MODULE Manufacturing

f Processes:
Theory of Metal Cutting &
V Machine Tools

Drilling
Lecture Notes: And
Milling
Joyjeet Ghose

Senior Lecturer,
Department of Production Engineering,
Birla Institute of Technology, Mesra
Drilling
• One of the most important and essential tools in any metalworking shop is
the drilling machine or drill press.
• Although the drilling machine is used primarily for drilling holes, is often
used for reaming,
reaming boring,
boring tapping,
tapping counterboring,
counterboring countersinking,
countersinking and
spotfacing.
• All drillingg machines operate
p on the same basic pprinciple.
p The spindle
p
turns the cutting tool, which is advanced either by hand or automatically
into a workpiece that is mounted on the table or held in a drill press vise.
• Successful
S ccessf l operation of any
an drilling machine requires
req ires a good knowledge
kno ledge
of the machine, proper set-up of the work, correct speed and feed, and
proper use of cutting fluids applied to the cutting tool and work.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Types of drilling machine
• Sensitive Drill Press
– The sensitive drilling machine is a small machine designed for drilling
small holes at high speed in light jobs.
– The name ‘sensitive’
sensitive is used to indicate that the feed is hand operated
and that the spindle and drilling head are counterbalanced so that the
operator can ‘feel’ the pressure needed for efficient cutting.
– The drill press has the same motions as simple drill press one plus a
telescoping screw for raising and lowering the table and a sliding ‘drill
head’.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Sensitive Drill Press

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Types of drilling machine
• Simple Drill Press or Upright drilling Machine:
– A simple drilling machine is designed for handling medium sized
workpieces.
– In
I construction
t ti the th machine
hi is i similar
i il tot sensitive
iti drilling
d illi machine,hi
but it is heavier and larger than a sensitive drilling machine and is
supplied
pp with ppower feed arrangement.
g
– A simple drill press may be floor mounted, or have a shorter main post
and be mounted on a bench.
– The
h table
bl on a floor
fl model
d l can be
b raised
i d or lowered
l d andd rotatedd aroundd
the machine column. The spindle rotates and can be raised and
lowered.
– Stops can be set to limit and regulate the depth.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Types of drilling machine
• Radial Drilling Machine
– For handling medium to very large size castings, weldments, or
forgings, radial drills are ideal.
– The
Th length
l th off theth arm along
l which
hi h the
th spindle
i dl housing
h i rides
id specifies
ifi
their size.
– This arm can be from 3 to 12 feet long.
– The column that holds the arm may be from 10 to 30 inches in
diameter.
– For very large work, the arm may be rotated 180 degrees and work
placed on the shop floor.
– Speeds and feeds are dialed in by the machine operator and are the
same as for other drill presses.
– Drillingg is either hand or ppower feed.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Types of drilling machine

A Radial Drilling Machine

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Types of drilling machine

A Radial Drilling Machine

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Types of drilling machine
• Multi Spindle Drilling Machine
– The spindle locations are adjustable, and
the number of spindles may be from two to
eight.
eight
– Drills, reamers, countersinks, etc., can be
used in the spindles.
p
– The RPM and feed rate of all spindles in
one drill head are the same, and the
horsepower needed is the sum of the
power for all cutting tools used.
– In this type
yp of machine,, a large
g number of
holes may be drilled at one time.
– Several different diameters of drills may be
usedd att the
th same time.
ti

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Types of drilling machine
• Gang Drilling Machine
– An economical way to perform several
different operations on one piece is by
gang drilling.
drilling
– This might include drilling two or more
sizes of holes, reaming, g tapping,
pp g and
countersinking.
– The work is held in a vise or special
fi t re and is easily
fixture easil moved
mo ed along the
steel table from one spindle to the next.
– The drill presses
p usuallyy run
continuously so the operator merely
lowers each spindle to its preset stop to
perform the required machining
operation.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Drilling Machine Components
• The sensitive drilling machine construction features are discussed in this
section because its features are common to most other drilling machines.

A sensitive drill press

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Drilling Machine Components
• Base: The base is the main supporting member of the machine. It is heavy
gray iron or ductile iron casting with slots to support and hold work that is
too large for the table

A sensitive drill press

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Drilling Machine Components
• Column: The round column may be made of gray cast iron or ductile iron
for larger machines, or steel tubing for smaller bench drill presses. It
supports the table and the head of the drilling machine. The outer surface
is machined to function as a precision way of aligning the spindle with the
table.

A sensitive drill press

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Drilling Machine Components
• Table: The table can be adjusted up or down the column to the proper
height. It can also be swiveled around the column to the desired working
position. Most worktables have slots and holes for mounting vises and
other work
work-holding
holding accessories.
accessories Some tables are semi universal,
universal meaning
that they can be swiveled about the horizontal axis..

A sensitive drill press

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Drilling Machine Components
• Head: The head houses the spindle, quill, pulleys, motor, and feed
mechanism. The V-belt from the motor drives a pulley in the front part of
the head, which in turn drives the spindle. The spindle turns the drill.
Speeds on a stepped V pulley drive are changed by changing the position
of the V-belt. Speeds on a variable speed drive mechanism are changed by
a hand wheel on the head. The spindle must be revolving when this is
done.

A sensitive drill press

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Drilling Machine Components
• Quill assembly: The spindle rotates within the Quill on bearings. The
quill moves vertically by means of a rack and pinion. The quill assembly
makes it possible to feed or withdraw the cutting tool from the work.
Located on the lower end of the spindle is either a Morse tapered hole or a
threaded stub where the drill chuck is mounted. For drilling larger holes,
the drill chuck is removed and Morse tapered cutting tools are mounted.

Video showing quill operation

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Size or specification of a drilling machine
• The size (capacity) of a drilling machine is determined by all the
following features:
– Twice the distance from the center of the spindle to the inner face of
the column
– The maximum length of quill travel
– The size of the Morse taper in the spindle
– The horsepower of the motor.
– Number of spindle speeds and feeds.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Operational Set
Set--up of drilling
• In drilling operations the three most common work holding methods are:
– Vises
– Angle Plate
– Drill Jigs
– Clamps and bolts

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Operational Set
Set--up of drilling
• Vises:
– Vises are widely used for holding work of regular size and shape,
such as flat, square, and rectangular pieces.
– Parallels
P ll l are generally ll usedd to
t supportt the
th workk andd protect
t t the
th vise
i
from being drilled.
– Vises should be clamped to the table of the drill press to prevent them
from spinning during operation.
– Angular vises tilt the workpiece and provide a means of drilling a hole
at an angle
l without
ih tilting
il i the
h table.
bl

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Operational Set
Set--up of drilling
• Angle Plates:
– An angle plate supports work on its edge. Angle plates accurately
align the work perpendicular to the table surface, and they generally
have holes and slots to permit clamping to the table and holding of the
workpiece.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Operational Set
Set--up of drilling
• Drill Jigs:
– A drill jig is a production tool used when a hole, or several holes, must
be drilled in a large number of identical parts.
– The
Th drill
d ill jig
ji has
h severall functions.
f ti
– First, it is a work holding device, clamping the work firmly. Second, it
locates work in the correct position for drilling.
– The third function of the drill jig is to guide the drill straight into the
work. This is accomplished by use of drill bushings.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Tool Holding Devices
• Drill Chucks: Drilling tools which are small has straight shanks, and are
generally held in a drill chuck. The most common drill chuck uses a key to
lock the cutting tool. The other variety does not require any key and the
drill can be loaded and unloaded very quickly,
quickly and are therefore
commonly used in production works.

