves
c) gears
d) all of the mentioned

4. Which of the following motion does a milling machine has?

a) vertical motion
b) crosswise motion
c) longitudinal motion
d) all of the mentioned

5. The various milling process may be classified in ______ categories.

a) 1
b) 2
c) 3
d) none of the mentioned
 Conclusion
 Milling is a process of producing flat and complex shapes with the use of multi-
tooth cutting tool, which is called a milling cutter and the cutting edges are called
teeth.
 The axis of rotation of the cutting tool is perpendicular to the direction of feed,
either parallel or perpendicular to the machined surface.
 The machine tool that traditionally performs this operation is a milling machine.
Milling is an interrupted cutting operation: the teeth of the milling cutter enter and
exit the work during each revolution.
 This interrupted cutting action subjects the teeth to a cycle of impact force and
thermal shock on every rotation.
 The tool material and cutter geometry must be designed to withstand these
conditions. Cutting fluids are essential for most milling operations.

Demo Videos
http://youtube.com/watch?v=aeOaAZRwpfY
References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 2
1. Profile milling machine: This machine duplicates the full size of the template attached
to the machine. This is practically a vertical milling machine of bed type in which the
spindle can be adjusted vertically and the cutter head horizontally across the table. The
movement of the cutter is regulated by a hardened guide pin.
2. Pantograph milling machine: This machine can duplicate a work by using a pantograph
mechanism which permits the size of the work piece reproduced to be smaller than,
equal to or greater than the size of a template or model used for the purpose.
Pantograph machines are available in two dimensional or three dimensional models.
Two dimensional models are used for engraving letters or other designs, whereas three
dimensional models are employed for copying any shape and contour of the work
piece. The tracing stylus is moved manually on the contour of the model to be
duplicated and the milling cutter mounted on the spindle moves in a similar path on the
work piece.
3. Planetary milling machine: In this machine, the work is held stationary while the
revolving cutter(s) move in a planetary path to finish a cylindrical surface on the work
either internally or externally or simultaneously. This machine is particularly adapted,
for milling internal or external threads of different pitches.
4. Rotary table milling machine: The construction of this machine is the modification of a
vertical milling machine and is adapted for machining flat surfaces. Such open or
closed ended high production milling machines possess one large rotary work table
rotates about a vertical axis and one or two vertical spindles. The positions of the work
piece(s) and the milling head are adjusted according to the size and shape of the work
piece.
5. Drum milling machine: These machines are of the continuous- operation type. They are
mostly found in large-lot and mass production shops for production of large parts such
as motor blocks, gear cases, and clutch housings. Two flat surfaces of the work piece
can be milled simultaneously.
 Course Material for Unit - III
Name of the Course : Manufacturing Technology

Name of the Unit : Shaper, Planer and Milling processes

Name of the Topic : Mechanisms, holding devices, types of milling

operation.

 Objectives: To understand the difference between shaper planner and slotter

in manufacturing domain.

1. Outcomes: Upon successful completion, the student should be able to

understand the shaper, planer and slotter machines.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Up milling and down milling are the subtype of ________ milling process.
a) peripheral milling
b) face milling
c) both peripheral milling and face milling
d) none of the mentioned

2. Which of the following milling is known as conventional milling?

a) up milling
b) down milling
c) both up milling and down milling
d) none of the mentioned

3. Which of the following process is also known as climb milling?

a) up milling
b) down milling
c) both up milling and down milling
d) none of the mentioned

4. The thickness of the chip in up milling is _______ at the beginning of the cut.
a) minimum
b) maximum
c) zero
d) none of the mentioned
5. The thickness of the chip in up milling is _______ in when the cut terminates.
a) minimum
b) maximum
c) zero
d) none of the mentioned

6. The cutting force is directed _____ and this tends to lift the work from the fixture in
up milling.
a) upward
b) downward
c) can’t say anything
d) none of the mentioned

7. The cutting action can be done from both sides of the table to finish the job. This is
the advantage of _____ process.
a) up milling
b) down milling
c) can’t say anything
d) none of the mentioned

8. More depth of cut can be used in ______milling process.

a) up milling
b) down milling
c) can’t say anything
d) none of the mentioned

9. Difficulty is experienced in pouring coolant just on the cutting edge from where the
chip begins. This is the disadvantage of______ process.
a) up milling
b) down milling
c) can’t say anything
d) none of the mentioned

10. The work is pulled by cutter teeth and hence the job may get spoiled or
breakaway. This is the disadvantage of _____ process.
a) up milling
b) down milling
c) can’t say anything
d) none of the mentioned
3. Mechanism of a column and knee type milling machine

This mechanism is composed of spindle drive mechanism and table feed mechanism.
The spindle drive mechanism is incorporated in the column. All modern machines are
driven by individual motors housed within the column, and the spindle receives power
from a combination of gears and clutch assembly. Multiple speed of the spindle may
be obtained by altering the gear ratio. Fig. 3.64 illustrates the power feed mechanism
contained within the knee of the machine to enable the table to have three different
feed movements, i.e. longitudinal, cross and vertical.

Fig. 3.64 Power feed mechanism of a column and knee type milling machine

The power is transmitted from the speed gear box consisting of change gears to the
feed shaft in the knee of the machine by a telescopic feed shaft. Both ends of the
telescopic feed shaft are provided with universal joints. Telescopic feed shaft and
universal joints are necessary to allow vertical movement of the knee, gear 14,
attached to the jaw clutch 20. The jaw clutch 20 is keyed to the feed shaft and drives
gear 13, which is free to rotate on the extreme end of the cross feed screw. Bevel gear
22 is free to rotate on feed shaft and is in mesh with gear 19 fastened to the evaluating
screw. 16 serve as a nut for 15, and it is screwed in nut 17. Therefore, 15 and 16 serve
as a telescopic screw combination and a vertical movement of the knee is thus
possible. As soon as the clutch 20 is engaged with the clutch attached to the bevel
gear 22 by means of a clutch operating lever, the bevel gear 22 rotates and this being
in mesh with gear 19 causes the elevating screw to rotate in nut 16 giving a vertical
movement of the knee.
The bevel gear 3 meshes with bevel gear 2 which is fastened to the table feed screw.
Therefore, longitudinal feed movement of the table is possible through gears 18, 25,
24, 5, 3, & 2.
 4. Work holding devices used in a milling machine
It is necessary that the work piece should be properly and securely held on the milling
machine table for effective machining operations. The work piece may be supported
on the milling machine table by using any one of the following work holding devices
depending upon the geometry of the work piece and nature of the operation to be
performed.
o T-bolts and clamps.
o Angle plate.
o V-blocks.
o Vices.
o Special fixtures.
o Dividing heads.
T-bolts and clamps: Bulky work pieces of irregular shapes are clamped directly on
the milling machine table by using T-bolts and clamps. Fig. 3.65 illustrates the use of T-
bolts and clamps. Different designs of clamps are used for different patterns of work. Fig.
3.65 shows the different types of clamps.

Fig. 3.65 Different types of clamps

Angle plate: Sometimes a titling type angle plate in which one face can be adjusted
relative to another face for milling at a required angle is also used. Fig. 3.66 shows a
tilting type angle plate.

Fig. 3.66 Tilting type angle plate

Special fixtures: The fixtures are special devices designed to hold work for specific
operations more efficiently than standard work holding devices. Fixtures are especially useful
when large numbers of identical parts are being produced. By using fixtures loading, locating,
clamping and unloading time is greatly minimized.

5. MILLING OPERATIONS
Milling machines are mostly general purpose machine tools and used for piece or small lot
production. In general, all milling operations can be grouped into two types. They are:
peripheral milling and face milling.
Peripheral milling: Here, the finished surface is parallel to the axis of rotation of the cutter
and is machined by cutter teeth on the periphery of the cutter. Fig. 3.91 schematically
shows the peripheral milling operation.

Fig. 3.91 Schematic view of the peripheral milling operation

Face milling: The peripheral cutting edges do the actual cutting, whereas the face cutting
edges finish up the work surface by removing a very small amount of material. Fig. 3.92
schematically shows the face milling operation.

Fig. 3.92 Schematic view of the face milling operation

Special type - End milling: It may be considered as the combination of peripheral and
face milling operation. The cutter has teeth both on the end face and on the periphery. The
cutting characteristics may be of peripheral or face milling type according to the cutter
surface used. Fig. 3.93 schematically shows the different end milling operation.
 Fig. 3.93 Schematic views of the different end milling operations

According to the relative movement between the tool and the work, the peripheral milling
operation is classified into two types. They are: up milling and down milling.

Up milling or conventional milling: Here, the cutter rotates in the opposite direction to
the work table movement. In this, the chip starts as zero thickness and gradually increases
to the maximum. The cutting force is directed upwards and this tends to lift the work
piece from the work holding device. Each tooth slides across a minute distance on the
work surface before it begins to cut, producing a wavy surface. This tends to dull the
cutting edge and consequently have a lower tool life. As the cutter progresses, the chip
accumulate at the cutting zone and carried over with the teeth which spoils the work
surface. Fig. 3.94 (a) schematically shows the up milling or conventional milling process.

Fig. 3.94 Schematic views of (a) Up milling process and (b) Down milling process

Down milling or Climb milling: This is suitable for obtaining fine finish on the work
surface. The cutting force acts downwards and this tends to seat the work piece firmly in
the work holding device. The chips are deposited behind the cutter and do not interfere
with the cutting. Climb milling allows greater feeds per tooth and longer tool life between
regrinds than up milling. Fig. 3.94 (b) schematically shows the down or climb milling
process.

6. Basic functions of milling machine

Milling machines of various types are widely used for the following purposes:
Producing flat surface in horizontal, vertical and inclined planes as shown in Fig. 3.95.
 Fig. 3.95 Producing flat surface in horizontal, vertical and inclined planes

Machining slots of various cross sections as shown in Fig. 3.96.

Fig. 3.96 Machining slots of various cross sections

Slitting or parting operation as shown in Fig. 3.97.

Fig. 3.97 Parting by slitting saw Fig. 3.98 Straddle milling

Cutting teeth of spur gears, straight toothed bevel gears, worm wheels, sprockets in piece
or batch production. These are illustrated in Fig. 3.102 (a, b and c).
Fig. 3.102 (a) Cutting teeth of spur gear by disc type cutter (b) Cutting teeth of spur gear
by end mill (c) Cutting teeth of straight toothed bevel gear by disc type cutter

Test after completion

1. As the cutter progress, the chip accumulate at the cutting zone, spoils the work
surfaces. This is the disadvantage of ______ process.
a) up milling
b) down milling
c) can’t say anything
d) none of the mentioned

2. Cutter teeth wears out soon as in the beginning itself the teeth comes in contact with
the hard surface of the work piece. This is the disadvantage of _______ process.
a) up milling
b) down milling
c) can’t say anything
d) none of the mentioned

3. The burr on the surface cleans during the cutting operation. This is the advantage of
_______ process.
a) up milling
b) down milling
c) can’t say anything
d) none of the mentioned

4. Up milling is the process of removing metal by a cutter which is rotated _______

direction of the travel of the work piece.
a) in the same
b) against the
c) can’t say anything
d) none of the mentioned
 5. Down milling is the process of removing metal by a cutter which is rotated _______
direction of the travel of the work piece.
a) in the same
b) against the
c) can’t say anything
d) none of the mentioned

Conclusion
 Intermittent cutting nature and usually complex geometry necessitate making the
milling cutters mostly by HSS which is unique for high tensile and transverse
rupture strength, fracture toughness and formability almost in all respects i.e.
forging, rolling, powdering, welding, heat treatment, machining (in annealed
condition) and grinding.
 Tougher grade cemented carbides are also used without or with coating, where
feasible, for high productivity and product quality. In some cutters tungsten
carbide teeth are brazed on the tips of the teeth or individually inserted and held in
the body of the cutter by some mechanical means. Carbide tipped cutter is
especially adapted to heavy cuts and increased cutting speeds.
 Plain milling cutters are hollow straight HSS cylinder of 40 to 80 mm outer
diameter having 4 to 16 straight or helical equi-spaced flutes or cutting edges on
the circumference.
 Form cutters have irregular profiles on the cutting edges in order to generate an
irregular outline of the work. These disc type HSS cutters are generally used for
making grooves or slots of various profiles.
 Gear milling cutters are made of HSS and available mostly in disc form like slot
milling cutters and also in the form of end mill for producing teeth of large
module gears.

Demo Videos
http://youtube.com/watch?v=qDStbE3W2VI

References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.
 Answers to the assignments with full explanation
Assignment 3

1. Form milling type cutters are also used widely for cutting slots are flutes of different
cross section e.g. the flutes of twist drills, milling cutters, reamers etc., and gushing of
hobs, taps, short thread milling cutters etc.
2. These shank type solid HSS or carbide cutters having threaded like annular grooves
with equi- spaced gushing are used in automatic single purpose milling machines for
cutting the threads in large lot production of screws, bolts etc. Both internal and
external threads are cut by the tool. These milling cutters are used for long thread
milling also (e.g. lead screws, power screws, worms etc.,).
3. Corner rounding milling cutters have teeth curved inwards on the circumferential
surface to form the contour of a quarter circle. The cutter produces a convex quarter
circular surface on the work piece. These are used for cutting a radius on the corners or
edge of the work piece. The diameter of the cutter ranges from 1.5 mm to 20 mm.
4. Angle milling cutters are made as single or double angle cutters and are used to
machine angles other than 900. The cutting edges are formed at the conical surface
around the periphery of the cutter. The double angle milling cutters are mainly used for
cutting spiral grooves on a piece of blank.
5. Woodruff key slot milling cutters are small standard cutters similar in construction to a
thin small diameter plain milling cutter, intended for the production of woodruff key
slots. The cutter is provided with a shank and may have straight or staggered teeth.
 Course Material for Unit - III
Name of the Course : Manufacturing Technology

Name of the Unit : Shaper, Planer and Milling processes

Name of the Topic : Milling tool nomenclature and its specifications,

Indexing – Types-Simple, Compounding and
differentials.

 Objectives: To understand the difference between shaper planner and slotter

in manufacturing domain.

1. Outcomes: Upon successful completion, the student should be able to

understand the shaper, planer and slotter machines.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. For down milling, _______ machines are used.

a) light
b) moderate
c) rigid
d) none of the mentioned

2. Narrow slots can be milled in _________ milling process.

a) up milling
b) down milling
c) can’t say anything
d) none of the mentioned
3. The cutting edges are spaced ______ on the circumference of the cutter.
a) equally
b) unequally
c) can’t say anything
d) none of the mentioned

4. The milling cutters are revolving tools having ______ cutting edges.
a) only one
b) only two
c) only three
d) none of mentioned

5. The cutting elements intermittently engages ______

a) work piece
b) remove material
c) both work piece and remove material
d) none of the mentioned

6. Milling cutters are broadly classified into______ types.

a) 1
b) 2
c) 3
d) none of the mentioned

7. Milling cutters may be made of______

a) high speed steel
b) cemented tipped
c) super high speed steel
d) all of the mentioned
8. The cutters having a bore at center are mounted and keyed on a short shaft called_____
a) arbor
b) shank
c) can’t say anything
d) none of the mentioned

9. Arbor is connected with the milling machine spindle by_____

a) draw bolt
b) driving bolt
c) both draw bolt and driving bolt
d) none of the mentioned

10. The indexing operation can also be adapted for producing ______ headed bolts.
a) hexagonal
b) square
c) both hexagonal and square
d) none of the mentioned

3. Elements of a plain milling cutter

Fig. 3.89 Elements of a plain milling cutter

The major parts and angles of a plain milling cutter are illustrated in Fig. 3.89.

