Grinding

• Machining materials which are too hard for other machining

processes such as tool and die steels and hardened steel
materials,
• To machine above mentioned materials in finishing state
grinding is used.
• Close dimensional accuracy of the order of 0.003 to 0.005 mm
, and High degree of surface smoothness such as Ra = 0.0015
to .0125 mm can be achieved easily
• Specific energy of grinding  50 J/mm3
• Specific energy of other processes  2 to 5 J/mm3
• Grinding is a process utilising bonded abrasives to remove
material from very hard surfaces, and in the process generate
good surface finish and high dimensional accuracy.
Grinding
• Grinders can be broadly classified as
-Roughing or No precision grinders
- Precision Grinders
• Roughing or No precision grinders

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Grinding
• Roughing or No precision grinders
Class of grinders includes following machines
i) Bench , Pedestal or Floor grinders
ii) Swing Frame grinders
iii) Portable and flexible shaft grinders
iv) Belt Grinders

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 Grinding
i) Bench , Pedestal or Floor grinders 
• Used for off hand grinding of various materials and
cutting tools in tool rooms foundries and general repair
shop.
• Carries a horizontal spindle having grinding wheels
on both sides of the spindle.

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 Grinding
i) Bench , Pedestal or Floor grinders 
• It can be bolted on a suitable height on a bench or on a
stand.
• These grinders can also be used for polishing/ buffing by
replacing grinding wheels by polishing wheels./buffing
wheels.

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 Grinding
ii) Swing Frame Grinder 
• Grinding wheel is driven by motor using belt
drives.
• Rotating wheel and frame is swung by operator on
required grinding area.

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 Grinding
iii) Portable and Flexible Shaft Grinders
• Resembles as portable drill machine and portable steel
cutters (in construction and operation)
• In place of drill chuck and cutter a small grinding wheel is
mounted on to the spindle with safety guard , safety
guard is also provided over the wheel

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 Grinding
iv) Flexible shaft grinder
• It consist of flexible shaft driven by electric motor
• Shaft carries a chuck or collet at its end on which small
grinding wheel/tools is mounted
• Electric motor is mounted on a fixed stand

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 Grinding
v) Belt Grinders 
• These consist of running abrasive belt instead of grinding
wheel
• Generally used in mass production industries
• Belts keep on running on rollers or pulleys and work is fed
against abrasive coated belt
• w/p is fed usually manually on to the open abrasive side
of the belt and pressed against belt to perform grinding

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 Grinding
Cylindrical Grinders 
• It involves holding the w/p rigidly on centres ,in a chuck
or in a fixture , rotating job about its axis and then feeding
fast revolving grinding wheel against the job.
• If job is larger than face of grinding wheel then either job
or grinding wheel is traversed over each other.
• Traversing of wheel or job is done either using hydraulic
or mechanical power or by hand.

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 Grinding
Cylindrical Grinders 
• Feed is given to work or wheel at the completion of each
traversing movement.
• If face width of grinding wheel is more or equal to length
of the work surface to be ground ,the wheel may be fed in
with no traversing movement of it or that of work. Also
known as ‘plunge grinding’

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 Grinding
Cylindrical Grinders 
Depending on difference in design and particular
requirements other forms of cylindrical grinders could be
Roll grinders, Camshaft grinders , crank shaft grinders etc.

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 Grinding
Cylindrical Grinders 
• Simplest form of cylindrical grinder is a tool post grinder
which is used on lathes to perform internal and external
grinding
Cylindrical Grinding Machines are of following two types
1 Plain Cylindrical grinders
2 Universal Cylindrical grinders

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 Grinding
Common principle of cylindrical grinding involves following
basic movement
• W/p should revolve.
• Grinding wheel should revolve.

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 Grinding
• Either w/p or grinding wheel should have a traversing
movement past the other.
• Either the wheel should be fed into the work or work on
to the wheel.

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 Grinding
Plain Cylindrical Grinders 
• Usually w/p is held b/w two centres.
• One centre is at head stock and other at tail stock.
• the rotating work is traversed across the face of
the rotating grinding wheel.
• At the end of each traverse, the wheel is fed into
the work by an amount equal to the depth of cut.
• Tailstock and headstock both can be moved along
the table.