Key and keyless chucks

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Tool Holding Devices
• Sleeves: Drilling tools with tapered shanks are available in many different
sizes. When a cutting tool that has a smaller taper than the spindle taper
used, a sleeve must be fitted to the shank of the cutting tool.
• Sockets: If the cutting tool has a tapered shank larger than the spindle
taper, a socket is used to reduce it to the correct size.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Types of Drills

• Two fluted or Twist drills: This is the most common type of tool in use.use
It has spiral flutes or grooves that run lengthwise around the body of the
drill. Twist drills may have straight or tapered shank. Straight shank twist
d ill within
drill i hi the
h range off 0.2
0 2 to 1.6
1 6 mm diameters
di are called
ll d Jobber’s
bb ’
drill.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Types of Drills

• High Helix Drills: This drill has a high helix angle, which improves
cutting efficiency but weakens the drill body.
body It is used for cutting softer
metals and other low strength materials.
• Low Helix Drills: A lower than normal helix angle is sometimes useful
t preventt the
to th tool
t l from
f ‘
‘running
i ahead’
h d’ or grabbing’
bbi ’ when
h drilling
d illi brass
b
and similar materials.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Types of Drills

• Straight Flute Drills: Straight flute drills are an extreme case of low
helix drills. They are used for drilling brass, copper and sheet metal or
other soft materials. Here the rake angle is zero. In drilling brass, twist
drills tends to advance faster than the rate of feed and the drill digs into
the metal, therefore in such cases Straight flute drills are used.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Types of Drills

• Step Drill: Two or more diameters may be ground on a twist drill to

pproduce a hole with stepped
pp diameters.
• Oil Hole Drills: Small holes through the lands, or small tubes in slots
milled in the lands, can be used to force oil under pressure to the tool
point These drills are especially useful for drilling deep holes in tough
point.
materials.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Types of Drills

• Three and Four Fluted Drills: There are drills with three or four flutes
which resemble standard twist drills except that they have no chisel edge.
edge
They are used for enlarging holes that have been previously drilled or
punched. These drills are used because they give better productivity,
accuracy and surface finish than a standard drill would provide on the
accuracy,
same job.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Types of Drills

• Centre Drills: It is a combination of twist drill and countersink is a

useful tool for machining ‘center holes’ on bars to be turned or ground
between centers. The end of this tool resembles a standard drill. The
countersink starts a short distance back on the body.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Twist Drill Geometry and Nomenclature

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Twist Drill Geometry and Nomenclature

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Twist Drill Geometry and Nomenclature

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Twist Drill Nomenclature (Elements of a drill)
• Axis: The axis of the drill is the
centerline of the tool. It runs through
the web and is perpendicular to the
diameter
• Body: The body of the drill extends
from the shank to the point, and
contains the flutes. During
sharpening, it is the body of the drill
that is ppartiallyy gground away. y
• Shank: The shank is the part of the
drill that is held and driven. It may be
straight
i h or tapered. d Smaller
S ll diameter
di
drills normally have straight shanks.
Larger
g drills have shanks gground with
a taper and a tang to insure accurate
alignment and positive drive.
• Point:
P i t The Th point i t is
i the
th cutting
tti endd off
the drill.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Twist Drill Nomenclature (Elements of a drill)
• Tang: The tang is a flattened portion at
the end of the shank that fits into a
driving slot of the drill holder on the
spindle of the machine.
machine
• Neck: Some drills are made with a
relieved portion between the body and
the shank. This is called the drill neck.
• Flutes: Flutes are grooves that are cut
or formed in the body of the drill to
allow fluids to reach the point and
chips to reach the workpiece surface.
Al h h straight
Although i h flutes
fl are usedd ini
some cases, they are normally helical.
The main function of the flutes is to
form the cutting edges on the point, to
allow the chips to escape and to permit
the cutting fluid to reach the cutting
edges.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Twist Drill Nomenclature (Elements of a drill)
• Face: The portion of the flute surface
adjacent
dj to the
h lip
li on which
hi h the
h chip
hi
impinges as it cuts from the work.
• Flank: Flank is that surface on a drill
point which extends behind the lip of
the following flute.
• Land: It is the cylindrically ground
surface on the leading edges of the
drill flutes. The width of the land is
measured at right angles to the flute
helix. The drill is full size only across
the lands at the point end. Land keeps
the drill aligned.
aligned
• Web: The web is the central portion
of the drill situated between the roots
off the
th flutes
fl t andd extending
t di fromf th
the
point towards the shank.
• Chisel Edge: The edge formed by the
intersection of the flanks.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Twist Drill Nomenclature (Elements of a drill)
• Lips: The lips are the primary cutting
edges of the drill. They extend from
the chisel point to the periphery of the
drill Both lips should be of equal
drill.
length and should have same
inclination is the drill axis (590 in
general)l)
• Length: Along with its outside
diameter,, the axial length
g of a drill is
listed when the drill size is given. In
addition, shank length, flute length,
and neck length are often used.
used
• Body Diameter Clearance: It is
pportion of the bodyy surface which is
reduced in diameter to provide
diametral clearance.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Twist Drill Nomenclature (Drill Angles)
• Helix Angle or Rake angle: The angle that
the leading edge of the land makes with the
drill axis is called the helix angle. The
usual value of rake angle g is 300 . Smaller
the rake angle, greater will be the torque
required to drive the drill at a given feed.
• Point Angle: The included angle between
the drill lips is called the point angle. The
usual point angle is 1180 .
• Lip Clearance Angle:. It is measured at
the periphery. The angle formed by the
flank and a plane at right angles to the drill
axis. The clearance angle in most cases is
120 .
• Chisel
Chi l Edge
Ed Angle:
A l It is i the
th anglel between
b t
the lip and the chisel edge, as seen from the
end of the drill. The usual value of the
angle varies from 1200 to 1350 .

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Drilling Operations
• Drilling:
– First, a center drill should be used .
– Center drilling is done for accurately locating a hole to be drilled
afterwards.
afterwards
– If the hole is large, its a good idea to drill a smaller pilot hole before
drilling the final one.
– The
Th hole
h l will
ill be
b more accuratelyl positioned,
i i d rounder,d andd theh bits
bi will
ill
last longer.
– If the hole is deeper p than it is wide. use coolant and back off
occasionally to clear the chips.
– As you step up in drill size, you will need to reduce the spindle speed.
– If drilling a through hole,
hole ensure that the bit will not drill the table
after moving through your work.
– To set a desired depth of hole, there is a depth stop on the quill.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Drilling Operations
• Reaming: A reamer is used to enlarge a previously
d ill d hole,
drilled h l to provide id a higher
hi h tolerance
l andd to
improve the surface finish of the hole. This is the
operation of sizing and finishing a hole already made by
drilling. Reaming is done by means of a cutting tool
called reamer having multiple cutting edges. Reaming
makes the hole smother, straighter and more accurate.
• Boring: A drilled hole may not be concentric with the
axis of rotation of the spindle, may not be circular or
mayy not have the required
q dimension and surface finish.
Boring is done particularly to ensure correct location of
a hole. This operation is also used for enlarging a hole.
Boring uses a adjustable cutting tool with only one
cutting edge.
• Counterboring: Counterboring produces a larger step
in a hole to allow a bolt head to be seated below the part
surface. This is the operation of enlarging the end of a
hole cylindrically. The enlarged hole forms a square
shoulder with original hole. hole This is done to
accommodate heads of bolts and studs.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Drilling Operations
• Video showing a reaming operation

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Drilling Operations
• Countersinking: Countersinking is similar to
counterboring
b i except thath the
h step is
i angular
l to allow
ll flat-
fl
head screws to be seated below the surface. Counter
sinking is the tapering of the entrance of the hole. Thus
this is the operation of making a cone shaped enlargement
of the end of a hole to provide a recess for flat head screw
or countersunk rivet.
• Spotfacing: Spotfacing is used to provide a flat-
machined surface on a part. It removes only enough
material
t i l aroundd a hole
h l tot produce
d a machined
hi d surface
f
normal to the hole axis to provide seat for the washer.
• Tapping: A tap is used to provide internal threads on a
previously drilled hole by means of a tool called tap.
pp g This is an operation
• Lapping: p of finishingg a hole byy
removing small amounts of material by means of a
lapping tool. The lapping tool consists of fine abrasive
pparticles embedded into a soft material called lapp

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Drilling Operations

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Operating Conditions
• Drilling Speed: Cutting speed may be referred to as the rate that a point
on a circumference of a drill will travel per minute. It is expressed in
meter per minute (m/min). π dN
V = m/min
1000
Where: N = revolutions per minute (rpm), and d = the drill diameter in
mm.