Body of cutter:
The part of the cutter left after exclusion of the teeth and the portion to which the
teeth are attached.

Cutting edge:
The edge formed by the intersection of the face and the circular land or the surface
left by the provision of primary clearance.

Face:
The portion of the gash adjacent to the cutting edge on which the chip impinges as it
is cut from the work.

Fillet:
The curved surface at the bottom of gash that joins the face of one tooth to the back of
the tooth immediately ahead.

Gash:
The chip space between the back of one tooth and the face of the next tooth.

Outside diameter:
The diameter of the circle passing through the peripheral cutting edge.

Root diameter:
The diameter of the circle passing through the bottom of the fillet.

Cutter angles:
Similar to a single point cutting tool, the milling cutter teeth are also provided with
rake, clearance and other cutting angles in order to remove metal efficiently.

Relief angle:
The angle in a plane perpendicular to the axis. The angle between land of a tooth and
tangent to the outside diameter of cutter at the cutting edge of that tooth.

Lip angle:
The included angle between the land and the face of the tooth, or alternatively the
angle between the tangent to the back at the cutting edge and the face of the tooth.

Primary clearance angle:

The angle formed by the back of the tooth with a line drawn tangent to the periphery
of the cutter at the cutting edge.
Secondary clearance angle:
The angle formed by the secondary clearance surface of the tooth with a line drawn
tangent to the periphery of the cutter at the cutting edge.

Rake angle (Radial):

The angle measured in the diametral plane between the face of the tooth and a radial
line passing through the tooth cutting edge. The rake angle which may be positive,
negative or zero is illustrated in Fig. 3.90.

Fig. 3.90 Three types of rake angle of a plain milling cutter

4. Indexing head or dividing head

It is a special work holding device used in a milling machine. Dividing head can also
be considered as a milling machine attachment. Fig. 3.67 shows a dividing head used
in a milling machine.

Fig. 3.67 Dividing head

 An important function and use of milling machines is for cutting slots, grooves etc.
which are to be equally spaced around the circumference of a blank, for example, gear
cutting, ratchet wheels, milling cutter blanks, reamers etc. This necessitates holding of
the blank (work piece) and rotating it the exact amount for each groove or slot to be
cut. This process is known as “indexing”. The dividing head is the device used for this
purpose. It is lined and bolted to the machine table so that the axis passing through the
head stock centre and tail stock centre is at right angle to the spindle axis of the
machine. The head stock of the dividing head consists of a spindle to which a 40 tooth
worm wheel is keyed. A single threaded worm meshes with this wheel. The worm
spindle projects from the front of the head and has a crank and handle attached. The
head spindle is bored with a tapered hole and is also screwed on its end.
The work piece is mounted between centres, one inserted into the dividing head
spindle and the other into the tail stock. The work piece may also be mounted on a
mandrel between these centres. A chuck may be mounted on the spindle nose for
holding short work pieces having no centre holes. The work piece is rotated by
turning the index crank by means of handle.
By using different circles of holes and index plates, any fractional part of a turn of the
index crank can be obtained. The two sector arms shown on front of the index plate
are used for avoiding counting of holes during indexing.

Index plate:
It helps to accomplish indexing (dividing) of the work into equal divisions. It is a
circular plate approximately 6 mm thick, with holes (equally spaced) arranged in
concentric circles. The space between two subsequent holes is same for each circle;
however it is different for different circles. A plate can have through holes or blind
holes on its faces.
For a plain dividing head, the index plate is fixed to the body of the dividing head
while in the case of universal dividing head it is mounted on the sleeve of the worm
shaft. Various manufactures in U.S.A. and other countries have produced index plates
with different number of hole circles.

For example: The index plates available with the Brown and Sharpe milling
machines are:

Plate No. 1 - 15, 16, 17, 18, 19, 20

Plate No. 2 - 21, 23, 27, 29, 31, 33
Plate No. 3 - 37, 39, 41, 43, 47, 49

Methods of indexing: The various methods of indexing are discussed below:

Direct indexing: In this, the index plate is directly mounted on the dividing head
spindle. The intermediate use of worm and worm wheel is avoided. For indexing, the
index pin is pulled out on a hole, the work and the index plate are rotated the desired
number of holes and the pin is engaged. Both plain and universal heads can be used in
this manner. Direct indexing is the most rapid method of indexing, but fractions of a
complete turn of the spindle are limited to those available with the index plate. With a
standard indexing plate having 24 holes, all factors of 24 can be indexed, that is, the
work can be divided into 2,3,4,6,8,12 and 24 parts.

Simple or plain indexing: In this, the index plate selected for the particular
application, is fitted on the worm shaft and locked through a locking pin. To index the
work through any required angle, the index crank pin is withdrawn from a hole in the
index plate. The work piece is indexed through the required angle by turning the
index crank through a calculated number of whole revolutions and holes on one of the
hole circles, after which the index pin is relocated in the required hole. If the number
of divisions on the job circumference (that is number of indexing) needed is z, then
the number of turns (n) that the crank must be rotated for each indexing can be found
from the formula: n = - turns.

Example 3.1: Indexing 28 divisions.

The rotation of the index crank = __ = __ = __ = 1 turns.

This can be done as follows using any one of the Brown and Sharpe plates.
One full rotation + 9 holes in 21 hole circle in plate No. 2.
One full rotation + 21 holes in 49 hole circle in plate No. 3.

Compound indexing: When the available capacity of the index plates is not
sufficient to do a given indexing, the compound indexing method can be used. First,
the crank is moved in the usual fashion in the forward direction. Then a further
motion is added or subtracted by rotating the index plate after locking the plate with
the plunger. This is termed as compound indexing. For example, if the indexing is
done by moving the crank by 5 holes in the 20 hole circle and then the index plate
together with the crank is indexed back by a hole with the locking plunger registering
in a 15 hole circle as shown in Fig. 3.68.
 Fig. 3.68 An example of compound indexing

Differential indexing: This is an automatic way to carry out the compound indexing
method. In this the required division is obtained by a combination of two movements:
o The movement of the index crank similar to the simple indexing.
o The simultaneous movement of the index plate, when the crank is
turned.
Fig. 3.69 schematically shows the arrangement for differential indexing.

Fig. 3.69 Arrangement for differential indexing

In differential indexing, the index plate is made free to rotate. A gear is connected to the back
end of the dividing head spindle while another gear is mounted on a shaft and is connected to
the shaft of the index plate through bevel gears as shown in Fig.3.69. When the index crank is
rotated, the motion is communicated to the work piece spindle. Since the work piece spindle
is connected to the index plate through the intermediate gearing as explained above, the index
plate will also start rotating. If the chosen indexing is less than the required one, then the
index plate will have to be moved in the same direction as the movement of the crank to add
the additional motion. If the chosen indexing is more, then the plate should move in the
opposite direction to subtract the additional motion.
The direction of the movement of the index plate depends upon the gear train employed. If an
idle gear is added between the spindle gear and the shaft gear in case of a simple gear train,
then the index plate will move in the same direction to that of the indexing crank movement.
In the case of a compound gear train an idler is used when the index plate is moved in the
opposite direction.
Angular indexing: Sometimes it is desirable to carry out indexing using the actual
angles rather than equal numbers along the periphery. Here, angular indexing would
be useful. The procedure remains the same as in the previous cases, except that the
angle will have to be first converted to equivalent divisions. Since 40 revolutions of
the crank equals to a full rotation of the work piece, which means 3600, one
revolution of the crank is equivalent to 90. The formula to find the index crank
movement is given below.

Index crank movement = Angular displacement of work (in degrees) / 9

= Angular displacement of work (in minutes) / 540
= Angular displacement of work (in seconds) / 32400

Test after completion

1. Indexing is accomplished by using a special attachment known as__________
a) dividing head
b) index head
c) both dividing head and index head
d) none of the mentioned

2. The dividing heads are of ____ types.

a) 1
b) 2
c) 3
d) none of the mentioned

3. Which of the following is not the type of dividing heads?

a) plain dividing head
b) universal dividing head
c) optical dividing head
d) all of the mentioned

4. Which of the following dividing head is also known as simple dividing head?
a) plain dividing head
b) universal dividing head
c) optical dividing head
d) all of the mentioned
 5. Which of the following is the most common type of indexing arrangement used in
workshops?
a) plain dividing head
b) universal dividing head
c) optical dividing head
d) all of the mentioned

Conclusion
 The cutters have a bore at the centre are mounted and keyed on a short shaft
called arbor.
 A milling machine collet is a form of sleeve bushing for reducing the size of
the taper hole at the nose of the spindle so that an arbor or a milling cutter
having a smaller shank than the spindle taper can be fitted into it.
 An adapter is a form of collet used on milling machine having standardized
spindle end. Cutters having straight shanks are usually mounted on adapters.
An adapter can be connected with the spindle by a draw bolt or it may be
directly bolted to it.
 Straight shank cutters are usually held on a special adapter called “spring
collet” or “spring chuck”. The cutter shank is introduced in the cylindrical
hole provided at the end of the adapter and then the nut is lightened. This
causes the split jaws of the adapter to spring inside, and grip the shank firmly.
 The face milling cutters of larger diameter having no shank are bolted directly
on the nose of the spindle. For this purpose four bolt holes are provided on the
body of the spindle.

Demo Videos
http://youtube.com/watch?v=a-GkDjXGJI0

References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.
 Answers to the assignments with full explanation
Assignment 4
1. Amongst the column and knee type conventional milling machines, horizontal arbor
type is very widely used, where various types and sizes of milling cutters having axial
bore are mounted on the horizontal arbor.
2. For milling by solid end mill type and face milling cutters, separate vertical axis type
milling machines are available. But horizontal arbor type milling machines can also be
used for those operations to be done by end milling and smaller size face milling
cutters by using the universal milling attachment. The rotation of the horizontal spindle
is transmitted into rotation about vertical axis and also in any inclined direction by this
attachment which thus extends the processing capabilities and application range of the
milling machine.
3. The main characteristics of face milling cutters are:
 Usually large in diameter (80 to 800 mm) and heavy.
 Used only for machining flat surfaces in different orientations.
 Mounted directly in the vertical and / or horizontal spindles.
 Coated or uncoated carbide inserts are clamped at the outer edge of the
carbon steel body.
 Generally used for high production machining of large jobs.
4. The common characteristics of end milling cutters are:
 Mostly made of High Speed Steel.
 4 to 12 straight or helical teeth on the periphery and face.
 Diameter ranges from about 1 mm to 40 mm.
 Very versatile and widely used in vertical spindle type milling
machines.
 End milling cutters requiring larger diameter are made as a separate
cutter body which is fitted in the spindle through a taper shank arbor
(Shell end mills).
5. Tool form cutters: Form milling type cutters are also used widely for cutting slots are
flutes of different cross section e.g. the flutes of twist drills, milling cutters, reamers
etc., and gushing of hobs, taps, short thread milling cutters etc.
 Course Material for Unit - IV
Name of the Course : Manufacturing Technology

Name of the Unit : Abrasive Processes

Name of the Topic : Abrasive processes: grinding wheel –

specifications and selection.

 Objectives: To provide knowledge on different types of grinding machines

and related tools for manufacturing various components.

1. Outcomes: Upon successful completion, the student should be able to

understand the application grinding operation in manufacturing.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Grinding wheel is specified as “A 46 K 5 B 17”. Grain size of a wheel will be

a) Coarse
b) Medium
c) Fine
d) Very Fine

2. Grinding wheel is specified as “C 8 K 5 B 17”. Grain size of a wheel will be

a) Coarse
b) Medium
c) Fine
d) Very Fine
3. Grinding wheel is specified as “A 600 K 5 B 17”. Grain size of a wheel will be
a) Coarse
b) Medium
c) Fine
d) Very Fine

4. Which of the following specified grinding wheel will have Aluminium oxide abrasive?
a) Z 46 K 5 B 17
b) C 600 K 5 B 17
c) C 8 K 5 B 17
d) A 80 K 5 B 17

5. Which of the following specified grinding wheel will have Zirconia abrasive?
a) Z 46 K 5 B 17
b) C 600 K 5 B 17
c) C 8 K 5 B 17
d) A 80 K 5 B 17

6. Operation done to make periphery of grinding wheel concentric with its axis to recover
its lost shape is known as
a) Loading
b) Glazing
c) Dressing
d) Trueing

7. Removing dull grains in order to make grinding wheel sharp is known as

a) Loading
b) Glazing
c) Dressing
d) Trueing
8. Which of the following will be better to use for machining of soft work piece?
a) V-bond
b) R-bond
c) Both V and R bond
d) None of the mentioned

9. Which of the following grinding wheel would be more economical for grinding of hard
work piece?
a) Soft grinding wheel
b) Hard grinding wheel
c) Both hard and soft grinding wheel
d) None of the mentioned

10. Which of the following grinding wheel would be more economical for grinding of
soft work piece?
a) Soft grinding wheel
b) Hard grinding wheel
c) Both hard and soft grinding wheel
d) None of the mentioned

3. ABRASIVE PROCESSES: GRINDING

Grinding is the most common form of abrasive machining. The art of grinding goes back
many centuries. Over 5000 years ago the Egyptians abraded and polished building stones
to hairline fits for the pyramids. Grinding is a metal cutting process which engages an
abrasive tool whose cutting elements are grains of abrasive material known as grit. These
grits are characterized by sharp cutting points, high hot hardness, wear resistance and
chemical stability. The grits are held together by a suitable bonding material to give shape
of an abrasive tool. Simply it is a metal removal process in which the metal is removed
with the help of rotating grinding wheel. Fig. 4.1 illustrates the cutting action of abrasive
grits of disc type grinding wheel similar to cutting action of teeth of the cutter in slab
milling.
 Fig. 4.1 Cutting action of abrasive grains

Fig. 4.2 Grinding wheel and work piece interaction

3.1 Applications of grinding

 To remove small amount of metal from work pieces and finish then to close
tolerances.
 To obtain a better surface finish.
 To machine hard surfaces that cannot be machined by high-speed steels.
 Grinding of tools and cutters and resharpening of the same.
 Grinding of threads.
 Stock removal (abrasive milling) finishing of flat as well as cylindrical surface.
 Descaling and deburring.

3.2 Advantages of grinding

 Dimensional accuracy and good surface finish.
 Good form and locational accuracy.
 Applicable to both hardened and unhardened material.