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 Grinding
Plain Cylindrical Grinders 
•upper table carries tailstock, headstock and the work piece
and can be swivelled in a horizontal plane
• Angle of swivel can be maximum of 10°on either side , along
the circular ways provided on the lower table , enabling
grinding of tapered surfaces.

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 Grinding Plain Cylindrical Grinders 
•lower table is mounted over horizontal guide ways to provide
longitudinal traverse to the upper table, and hence the work.
•Table movements can be both by hand as well as by power.

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 Grinding
Plain Cylindrical Grinders 
•Wheel and work are so adjusted that the grinding force
is directed downwards to ensure proper stability.

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21
Grinding
Universal Cylindrical Grinders 
•Universal cylindrical grinder carries all the parts and
movements of a plain cylindrical grinder , in addition,
carries the following advantageous features.
• Its headstock can be made to carry a live or dead
spindle, as desired,
• The headstock can itself be swivelled in a
horizontal plane.
• Its wheel head can be raised or lowered and can
also be swivelled to ±90° to grind tapered surfaces
having large taper angles.

Vivek Chawla
CENTRELESS GRINDERS
•Grinders are also a type of cylindrical grinders only, but the
principle of centre less grinding differs from centre type
grinding.

•Work is supported by a combination of a grinding wheel, a

regulation wheel and a work rest blade.

•Principle of centre less grinding is used for both the external

grinding as well as internal grinding.

Viv
CENTRELESS GRINDERS

•Hollow cylindrical and taperd work pieces, like bushes,

pistons, valves, tubes and balls, etc., which either do not or
cannot have centres, are best ground on centre less grinders.

•It carries a heavy base and two wheel heads, one carrying
the grinding wheel (larger one) and the other regulating
wheel (smaller one). The work piece rests on the blade of the
work rest between these two wheels.

Viv
25
26
CENTRELESS GRINDERS
•Each head carries a separate wheel truing mechanism for the
wheel it carries.
•Main driving motor is housed in housing.
•Left hand panel carries controls for speed adjustments.
•Right hand panel carries controls for hydraulic mechanism,
speed adjustment of regulating wheel , automatic working
cycle switch, start and stop switches.

Vivek Chawla
CENTRELESS GRINDERS
•Grinding operation is performed by the grinding wheel.

•Regulating wheel is to provide the required support to the

work piece while it is pushed away by the cutting pressure of
the grinding wheel.

•Regulating Wheel, helps the work piece to remain in contact

with grinding wheel.

Vivek Chawla
29
CENTRELESS GRINDERS
•Work piece, while rotating, rests on the blade of the
work rest.
•Regulating wheel essentially carries rubber bond and
helps in the rotation of work piece due to friction.
•Directions of rotation of the two wheels are the
same.
•Common methods used for feeding the work are:
Through feed.
In feed.
End feed.

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CENTRELESS GRINDERS
Through feed grinding
•w/p is simultaneously given an axial movement , by the
regulating wheel and guides so as to pass between the
wheels.
•axis of the regulating wheel is inclined at 2 to 10 degrees
with the vertical.

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CENTRELESS GRINDERS
Through feed grinding

•amount of stock to be removed is determined by how many

time a work piece has to pass between the wheels.
•method is used for straight cylindrical objects
actual feed (f) = π d n x sin α
f = feed in mm/min; n = revolutions/min.
d = dia. of regulating wheel (in mm)
α = angle of inclination of regulating wheel.
Vivek Chawla
CENTRELESS GRINDERS

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CENTRELESS GRINDERS
In feed grinding 
•method is used for grinding circular, shouldered (kind of
chamfer ), formed components.
•After placing the work piece on the blade of the work rest,
the regulating wheel is again pushed in to press against the
work.
•Work rest is made to have an
end stop at the rear end.

Vivek Chawla
CENTRELESS GRINDERS
In feed grinding 

•Both regulating and grinding wheels are more in width than

the work length to be ground.

•Axis of the regulating wheel

is inclined a little, say about
half a degree, from
the horizontal.

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CENTRELESS GRINDERS
End feed grinding 
•It is a sort of form grinding
•because both the wheels, i.e., the grinding wheel and the
regulating wheel are dressed to contain the required shape or
form.

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CENTRELESS GRINDERS
End feed grinding 

•Work piece is fed longitudinally from the side of the wheels.