• Drilling Feed: Drilling feed rates are selected to maximize productivity

while maintaining chip control. Feed (fr) in drilling operations is
expressed in mm per revolution, which is the distance the drill moves in
mm for each revolution of the drill. The feed (fm) mayy also be expressed
p
as the distance traveled by the drill in a single minute.

f m = f r × N mm/min

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Machining time in drilling (T)

L
T=
N × fr
Where,

L = l1 + l 2 + l 3 + l 4
l3
l1 = Length of the work piece. l2
l 2 = Approach of the drill. l1
l 3 = length of the drill point . l4
l 4 = Overtravel.

D
2 D
l3 = = = 0.29 D
tanα 2 × tan59

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Material Removal rate (MRR)

MRR = Volume of material removed per min

MRR = Area of cross - section of the hole × tool travel rate
π
MRR = D 2 × f r × N mm 3 /min
4

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Milling
• Plain milling machine was first developed by Eli Whitney in 1818.
• Joseph R Brown a member of Brown and sharpe company developed
universal milling machine in 1861.
• Milling machines are very versatile.
versatile
• They are usually used to machine flat surfaces, but can also produce
irregular surfaces.
• They
Th can also l beb usedd to drill,
d ill bore,
b cut gears, andd produce
d slots.
l
• The milling process:
– Typically uses a multi
multi-tooth
tooth cutter
– Work is fed into the rotating cutter
– Capable of high MRR
– Well suited for mass production applications
• The milling process can be distinguished from other metal cutting
operations by the chips produced.
• In a milling operation discontinuous chips are produced due to geometry
alone, whereas in operation discontinuous chips are produced due to
fracture of the chips

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Types of Milling Machines
• Column and Knee Machines
– Plain or horizontal milling machine
– Vertical milling machine
– Universal milling machine
– Omniversal milling machine
yp Milling
• Bed Type g Machines
– Simplex Milling Machines
– Duplex Milling Machines
– Triplex
T i l Milling
Milli Machines
M hi
• Special Purpose Milling Machines
– Planer Type Milling Machines
– Profile Milling Machines
– Rotary Milling Machines
– Drum Milling Machines

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Column and Knee Type Milling Machines

• In this type of milling machines, the table is mounted on a knee casting,

which is mounted on the vertical slides of the main column.
• The
Th knee
k i vertically
is ti ll adjustable
dj t bl on the
th column
l so that
th t the
th table
t bl can move
up and down to accommodate work piece of various sizes.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Column and Knee Type Milling Machines

• Plain or horizontal milling machine

– In this type of milling machines the table may be fed by hand or
power against
i t a rotating
t ti cutter
tt mounted t d on the
th horizontal
h i t l arbor.
b
– The table may fed in longitudinal, cross or vertical directions.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Column and Knee Type Milling Machines

• Vertical milling machine

– In this type of milling machines the spindle is vertical to the table.
– The table may fed in longitudinal,
longitudinal cross or vertical directions.
directions
– The end milling and face milling cutter are used in this type of
machines.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Column and Knee Type Milling Machines

Video illustrating that the table may fed in longitudinal, cross or

vertical directions
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Column and Knee Type Milling Machines
• Universal milling machine
– In this type of milling machines the table is mounted on a circular
swiveling base which is graduated in degrees.
– This additional features enable it to perform helical milling operations
which cannot be done in Plain or horizontal milling machine.
– The machine can produce spur, and spiral gears, twist drills, reamers,
and milling cutters.
cutters
– The capacity of the machines can be increased by the use of several
milling attachments like: dividing head, vertical milling attachment,
slotting
l i attachment
h etc.
– this type of milling machines are mainly used for tool room works

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Column and Knee Type Milling Machines

Photograph of an universal milling machine

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Column and Knee Type Milling Machines
• Omniversal milling machine
– In this type of milling machines the table besides having all the
movements of a universal milling machine, can be tilted in a vertical
plane.
plane
– This additional feature enables it to machine tapered spiral grooves in
reamers and bevel gears.
g

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Bed Type Milling Machines
• High production calls for heavy cuts, and the rigidity of a knee and column
type off milling
illi machine
hi may not beb sufficient
ffi i to takek the
h high
hi h forces.
f
• A bed-type milling machine is often ideal for this kind of work.
• In this machine the table is supported
pp directly
y on a heavyy bed,, while the
column is placed behind the bed.
• Its advantages lie in its higher productivity, its adaptability to large sized
machines, and its ease of modification to special applications.
• The chief disadvantage of a bed-type milling machine compared to one of the
knee and column type is that it is less versatile for machining small parts.
• Depending
D di upon the th numberb off spindles
i dl they
th are off three
th t
types: Si l
Simplex
Milling Machines, Duplex Milling Machines, and Triplex Milling Machines,
• Duplex bed-type milling machines have two columns and spindles for milling
two surfaces
f on a part simultaneously.
i l l

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Special Purpose Milling Machines
• Planer Type Milling Machines
• The general arrangement of these types of machines is similar to that for
planers, except that in place of individual tool bits, milling heads are
installed.
installed
• The table of the machine carries the work (slowly for feed unlike planer)
ppast the rotatingg cutter heads, which are individuallyy ppowered and can be
run at different speeds if necessary.
• As many as four cutter heads can be used, with two mounted on the cross
rail and two
t o on the vertical
ertical pillars.
pillars
• Planer-type machines are used mostly for machining parts like the
bedwaysy for largeg machine tools,, and other longg workpieces
p that require
q
accurate flat and angular surfaces or grooves.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Special Purpose Milling Machines
• Profile Milling Machines
– Hydraulic-type profilers have a stylus that is brought into contact with
the template to start the operation.
– The operator then moves the stylus along the template,template causing
hydraulic fluid under pressure to flow to the proper actuating
cylinders.
– The table moves the work past the cutter,
cutter duplicating the shape of the
template.
– An accurate pattern of the cavity is made of wood, plaster, or soft
metal.
l
– The stylus follows the contour of the pattern guiding the cutter as it
machines out the cavity.y
– Numerically controlled milling machines are also used for this type of
work.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Special Purpose Milling Machines
• Rotary table Milling Machines
– The construction of the machine is a modification of the vertical
milling machine and is adapted for machining flat surfaces at high
production rates.
rates
– The face milling cutters are mounted on two or more vertical spindles.
– Number of workpieces are clamped on a horizontal rotary circular
table.
– The cutters may be set at different heights w.r.t. work., so that when
one off the
h cutters is
i taking
ki a roughing
hi cut theh other
h isi finishing
fi i hi the
h
work.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Special Purpose Milling Machines
• Drum Milling Machines
– This is a variation of the rotary table milling machines.
– In this machine, the work supporting table , called drum, rotates about
a horizontal
h i t l axis. i
– The face milling cutters ( 3 to 4) also rotates about a horizontal axis.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Components of Column and Knee Type Milling Machines