4. GRINDING WHEELS
Grinding wheel consists of hard abrasive grains called grits, which perform the cutting or
material removal, held in the weak bonding matrix. A grinding wheel commonly
identified by the type of the abrasive material used. The conventional wheels include
Aluminium Oxide (Al2O3) and Silicon Carbide (SiC) wheels while diamond and CBN
(Cubic Boron Nitride) wheels fall in the category of super abrasive wheel. Thus, it forms
a multi-edge cutter.
4.1 Grinding wheel and work piece interaction

1. Grit-work piece (forming chip)

2. Chip-bond
3. Chip-work piece.
4. Bond-work piece

Except the grit-work piece interaction which is expected to produce chip, the remaining
three undesirably increases the total grinding force and power requirement. Therefore,
efforts should always be made to maximize grit-work piece interaction leading to chip
formation and to minimize the rest for best utilization of the available power.

4.2 Interaction of grit with the work piece

The importance of the grit shape can be easily realized because it determines the grit
geometry e.g. rake and clearance angle as illustrated in Fig. 4.3. It appears that the grits
do not have definite geometry unlike a cutting tool and the grit rake angle may vary from
+450 to -600 or more.

Fig. 4.3 Variation in rake angle with grits of different shape

Grit with favourable geometry can produce chip in shear mode. However, grits having
large negative rake angle or rounded cutting edge do not form chips but may rub or make
a groove by ploughing leading to lateral flow of the work piece material as illustrated in
Fig. 4.4

Fig. 4.4 Grits engage shearing, ploughing and rubbing

4.3 SPECIFICATION OF GRINDING WHEEL

A grinding wheel requires two types of specification:

1. Geometrical specification.
2. Compositional specification.

4.3.1 Geometrical specification

This is decided by the type of grinding machine and the grinding operation to be
performed in the work piece. This specification mainly includes wheel diameter, width
and depth of rim and the bore diameter. The wheel diameter, for example can be as high
as 400mm in high efficiency grinding or as small as less than 1mm in internal grinding.
Similarly, width of the wheel may be less than an mm in dicing and slicing applications.
Standard wheel configurations for conventional and super abrasive grinding wheels are
shown in Fig. 4.10 and Fig. 4.11.

Fig. 4.10 Standard wheel configuration for conventional grinding wheels

Fig. 4.11 Standard wheel configuration for super abrasive wheel
 4.3.2 Compositional specifications
Specification of a grinding wheel ordinarily means compositional specification. Conventional
abrasive grinding wheels are specified encompassing the following parameters.
o The type of grit material.
o The grit size.
o The bond strength of the wheel, commonly known as wheel hardness.
o The structures of the wheel denoting the porosity i.e. the amount of inter grit
spacing.
o The type of bond material.

Marking system for super abrasive grinding wheel

Marking system for super abrasive grinding wheel is somewhat different as illustrated
below:

R D 120 N 100 M 4

where
 The letter ‘R’ is manufacture’s code indicating the exact type of super abrasive
used.

 The letter ‘D’ denotes that the type of abrasive is Diamond. In case of Cubic
Boron Nitride (CBN) the letter ‘B’ is used.

 The number ‘120’ specifies the average grain size in inch mesh. However, a two
Number designation (e.g. 120/140) is utilized for controlling the size of super
abrasive grit.

 Like conventional abrasive wheel, the letter ‘N’ denotes the hardness of the wheel.
However, resin and metal bonded wheels are produced with almost no porosity
and effective grade of the wheel is obtained by modifying the bond formulation.

 The number ‘100’ is known as concentration number indicating the amount of

abrasive contained in the wheel. The number ‘100’ corresponds to an abrasive
content of 4.4 carats/cm3. For diamond grit, ‘100’ concentration is 25% by
volume. For CBN the corresponding volumetric concentration is 24%.

 The letter ‘M’ denotes that the type of bond is metallic. The other types of bonds
used in super abrasive wheels are resin, vitrified or metal bond, which make a
composite structure with the grit material. However, another type of super
abrasive wheel with both diamond and CBN is also manufactured where a single
layer of super abrasive grits are bonded on a metal perform by a galvanic metal
layer or a brazed metal layer as illustrated in Fig. 4.12
Fig. 4.12 Comparison of brazed type and galvanic type bonded single layer CBN
grinding wheel

4.4 SELECTION OF GRINDING WHEEL

Selection of a proper grinding wheel is very important for getting the best results in
grinding work.
The selection will depend upon the following factors:

1. Constant factors
a. Physical and chemical properties of material to be ground.
b. Amount and rate of stock to be removed.
c. Area of contact.
d. Types of grinding machine.

2. Variable factors
a. Work speed.
b. Wheel speed.
c. Condition of the grinding machine.
d. Personal factor.
e. Type of grinding (stock removal grinding or form finish grinding).

4.4.1 Types of abrasives

Abrasives may be classified into two types:
1. Natural abrasives - Emery (50 - 60 % crystalline Al2O3 + Iron Oxide), Sandstone
or Solid Quartz, Corundum (75 - 90 % crystalline Al2O3 + Iron Oxide) and
Diamond.
2. Artificial abrasives – Aluminium Oxide (Al2O3), Silicon Carbide (SiC), Artificial
diamond, Boron Carbide and Cubic Boron Nitride (CBN).

The abrasives that are generally used are

1. Aluminium Oxide. (Al2O3)
2. Silicon Carbide. (SiC)
3. Diamond.
4. Cubic Boron Nitride. (CBN)

1. Aluminium oxide (Al2O3):

Aluminium oxide may have variation in properties arising out of differences in
chemical composition and structure associated with the manufacturing process. Pure
Al2O3 grit with defect structure like voids leads to unusually sharp free cutting action
with low strength and is advantageous in fine tool grinding operation, and heat
sensitive operations on hard, ferrous materials. Regular or brown aluminium oxide
(doped with TiO2) possesses lower hardness and higher toughness than the white
Al2O3 and is recommended heavy duty grinding to semi finishing. Al2O3 alloyed with
chromium oxide (<3%) is pink in colour. Mono crystalline Al2O3 grits make a balance
between hardness and toughness and are efficient in medium pressure heat sensitive
operation on ferrous materials.
Microcrystalline Al2O3 grits of enhanced toughness are practically suitable for stock
removal grinding. Al2O3 alloyed with zirconia also makes extremely tough grit mostly
suitably for high pressure, high material removal grinding on ferrous material and are
not recommended for precision grinding.

2. Silicon Carbide. (SiC):

Black carbide containing at least 95% SiC is less hard but tougher than green SiC and
is efficient for grinding soft nonferrous materials. Green silicon carbide contains at
least 97% SiC. It is harder than black variety and is used for grinding cemented
carbide. Trade names: Carborundum, Crystolon, Electrolon, etc.

3. Diamond:
Diamond grit is best suited for grinding cemented carbides, glass, sapphire, stone,
granite, marble, concrete, oxide, non-oxide ceramic, fibre reinforced plastics, ferrite,
graphite. Natural diamond grit is characterized by its random shape, very sharp
cutting edge and free cutting action and is exclusively used in metallic, electroplated
and brazed bond.
Mono crystalline diamond grits are known for their strength and designed for
particularly demanding application. These are also used in metallic, galvanic and
brazed bond. Polycrystalline diamond grits are more friable than mono crystalline one
and found to be most suitable for grinding of cemented carbide with low pressure.
These grits are used in resin bond.
4. Cubic Boron Nitride (CBN)
Diamond though hardest is not suitable for grinding ferrous materials because of its
reactivity. In contrast, CBN the second hardest material, because of its chemical
stability is the abrasive material of choice for efficient grinding of HSS, alloy steels,
HSTR alloys.
Presently CBN grits are available as mono crystalline type with medium strength and
blocky mono crystals with much higher strength. Medium strength crystals are more
friable and used in resin bond for those applications where grinding force is not so
high. High strength crystals are used with vitrified, electroplated or brazed bond
where large grinding force is expected.
Microcrystalline CBN is known for its highest toughness and auto sharpening
character and found to be best candidate for HEDG and abrasive milling. It can be
used in all types of bond.

Test after completion

1. Which of the following grinding wheel would be more economical for grinding of
hard work piece?
a) Open structure grinding wheel
b) Dense structure wheel
c) Both dense and open structure grinding wheel
d) None of the mentioned

2. Which of the following grinding wheel would be more economical for grinding of
soft work piece?
a) Open structure grinding wheel
b) Dense structure wheel
c) Both dense and open structure grinding wheel
d) None of the mentioned

3. Material removal rate of grinding process in comparison to material removal rate in

facing on a lathe is
a) Small
b) Large
c) Same
d) Can’t say about material removal rate

4. Material removal rate in grinding operation is small due to

a) Negative rake angle
b) Positive rake angle
c) Zero rake angle
d) Material removal rate does not depend on the rake angle
 5. Grinding ratio generally lies between
a) 0.5-10
b) 100-200
c) 1000-200
d) 30-40

Conclusion
 In bonded abrasive processes, the particles are held together within a matrix,
and their combined shape determines the geometry of the finished work piece.
For example, in grinding the particles are bonded together in a wheel. As the
grinding wheel is fed into the part, its shape is transferred onto the work piece.
 In loose abrasive processes, there is no structure connecting the grains. They
may be applied without lubrication as dry powder, or they may be mixed with
a lubricant to form a slurry. Since the grains can move independently, they
must be forced into the work piece with another object like a polishing cloth or
a lapping plate.
 A grinding wheel is an expendable wheel that is composed of an abrasive
compound used for various grinding (abrasive cutting) and abrasive
machining operations. They are used in grinding machines.
 The manufacture of these wheels is a precise and tightly controlled process,
due not only to the inherent safety risks of a spinning disc, but also the
composition and uniformity required to prevent that disc from exploding due
to the high stresses produced on rotation.
 Grinding wheels with diamond or Cubic Boron Nitride (CBN) grains are
called super abrasives. Grinding wheels with Aluminium Oxide (corundum),
Silicon Carbide or Ceramic grains are called conventional abrasives.

Demo Videos
http://youtube.com/watch?v=7PL34Kpcsxo

References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.
 Answers to the assignments with full explanation
Assignment 1
1. Grain size, from 8 (coarsest) 1200 (finest), determines the physical size of the
abrasive grains in the wheel. A larger grain will cut freely, allowing fast
cutting but poor surface finish. Ultra-fine grain sizes are for precision finish
work.
2. Wheel grade, from A (soft) to Z (hard), determines how tightly the bond holds
the abrasive. Grade affects almost all considerations of grinding, such as
wheel speed, coolant flow, maximum and minimum feed rates, and grinding
depth.
3. Grain spacing, or structure, from 1 (densest) to 16 (least dense). Density is the
ratio of bond and abrasive to air space. A less-dense wheel will cut freely, and
has a large effect on surface finish. It is also able to take a deeper or wider cut
with less coolant, as the chip clearance on the wheel is greater.
4. Wheel bond, how the wheel holds the abrasives, affects finish, coolant, and
minimum/maximum wheel speed.
5. Dressing of the super abrasive wheel is commonly done with soft conventional
abrasive vitrified stick, which relieves the bond without affecting the super
abrasive grits. However, modern technique like electrochemical dressing has
been successfully used in metal bonded super abrasive wheel. The wheel acts
like an anode while a cathode plate is placed in front of the wheel working
surface to allow electrochemical dissolution.
6. Electro discharge dressing is another alternative route for dressing metal
bonded super abrasive wheel. In this case a dielectric medium is used in place
of an electrolyte. Touch-dressing, a new concept differs from conventional
dressing in that bond material is not relieved. In contrast the dressing depth is
precisely controlled in micron level to obtain better uniformity of grit height
resulting in improvement of work piece surface finish.
 Course Material for Unit - IV
Name of the Course : Manufacturing Technology

Name of the Unit : Abrasive Processes

Name of the Topic : Cylindrical grinding, surface grinding, Centre less

grinding, internal grinding.

 Objectives: To provide knowledge on different types of grinding machines

and related tools for manufacturing various components.

1. Outcomes: Upon successful completion, the student should be able to

understand the application grinding operation in manufacturing.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Which of the following range of numbers represents dense structure of

abrasives?
a) 0-7
b) 8-10
c) 10-12
d) 12-16

2. Which of the following range of numbers represents open structure of

abrasives?
a) 0-3
b) 4-6
c) 8-16
d) None of the mentioned

3. Resin bond is also known

a) Vitrified bond
b) Rubber bond
c) Silicate bond
d) Bakelite bond
4. Which of the following will be better to use for machining of hard work piece?
a) V-bond
b) R-bond
c) Both V and R bond
d) None of the mentioned

5. Grain number of grinding wheel is ___ to grain size.

a) Directly proportional
b) Inversely proportional
c) Does not depend
d) None of the mentioned

6. Which of the following is a correct range for grain number of the grinding
wheel for coarse grains?
a) 220-600
b) 80-180
c) 30-60
d) 10-24

7. Which of the following is the correct range for grain number of the grinding
wheel for medium grains?
a) 220-600
b) 80-180
c) 30-60
d) 10-24

8. Which of the following is the correct range for grain number of the grinding
wheel for very fine grains?
a) 220-600
b) 80-180
c) 30-60
d) 10-24

9. Which of the following grinding machine will give a better result for rough
machining?
a) Fine grain
b) Very fine grain
c) Coarse grain
d) None of the mentioned
10. Which of the following grinding machine will give a better result for finish
machining operation?
a) Fine grain
b) Medium grain
c) Coarse grain
d) None of the mentioned

3. Types of Grinding Processes

Straight wheel

Straight wheel

To the right is an image of a straight wheel. These are by far the most common
style of wheel and can be found on bench or pedestal grinders. They are used on
the periphery only and therefore produce a slightly concave surface (hollow
ground) on the part. This can be used to advantage on many tools such as chisels.
Straight Wheels are generally used for cylindrical, centre less, and surface
grinding operations. Wheels of this form vary greatly in size, the diameter and
width of face naturally depending upon the class of work for which is used and the
size and power of the grinding machine.

Cylinder or wheel ring:

Cylinder wheels provide a long, wide surface with no centre mounting support
(hollow). They can be very large, up to 12" in width. They are used only in
vertical or horizontal spindle grinders. Cylinder or wheel ring is used for
producing flat surfaces, the grinding being done with the end face of the wheel.

Tapered wheel:
A straight wheel that tapers outward towards the centre of the wheel. This
arrangement is stronger than straight wheels and can accept higher lateral loads.
Tapered face straight wheel is primarily used for grinding thread, gear teeth etc.

Straight cup:
Straight cup wheels are an alternative to cup wheels in tool and cutter grinders,
where having an additional radial grinding surface is beneficial.

Dish cup:
A very shallow cup-style grinding wheel. The thinness allows grinding in slots
and crevices. It is used primarily in cutter grinding and jig grinding.
Saucer wheel
A special grinding profile that is used to grind milling cutters and twist drills. It is
most common in non-machining areas, as saw filers use saucer wheels in the
maintenance of saw blades.