•It advances between the revolving wheels, its surface is
ground till its last end touches the end stop.
•Method can be used for grinding of both spherical and
tapered surfaces, but it suits best to the grinding of short
tapered surfaces. Vivek Chawla
Internal Centre-less Grinding
• It is also possible to apply centre-less grinding for
internal surfaces as well. However in this case the
work piece need to be supported by two support
rolls.
• The main advantage of the process is that the
ground hole will be concentric with the outside
diameter of the work.
• The process is capable of grinding straight
cylindrical or tapered holes.
• These holes can be blind, through, interrupted, or
even with a shoulder.
Advantages of centerless grinding
•The need for centering and use of fixtures, etc., is totally
eliminated.
•It can be applied equally to both external and internal
grinding.
•Once a set-up has been made, it is a faster method than
centre-type grinding.

•no chucking of work is needed , the idle time of

the machine is almost negligible.

•there is no end thrust, there are no chances of any springy

action or distortion in long work pieces.
Vivek Chawla
Advantages of centerless grinding
•operating conditions automatically provide a true floating
type centre for the work piece
•common errors normally associated with the centres and
centre holes are automatically eliminated
•Work piece is supported rigidly during the operation and can
be subjected to heavy cuts, resulting in a rapid and more
economical grinding , more material removal rate
•smaller grinding allowance is needed, the grinding time is
considerable reduced.
•Large grinding wheels are used and errors due to wheel wear
are reduced , requirement of wheel adjustment is minimum.
•very little maintenance is needed for the machine.

Vivek Chawla
Limitations of centerless grinding

•Set-up time or a centre less grinding operation is usually

large.

•This process is useful only for large volume production.

• It may be necessary to have special equipment for special

profiles and cause additional set-up time for special profiles.

•This process is not suitable for large work piece sizes.

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Surface Grinders
Surface grinders performs same operation as the planers,
shapers or milling machines, but with more precision and give
good surface finish.
Surface grinders grind flat surfaces, although irregular, curved
or tapered surfaces can also be ground on them.
Surface grinders can be classified as
• According to the table movement
(a) Reciprocating table type.
(b) Rotary table type.
• According to the direction of wheel spindles
(a) Vertical spindle type. (b) Horizontal spindle type.
• Special type and single purpose machines
(a) Face grinders. (b) Way grinders
Vivek Chawla (c) Wet belt grinders.
Surface Grinders
Reciprocating Table Type Surface Grinders
•reciprocating table type surface grinder may have a
horizontal spindle of the grinding wheel or a vertical spindle
of the same
Horizontal spindle Grinders
•Horizontal spindle carries straight wheel.
•Vertical spindle carries cup type wheel.
•Hydraulic drives are used for driving these grinders.

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Surface Grinders
Horizontal spindle Grinders
•Cutting is done on the periphery of the straight wheel in case
of horizontal spindle type, and on the revolving edge of the
cup wheel on vertical spindle machines
•Work piece is usually held on a magnetic chuck on these
machines. They are vastly used for grinding flat surface .
•machine size is designated by the dimensions of the working
area of the table

Vivek Chawla
Surface Grinders
Horizontal spindle Grinders
•longitudinal feed to the work is given by reciprocating the
table.
•Cross feed can be given by two methods.
•mount the table on a saddle and then cross feed can be
given by moving the saddle.
•Cross feed can be given by moving the wheel-head in and
out.
•In feed is provided by lowering the wheel head along the
column.

Vivek Chawla
Principle of grinding machines

48
Surface Grinders
vertical spindle Grinders
•Table and work piece, reciprocate under grinding wheel.
•wheel covers all or a major portion of the width of the job.
•Cross feed to the work can be given by moving the saddle.
•Manual or power feed can be employed to feed the wheel-
head vertically.
•individual motor drive is usually provided to rotate the
wheel.

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Surface Grinders

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Rotary Table Surface Grinders
•These are made of two type
Horizontal spindle grinder , Vertical spindle grinder
•A magnetic chuck ,mounted on table holds the job.
•table is made to rotate under the revolving wheel, both
rotating in opposite directions.

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Rotary Table Surface Grinders
•vertical feed to the wheel is given by moving the wheel-head
along a column and the cross feed by the horizontal
movement of the wheel spindle.
•straight wheel is used on the machines, and wheel cuts on its
periphery.
•machines carry the provision to raise or lower the table , and
can incline the same to grind tapered surfaces.