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Components of Column and Knee Type Milling Machines
• Column
• The
Th column,
l which
hi h is
i usually
ll
combined with the base as a single
casting, is cast gray iron or ductile
iron.
iron
• The column houses the spindle,
bearings, and the necessary gears,
clutches shafts,
clutches, shafts pumps,
pumps and shifting
mechanisms for transmitting power
from the electric motor to the spindle
at the selected speed.
p
• Some of the necessary controls are
usually mounted on the side of the
column.
• The base is usually hollow, and in
many cases serves as a sump for the
cuttingg fluid.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Components of Column and Knee Type Milling Machines
• Column (contd…)
• A pump andd filtration
fil i system can be b
installed in the base.
• The hole in the center of the base
h
houses th supportt for
the f the
th screw that
th t
raises and lowers the knee.
• The machined vertical slide on the
f t off the
front th column
l may be
b off the
th
square or dovetail type.
• The knee moves up and down on this
slide.
slide
• The large hole in the face of the
column casting is for the spindle.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Components of Column and Knee Type Milling Machines
• Spindle
• On
O a horizontal
h i l milling
illi machine,
hi
the spindle is one of the most
critical parts.
• It is
i usually
ll machined
hi d from
f an alloy
ll
steel forging and is heat treated to
resist wear, vibration, thrust, and
bending loads.
loads
• The spindle is usually supported by
a combination of ball and straight
roller bearings,
bearings or by tapered roller
bearings that absorb both radial
loads and end thrust loads.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Components of Column and Knee Type Milling Machines
• Spindle (contd….)
• Spindles
S i dl are hollow
h ll so that
h a drawbar
d b
can be used to hold arbors securely in
place.
• The
Th front
f t off the
th spindle
i dl is
i machined
hi d
to accept standard arbors.
• The two keys that fit into
corresponding
di slots
l t in
i the
th arbor
b do
d the
th
actual driving of the arbor.
• The internal taper, which is accurately
gro nd so that it is concentric with
ground ith the
spindle, locates the arbor.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Components of Column and Knee Type Milling Machines
• Knee
• The
Th knee
k i a casting
is i that
h isi movedd
up or down the slide on the front of
the column by the elevating screw.
• The
Th vertical
ti l slide
lid matest withith the
th
slide on the front of the column, and
the horizontal slide carries the
saddle.
saddle
• It contains the necessary gears,
screws, and other mechanisms to
provide power feeds in all
directions.
• The operator can select various feed
rates with the controls mounted on
the knee.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Components of Column and Knee Type Milling Machines
• Saddle
• The
Th saddle ddl forf a plain
l i milling
illi
machine is a casting with two slides
machined at an exact 90 degree angle
to each other.
other
• The lower slide fits the slide on the
top of the knee, and the upper slide
accepts the slide on the bottom of the
table.
• Locks for both the cross slide and
table is fitted to the saddle,
saddle along with
the nuts that engage with the cross
feed and table feed screws.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Components of Column and Knee Type Milling Machines
• Table
• The
Th bottom
b off the
h table bl has
h a
dovetail slide that fits in the slide on
top of the saddle.
• The
Th top
t off the
th table
t bl has
h severall full
f ll
length T-slots for mounting vises or
other work holding fixtures.
• A dial
di l graduated
d t d ini thousandths
th dth off
an inch is provided to allow for
accurate table movement and
placement.
placement

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Milling Machines Size
• The size of a Milling Machines is specified by:
– Dimension of the working surface of the table.
– Maximum longitudinal, cross, and vertical feed of the table.
– Ranges of spindle speeds available.
– Ranges of feeds available.
– Power
P available.
il bl
– Spindle nose taper.
– Gross weight etc
etc.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Work Holding in a Milling Machines
• Plain Vise:
• Plain milling vises the movable jaw
moves on either a dovetail or
rectangular slide.
slide
• The vises are usually cast of high-grade
ggrayy cast iron or ductile iron and can be
heat-treated.
• Swivel-Base Vise:
• Theh base,
b which
hi h is
i graduated
d d in
i degrees,
d
is slotted for keys that align it with the
T-slots in the table.
• The upper part of the vise is held to the
base by T-bolts that engage a circular T-
slot.
l t

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Work Holding in a Milling Machines
• A universal vise:
• The base of the vise is graduated in
degrees and held to the table by T
bolts.
bolts
• The intermediate part of the vise has
a horizontal ppivot uponp which the
vise itself can rotate 90 degrees.
• Because there are several joints and
pi ots in the vise
pivots ise assembly,
assembl the
universal vise is usually the least
rigid of the various types of milling
machine vises.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Work Holding in a Milling Machines
• Angle Plates
– Plain angle plates are available in T-slotted or blank form and are
usually strong iron castings.
– Adjustable
Adj t bl angle l plates
l t may tilt ini one direction
di ti only l or have
h a swivel
i l
base.
– They are very useful for milling workpieces that are irregular in shape
and cannot be held easily in a vise.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Work Holding in a Milling Machines
• Rotary Table:
– The face of the rotary table has four or more T slots and an accurately
bored hole in the center, which is concentric with the axis about which
the table rotates.
rotates
– The base of the rotary table, which houses the worm drive mechanism,
is ggraduated in degrees,
g , and the handwheel can be ggraduated in
increments as small as of 1 degree.
– On some rotary tables an index plate may be attached to the base.
– Rotary tables can also be geared to the table feed screw.
– When set up in this manner, the rotary table can be used to make plate
cams and to generate a number of other irregular shapes.
shapes

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Work Holding in a Milling Machines

a)) Rotary
R t ttables
bl can b
be usedd on b
both
th vertical
ti l anddh
horizontal
i t l milling
illi machines.
hi
(b) A rotary table that can also be tilted.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Tool Holding in a Milling Machines

• A
Arbors:
b
• The cutters having bore at the centre are keyed on a short shaft called
arbor.
• A draw
d b l that
bolt h goes through
h h the
h spindle
i dl off the
h machine,
hi screws intoi the
h
small end of the taper and draws the arbor tightly into the tapered hole in
the milling machine spindle.
• Power
P i transmitted
is i d from
f the
h spindle
i dl to the
h arbor
b by
b two short
h keys
k that
h
engage with the slots on the flange of the arbor.
• One or more cutters can be mounted on the arbor, either adjacent to each
other
th or separated
t d by
b spacers andd shims.
hi

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Tool Holding in a Milling Machines

Arbors

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Tool Holding in a Milling Machines

• Collets:
• On some vertical millingg machines the spindle
p is bored to accept
p a collet
that has a partly straight and partly tapered shank.
• The collet is secured by a drawbar that is screwed into a tapped hole in the
b k off the
back h collet
ll andd tightened
i h d from
f the
h top off the
h spindle.
i dl