Diamond wheels

Diamond wheel

Diamond wheels are grinding wheels with industrial diamonds bonded to the
periphery.
They are used for grinding extremely hard materials such as carbide cutting tips,
gemstones or concrete. The saw pictured to the right is a slitting saw and is
designed for slicing hard materials, typically gemstones.

Mounted points:
Mounted points are small grinding wheels bonded onto a mandrel. Diamond
mounted points are tiny diamond rasps for use in a jig grinder doing profiling
work in hard material. Resin and vitrified bonded mounted points with
conventional grains are used for deburring applications, especially in the foundry
industry.

Cut off wheels:

Cut off wheels, also known as parting wheels, are self-sharpening wheels that are
thin in width and often have radial fibres reinforcing them. They are often used in
the construction industry for cutting reinforcement bars (rebar), protruding bolts
or anything that needs quick removal or trimming. Most handymen would
recognise an angle grinder and the discs they use.

4.1 Cylindrical grinding

The cylindrical grinder is a type of grinding machine used to shape the outside of
an object. The cylindrical grinder can work on a variety of shapes; however the
object must have a central axis of rotation. This includes but is not limited to such
shapes as a cylinder, an ellipse, a cam, or a crankshaft.
Cylindrical grinding is defined as having four essential actions:

1. The work (object) must be constantly rotating.

2. The grinding wheel must be constantly rotating.
3. The grinding wheel is fed towards and away from the work.
4. Either the work or the grinding wheel is traversed with respect to the other.

While the majority of cylindrical grinders employ all four movements, there are
grinders that only employ three of the four actions.
There are five different types of cylindrical grinding: outside diameter (OD)
grinding, inside diameter (ID) grinding, plunge grinding, creep feed grinding, and
centre less grinding.

A basic overview of Outside Diameter Cylindrical Grinding. The Curved arrows

refer to direction of rotation.
4.2 Outside Diameter Grinding
OD grinding is grinding occurring on external surface of an object between the
centres. The centres are end units with a oint that allow the object to be rotated.
The grinding wheel is also being rotated in the same direction when it comes in
contact with the object. This effectively means the two surfaces will be moving
opposite directions when contact is made which allows for a smoother operation
and less chance of a jam up.

Plunge grinding:
A form of OD grinding, however the major difference is that the grinding wheel
makes continuous contact with a sin le point of the object instead of traversing the
object.

Creep feed grinding:

Creep Feed is a form of grinding where a full depth of cut is removed in a single
pass of the wheel. Successful operation of this technique can reduce
manufacturing time by 50%, but often the grinding machine being used must be
designed specifically for this purpose.

4.2 Surface Grinding

Surface grinding is used to produce a smooth finish on flat surfaces. It is a widely

used abrasive machining process in which a spinning wheel covered in rough
particles (grinding wheel) cuts chips of metallic or non-metallic substance from a
work piece, making a face of it flat or smooth.
Surface grinding is the most common of the grinding operations. It is a finishing
process that uses a rotating abrasive wheel to smooth the flat surface of metallic or
non-metallic materials to give them a more refined look or to attain a desired
surface for a functional purpose.

The surface grinder is composed of an abrasive wheel, a work holding device

known as a chuck, and a reciprocating or rotary table. The chuck holds the
material in place while it is being worked on. It can do this one of two ways:
ferromagnetic pieces are held in place by a magnetic chuck, while non-
ferromagnetic and non-metallic pieces are held in place by vacuum or mechanical
means. A machine vice (made from ferromagnetic steel or cast iron) placed on the
magnetic chuck can be used to hold non-ferromagnetic work pieces if only a
magnetic chuck is available.

Factors to consider in surface grinding are the material of the grinding wheel and
the material of the piece being worked on.

Typical work piece materials include cast iron and mild steel. These two materials
don't tend to clog the grinding wheel while being processed. Other materials are
aluminium, stainless steel, brass and some plastics. When grinding at high
temperatures, the material tends to become weakened and is more inclined to
corrode. This can also result in a loss of magnetism in materials where this is
applicable.

The grinding wheel is not limited to a cylindrical shape and can have a myriad of
options that are useful in transferring different geometries to the object being
worked on. Straight wheels can be dressed by the operator to produce custom
geometries. When surface grinding an object, one must keep in mind that the
shape of the wheel will be transferred to the material of the object like a mirror
image.

Spark out is a term used when precision values are sought and literally means
"until the sparks are out (no more)". It involves passing the work piece under the
wheel, without resetting the depth of cut, more than once and generally multiple
times. This ensures that any inconsistencies in the machine or work piece are
eliminated.

A surface grinder is a machine tool used to provide precision ground surfaces,

either to a critical size or for the surface finish.
The typical precision of a surface grinder depends on the type and usage, however
+/- 0.002 mm (+/- 0.0001") should be achievable on most surface grinders.

The machine consists of a table that traverses both longitudinally and across the
face of the wheel. The longitudinal feed is usually powered by hydraulics, as may
the cross feed, however any mixture of hand, electrical or hydraulic may be used
depending on the ultimate usage of the machine (i.e.: production, workshop, cost).
The grinding wheel rotates in the spindle head and is also adjustable for height, by
any of the methods described previously. Modern surface grinders are semi-
automated, depth of cut and spark-out may be pre-set as to the number of passes
and, once set up, the machining process requires very little operator intervention.

Depending on the work piece material, the work is generally held by the use of a
magnetic chuck. This may be either an electromagnetic chuck, or a manually
operated, permanent magnet type chuck; both types are shown in the first image.

The machine has provision for the application of coolant as well as the extraction
of metal dust (metal and grinding particles).

Types of surface grinders

Horizontal-spindle (peripheral) surface grinders. The periphery (flat edge) of the
wheel is in contact with the work piece, producing the flat surface. Peripheral
grinding is used in high- precision work on simple flat surfaces; tapers or angled
surfaces; slots; flat surfaces next to shoulders; recessed surfaces; and profiles.

Vertical-spindle (wheel-face) grinders. The face of a wheel (cup, cylinder, disc, or

segmental wheel) is used on the flat surface. Wheel-face grinding is often used for
fast material removal, but some machines can accomplish high-precision work.
The work piece is held on a reciprocating table, which can be varied according to
the task, or a rotary-table machine, with continuous or indexed rotation. Indexing
allows loading or unloading one station while grinding operations are being
performed on another.

Disc grinders and double-disc grinders. Disc grinding is similar to surface

grinding, but with a larger contact area between disc and work piece. Disc
grinders are available in both vertical and horizontal spindle types. Double disc
grinders work both sides of a work piece simultaneously. Disc grinders are
capable of achieving especially fine tolerances.

4.3 Centre less grinding

Center less grinding is a form of grinding where there is no collet or pair of
centers holding the object in place. Instead, there is a regulating wheel positioned
on the opposite side of the object to the grinding wheel. A work rest keeps the
object at the appropriate height but has no bearing on its rotary speed. The work
blade is angled slightly towards the regulating wheel, with the work piece
centreline above the center lines of the regulating and grinding wheel; this means
that high spots do not tend to generate corresponding opposite low spots, and
hence the roundness of parts can be improved.
 A schematic of the centre less grinding process.

Centerless grinding is much easier to combine with automatic loading procedures

than centered grinding; through feed grinding, where the regulating wheel is held
at a slight angle to the part so that there is a force feeding the part through the
grinder, is particularly efficient.

4.4 Internal Grinding

A basic overview of Internal Diameter Cylindrical Grinding. The Curved Arrows

refer to direction of rotation.

ID grinding is grinding occurring on the inside of an object. The grinding wheel is

always smaller than the width of the object. The object is held in place by a collet,
which also rotates the object in place. Just as with OD grinding, the grinding
wheel and the object rotated in opposite directions giving reversed direction
contact of the two surfaces where the grinding occurs.
 Test after completion
1. Which of the following symbol’s range of alphabet represent hard grain in
grinding wheel?
a) D – H
b) I – P
c) A – D
d) Q – Z

2. Among the conventional machining processes, maximum specific energy is

consumed in
(a) Turning
(b) Drilling
(c) Planning
(d) Grinding

3. Ideal surface roughness, as measured by the maximum height of unevenness, is

best achieved when, the material is removed by
(a) an end mill
(b) a grinding wheel
(c) a tool with zero nose radius
(d) a ball mill.

4. Consider the following statements in respect of grinding?

1. The pitch of the grit cutting edges is larger than the pitch of the milling cutter.
2. The cutting angles of the grits have a random geometry.
3. The size of the chip cuts is very small for grinding.
Which of the statements given above are correct?
(a) 1 and 2
(b) 2 and 3
(c) 1 and 3
(d) 1, 2 and 3

5. In machining using abrasive material, increasing abrasive grain size

(a) Increases the material removal rate
(b) Decreases the material removal rate
(c) First decreases and then increases the material removal rate
(d) First increases and then decreases the material removal rate
 Conclusion
 The headstock supports the work piece by means of a dead centre and
drives it be means of a dog, or it may hold and drive the work piece in a
chuck.
 The tail stock can be adjusted and dampen in various positions to
accommodate different lengths of work piece.
 The wheel head carries a grinding wheel and its driving motor is mounted
on a slide at the top and rear of the base. The wheel head may be moved
perpendicularly to the table ways, by hand or power, to feed the wheel to
the work.
 Internal grinding is employed chiefly for finishing accurate holes in
hardened parts, and also when it is impossible to apply other more
productive methods of finishing accurate hold, for example, precision
boring, honing etc.
 Roll grinding is a specific case of cylindrical grinding wherein large work
pieces such as shafts, spindles and rolls are ground.

Demo Videos
http://youtube.com/watch?v=Vcfau3bJ8hE
References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 2
1. Centreless grinding makes it possible to grind cylindrical work pieces without actually
fixing the work piece using centres of a chuck. As a result no work rotation is
separately provided. The process consists of two wheels, one large grinding wheel and
another smaller regulating wheel. The work is held on a work rest blade. The regulating
wheel is mounted at an angle to the plane of the grinding wheel.
2. The centre of the work piece is slightly above the centre of the grinding wheel. The
work piece is supported by the rest blade and held against the regulating wheel by the
grinding force. As a result the work rotates at the same surface speed as that of
regulating wheel. The axial feed of the work piece is controlled by the angle of tilt of
the regulating wheel. Typical work speeds are about 10 to 50m/min.
3. There are two general methods of internal grinding:
 With a rotating work piece.
 With the work piece held stationary.
4. The first method is used in grinding holes in relatively small work pieces, mostly
bodies of revolution, for example, the bores of gears and the inner surfaces of ball
bearing rings. The work piece is held in a chuck or special fixture and rotated in the
same manner as in a lathe. A straight type grinding wheel is rotated and has two feed-
longitudinal feed along the wheel axis and is thus reciprocated back and forth through
the length of the hole, and intermittent cross feed(radial feed) at the end of each pass,
which determines the depth of cut.
5. The second method of internal grinding is used for grinding holes in large bulky work
pieces (housing-type parts) that are inconvenient or even impossible to clamp in a
chuck of the grinder. They are mounted on the table of a planetary grinding machine. In
addition to rotation about its axis, the wheel spindle of this type of machine also rotates
with a planetary motion about the axis of the hole being ground. Axial motion of the
wheel provides the longitudinal feed.
 Course Material for Unit - IV
Name of the Course : Manufacturing Technology

Name of the Unit : Abrasive Processes

Name of the Topic : Micro finishing methods - Typical applications –

concepts of surface integrity.

 Objectives: To provide knowledge on different types of grinding machines

and related tools for manufacturing various components.

1. Outcomes: Upon successful completion, the student should be able to

understand the application grinding operation in manufacturing.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Which one of the following is NOT used as abrasive material in grinding

wheels?
(a) Aluminium oxide
(b) Silicon carbide
(c) Cubic boron nitride
(d) Manganese oxide

2. Which one of the following materials is used as the bonding material for
grinding wheels?
(a) Silicon carbide
(b) Sodium silicate
(c) Boron carbide
(d) Aluminium oxide

3. Grinding wheel is said to be loaded when the

(a) metal particles get embedded in the wheel surface blocking the interspaces
between cutting grains.
(b) bonding material comes on the surface and the wheel becomes blunt.
(c) work piece being ground comes to a stop in cylindrical grinding.
(d) grinding wheel stops because of very large depth of cut
4. Specific cutting energy is more in grinding process compared to turning
because
(a) grinding (cutting) speed is higher
(b) the wheel has multiple cutting edges (grains)
(c) ploughing force is significant due to small chip size
(d) grinding wheel undergoes continuous wear

5. Specific energy requirements in a grinding process are more than those in

turning for the same metal removal rate because of the
(a) specific pressures between wheel and work being high.
(b) size effect of the larger contact areas between wheel and work.
(c) high cutting velocities
(d) high heat produced during grinding.

6. If the chip-tool contact length is reduced slightly by grinding the tool face,
then
(a) both cutting force and interface temperature would decrease
(b) both cutting force and interface temperature would increase
(c) the cutting force would decrease but the interface temperature would
increase
(d) the cutting force would increase but the interface temperature would
decrease

7. In sheet metal work, the cutting face on the tool can be reduced by
(a) grinding the cutting edges sharp
(b) increasing the hardness of tool
(c) providing shear angle on tool
(d) increasing the hardness of die

8. The ratio of thrust force to cutting force is nearly 2.5 in

(a) turning
(b) broaching
(c) grinding
(d) plain milling.

9. Assertion (A): Vitrified bond is preferred for thin grinding wheels.

Reason (R): Vitrified bond is hard brittle.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R arc true but R is NOT the correct explanation of A
(c) A is true hut R is false
(d) A is false but R is true
10. Which one of the following grinding wheels (with Grade, Grit and Bond)
is suitable for cutter grinding?
(a) K 60 vitrified
(b) K 320 vitrified
(c) T 60 resinoid
(d) T 320 resinoid

3. SURFACE FINISHING PROCESSES OR MICRO FINISHING

PROCESSES

To ensure reliable performance and prolonged service life of modern

machinery, its components require to be manufactured not only with high
dimensional and geometrical accuracy but also with high surface finish. The
surface finish has a vital role in influencing functional characteristics like wear
resistance, fatigue strength, corrosion resistance and power loss due to friction.

Unfortunately, normal machining methods like turning, milling or even

classical grinding cannot meet this severe requirement. Table 4.4 illustrates
gradual improvement of surface roughness produced by various processes
ranging from precision turning to super finishing including lapping and
honing. The typical surface finishes for these operations are presented in the
table 4.5

Table 4.4 Table 4.5

 4. Honing

This process is used primarily to remove the grinding or the tool marks left on the
surface by previous operations. However, it can be used for external cylindrical
surfaces as well as flat surfaces. It is most commonly used for internal surfaces.

The advantages of honing are:

 Correction of geometrical accuracy.
 Dimensional accuracy.

Honing is a finishing process performed by a honing tool called as hone [shown in

Fig. 4.34], which contains a set of three to a dozen and more bonded abrasive sticks. The
sticks are equally spaced about the periphery of the honing tool. The sticks are held against
the work surface with controlled light pressure, usually exercised by small springs.