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Tool Holding in a Milling Machines
• Bolted cutters
– Face milling cutters of larger diameter having no shank are bolted
directly on the nose of the spindle.
• Screwed
S d on cutters
tt
– Small cutters having threaded holes at the centre are screwed on the
threaded nose of the arbor.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Milling Machines Attachments
• Dividing Heads (plain or universal type)
• The indexing head, also known as the dividing
head, can be used on vertical and horizontal
milling machines to space the cuts for such
operations as making splines, gears, worm
wheels, and many other parts requiring
accurate division.
• It can also be geared to the table screw for
helical milling operations such as cutting
flutes in twist drills and making helical gears.
• The spindle of the indexing head can be fitted
with a chuck, or with other work holding
devices, including collets or a center.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Milling Machines Attachments
• Vertical Heads
– Vertical heads are generally attached to the face of the column or to
the overarm of a horizontal milling machine.
– The head is a semisemi-universal
universal type,
type which pivots only on the axis
parallel to the centerline of the spindle, or it is fully universal.
• Slotting Attachment
– This attachment that is bolted to the column of a horizontal milling
machine can be swiveled 90 degrees in either direction from the
vertical position.
– It is used primarily in tool making and prototype work for cutting
keyways, internal splines, and square or rectangular cavities.
– The crank that actuates the reciprocating slide is driven directly by the
spindle, and the stroke is adjustable.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Milling Machines Attachments
• Rack-Milling Attachment
– The rack-milling attachment bolts to the Face of the column and is
used for cutting rack teeth on a job mounted on the table.
– The attachment uses a gear train which enables its spindle to be at a
right angle to the main spindle of the machine.
– Both spur and helical racks can be milled with this attachment, and it
can also be used to mill worms.
worms
• High Speed Attachment
– When spindle
p speeds
p beyond
y the operating
p g range
g of the machine are
necessary, high speed attachments can be placed on both horizontal
and vertical milling machines.
– A gear train is generally used to step up the speed as much as 4 to 6
times, which allows more efficient use of small cutters.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Milling Machines Attachments
• Universal Milling Attachment
– The Universal milling attachment is similar to the vertical milling
attachment, but it has added arrangement for swiveling the spindle
about two mutuallyy pperpendicular
p axes.
– The feature permits the spindle axis to swivel at any angle and
machine any compound angular work surface.
• Circular Milling Attachment (rotary table)
– The face of the rotary table has four or more T slots and an accurately
bored hole in the center, which is concentric with the axis about which
the
h table
bl rotates.
– The base of the rotary table, which houses the worm drive mechanism,
is ggraduated in degrees,
g , and the handwheel can be ggraduated in
increments as small as of 1 degree.
– On some rotary tables an index plate may be attached to the base.
– Rotary tables can also be geared to the table feed screw.
screw
– When set up in this manner, the rotary table can be used to make plate
cams and to generate a number of other irregular shapes.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Milling Cutters
• The variety of milling cutters
available for all types of
milling machines helps make
milling a very versatile
machining process.
• Cutters are made in a large
range of sizes and of several
different cutting tool materials.
• Different types of milling
cutters are discussed next.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Plain Milling Cutters
• Plain Milling Cutters are cylindrical in shape and have teeth on the
circumferential
i f i l surface
f only.
l
• The cutters are intended for production of flat surfaces parallel to the axis
of rotation of the spindle.
p
• Plain Milling Cutters are of the following types:
– Light Duty Plain Mill: This cutter is a general purpose cutter for
peripheral milling operations.
operations Narrow cutters (less than 20mm width)
have straight teeth, while wide ones have helical teeth (about 25
degrees helix).
– Heavy Duty Plain Mill: A heavy h d
duty plain
l i mill
ill is
i similar
i il to the
h light
li h
duty mill except that it is used for higher rates of metal removal. To
aid it in this function, the teeth are more widely spaced and the helix
angle is increased to about 45 degrees.
– Helical Plain Mill: In Helical Plain Mill the teeth are helical and the
g ranges
helix angle g from 45 to 60 degrees.
g

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Plain Milling Cutters (images)

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Side Milling cutters
• The side milling cutter has a cutting edge on the sides as well as on the
periphery.
i h
• Therefore they are intended for removing metals from the side of a work.
• This allows the cutter to mill slots.
slots
• Different types of side milling cutters are:
– Plain side milling cutter: Plain side milling cutter have straight
circumferential
i f i l teethh andd have
h side
id teethh on both
b h sides
id
– Staggered teeth side milling cutter: They have alternate teeth with
pp
opposite helix angle.
g This design g of the cutter increases chipp space
p and
helps in milling deep and narrow slots or key ways.
– Half side milling cutter: They have teeth on the circumference and
on one side only.
only It is used for milling shoulders.
shoulders Two cutters of this
type are often mounted on a single arbor for straddle milling.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Side Milling cutters

(a) staggered-tooth cutter, (b) side milling cutter

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Form Milling Cutters
• A form mill is a peripheral cutter whose edge is shaped to produce a
special configuration on the surface.
• One example of his class of tool is the gear tooth cutter.
• The
Th exactt contour
t off the
th cutting
tti edge
d off a form
f mill
ill is
i reproduced
d d on the
th
surface of the workpiece.
• They are of the following types:
– Convex milling cutter
– Concave milling cutter
– Corner rounding milling cutter
– Gear milling cutter

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Form Milling Cutters

(f) convex milling cutter, (g) concave milling cutter, (h) corner rounded milling cutter.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Form Milling Cutters

Gear Milling cutters

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Angle Milling Cutters
• On angle cutters, the peripheral cutting edges lie on a cone rather than on a
cylinder.
• A single or double angle may be provided.
• Available
A il bl ini different
diff varieties
i i off included
i l d d angle.
l

(d) single-angle milling cutter, (e)

double angle milling cutter,

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Metal slitting saws
• Metal saws resemble a plain milling cutter or
a side milling cutter in appearance but they
are of very small width.
• They are mainly used for parting off
operations.
• Theyy mayy have straight
g or staggered
gg teeth.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

End Milling Cutters
• End mills are shank mounted and can be used on vertical and horizontal
milling machines for a variety of facing, slotting, keyways, pockets, and
profiling operations.
• End mills have cutting edges on the end as well as on the periphery of the
cutter.
• The pperiphery
p y teeth mayy be straight
g or helical.
• End mills are of the following types:
– Tapered shank End mill
– Straight shank End mill
– Shell End mill

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

End Milling Cutters (images)

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

End Milling Cutters

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

T-slot and Dove -Tail Milling Cutters
• T-slot and Dove tail Milling Cutters are special forms of end mills for
producing
d i T-slotsl andd dove
d tail
il slots.
l
• Have teeth on periphery and both sides
• Used for milling the wide groove of a T T-slot
slot
• In order to use them, a vertical groove must first be made with a slotting
mill or an end mill to provide a clearance for the shank
• T-slot
T l cutter must be b fed
f d carefully,
f ll because
b i cuts in
it i 5 surfaces
f

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Plain Milling Cutter Nomenclature

• Outside Diameter: The outside diameter of a milling cutter is the

diameter of a circle passing through
thro gh the peripheral cutting
c tting edges.
edges It is the
dimension used in conjunction with the spindle speed to find the cutting
speed.
• Root Diameter: This diameter is measured on a circle passing through
the bottom of the fillets of the teeth.
• Tooth:
T th TheTh tooth
t th is
i the
th partt off the
th cutter
tt starting
t ti att the
th body
b d andd ending
di
with the peripheral cutting edge. Replaceable teeth are also called inserts.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Plain Milling Cutter Nomenclature

• Tooth Face: The tooth face is the surface of the tooth between the fillet
and the cutting edge, where the chip slides during its formation.
• Land: The area behind the cutting edge on the tooth that is relieved to
avoid interference is called the land.
land
• Flute: The flute is the space provided for chip flow between the teeth.
• G
Gash
s Angle:
g e Thee ggash
s angle
g e iss measured
e su ed be
between
wee thee tooth
oo face
ce andd thee
back of the tooth immediately ahead.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Plain Milling Cutter Nomenclature

• Fillet: The fillet is the radius at the bottom of the flute, provided to allow
chipp flow and chipp curling. g
• Peripheral Cutting Edge: The cutting edge aligned principally in the
direction of the cutter axis is called the peripheral cutting edge. In
pperipheral
p milling,
g, it is this edge
g that removes the metal.
• Face Cutting Edge: The face cutting edge is the metal removing edge
aligned primarily in a radial direction. In side milling and face milling,
this edge actually forms the new surface, although the peripheral cutting
edge may still be removing most of the metal. It corresponds to the end
cutting edge on single point tools.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Plain Milling Cutter Nomenclature

• Relief Angle: This angle is measured between the land and a tangent to
the
h cutting
i edge
d at the h periphery.
i h
• Clearance Angle: The clearance angle is provided to make room for
chips, thus forming the flute.
flute Normally two clearance angles are
provided to maintain the strength of the tooth and still provide sufficient
chip space.
• Radial Rake Angle: The radial rake angle is the angle between the tooth
face and a cutter radius, measured in a plane normal to the cutter axis.
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Plain Milling Cutter Nomenclature

• Helix angle or Axial Rake Angle (not shown): The axial rake angle is
measured between the peripheral cutting edge and a plane containing the
axis of the cutter, when looking radially at the point of intersection.
• Lip angle: The angle included between the face and land of the tooth.
tooth

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Milling processes
• Various milling operations performed by different milling cutters can be
grouped under two milling processes.
• They are : (a) Peripheral milling (slab milling), (b) Face milling

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Peripheral milling
• Peripheral milling is the process of milling a surface that is parallel to the
axis of the cutter and basically flat.
• It is done on plain or universal horizontal milling machines with cutters of
varying widths that have teeth only on the periphery.
periphery
• In Peripheral milling the cutting force is not uniform through out the
length
g of the cut byy each tooth.
• According to the relative movement of the tool and the work, Peripheral
milling is classified under two headings: Up milling (or conventional
milling) and down milling (or climb milling).
milling)

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Up milling (or conventional milling)
• Most common method of feed
• Feed work against the rotation of the cutter i.e. wheel rotation is opposite
of the feed.
• The chip formed by each cutter tooth starts out very thin and increases its
thickness.
• As the chip thickness per tooth is not uniform, the cutting force in Up
milling increases from zero
ero to maximum.
ma im m
• The cutting force is directed upward and tends to lift the workpiece from
the fixture.
• Need more clamping force to hold the work part still.
• The surface milled by Up milling appears to be slightly wavy as the cutter
do not begin their cut as soon as they touch the work surface.
surface The teeth
slides a minute distance at the beginning and then the cut is started.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Down milling (or climb milling)
• The cutter rotation is parallel to the feed.
• The chip formed by each cutter tooth starts out thick and leaves out thin.
• The cutting force in Up milling decreases from maximum to zero .
• Load of the cutter tends to “pull” the work into the cutter.
• Downward motion increases the load on the table ways
• Thi method
This th d can “pull”
“ ll” the
th workk into
i t the
th cutter
tt andd scrap the
th workk and/or
d/
damage the fixture and tool.
• Machine must be veryy rigid g to safelyy utilize climb millingg ((CNC
machines)
• Need less clamping force to hold the work part still.
• Suited for machining of thin and hard to hold parts

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Down milling (or climb milling)
• Advantages of Climb milling:
– Suited to machine thin and hard-to-hold parts since the workpiece is
forced against the table or holding device by the cutter.
– Work
W k needd nott be
b clamped
l d as tightly.
ti htl
– Consistent parallelism and size may be maintained, particularly on
thin parts.
p
– It may be used where breakout at the edge of the workpiece could not
be tolerated.
– It requires upto 20% less power to cut by this method.
– It may be used when cutting off stock or when milling deep, thin slots.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Down milling (or climb milling)
• Disadvantages:
– It cannot be used unless the machine has a backlash eliminator and the
table jibs have been tightened.
– It cannott be
b usedd for
f machining
hi i castings
ti or hot
h t rolled
ll d steel,
t l since
i the
th
hard outer scale will damage the cutter.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Face milling
• Face milling is performed to produce flat surfaces at right angles to the
axis of rotation of the cutter
• The peripheral cutting edge do the actual cutting, whereas the face cutting
edges finish up the work surface by removing small amount of material.
material
• In Face milling operation both up and down milling may be considered to
be pperformed simultaneouslyy on the work surface.
• When the cutter rotates through half of the revolution, the direction of the
movement of the cutter is opposite to the direction of the feed and the
condition reverses
re erses when
hen the cutter
c tter rotates other half of the revolution.
re ol tion
• The thickness of the chip is minimum at the beginning and at the end of
the cut,, and it is maximum when the work ppasses through g the centre line
of the cutter,

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Peripheral Milling Operations
• Slab milling:
– Cutter
C width
id h extends
d beyond
b d the
h workk
piece on both sides
• Side Milling:
– For side milling, a cutter that has teeth
on the periphery, and on one or both
sides, is used.
– When a single cutter is being used, the
teeth on both the periphery and sides
may be cutting.
– The
h machined
hi d surfaces
f are usually
ll
either perpendicular or parallel to the
spindle.
• Angular
A l Milling:
Milli
– Angle cutters can be used to produce
surfaces that are at an angle to the
spindle
i dl for
f suchh operations
ti as making
ki
external dovetails or flutes in reamers.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Peripheral Milling Operations
• Slotting and Slitting Operations:
– These
Th operations
i are usedd for
f cutting
i
slots and parting off .
– Slotting and Slitting are usually done on
horizontal milling machines,
machines but can
also be done on vertical mills by using
the proper adaptors and accessories.
– Metal slitting cutters of various
diameters and widths are also used to
cut slots.
• Form Milling: g
– It is the operation of production of
irregular contours by using form cutters.
• Straddle Milling:
– In a typical straddle milling set-up two-
side milling cutters are used.
– The cutters are halfhalf-side
side or plain side
milling cutters, and have straight or
helical teeth.
– Stagger-tooth
gg side millingg cutters can
also be used.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Peripheral Milling Operations
• Gang Milling:
– In gang milling, three or more cutters are mounted on the arbor, and
several horizontal, vertical, or angular surfaces are machined in one
p
pass.
– When making a gang milling set-up, several different types of cutters
can be used, depending on the job to be done.
– Cutters used for producing vertical or angular surfaces must be of the
side- cutting type; plain milling cutters of the proper width can be used
for horizontal surfaces.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Face Milling Operations
• Conventional face milling:
– Diameter of tool is larger than work part’s
width.
• End milling:
– Cutters diameter is less than the work part’s
width.
width
• Profile milling:
– Outside periphery of flat part is cut.
cut
• Pocket milling:
– S
Similar to end milling,
g, but the shape
p created
is a shallow pockets in flat surfaces
• Surface contouring:
– A ball-nose cutter is fed back and forth
across the work part to create a contoured
surface perpendicular to the cutter

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Face Milling Operations (video)

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Face Milling Operations ( A slotting video)

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Different Milling Operations

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Cutting speed, feed, and Depth of cut
• Cutting speed: The cutting speed of a milling cutter is its peripheral
linear speed resulting from rotation. It is expressed in meters per minute.
πDN
V=
1000
• F
Feed:d The
Th feed
f d ini a milling
illi machinehi is
i defined
d fi d as theth rate
t with
ith which
hi h the
th
work piece advances under the cutter. The feed is expressed in a milling
machine byy the followingg three methods.
• Feed per tooth ( fz ): The feed per tooth is defined by the distance the
work advances in time between engagement by the two successive teeth.
It is expressed
e pressed in millimeters per tooth of the cutter.
c tter
• Feed per cutter revolution (fr): The feed per cutter revolution is defined
byy the distance the work advances in time when the cutter turns through g
one complete revolution. It is expressed in millimeters per revolution of
the cutter. fr = fz × z
• Feed
F d per minute
i t (fm):) The
Th feed
f d per minute
i t isi defined
d fi d by
b the
th distance
di t th
the
work advances in one minute. It is expressed in millimeters per minute.
fm = fr × N
fm = fz × z × N
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Cutting speed, feed, and Depth of cut
• Depth of cut: The depth of cut in milling is the thickness of the material
removedd in
i one pass off the
h workk under
d the
h cutter. ItI is
i the
h perpendicular
di l
distance measured between the original and final surface of the work
piece, and is expressed in mm.
• Machining Time: Machining Time, T is given by
L
T=
fm
L
T=
fz × z × N

• Where, L = l + l A , for slab milling and L = l + l A + lO for face milling.