The honing tool is given a complex rotational and oscillatory axial motion, which combine to
produce a crosshatched lay pattern [shown in Fig. 4.35] of very low surface roughness. In
addition to the surface finish of about 0.1 µm, honing produces a characteristic crosshatched
surface that tends to retain lubrication during operation of the component, thus contributing to
its function and service life.

A cutting fluid must be used in honing to cool and lubricate the tool and to help remove the
chips. A common application of honing is to finish the holes. Typical examples include bores
of internal combustion engines, bearings, hydraulic cylinders, and gun barrels.

Fig. 4.34 Honing tool

Fig. 4.35 Lay pattern produced by combination of rotary and oscillatory motion
The honing stones are given a complex motion so as to prevent every single grit from
repeating its path over the work surface. The critical process parameters are:
o Rotation speed.
o Oscillation speed.
o Length and position of the stroke.
o Honing stick pressure.

5. LAPPING

Lapping is a surface finishing process used on flat or cylindrical surfaces. Lapping is the
abrading of a surface by means of a lap (which is made of a material softer than the material
to be lapped), which has been charged with the fine abrasive particles.
The process is employed to get:
o Geometrically true surface.
o Extreme accuracy of dimension.
o Correction of minor imperfections in shape.
o Refinement of the surface finish, and
o Close fit between mating surfaces.

Lapping methods:
o Hand lapping for flat work.
o Hand lapping for external cylindrical work, (Ring lapping).
o Machine lapping.

In lapping, instead of a bonded abrasive tool, oil-based fluid suspension of very small free
abrasive grains (aluminium oxide and silicon carbide, with typical grit sizes between 300 and
600) called a lapping compound is applied between the work piece and the lapping tool.

The lapping tool is called a lap, which is made of soft materials like copper, lead or wood.
The lap has the reverse of the desired shape of the work part. To accomplish the process, the
lap is pressed against the work and moved back and forth over the surface in a figure-eight or
other motion pattern, subjecting all portions of the surface to the same action. Lapping is
sometimes performed by hand, but lapping machines accomplish the process with greater
consistency and efficiency.

The cutting mechanism in lapping is that the abrasives become embedded in the lap surface,
and the cutting action is very similar to grinding, but a concurrent cutting action of the free
abrasive particles in the fluid cannot be excluded. Lapping is used to produce optical lenses,
metallic bearing surfaces, gauges, and other parts requiring very good finishes and extreme
accuracy. Fig. 4.37 schematically represents the lapping process. Material removal in lapping
usually ranges from .003 to .03 mm but many reach 0.08 to 0.1mm in certain cases.
Characteristics of lapping process:
o Use of loose abrasive between lap and the work piece.
o Usually lap and work piece are not positively driven but are guided in contact
with each other.

Fig. 4.37 Schematics of lapping process showing the lap and the cutting action of suspended
abrasive particles.

Cast iron is the mostly used lap material. However, soft steel, copper, brass, hardwood as
well as hardened steel and glass are also used.

Abrasives of lapping:
o Al2O3 and SiC, grain size 5~100µm.
o Cr2O3, grain size 1~2 µm.
o B4C3, grain size 5-60 µm.
o Diamond, grain size 0.5~5 V.
Vehicle materials for lapping:
o Machine oil.
o Rape oil.
o Grease.
Technical parameters affecting lapping processes are:
o Unit pressure.
o The grain size of abrasive.
o Concentration of abrasive in the vehicle.
o Lapping speed.

Lapping is performed either manually or by machine. Hand lapping is done with abrasive
powder as lapping medium, whereas machine lapping is done either with abrasive powder or
with bonded abrasive wheel.
6. SUPER FINISHING
Super finishing is a micro finishing process that produces a controlled surface condition on
parts which is not obtainable by any other method. It is abrasive process which utilizes
either a bonded abrasive like honing for cylindrical surfaces or a cup wheel for flat
surfaces. Fig. 4.38 schematically shows the super finishing process.

Fig. 4.38 Schematics of the super finishing process.

Super finishing is a finishing operation similar to honing, but it involves the use of a single
abrasive stick.

The operation also called ‘micro stoning’ consists of scrubbing a stone against a surface to
produce a fine quality metal finish.

Super finishing is generally used for:

 Removing surface fragmentation.
 Reducing surface stresses and burns and thus restoring surface integrity.
 Correcting inequalities in geometry.
 Super finishing produces a high wear resistant surface on any objet which is
symmetrical.

7. Burnishing
The burnishing process consists of pressing hardened steel rolls or balls into the surface of
the work piece and imparting a feed motion to the same. Ball burnishing of a cylindrical
surface is illustrated in Fig. 4.43. During burnishing considerable residual compressive stress
is induced in the surface of the work piece and thereby fatigue strength and wear resistance of
the surface layer increase.

Fig. 4.43 Scheme of ball burnishing

8. Magnetic field assisted polishing

Fig. 4.45 scheme of magnetic field assisted polishing

Magnetic field assisted polishing is particularly suitable for polishing of steel or

ceramic roller. The process is illustrated schematically in Fig. 4.45. A ceramic or a steel
roller is mounted on a rotating spindle. Magnetic poles are subjected to oscillation,
thereby, introducing a vibratory motion to the magnetic fluid containing these magnetic
and abrasive particles.
This action causes polishing of the cylindrical roller surface. In this technique, the
material removal rate increases with the field strength, rotational speed of the shaft and
mesh number of the abrasive. But the surface finish decreases with the increase of
material removal rate.

9. BUFFING

Fig. 4.46 Schematics of the buffing operation

Buffing is a finishing operation similar to polishing, in which the abrasive grains in a

suitable carrying medium such as grease are applied at suitable intervals to the buffing
wheel. Negligible amount of material is removed in buffing while a very high luster is
generated on the buffed surface. Fig. 4.46 schematically shows the buffing process.

As in polishing, the abrasive particles must be periodically replenished. As in

polishing, buffing is usually done manually, although machines have been designed to
perform the process automatically.
10. Concepts of surface Integrity

Surface integrity is the surface condition of a work piece after being modified by a
manufacturing process. The surface integrity of a work piece or item changes the
material's properties. The consequences of changes to surface integrity are a
mechanical engineering design problem, but the preservation of those properties are a
manufacturing consideration.

Surface integrity can have a great impact on a parts function; for example, Inconel 718
can have a fatigue limit as high as 540 MPa (78,000 psi) after a gentle grinding or as
low as 150 MPa (22,000 psi) after electrical discharge machining (EDM).
There are two aspects to surface integrity: topography characteristics and surface layer
characteristics. The topography is made up of surface roughness, waviness, errors of
form, and flaws. The surface layer characteristics that can change through processing
are: plastic deformation, residual stresses, cracks, hardness, over aging, phase changes,
recrystallization, intergranular attack, and hydrogen embrittlement. When a traditional
manufacturing process is used, such as machining, the surface layer sustains local
plastic deformation.

The processes that affect surface integrity can be conveniently broken up into three
classes: traditional processes, non-traditional processes, and finishing treatments.
Traditional processes are defined as processes where the tool contacts the work piece
surface; for example: grinding, turning, and machining. These processes will only
damage the surface integrity if the improper parameters are used, such as dull tools, too
high feed speeds, improper coolant or lubrication, or incorrect grinding wheel hardness.
Non-traditional processes are defined as processes where the tool does not contact the
work piece; examples of this type of process include EDM, electrochemical machining,
and chemical milling. These processes will produce different surface integrity
depending on how the processes are controlled; for instance, they can leave a stress-
free surface, a remelted surface, or excessive surface roughness. Finishing treatments
are defined as processes that negate surface finishes imparted by traditional and non-
traditional processes or improve the surface integrity. For example, compressive
residual stress can be enhanced via peening or roller burnishing or the recast layer left
by EDMing can be removed via chemical milling.

Finishing treatments can affect the workpiece surface in a wide variety of manners.
Some clean and/or remove defects, such as scratches, pores, burrs, flash, or blemishes.
Other processes improve or modify the surface appearance by improving smoothness,
texture, or colour. They can also improve corrosion resistance, wear
resistance, and/or reduce friction. Coatings are another type of finishing treatment
that may be used to plate an expensive or scarce material onto a less expensive base
material.
Variables
Manufacturing processes have five main variables: the work piece, the tool, the
machine tool, the environment, and process variables. All of these variables can affect
the surface integrity of the work piece by producing:

• High temperatures involved in various machining processes.

• Plastic deformation in the work piece (residual stresses).
• Surface geometry (roughness, cracks, distortion).
• Chemical reactions, especially between the tool and the work piece.

Test after completion

1. Abrasive material used in grinding wheel selected for grinding ferrous alloys is
(a) silicon carbide
(b) diamond
(c) aluminium oxide
(d) boron carbide

2. Assertion (A): The ratio of cutting force to thrust force is very high in grinding
process as compared to other machining processes.
Reason (R): Random orientation and effective negative rake angles of abrasive grains
increase the cutting force and adversely affect the cutting action and promote rubbing
action.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R arc true but R is NOT the correct explanation of A
(c) A is true hut R is false
(d) A is false but R is true

3. The size effect refers to the increase in specific cutting energy at low values of
undeformed chip thickness. It is due to which one of the following?
(a) Existence of ploughing force
(b) Work hardening
(c) High strain rate
(d) Presence of high friction at chip-tool interface.

4. Soft materials cannot be economically grind due to

(a) the high temperatures involved
(b) frequent wheel clogging
(c) rapid wheel wear
(d) low work piece stiffness.
 5. Given that the peripheral speed of the grinding wheel of 100 mm diameter for
cylindrical grinding of a steel work piece is 30 m/s, what will be the estimated
rotational speed of the grinding wheel in revolution per minute (r.p.m.)?
(a) 11460
(b) 5730
(c) 2865
(d) 95

Conclusion
 Polishing is used to remove scratches and burrs and to smooth rough surfaces while
buffing is used to provide attractive surfaces with high luster. The dimensional
accuracy of the parts is not affected by polishing and buffing operations.
 Polishing is a surface finishing process to a smooth and lustrous surface. Polishing is
done with very fine abrasive particles of Al2O3 or diamond in loose form smeared on
the polishing wheel with the work rubbing against the flexible wheel.
 Electro polishing is the reverse of electroplating. Here, the work piece acts as anode
and the material is removed from the work piece by electrochemical dissolution.
 The process is particularly suitable for polishing irregular surface since there is no
mechanical contact between work piece and polishing medium.
 The electrolyte electrochemically etches projections on the work piece surface at a
faster rate than the rest, thus producing a smooth surface. This process is also suitable
for deburring operation.

Demo Videos
http://youtube.com/watch?v=BCy6OYj917o

References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.
 Answers to the assignments with full explanation
Assignment 3

1. With the advent of precision brazing technique, efforts can be made to manufacture
honing stick with single layer configuration with a brazed metal bond. Like brazed
grinding wheel such single layer brazed honing stick are expected to provide
controlled grit density, larger grit protrusion leading to higher material removal rate
bonded counterpart. and longer life compared to what can be obtained with a
galvanically.
2. Surface integrity describes not only the topological (geometric) features of surfaces
and their Physical and chemical properties, but also their mechanical and
metallurgical properties and Characteristics. Surface integrity is an important
consideration in manufacturing operations, because it influences such properties as
fatigue strength, resistance to corrosion, and service life.
3. Honing is also a surface finishing process like grinding, which uses a “hone” tool that
consists of stones to abrade the metals. Buffing is used give much high lustrous,
reflective finish that cannot be obtained by polishing. The buffing process consists of
applying a very fine abrasive with rotating wheel.
4. Lapping is a high degree of surface finishing process used for producing
geometrically accurate flat, cylindrical and spherical surfaces. In the lapping process,
a layer of fine abrasive particles usually suspended in a liquid, is held in between the
work piece and the lap.
5. Polishing is the surface finishing operation performed by a polishing wheel, for the
purpose of removing appreciable metal to take out scratches, hole marks, Pits and
other defects from rough surfaces.
 Course Material for Unit - IV
Name of the Course : Manufacturing Technology

Name of the Unit : Abrasive Processes

Name of the Topic : Broaching machines: broach construction – push,

pull, surface and continuous broaching machines.

 Objectives: To provide knowledge on different types of grinding machines

and related tools for manufacturing various components.

1. Outcomes: Upon successful completion, the student should be able to

understand the application grinding operation in manufacturing.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Which of the following materials are used in grinding wheel?

1. Aluminium oxide 2. Cubic boron nitride 3. Silicon carbide
Select the correct answer using the codes given below:
(a) 1, 2 and 3
(b) 1 and 2
(c) 2 and 3
(d) 1 and 3

2. Consider the following statements in respect of a grinding wheel of specification, 51-

A- 36-L-7-R-23, using the standard alphanumeric codification:
1. Abrasive used in the wheel is aluminium oxide
2. The grain size of abrasive is medium
3. The wheel grade is medium hard
4. It has an open structure
5. It has resinoid as bonding agent
Which of these statements are correct?
(a) 1, 2 and 3
(b) 1, 3 and 4
(c) 2, 3 and 5
(d) 1, 4 and 5
3. The marking on a grinding wheel is '51 A 36 L 5 V 93'. The code '36' represents the
(a) structure
(b) grade
(c) grain- size
(d) manufacturer's number

4. The sequence of markings "S 14 K 14 S" on a grinding wheel represents respectively

(a) bond type, structure, grade, grain size and abrasive type
(b) abrasive type, grain size, grade, structure and bond type
(c) bond type, grade, structure, grain size and abrasive type
(d) abrasive type, structure, grade, grain size and bond type

5. In the grinding wheel of A 60 G 7 B 23, B stands for

(a) resinoid bond
(b) rubber bond
(c) shellac bond
(d) silicate bond.

6. Tool life in the case of a grinding wheel is the time

(a) between two successive regrinds of the wheel
(b) taken for the wheel to be balanced
(c) taken between two successive wheel dressings
(d) taken for a wear of 1mm on its diameter

7. Assertion (A): Hard wheels are chosen for grinding hard metals.
Reason (R): In hard wheels only the abrasive grains are retained for long time.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R arc true but R is NOT the correct explanation of A
(c) A is true hut R is false
(d) A is false but R is true

8. Consider the following statements regarding grinding of high carbon steel:

1. Grinding at high speed results in the reduction of chip thickness and cutting forces
per grit.
2. Aluminium oxide wheels are employed.
3. The grinding wheel has to be of open structure.
Of these statements
(a) 1,2 and 3 are correct
(b) 1 and 2 are correct
(c) 1 and 3 are correct
(d) 2 and 3 are correct.
9. Consider the following reasons:
1. Grinding wheel is soft
2. RPM of grinding wheel is too low
3. Cut is very fine
4. An improper cutting fluid is used
A grinding wheel may become loaded due to reasons stated at
(a) 1 and 4
(b) 1 and 3
(c) 2 and 4
(d) 2 and 3

10. Assertion (A): The grade of a grinding wheel is a measure of hardness of the
abrasive used for the wheel.
Reason (R): Grading is necessary for making right selection of the wheel for a
particular work.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R arc true but R is NOT the correct explanation of A
(c) A is true hut R is false
(d) A is false but R is true

3. Broaching Machines

Broaching machines are relatively simple as they only have to move the broach in a
linear motion at a predetermined speed and provide a means for handling the broach
automatically. Most machines are hydraulic, but a few specialty machines are
mechanically driven. The machines are distinguished by whether their motion is
horizontal or vertical. The choice of machine is primarily dictated by the stroke
required. Vertical broaching machines rarely have a stroke longer than 60 in (1.5 m).
• Vertical broaching machines can be designed for push broaching, pull-down
broaching, pull-up broaching, or surface broaching. Push broaching machines are
similar to an arbor press with a guided ram; typical capacities are 5 to 50 tons. The two
ram pull-down machine is the most common type of broaching machine. This style
machine has the rams under the table. Pull-up machines have the ram above the table;
they usually have more than one ram. Most surface broaching is done on a vertical
machine.

• Horizontal broaching machines are designed for pull broaching, surface broaching,
continuous broaching, and rotary broaching. Pull style machines are basically vertical
machines laid on the side with a longer stroke. Surface style machines hold the broach
stationary while the work pieces are clamped into fixtures that are mounted on a
conveyor system. Continuous style machines are similar to the surface style machines
except adapted for internal broaching.

• Horizontal machines used to be much more common than vertical machines, however
today they represent just 10% of all broaching machines purchased. Vertical machines
are more popular because they take up less space.

4. Push Type Broaching Machine

Vertical internal push-down: Vertical push-down machines are often nothing more than
general-purpose hydraulic presses with special fixtures. They are available with
capacities of 2 to 25 tons, strokes up to 36" and speeds as high as 40 FPM. In some
cases, universal machines have been designed which combine as many as three
different broaching operations, such as push, pull, and surface, simply through the
addition of special fixtures.
5. Pull Type Broaching Machine

Vertical internal pull-up: The pull-up type, in which the workpiece is placed below the
worktable, was the first to be introduced. Its principal use is in broaching round and
irregular shaped holes. Pull-up machines are now furnished with pulling capacities of 6
to 50 tons, strokes up to 72", and broaching speeds of 30 FPM. Larger machines are
available; some have electro-mechanical drives for greater broaching speed and higher
productivity.

Vertical internal pull-down: The more sophisticated pull-down machines, in which the
work is placed on top of the table, were developed later than the pull-up type. These
pull-down machines are capable of holding internal shapes to closer tolerances by
means of locating fixtures on top of the worktable. Machines come with pulling
capacities of 2 to 75 tons, 30" to 110" strokes, and speeds of up to 80 FPM.

6. Surface broaches

The broaches used to remove material from an external surface are commonly known
as surface broaches. Such broaches are passed over the work piece surface to be cut, or
the work piece passes over the tool on horizontal, vertical or chain machines to produce
flat or contoured surfaces.

While some surface broaches are of solid construction, most are of built-up design,
with sections, inserts or indexable tool bits that are assembled end-to-end in a broach
holder or sub holder. The holder fits on the machine slide and provides rigid alignment
and support.
 7. Continuous Chain Broaching

Continuous chain, or simply chain broaching refers to the type of machine that is used
to broach a piece part.
Chain broaching is oriented towards high volume production, and is an extremely fast
and efficient operation. However, because the fixtures used to hold the piece parts are
mounted on chains that are driven by sprockets, it is difficult to hold extremely close
tolerances. This process is suitable for high-volume, external cutting.

Continuous Chain Broaching Machine

A chain broaching machine resembles a very long tunnel, through which passes a series of
holding fixtures, or cars. Piece parts are loaded, usually automatically, into the cars, which
themselves are mounted on, and carried through the tunnel by a very large continuous chain.
The broach tooling is mounted on the inside walls of the tunnel, and this tooling cuts the
piece part as it passes through the tunnel.
 Test after completion
1. The hardness of a grinding wheel is determined by the
(a) hardness of abrasive grains
(b) ability of the bond to retain abrasives
(c) hardness of the bond
(d) ability of the grinding wheel to penetrate the work piece

2. Dry and compressed air is used as cutting fluid for machining

(a) steel
(b) aluminium
(c) cast iron
(d) brass

3. Consider the following statements:

The set-up for internal centreless grinding consists of a regulating wheel, a pressure roll
and a support roll, between which the tubular work piece is supported with the grinding
wheel within the tube, wherein
1. the grinding wheel, work piece and regulating wheel centers must lie on one line
2. the directions of rotation of work piece and grinding wheel are same
3. the directions of rotation of pressure roll, support roll and regulating wheel are
same
4. the directions of rotation of grinding wheel and regulating wheel are same Which
of these statements are correct?
(a) 1, 2 and 3
(b) 1, 3 and 4
(c) 2 and 3
(d) 3 and 4

4. In centreless grinding, the work piece centre will be

(a) above the line joining the two wheel centres
(b) below the line joining the two wheel centres
(c) on the line joining the two wheel centres
(d) at the intersection of the line joining the wheel centres with the work plate plane.
 5. Which of the following pairs are correctly matched?
1. Drill press: Trepanning 2. Centreless grinding: Through feeding
3. Capstan lathe: Ram type turret
Select the correct answer using the codes given below:
Codes:
(a) 1 and 2
(b) 1, 2 and 3
(c) 1 and 3
(d) 2 and 3

Conclusion
 Machining by broaching is preferably used for making straight through holes of
various forms and sizes of section, internal and external through straight or helical
slots or grooves, external surfaces of different shapes, teeth of external and internal
splines and small spur gears etc.
 Broaches can be broadly classified in several aspects such as:
 Internal broaching or external broaching.
 Pull type or Push type.
 Ordinary cut or Progressive type.
 Solid, Sectional or Modular type.
 Profile sharpened or form relieved type.
 During operation a pull type broach is subjected to tensile force, which helps in
maintaining alignment and prevents buckling.
 Broaches are mostly made in single pieces especially those used for pull type internal
broaching.
 The broach is composed of a series of teeth, each tooth standing slightly higher than
the previous one. This rise per tooth is the feed per tooth and determines the material
removed by the tooth. There are basically three sets of teeth present in a broach. The
roughing teeth that have the highest rise per tooth removes bulk of the material.

Demo Videos
http://youtube.com/watch?v=6XIQy6Mon54
References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.
 Answers to the assignments with full explanation
Assignment 4

1. The pull end of the broach is attached to the pulling mechanism of the broaching
machine with the front pilot aligning the broach properly with respect to the work
piece axis before the actual cutting starts. The rear pilot helps to keep the broach to
remain square with the work piece as it leaves the work piece after broaching.
Broaching speeds are relatively low.
2. Being a cutting tool, broaches are also made of materials having the usual cutting tool
material properties, i.e., high strength, hardness, toughness and good heat and wear
resistance. For ease of manufacture and resharpening the complex shape and cutting
edges, broaches are mostly made of HSS. To enhance cutting speed, productivity and
product quality, now-a-days cemented carbide segments (assembled) or replaceable
inserts are also used specially for stronger and harder work materials like cast irons
and steels. TiN coated carbides provide much longer tool life in broaching. Since
broaching speed (velocity) is usually quite low, ceramic tools are not used.
3. The basic function of a broaching machine is to provide a precise linear motion of the
tool past a stationary work position. There are two principal modifications of the
broaching machines, horizontal, and vertical. The former are suitable for broaching of
relatively long and small diameter holes, while the later are used for short lengths and
large diameters.
4. PUSH BROACHING MACHINES: In these machines the broach movement is
guided by a ram. These machines are simple, since the broach only needs to be
pushed through the component for cutting and then retracted. The work piece is fixed
into a boring fixture on the table. Even simple arbor presses can be used for push
broaching.
5. PULL BROACHING MACHINES: These machines consist of a work holding
mechanism, and a broach pulling mechanism along with a broach elevator to help in
the removal and threading of the broach through the work piece. The work piece is
mounted in the broaching fixture and the broach is inserted through the hole present in
the work piece.
 Course Material for Unit - V
Name of the Course : Manufacturing Technology

Name of the Unit : Gear Manufacturing Processes

Name of the Topic : Gear manufacturing processes - Gear Machining-

Forming or Form cutting.

 Objectives: To identify the basic gear manufacturing machines used in

industries.

1. Outcomes: Upon successful completion, the student should be able to

understand the gear manufacturing used in industries.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Honing Process gives surface finish of what order?

(a) 10 µm (CLA)
(b) 1.0 µm (CLA)
(c) 0.1 µm (CLA)
(d) 0.01 µm (CLA)

2. CLA value for Honing process is

(a) 6
(b) 0.05 - 3.0
(c) 0.05 - 1.0
(d) 0.025 - 0.1

3. Gear lapping
(a) an operation after heat treatment
(b) an operation prior to heat treatment
(c) an independent operation for gear reconditioning
(d) none of the above.
4. A surface finish of 0.025 – 0.1 micrometer CLA values is to be produced. Which
machining process would you recommend?
(a) Grinding
(b) Rough turning
(c) Lapping
(d) Honing

5. Which one of the following processing sequences will give the best accuracy as
well as surface finish?
(a) Drilling, reaming and grinding
(b) Drilling, boring and grinding
(c) Drilling, reaming and lapping
(d) Drilling, reaming and electroplating

6. Buffing wheels are mode of

(a) softer metals
(b) cotton fabric
(c) carbon
(d) graphite

7. Gear shaping is related to ____________.

A. Template
B. Form tooth process
C. Hob
D. Generating

8. Which of the following methods produces gear by generating process __________.

A. Hobbing
B. Casting
C. Punching
D. Milling
9. Gears are best mass produced by _________________.
A. Milling
B. Hobbing
C. Shaping
D. Forming

10. Which of the following is a gear finishing operation ___________.

A. Milling
B. Hobbing
C. Shaping
D. Shaping and brushing
3. Gear
Gears can be manufactured by most of manufacturing processes discussed so far (casting,
forging, extrusion, powder metallurgy, blanking). But as a rule, machining is applied to
achieve the final dimensions, shape and surface finish in the gear. The initial operations
that produce a semi finishing part ready for gear machining as referred to as blanking
operations; the starting product in gear machining is called a gear blank.
Two principal methods of gear manufacturing include Gear forming, and Gear
generation.
Each method includes a number of machining processes, the major of them included in
this section.
Gear forming
In gear form cutting, the cutting edge of the cutting tool has a shape identical with the
shape of the space between the gear teeth.
Two machining operations, milling and broaching can be employed to form cut gear
teeth.
Two principal methods of gear manufacturing include:
 Gear forming
- where the profile of the teeth are obtained as the replica of the form of
the cutting tool (edge); e.g., milling, broaching etc.

 Gear generation
- where the complicated tooth profile are provided by much simpler form
cutting tool (edges) through rolling type, tool – work motions, e.g., hobbing, gear shaping
etc.

Each method includes a number of machining processes, the major of them discussed in
this section.
Manufacture of gears needs several processing operations in sequential stages depending
upon the material and type of the gears and quality desired. Those stages generally are:
 Preforming the blank without or with teeth.
 Annealing of the blank, if required, as in case of forged or cast steels.
 Preparation of the gear blank to the required dimensions by machining.
 Producing teeth or finishing the preformed teeth by machining.
 Full or surface hardening of the machined gear (teeth), if required.
 Finishing teeth, if required, by shaving, grinding etc.
 Inspection of the finished gears.
4. GEAR FORMING
Production of gears by gear forming method uses a single point cutting tool or a milling
cutter having the same form of cutting edge as the space between the gear teeth being cut.
This method uses simple and cheap tools in conventional machines and the setup required
is also simple. The principle of gear forming is shown in Fig. 4.66.
4.1 Shaping, planing and slotting
Fig. 4.67 schematically shows how teeth of straight toothed spur gear can be produced in
shaping machine. Both productivity and product quality are very low in this process. So
this process is used only for making one or few teeth on one or two pieces of gears as and
when required for repair and is used for making teeth of large gears whereas slotting,
generally, for internal gears.
Fig. 4.66 Principle of gear forming Fig. 4.67 Gear teeth cutting in ordinary
shaping machine

4.2 Milling
Gear teeth can be produced by both disc type and end mill type form milling cutters in a
milling machine. Fig. 4.68 illustrates the production of external spur gear teeth by using
disc type and end mill type cutters. Fig. 4.69 shows the form cutters used for finishing
cuts and for rough cuts. Fig. 4.70 illustrates the production of external helical gear teeth
by using form milling cutter. Fig. 4.71 shows the dividing head and foot stock used to
index the gear blank in form milling.

Fig. 4.68 Producing external teeth by form milling cutters

(a) disc type and (b) end mill type

Fig. 4.69 Form milling cutters

Fig. 4.70 Producing external teeth by form milling Fig. 4.71 Dividing head and
cutters (a) single helical and (b) double helical teeth footstock used to index the gear
blank in form milling

The work piece is actually mounted in the dividing head. In form milling, indexing of the
gear blank is required to cut all the teeth. Indexing is the process of evenly dividing the
circumference of a gear blank into equally spaced divisions. The index head of the
indexing fixture is used for this purpose.

The index fixture consists of an index head (also dividing head, gear cutting attachment)
and footstock, which is similar to the tailstock of a lathe. The index head and footstock
attach to the worktable of the milling machine. An index plate containing graduations is
used to control the rotation of the index head spindle. Gear blanks are held between
centers by the index head spindle and footstock. Work pieces may also be held in a chuck
mounted to the index head spindle or may be fitted directly into the taper spindle recess of
some indexing fixtures.

Production of gear teeth by form milling are characterized by:

 Use of HSS form milling cutters.
 Use of ordinary milling cutters.
 Low production rate:
o Need of indexing after machining each tooth gap.
o Slow speed and feed.
 Low accuracy and surface finish.
 Inventory problem – due to need of a set of eight cutters for each module –
pressure angle combination.
 End mill type cutters are used for teeth of large gears and / or module.
4.3 Fast production of teeth of spur gears by parallel multiple teeth shaping

In principle, it is similar to ordinary shaping but all the tooth gaps are made
simultaneously, without requiring indexing, by a set of radially in feeding single point
form tools as indicated in Fig. 4.72. This old process was highly productive but
became almost obsolete for very high initial and running costs.