• l = length of the job
• lA= length of approach.
• LO = length of over travel.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Calculation of lA for Slab milling

D/2
d

Work piece

lA
l
2 2
⎛ D⎞ ⎛ D ⎞
lA = ⎜ ⎟ − ⎜ − d ⎟
⎝2⎠ ⎝2 ⎠
l A = d (D − d )

where,
h d is
i the
th depth
d th off cutt

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Calculation of lA and lO for Face milling

D D
l A = lO = , for W >
2 2
l A = lO = W (D − W ) , for W <
D
2
Where, W is the widthof the cut

lA l lo

lA l lo D W Machined surface
Work p
piece
W W k piece
Work i
D
D
Case when W >
D Case when W <
2 2

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Material removal rate
• Material removal rate (MRR):

MRR = l×W ×d mm3

T min

MRR = W × d × fm mm3 ⎛ as l = f ⎞
⎜ m⎟
min ⎝ T ⎠

MRR = W × d × f z × z × N mm3
min

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

THE DIVIDING HEAD OR INDEXING HEAD
• A dividing head is one of the most important attachments of the milling
machine.
hi
• The dividing heads are used for dividing the periphery of the work piece
into a desired number of equal
q pparts,, i.e. indexingg the work ppiece through
g
a certain angle automatically after every operation, thus enabling the
setting of job in new angular position in relation to the cutter.
• It is thus used to divide the circumference of a work piece into equally
spaced divisions when milling gears, splines, squares, squares and
hexagons.
• It may
ma also be usedsed to rotate the work
ork piece at predetermined ratio to the
table feed rate to produce cams and helical grooves on gears, drills,
reamers and other parts.
• Diving heads are of the following three types:
– Plain dividing head.
– Universal dividing head.
head
– Optical dividing head.
• Optical dividing heads are the most precise, but detailed description of
this is beyond the scope of the lecture.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Plain dividing head
• This type of dividing head carries a indexing plate directly mounted on its
spindle and has no use of the worm and worm wheel.wheel
• It is the simplest of all dividing head and it is used only in direct
indexing.
• The
Th indexing
i d i plate l t contains
t i three
th setst off hole
h l circles
i l or slots:
l t 24,
24 30,
30 andd
36.
• The numbers of divisions possible are limited to numbers that are factors
off 24,
24 30,
30 andd 36 only.
l
24 2, 3, 4, 6, 8, 12, 24

Plate hole circles or slots 30 2, 3, 5, 6, 10, 15, 30

36 2, 3, 4, 6, 9, 12, 18, 36

• The job is held between centres, one on the dividing head spindle and the
other on the tailstock.
• A spring loaded plunger pin is engaged in the proper slot for locking
locking.
• After each cut the plunger pin is unlocked from the slot and the index
plate along with job is rotated through required number of slots that is
required to index the job.
job

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Universal dividing head

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Universal dividing head
• It consists of robust body which houses
the
h worm drive,
di which
hi h consists
i off a
worm and worm wheel.
• The dividingg head spindle
p carries a
worm wheel.
• The spindle carrying the worm, which
meshes with the worm wheel,
wheel carries a
crank at its outer end.
• The index pin works inside a spring
loaded plunger.
pl nger
• This plunger can slide radially along a
slot provided in the crank in order to
adjust the pin position along a desired
hole circle on the index plate.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Universal dividing head
• The index plate is also mounted on the
same spindle
i dl as the
h crank, k but
b on a
sleeve such that the worm spindle and
hence the crank, can move
independently on the index plate.
• The sector arms provided on the index
pplate are usuallyy detachable typeyp and
can be set at a desired angle with
another in order to set a definite
distance alongg a desired hole circle.
• The spindle carrying the worm wheel is
provided with a job carrier and a centre
at its front end.
end

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Universal dividing head
• The worm wheel generally has 40 teeth.
• As a result, a full rotation of the work
piece is produced by 40 full revolutions
of the index crank.
crank
• The index plates used in Universal
dividingg head are of two types
yp namelyy
Brown and Sharpe, and Cincinnati and
Parkinson index plates .

Brown and sharpe Hole circles

index plates
Plate number 1 15, 16, 17, 18,
19, 20
Plate number 2 21, 23, 27, 29,
31, 33
Plate number 3 37,, 39,, 41,, 43,,
47, 49

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Universal dividing head Index plate

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Universal dividing head
• Universal dividing head performs the following operations:
– It in conjunction with tailstock acts both as a holding as well as
supporting device for the work during the operation.
– It sets
t the
th workk piece
i i a desired
in d i d position
iti in
i relation
l ti tot the
th machine
hi
table.
– After each cut it rotates the job through a desired angle thus indexes
the periphery of the work.
– It provides continuous rotary motion to the job during milling of
h li l grooves.
helical

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Indexing methods
• Indexing the job means dividing the periphery into a desired number of
equal divisions.
• It is accomplished by a controlled movement of the crank such that the job
rotates through a definite angle after each cut is over.
over
• The following methods of indexing are commonly used:
– Direct indexing.
– Plain or simple indexing.
– Compound indexing.
– Differential indexing.
– Angular indexing.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Direct indexing
• Direct indexing is also called rapid indexing, is used when large number
of identical pieces are indexed by small number of divisions.
• The operation may be performed by plain dividing head and universal
dividing head.
head
• When using universal dividing head is used, the worm and the worm
wheel is first disengaged.
g g
• The required number of divisions may be obtained by means of rapid
index plate is generally fitted to the front end of the spindle nose.
• The
h plate
l h 24 equally
has ll spacedd holes,
h l into
i any one off the
h hole
h l a spring
i
loaded pin is pushed to lock the spindle with the frame.
• While indexing,
indexing the pin is first taken out and then the spindle is rotated by
hand, and after required position is reached it is again locked by the pin.
• When the plate is turned through the required part of the revolution, the
dividing head spindle and the work are also turned through the same part
of revolution.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Direct indexing
• With a rapid index plate having 24 holes or slots, it is possible to divide
the work into equal divisions of 2, 3, 4, 6, 8, 12, 24 parts, which are all
factors of 24.
• Rule for direct indexing:
– To find the index movement, divide the total number of holes in direct
index pplate byy the number of divisions required
q on the work.
– When the direct index plate has 24 holes, the formula for indexing is:

24
No. of holes to be moved =
N
Where N is the number of divisions required

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Plain or simple indexing
• The method of indexing is used when the direct method of indexing
cannot be employed for obtaining the required no. of divisions on the
work.
• For example,
example if the work is required to be divided into 22 equal divisions
the direct indexing cannot be used, because 22 is not divisible into any of
the hole circles on the direct index plate.
• For such cases, simple indexing can easily be used.
• For this, a universal dividing head is used.
• This
hi method
h d off indexing
i d i involves
i l the
h use off crank,
k worm, worm wheelh l
and index plate.
• As already described,
described the worm wheel carries 40 teeth and the worm is
single start.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Plain or simple indexing
• The worm wheel is directly mounted on the spindle.
• During the cut the crank pin remains fixed on the hole circle.
• When the crank pin is pulled outwards and the crank is rotated, the worm
will rotate,
rotate which in turn,
turn will rotate the worm wheel,wheel and hence the
spindle and the work.
• Since the worm has single start thread and the worm wheel 40 teeth, with
one turn of the crank (i.e.
(i e of the worm) the worm wheel will rotate
through one pitch distance, i.e., equal to 1/40 of a revolution.
• Similarly 2 turns of the crank the worm wheel will rotate through 1/20 of
a revolution.
l i
• Thus the crank will have to rotate through 40 turns in order to rotate the
work byy one complete
p turn.
• The holes in the index plate serves to sub divide the rotation of the index
crank.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Plain or simple indexing (example)
• Now suppose we want to divide the work into a no. of divisions, the
corresponding crank movements will be given as follows:
40
For two divsions on the work, the crank will make = 20 turns ffor each divisions
2
40
Similarly for N divsions on the work,the crank will make turns for each divisions
N
F 23 divsions
For di i on the
th work,
k
40 17
Crank movement = =1
23 23
That means the crank has to be moved by one complete rotation plus 17 holes of the
23 hole circle

For 60 divsions on the work,

40 2 2 × 6 12
C k movementt =
Crank = = =
60 3 3 × 6 18
That means the crank has to be moved by 12 holes of the 18 hole circle.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Compound indexing
• This method of indexing is employed when the number of divisions
required is outside the range that can be obtained by simple indexing.
• It involves the use of two separate simple indexing movements and is
performed in two stages:
• By turning the crank a definite amount in one direction in the same way as
in simple
p indexing. g
• By turning both the index plate and the crank, either in same or reverse
direction, thus adding further movement to or subtracting from that
obtained in first stage.
stage
• Principle of compound indexing:
• Let us consider that the crank is turned 3 holes on a 18 holes circle and the
index plate and crank both turned further 5 holes on 20 holes circle.
• On account of these two movements the worm will be turned through:

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Compound indexing
3 5 5
+ = of a revolution
18 20 12
since 40 truns of the worm turn the work through 1 revolution
5 5
Therfore, of turn of the worm will turn the work through of a revolution.
12 12 × 40
5 1
i.e.,, off turn off the worm will turn the work through
g off a revolution.
12 96
This will enable 96 divisions on the work.