Fig. 4.72 High production of straight teeth of external spur gears by parallel shaping
 Test after completion
1. Teeth of internal spur gears can be accurately cut in a
(a) milling machine
(b) gear shaping machine
(c) slotting machine
(d) hobbing machine

2. Gear hobbing produces more accurate gears than milling because in hobbing.
(a) there is a continuous indexing operation
(b) pressure angle is larger than in milling
(c) hob and work piece both are rotating
(d) a special multi-tooth cutter (hob) is used

3. Internal gear cutting operation can be performed by

(a) milling
(b) shaping with rack cutter
(c) shaping with pinion cutter
(d) hobbing

4. Which of following gear manufacturing processes is based on generation principle?

(a) Gear hobbing
(b) Gear shaping
(c) Gear milling
(d) Gear shaving

5. Gear forming operation can be performed by

A. Shaping
B. Milling
C. Broaching
D. Any one of the above

Conclusion
 In form milling, the cutter called a form cutter travels axially along the length
of the gear tooth at the appropriate depth to produce the gear tooth.
 After each tooth is cut, the cutter is withdrawn, the gear blank is rotated
(indexed), and the cutter proceeds to cut another tooth. The process continues
until all teeth are cut.
 Each cutter is designed to cut a range of tooth numbers. The precision of the
form-cut tooth profile depends on the accuracy of the cutter and the machine
and its stiffness. In form milling, indexing of the gear blank is required to cut
all the teeth.
  Indexing is the process of evenly dividing the circumference of a gear blank
into equally spaced divisions. The index head of the indexing fixture is used
for this purpose.
 The index fixture consists of an index head (also dividing head, gear cutting
attachment) and footstock, which is similar to the tailstock of a lathe.
 An index plate containing graduations is used to control the rotation of the
index head spindle. Gear blanks are held between centers by the index head
spindle and footstock. Work pieces may also be held in a chuck mounted to
the index head spindle or may be fitted directly into the taper spindle recess of
some indexing fixtures.

Demo Videos
http://youtube.com/watch?v=1A834AQjDIk
References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 1

1. Indexing is the process of dividing the periphery of a job in to equal number of

divisions. The indexing is used in both areas of the milling machine. One is tool
indexing it is to move the next tool for operations. Another one is work piece indexing
it is used to next operation area of the work piece.
2. The indexing mechanism is used in dividing heads. This dividing heads are attached
with the milling machine table and to perform the indexing operations. These are
classified as follows. 1. Plain or simple dividing head. 2. Universal dividing head
3.Optical dividing head.
3. The gears are manufactured by the forming process. The following are the gear
forming process used in various machines.
a. Gear cutting by single point form tool.
b. Gear cutting by shear speed shaping process.
c. Gear broaching.
d. Template method.
e. Gear milling using a formed end mill.
4. Often some gearing system (rack – and – pinion) is also used to transform rotary
motion into linear motion and vice-versa. There are large varieties of gears used in
industrial equipments as well as a variety of other applications.
5. But machining is applied to achieve the final dimensions, shape and surface finish in
the gear. The initial operations that produce a semi finishing part ready for gear
machining as referred to as blanking operations; the starting product in gear
machining is called a gear blank.
 Course Material for Unit - V
Name of the Course : Manufacturing Technology

Name of the Unit : Gear Manufacturing Processes

Name of the Topic : Gear generating process- Gear shaping, Gear

hobbing and Gear planning.

 Objectives: To identify the basic gear manufacturing machines used in

industries.

1. Outcomes: Upon successful completion, the student should be able to

understand the gear manufacturing used in industries.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Gear cutting with a hob does not involve the following motions
A. Indexing of the work
B. Rotation of hob
C. Rotation of blank
D. Radial feed of knob

2. Gear shaper can be used to cut following type of gear

A. Internal
B. Non-conventional
C. Accurate
D. All of the above
3. Milling method for gear cutting finds applications when following type of gears are to
be cut
A. External
B. Internal
C. Helical
D. Considerable variety

4. A gear has to be subjected to shock and vibration. Following type should be selected
A. Gear with full depth teeth
B. Hybrid gears
C. Bevel gears
D. Gear with stub teeth

5. Which of the following is gear finishing process

A. Gear shaving
B. Gear hobbing
C. Gear shaping
D. Gear milling

6. Which of the following is not a production process for gears

A. Milling
B. Stamping
C. Hot rolling
D. Extruding

7. Hobbing process is not suitable for cutting following type of gear

A. Spur
B. Helical
C. Worm
D. Bevel
8. Formed milling operation of cutting gears can be used for cutting following type of
gears
A. Spur
B. Worm
C. Helical
D. All of the above

9. Pressure applied on work piece in case of lapping operation is

A .0.01 kg/cm2
B. 0.1 kg/cm2
C. 0.5 kg/cm2
D. 1.0 kg/cm2

10. Buffing process is used

A. To achieve flatness
B. To achieve roundness
C. To improve surface finish
D. To obtain very smooth reflective surfaces

3. GEAR GENERATION
To obtain more accurate gears, the gear is generally generated using a cutter, which is
similar to the gear with which it meshes by following the general gear theory. The gears
produced by generation are more accurate and the manufacturing process is also fast.
Generation method is characterized by automatic indexing and ability of a single cutter to
cover the entire range of number of teeth for a given combination of module and pressure
angle and hence provides high productivity and economy. These are used for large
volume production.
In gear generating, the tooth flanks are obtained (generated) as an outline of the
subsequent positions of the cutter, which resembles in shape the mating gear in the gear
pair. In gear generating, two machining processes are employed, shaping and milling.
There are several modifications of these processes for different cutting tool used:
 Milling with a hob (gear hobbing).
 Gear shaping with a pinion-shaped cutter.
 Gear shaping with a rack-shaped cutter.
Cutters and blanks rotate in a timed relationship: a proportional feed rate between them is
maintained. Gear generating is used for high production runs and for finishing cuts.
3.1 Sunderland method using rack type cutter
Fig. 4.74 schematically shows the principle of this generation process where the rack type
HSS cutter (having rake and clearance angles) reciprocates to accomplish the machining
(cutting) action while rolling type interaction with the gear blank like a pair of rack and
pinion.

Fig. 4.74 External gear teeth generation by rack type cutter

The favourable and essential applications of this method (and machine) include:
 Moderate size straight and helical toothed external spur gears with high accuracy
and finish.
 Cutting teeth of straight or helical fluted cluster gears.

3.2 Gear shaping

In principle, gear shaping is similar to the rack type cutting process, except that, the linear
type rack cutter is replaced by a circular cutter as indicated in Fig. 4.75, where both the
cutter and the blank rotate as a pair of spur gears in addition to the reciprocation of the
cutter. Fig. 4.76 schematically shows the generating action of a gear-shaper cutter.
 Fig. 4.75 Setup of gear teeth generation by gear shaping operation with a pinion-shaped
cutter

Fig. 4.76 Generating action of a gear-shaper cutter; (Bottom) series of photographs

showing various stages in generating one tooth in a gear by means of a gear-shaper cutter,
action taking place from right to left. One tooth of the cutter was painted white.

The gear shaper cutter is mounted on a vertical ram and is rotated about its axis as it
performs the reciprocating action. The work piece is also mounted on a vertical spindle
and rotates in mesh with the shaping cutter during the cutting operation. The relative
rotary motions of the shaping cutter and the gear blank are calculated as per the
requirement and incorporated with the change gears.
The cutter slowly moves into the gear blank surface with incremental depths of cut, till it
reaches the full depth. The cutter and gear blank are separated during the return (up)
stroke and come to the correct position during the cutting (down) stroke.
 The additional advantages of gear shaping over rack type cutting are:
o Straight or helical teeth of both external and internal spur gears can be
produced with high accuracy and finish.
o Productivity is also higher.

3.3 Gear hobbing

Gear hobbing is a machining process in which gear teeth are progressively generated by a
series of cuts with a helical cutting tool (hob). The gear hob is a formed tooth milling cutter
with helical teeth arranged like the thread on a screw. These teeth are fluted to produce the
required cutting edges. All motions in hobbing are rotary, and the hob and gear blank rotate
continuously as in two gears meshing until all teeth are cut. This process eliminates the
unproductive return motion of the gear shaping operation. The work piece is mounted on a
vertical axis and rotates about its axis.

The hob is mounted on an inclined axis whose inclination is equal to the helix angle of the
hob. The hob is rotated in synchronization with the rotation of the blank and is slowly moved
into the gear blank till the required tooth depth is reached in a plane above the gear blank.

The tool-work configuration and motions in hobbing are shown in Fig. 4.77, where the HSS
or carbide cutter having teeth like gear milling cutter and the gear blank apparently interact
like a pair of worm and worm wheel. The hob (cutter) looks and behaves like a single or
multiple start worms. Having lesser number (only three) of tool – work motions, hobbing
machines are much more rigid, strong and productive than gear shaping machine. But
hobbing provides lesser accuracy and finish and is used only for cutting straight or helical
teeth (single) of external spur gears and worm wheels.

Fig. 4.77 Setup of gear hobbing operation

Fig. 4.78 shows the generation of different types of gears by gear hobbing. When bobbing a
spur gear, the angle between the hob and gear blank axes is 90° minus the lead angle at the
hob threads. For helical gears, the hob is set so that the helix angle of the hob is parallel with
the tooth direction of the gear being cut. Additional movement along the tooth length is
necessary in order to cut the whole tooth length. Machines for cutting precise gears are
generally CNC type and often are housed in temperature controlled rooms to avoid
dimensional deformations.

Fig. 4.78 Generation of external gear teeth by hobbing (a) spur gear (b) helical gear and (c)
worm wheel

3.4 Gear planning of spur gears with rack type cutters:

In this process Sunderland type of gear planer is used. The work piece axis is horizontal and
the cutter is mounted on vertical slide. The cutter traverses vertically downwards during
rolling motion of generation. For cutting spur gears the cutter reciprocates horizontally along
a line parallel to the work axis.

Test after completion

1. Which of the following is fastest method of cutting gears
A. Milling
B. Gear shaping
C. Gear hobbing
D. Gear burnishing

2. In helical milling, the ratio of the circumference of the gear blank to the lead of the helix
gives the
A. Angle setting of the machine table
B. Proper speed to use
C. Proper feed and depth of cut required
D. No. of teeth to be cut
3. The accurate spacing of teeth in a gear blank requires the use of
A. A dividing head
B. An index plate
C. A gear tooth vernier
D. A differential mechanism

4. Helical gears can be cut on following type of milling machine

A. Vertical
B. Horizontal
C. Universal
D. Drum-type

5. Burnishing is an operation of
A. Heat treatment
B. Deep boring
C. Gear finishing
D. Surface treatment

Conclusion
 The main disadvantage of gear shaping is that Worm and worm wheels
cannot be generated on a gear shaper. The cost of the gear shaping
machine is too high compare the other gear manufacturing machines. The
skilled labours also needed to operate the gear shaping machines.
 Gear hobbing is a machining process in which gear teeth are progressively
generated by a series of cuts with a helical cutting tool (hob).
 All motions in hobbing are rotary, and the hob and gear blank rotate
continuously as in two gears meshing until all teeth are cut when bobbing
a spur gear, the angle between the hob and gear blank axes is 90° minus
the lead angle at the hob threads.
 For helical gears, the hob is set so that the helix angle of the hob is parallel
with the tooth direction of the gear being cut.
 The cutting of a gear by means of a hob is a continuous operation. The hob
and the gear blank are connected by a proper gearing so that they rotate in
mesh.

Demo Videos
http://youtube.com/watch?v=9wOmvS92xqU
 References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 2

1. To start cutting a gear, the rotating hob is fed inward until the proper setting for tooth
depth is achieved, then cutting continues until the entire gear is finished.
2. The gear hob is a formed tooth milling cutter with helical teeth arranged like the thread
on a screw. These teeth are fluted to produce the required cutting edges.
3. The cutter axis is parallel to the gear axis. The cutter rotates slowly in timed
relationship with the gear blank at the same pitch-cycle velocity, with an axial primary
reciprocating motion; to produce the gear teeth. A train of gears provides the required
relative motion between the cutter shaft and the gear-blank shaft.
4. Cutting may take place either at the down stroke or upstroke of the machine. Because
the clearance required for cutter travel is small, gear shaping is suitable for gears that
are located close to obstructing surfaces such as flanges. The tool is called gear cutter
and resembles in shape the mating gear from the conjugate gear pair, the other gear
being the blank.
5. Gear shaping is one of the most versatile of all gear cutting operations used to produce
internal gears, external gears, and integral gear-pinion arrangements. Advantages of
gear shaping with pinion-shaped cutter are the high dimensional accuracy achieved and
the not too expensive tool. The process is applied for finishing operation in all types of
production rates.
 Course Material for Unit - V
Name of the Course : Manufacturing Technology

Name of the Unit : Gear Manufacturing Processes

Name of the Topic : Gear broaching and Bevel gear generation.

 Objectives: To identify the basic gear manufacturing machines used in

industries.

1. Outcomes: Upon successful completion, the student should be able to

understand the gear manufacturing used in industries.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. Consider the following processes for the manufacture of gears:

1. Casting 2. Powder metallurgy 3. Machining from bar stock 4. Closed die forging
The correct sequence in increasing order of bending strength of gear teeth is
(a) 1, 2, 3, 4
(b) 1, 2, 4, 3
(c) 2, 1, 4, 3
(d) 2, 1, 3, 4

2. In helical milling, the ratio of the circumference of the gear blank to the lead of the
helix determines the:
(a) Proper speed to use
(b) Proper feed and depth of cut required
(c) Angle setting of the machine table
(d) Gear ratio for table screw and dividing head
3. Gear cutting on a milling machine using an involute profile cutter is a
(a) gear forming process
(b) gear generating process.
(c) gear shaping process
(d) highly accurate gear producing process

4. By which one of the following machines the teeth of an internal spur gear can be cut
accurately?
(a) Milling machine
(b) Slotting machine
(c) Hobbing machine
(d) Gear-shaping machine

5. Gear shaping is a process of manufacturing gears.

Which one of the following principles is employed by it?
(a) Form cutting with cutter
(b) Generating tooth form with a reciprocating cutter
(c) Generating tooth form by a rotating cutter
(d) Generating form with a reciprocating and revolving cutter

6. Assertion (A): Gears produced by employing form-cutting principle using gear-milling

cutter on a milling machine are not very accurate.
Reason (R): Production of the correct gear tooth profile employing form-cutting
principle
would require a separate cutter for cutting different numbers of teeth even for the same
module and also errors are associated with inaccurate operation of indexing mechanism.
(a) Both A and R are true and R is the correct explanation of A
(b)) Both A and R arc true but R is NOT the correct explanation of A
(c) A is true hut R is false
(d) A is false but R is true
7. In gear hobbing
(a) only hob rotates
(b) only gear blank rotates
(c) both hob and gear blank rotate
(d) neither hob nor gear blank rotates

8. A spur gear of 40 teeth is machined in a gear lobbing machine using –a double start
hob cutter. The speed ratio between the hob and the blank is
(a) 1:20
(b) 1:40
(c) 40: 1
(d) 20: 1

9. A 60-teeth gear when hobbed on a differential hobber with a two-start hob, the index
change gear ratio is governed by which one of the following kinematic balance
equations?
(a) 1 revolution of gear blank = 1/60 of hob revolutions
(b) 1 revolution of gear blank = 2/60 of hob revolutions
(c) 1 revolution of hob = 2/60 of blank revolutions
(d) 1 revolution of hob = 1/60 of blank revolutions

10. Which of the following motions are not needed for spur gear cutting with a hob?
1. Rotary motion of hob 2. Linear axial reciprocator motion of hob
3. Rotary motion of gear blank 4. Radial advancement of hob.
Select the correct answer using the codes given below:
(a) 1, 2 and 3
(b) 1, 3 and 4
(c) 1, 2 and 4
(d) 2, 3 and 4
 3. Fast production of teeth of spur gears by Broaching

Teeth of small internal and external spur gears; straight or single helical, of relatively
softer materials are produced in large quantity by this process. Fig. 4.73 (a and b)
schematically shows how external teeth are produced by a broaching in one pass. The
process is rapid and produces fine surface finish with high dimensional accuracy.

Fig. 5.73 (a) High production of straight teeth of Fig. 5.73 (b) Broaching the teeth
external spur gears by broaching of a gear segment by horizontal
external broaching in one pass

4. Manufacture of bevel gears

In manufacture of bevel gears, first the blanks are performed by casting or forging
followed by machining to desired dimensions in lathes or special purpose machine.
Then the teeth are produced in the blank by machining. The way of machining and
machine tool are chosen based on the form of teeth and volume of production as follows:
Straight toothed bevel gear
 Forming by milling cutter – low productivity and quality hence employed for
production requiring less volume and precision.
 Generation – high accuracy and finish, hence applied for batch to mass
production.

Fig. 5.74 schematically shows the principle of forming and generation of teeth of straight
toothed bevel gear. In generation process, the inner flanks of two adjacent teeth are developed
with involute profile by the straight teeth of the cutters under rolling action.
 Teeth of spiral and hypoid bevel gears are produced by almost the same generation
principle but the cutter resembles face milling cutter as shown in Fig. 5.75.

Fig. 5.74 Production of teeth of straight toothed spur gear by (a) forming and (b) generation
 Fig. 5.75 Generation of teeth of spiral and hypoid bevel gear.

Test after completion

1. Which of the following methods are gear generating processes?

1. Gear shaping 2. Gear hobbing 3. Gear milling
Select the correct answer using the code given below:
(a) 1, 2 and 3
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1 and 3 only

2. Which one of the following is not a feature of gear hobbing process?

(a) High rate of production
(b) Generation of helical gears
(c) Very accurate tooth profile
(d) Generation of internal gears

3. Consider the following motions and setting in a hobbing machine:

1. Hob rotation
2. Job rotation
3. Axial reciprocating hob rotation
4. Tilting of hob to its helix angle
Which of these motions and setting in a hobbing machine are required to machine a spur
gear?
(a) 1, 2 and 3
(b) 2, 3 and 4
(c) 1, 2 and 4
(d) 1, 3 and 4
4. Internal gear cutting operation can be performed by
(A) milling
(B) shaping with rack cutter
(C) shaping with pinion cutter
(D) hobbing

5. Which of the following cannot be cut by hobbing process?

(a) Helical gears
(b) Bevel gears
(c) Worm gears
(d) Spur gears

Conclusion
 The most commonly practiced method is preforming the blank by casting, forging etc.
followed by pre-machining to prepare the gear blank to desired dimensions and then
production of the teeth by machining and further finishing by grinding if necessary.
 Generation – where the complicated tooth profile are provided by much simpler form
cutting tool (edges) through rolling type, tool – work motions, e.g., hobbing, gear
shaping etc.
 Generation method is characterized by automatic indexing and ability of a single
cutter to cover the entire range of number of teeth for a given combination of module
and pressure angle and hence provides high productivity and economy.
 The hob (cutter) looks and behaves like a single or multiple start worm.
 Having lesser number (only three) of tool – work motions, hobbing machines are
much more rigid, strong and productive than gear shaping machine.

Demo Videos
http://youtube.com/watch?v=BLZ2kO9vRD4
References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.
 Answers to the assignments with full explanation
Assignment 3

1. The screw like single or multi-start worms (gears) made of steel are generally made by
machining like long thread milling or by cold rolling like thread rolling followed by
heat treatment for surface hardening and finishing by grinding.
2. Special attention is paid to gear manufacturing because of the specific requirements to
the gears. The gear tooth flanks have a complex and precise shape with high
requirements to the surface finish. Gears can be manufactured by most of
manufacturing processes. (casting, forging, extrusion, powder metallurgy, blanking,
etc.)
3. High quality small metallic or non-metallic external gears are often produced in large
quantity by extrusion. Number of gears of desired width are obtained by parting from
the extruded rod of gear – section.
4. Small size high quality external or internal spur, bevel or spiral gears are also produced
by powder metallurgy process. Large size gears are rolled after briquetting and
sintering for more strength and life. Powder metallurgically produced gears hardly
require any further finishing work.
5. Mass production of small and thin metallic gears requiring less accuracy and finish are
often done by blanking from sheets by suitably designed die and punch. Such gears are
used for clocks, watches, meters, toys etc. However, quality gears can also be produced
by slight finishing (shaving) after blanking.
 Course Material for Unit - V
Name of the Course : Manufacturing Technology

Name of the Unit : Gear Manufacturing Processes

Name of the Topic : Gear Finishing Methods – Gear Shaving, Gear

Grinding, Gear lapping, Gear honing.

 Objectives: To identify the basic gear manufacturing machines used in

industries.

1. Outcomes: Upon successful completion, the student should be able to

understand the gear manufacturing used in industries.

2. Pre-requisites: To have a basic knowledge of Manufacturing Processes.

1. For the manufacture of full depth spur gear by hobbing process, the number of teeth to
be cut = 30, module = 3 mm and pressure angle = 20°. The radial depth of cut to be
employed should be equal to
(a) 3.75 mm
(b) 4.50 mm
(c) 6.00 mm
(d) 6.75 mm

2. While cutting helical gears on a non-differential gear hobber, the feed change gear ratio
is
(a) independent of index change gear ratio
(b) dependent on speed change gear ratio
(c) interrelated to index change gear ratio
(d) independent of speed and index change gear ratio.
3. Gear burnishing process for
(a) removing residual stresses from teeth roots
(b) surface finishing
(c) under-cut gears
(d) cycloidal gears

4. Gear burnishing is a process for

A. Surface finishing
B. Undercut gears
C. Cycloidal gears
D. Removing residual stresses from teeth roots

5. Gear finishing operation is called

A. Shaping
B. Milling
C. Hobbing
D. Burnishing

6. Face hobbed bevel gear sets tend to have their involute point location ________.
A. On the flank centre
B. On the addendum circle
C. Between addendum and dedendum circle
D. Between flank centre and the heel

7. In gear hobbing
A. Only hob rotates
B. Only gear blank rotates
C. Both hob and gear blank rotates
D. Neither hob nor gear blank rotates
8. Hobbing process is also used for which of the following application?
A. Punching
B. Metal bending
C. Rust removal
D. Sprocket cutting

9. For helical gears, the angle between hob’s spindle axis and work piece’s spindle axis
must be ________ as the helix angle of the helical gear.
A. Increased by the same amount
B. Increased by the half amount
C. Decreased by the same amount
D. Decreased by the half amount

10. Hobbing machines are characterized by

A. Production rate
B. Largest module or PCD it can generate
C. Accuracy of the machine
D. Size of the machine

3. Finishing of Gear Teeth

For smooth running, good performance and long service life, the gears need
• to be accurate in dimensions and forms
• to have high surface finish and
• to be hard and wear resistive at their tooth flanks

Which are achieved by some gear teeth finishing work after near accurate preforming and
machining. Small gears made by cold rolling generally do not require further finishing. If
a rolled gear needs further surface hardening only then little finishing by grinding and / or
lapping is done after hardening.
Gears produced to near-net-shape by die casting, powder metallurgy, extrusion, blanking
etc. need little finishing.
But machined and hardened gear teeth are essentially finished for accuracy and surface
finish.
4. Common methods of gear teeth finishing

Gear teeth, after preforming and machining, are finished generally by;
 for soft and unhardened gears
• gear shaving
• gear rolling or burnishing
 for hard and hardened gears
• grinding
• lapping
 for soft but precision gears
• shaving followed by surface hardening and then lapping

4.1 Gear shaving

The teeth of straight or helical toothed external spur gears and worm wheels of moderate
size and made of soft materials like aluminium alloy, brass, bronze, cast iron etc. and
unhardened steels are mostly finished by shaving process. Fig. 5.76 shows the different
types of shaving cutters which while their finishing action work apparently as a spur gear,
rack or worm in mesh with the conjugate gears to be finished. All those gear, rack or
worm type shaving cutters are of hard steel or HSS and their teeth are uniformly serrated
as shown in Fig. 5.77 (a) to generate sharp cutting edges.
While interacting with the gears, the cutting teeth of the shaving cutter keep on
smoothening the mating gear flanks by fine machining to high accuracy and surface
finish. For such minute cutting action, the shaving teeth need an actual or apparent
movement relative to the mating teeth along their length as indicated in Fig. 5.77 (b).

4.2 Gear rolling or burnishing

In this method the machined gear is rolled under pressure with three hardened master
gears of high accuracy and finish. The minute irregularities of the machined gear teeth are
smeared off by cold plastic flow, which also helps in improving the surface integrity of
the desired teeth.
 Fig. 5.76 Gear shaving cutters of (a) spur gear type (b) rack and (c) worm type

(a) (b)

Fig. 5.77 Cutting teeth of gear shaving (a) cutter and its (b) action
4.3 Gear teeth grinding

Grinding is a very accurate method and is, though relatively expensive, more widely used
for finishing teeth of different type and size of gears of hard material or hardened
surfaces. The properly formed and dressed wheel finishes the gear teeth flanks by fine
machining or abrading action of the fine abrasives.

Like gear milling, gear grinding is also done on two principles

 Forming
 Generation, which is more productive and accurate

Gear teeth grinding on forming principle

This is very similar to machining gear teeth by a single disc type form milling cutter as
indicated in Fig. 5.78 where the grinding wheel is dressed to the form that is exactly
required on the gear. Need of indexing makes the process slow and less accurate. The
wheel or dressing has to be changed with change in module, pressure angle and even
number of teeth. Form grinding may be used for finishing straight or single helical spur
gears, straight toothed bevel gears as well as worm and worm wheels.

Gear teeth grinding on generation principle

Fig. 5.79 schematically shows the methods of finishing spur gear teeth by grinding on
generation principle.
The simplest and most widely used method is very similar to spur gear teeth generation
by one or multi-toothed rack cutter. The single or multi-ribbed rotating grinding wheel is
reciprocated along the gear teeth as shown. For finishing large gear teeth a pair of thin
dish type grinding wheels are used as shown in Fig. 5.79 (c). Whatsoever, the contacting
surfaces of the wheels are made to behave as the two flanks of the virtual rack tooth.

wheel

gear

Fig. 5.78 Gear teeth finishing by form grinding

 v
(a) (b) (c)

Fig. 5.79 Gear teeth grinding on generation principle.

4.4 Gear teeth finishing by lapping

The lapping process only corrects minute deviations from the desired gear tooth profiles.
The gear to be finished after machining and heat treatment and even after grinding is run
in mesh with a gear shaped lapping tool or another mating gear of cast iron. An abrasive
lapping compound is used in between them. The gear tooth contact substantially improves
by such lapping.

Test after completion

1. As the number of threads on the hob increases, it’s accuracy __________.
A. Increases
B. Decreases
C. Remains same
D. Can’t say

2. Which of the following methods delivers the better rolling performance and higher
strength of the manufactured bevel gear?
A. Face milling completing and hard finishing by grinding
B. Face hobbing and hard finishing by lapping
C. Face milling with five-cut and hard finishing by lapping
D. Face milling completing and hard finishing by lapping
3. How many indexing methods are there for cutting a gear?
A. 2
B. 4
C. 6
D. 8

4. Ideally how many gear threads should be there on each hob thread?
A. 20
B. 30
C. 45
D. 10 times the number of hob threads

5. 5 in (125mm) capacity machine can generate gears up to ________ pitch diameter.

A. 5 in
B. 10 in
C. 15 in
D. 20 in

Conclusion

 As produced by any of the process described, the surface finish and dimensional
accuracy may not be accurate enough for certain applications. Several finishing
operations are available, including the conventional process of shaving, and a
number of abrasive operations, including grinding, honing, and lapping.
 Although many gears “as cut”, either hobbed, planned or shaped are entirely
satisfactory for their intended application, for others an additional finishing
process is either necessary or desirable.
 All the mechanical finishing processes in common uses are intended to amend
tooth shape by making the flanks confirm more nearly to the true or modified
involute desired and to improve surface finish and tooth spacing.
 Gear shaving is the newest method of gear finishing. It is cold working process
accomplished by rolling the gear in contact and under pressure with three
hardened burnishing gears.
 In this case, a cutter harder than the work and in the form of conjugate gear which
meshes with it in such a way that when rotated together, relative sliding between
the cutter and the work teeth obtained, is used.

Demo Videos
http://youtube.com/watch?v=_Yy3jZu4PXE
 References
1. Kalpakjian and Schmid, Manufacturing processes for engineering materials (5th Edition)-Pearson
India, 2014.

2. Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems,

Wiley, 3rd Edition, 2009.

3. Degarmo’s Materials and Processes in Manufacturing, Black & Kohser, Wiley, 2008.

4. Hajra Choudhury, “Elements of Workshop Technology, Vol. I and II”, Media Promotors Pvt Ltd.,
Mumbai, 2001.

Answers to the assignments with full explanation

Assignment 4

1. The teeth of the cutter are serrated normal to the tooth profiles and in operation, the
cutter and work are meshed together as helical gears with the planes of their respective
axes crossing. In action one member of the pair is driven and makes the other rotate,
the new parallelism of the axes causes sliding action between the teeth.
2. The value of the crossed axis angle controls the finish produced to some extent since
smaller the angle, finer the finish. Angles ranging between 8o to 45o are generally
found most satisfactory. Shaving improves gear tooth finish where the cutting process
has not provided the required standard, ex that with high-speed hobbing but the cut
gear must have small errors only in pitch, profile and concentricity. The process is ideal
for automotive gearbox gears after hobbing and before hardening.
3. Heat-treated gears can be finished either by grinding or by lapping. This process of
gear finishing is becoming obsolete these days, as the shaving process is quite
satisfactory and cheaper than gear-grinding. But when the high accuracy associated
with profile grinding is required, it is the only process to be used. By grinding, teeth
can be finished either by generation or by forming.
4. In the former the work is made to roll in contact with a flat faced rotating grinding
wheel, which corresponds to the face of the imaginary rack meshing with the gear. One
side of tooth is ground at a time. Later on the grinding wheel is given the shape as
formed by space between two adjacent teeth and both flanks are finished together. The
second method tends to be rather quicker, but both give equally accurate results and
which of the method is to be used depends upon the availability of the type of grinding
machine.
5. The disadvantage of gear-grinding is that considerable time is consumed in the process
and also the surfaces of the teeth have small scratches or ridged which increase both
wear and noise. To eliminate these defects ground gears are frequently lapped.