• Again suppose the crank is turned 5 holes on 18 holes circle in one

direction and then the index plate, along with the crank, turned 2 holes on
20 holes circle in a direction opposite to the former.
former On account of these
two movements the worm will be turned through:
5 2 64 8
− = = off a revolution
l ti
18 20 360 45
8 1
Now , the corresponding movement of the work will be = of a revolution
45 × 40 225
This will enable 225 divisions on the work.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Compound indexing Procedure
• Step 1:
– Select for trial any two hole circles on the same plate and on the
same side.
• Step 2:
Obtain the following fraction
Factors ofdivisions required × Factors of difference of the hole circles
Factors of 40 × Factors of first circle × Factors of second circle
• Step 3:
– If suitable index circles have been selected,
selected than all the factors in the
numerator will be cancelled by those in the denominator. That is you
will get unity in the numerator. If it does not happen, select another
set of circles and make another attempt in the same way as above.
above
– Now, suppose after simplification of the fraction:

Factors ofdivisions required × Factors of difference of the hole circles 1

=
Factors of 40 × Factors of first circle × Factors of second circle X
Where X may be any number

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Compound indexing Procedure
• Step 3 (contd…)
– If A and B denotes the number of holes on the two circles, then the
required indexing movement will be given by (B >A):
X X
−
A B
Simplify
p fy the same and neglect
g the common turns

• Step 4 (Check):
– After finding the above expression,
expression check that the algebraic sum of
the two movements, i.e. crank in one direction and index plate and
crank in same or opposite direction, should be equal to 40/N, where
N is the number of divisions required.
required Therefore,
Therefore

X X 40
± =
A B N

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Differential indexing
• The indexing method is called differential because the required division is
obtained by a combination of two movements:
– The movement of the index crank similar to the simple indexing.
– The
Th simultaneous
i lt movementt off the
th index
i d plate,
l t whenh the
th crankk is
i
turned.
• The rotation or differential motion of the index plate may take place in
same direction as the crank or opposite to it as may be required.
• The result is that the actual movement of the crank at every indexing is
automatically
i ll increased
i d or decreased
d d giving
i i the h required
i d index
i d movement
of the spindle.
• For this reason,
reason the differential indexing may be considered as an
automatic method of performing compound indexing.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Differential indexing

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Differential indexing
• While differential indexing, the locking
pin is disengaged with the index plate
which is screwed to a sleeve.
• A bevel gear is fastened to the other end
Worm wheel of the sleeve.
Spindle
• The index pplate, the sleeve and the bevel
Work piece gear are free to rotate on the driving
Worm
Change worm shaft.
Gears Dead Centre

Driving shaft
• The bevel
be el gear meshes with ith another
bevel gear on the bevel gear shaft.
Bevel Gears
Lock ppin • The change g ggears mayy be mounted
Index plate
between spindle shaft and the bevel gear
Index Clamp
Index pin
shaft.
• The
Th gear on the th spindle
i dl is
i the
th driving
di i
gear and the gear on the shaft is the
driven gear.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Differential indexing
• The change gear train may be simple or
compound.
• Now with this gearing arrangement, as
the index crank turned,
turned rotating the
Worm wheel spindle, the index plate is slowly rotated
in one direction or other, depending
Spindle
Work piece upon gearing.
Worm
Change • Thus the differential movement of the
Gears Dead Centre
crank is equal to its movement relative to
Driving shaft
the plate plus the movement of the plate.
Bevel Gears
Lock ppin
• Differential index heads are generally
Index plate
furnished with change gears as follows:
Index Clamp
Index pin
– 24, 24, 28, 32, 40, 44, 48, 56, 64, 72,
86 100.
86, 100

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Differential indexing
• With these change gears and three sets of
standard B & S index plate it is possible
to index any numbers from 1 to 382.
• Special gears having 46,
46 47,
47 52,
52 58,
58 68,
68
Worm wheel 70, 76, and 84 teeth may also be
furnished for numbers from 383 to 1008
Spindle
Work piece divisions.
Worm
Change • The differential method of indexing is
Gears Dead Centre
employed when the problem cannot be
Driving shaft
worked by plain indexing.
Bevel Gears
Lock ppin
Index plate

Index Clamp
Index pin

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Rule for Differential indexing
• The following are the steps to determine the gear ratio and number of
idl required
idlers i d to get the
h required
i d indexing
i d i movement off theh crank.
k

• Step 1:

Gear ratio =
No. of teeth in the driver gear
=
( )
A - N × 40
No. of teeth in the driven gear A
Where, A = the selected no. which can be index by plain indexing and the no. is approximately equal to N.
N = the rquired no. of divisions to be indexed.

• Step 2:
40
Index crank movement =
A

– For dividing the work into N divisions, the crank has to be turned N
times by 40/A revolution
Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005
Rule for Differential indexing
• Step 3:
– The index crank and the index plate should move in the same direction
or opposite to each other depending on the type of gearing ratio and
the selected number A.
– If (A-N) is positive the index plate must rotate in the same directions
as the crank and if ( A - N) is negative the index plate must rotate in a
direction opposite to that of the crank.
crank
– To achieve these conditions, the number of idler gears used depends
upon the following factors:
• If the
h gear train is simple
l andd (A – N) is positive, only
l one idler
dl gear is
used.
• If the gear train is compound and (A – N) is positive, no idler gear is
used.d
• If the gear train is simple and (A – N) is negative, two idler gear is used.
• Iff the gear
g train is compound
p and ((A – N)) is negative,
g onlyy one idler ggear
is use.

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Angular indexing
• The angular indexing is the process of dividing the periphery of a work in
angular
l measurements andd not byb the
h number
b off divisions.
di i i
• The indexing method is similar to the plain indexing.
• There are 360 degrees in a circle,
circle when the index crank is rotated by 40
numbers of revolutions; the spindle rotates through one complete
revolution or by 360 degrees.
• Th
Therefore,
f one complete
l turn off the
h crankk will
ill cause the
h spindle
i dl andd the
h
work to rotate through 360/40 equal to 9 degrees.
• Thus in order to turn a work through g a desired angle,
g , the number of turns
of the index crank required can be determined by dividing the angular
displacement of the work expressed in degrees by the number 9.
• If the angular displacement is expressed in minutes then the turns of the
index crank may be calculated by dividing the angle by 540.
• If the angle is expressed in seconds then it should be divided by a number
32400.
32400

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Angular indexing

Angular displacement of work in deg.

Index crank movement =
9
Angular displacement of work in min.
or , Index crank movement =
540
Angular displacement of work in sec.
or , Index crank movement =
32400

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005

Schematic diagram of universal dividing head

Spring loaded
Worm wheel index pin

Spindle

Index Clamp
Worm
Bevel Gear
I d plate
Index l t

Joyjeet Ghose, BIT, Mesra, Lecture notes on PE5005