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• Internal pump and piping arrangement for coolant.
• Protective guard for safety.

53
Creep Feed Grinding
•Depths of cut 100 to 1,000 times greater than in
conventional surface grinding.

•Feed rates reduced by about the same proportion.

•Material removal rate and productivity are

increased in creep feed grinding because the wheel
is continuously cutting.

• In conventional surface grinding, wheel is

engaged in cutting for only a portion of the stroke
length.
Creep Feed Grinding
Creep Feed Grinding
• In creep feed grinding the entire depth of cut
is completed in one pass only using very small
in feed rates.
• High depth of cut of the order of 1 to 30 mm
with low work speeds of the order of 1 to
0.025 m/min.
• Idle time (stopping and wheel/table reversal)
gets reduced since the grinding operation is
completed in one pass.
Creep Feed Grinding
• The cutting forces and consequently the
power required increases in the case of creep
feed grinding, but has a favourable Grinding-
ratio.
• Use soft and open wheels to take care of the
wheel dressing and accommodate large
volume of chips generated in the process.
• The grinding fluids used are oil based in view
of the low grinding speeds employed.
Different Grinding Operations.
Creep feed grinding
Loading & Glazing of Grinding Wheels
After continuous use of the grinding wheel, sharp
points (cutting points) of the abrasive grains
• become dull
•lose their cutting ability and sharpness.
• severely worn out.
•wheel face becomes smooth, instead of cutting into
work material, performs rubbing action only.
called Glazing of grinding wheel.
Glazing is
•more prominent in hard grinding wheel , cutting at
high speeds.
• less prominent in Softer wheel with slower speed.
•Effected wheel is called Glazed wheel.
Loading & Glazing of Grinding Wheels
•Some times cut particles of the work material adhere to
the face of the grinding wheel.
•These particles occupy the open space between the
cutting points.
•the sharpness of the cutting points is lost and wheel face
becomes smooth
•depriving the wheel of its cutting ability.
•known as loading of wheel and the effected wheel is
called 'Loaded' wheel.
Loading effect is more prominent with
• wheels carrying a hard bond
• grinding of softer material at slower cutting speeds
• grinding with deeper cuts
Dressing the Wheel
Functions:

•Breaks off dulled grits to expose new sharp

grains

•Removes chips clogged in the wheel

•Accomplished by a rotating disk, an abrasive stick, or

another grinding wheel operating at high speed, held
against the wheel being dressed as it rotates

•Required when wheel is in third region of wear curve.

Truing the Wheel

Truing - use of a diamond-pointed tool fed slowly and

precisely across wheel as it rotates

•Very light depth is taken (0.025 mm or less) against the

wheel

•Not only sharpens wheel, but restores cylindrical

shape and insures straightness across outside
Perimeter

Although dressing sharpens, it don’t guarantee the shape of

the wheel.
Size & Specifications of Grinding Machine
•size of a cylindrical grinder is designated by the diameter
and length of the largest work piece can accommodate
between centres and can be grinded.
•the height of centres above the table

•Size of a surface grinder is specified by the length and

breadth of its table and the maximum distance between
the table and the wheel.
•Rotary table surface grinder is specified by the diameter
of the rotary table or of the chuck, if used.
•Size of a centre type internal grinder is specified by the
maximum travel of the grinding wheel and the maximum
diameter of work piece bore that can be ground.
Size & Specifications of Grinding Machine
Size & Specifications of Grinding Machine
•power (or capacity).

•wheel diameter.

• maximum length of work piece that can be ground,

ranges of speeds and feeds.

• type of drive.
HOLDING THE WORK
•Various types of chucks, angle plates, V -blocks, steady
rests and specially designed fixtures can be used to hold
work on Grinding machine.
•most commonly used device on surface grinders is a
magnetic chuck of rectangular type and rotary type.
•on a rotary table type grinder is of circular type.
•chucks may be of permanent magnet type or of instant
magnetising type.
•instant magnetising or temporary magnet chucks are
operated by means of direct current (d.c) and can have
both, rectangular shape or circular shape
•When d.c is switched on, a temporary magnetic field is
created, which attracts and holds the job firmly.
HOLDING THE WORK
•On switch off of d.c job is released
•This procedure is possible only for ferrous work pieces
•In case of non ferrous work pieces ,the job is mounted
on ferrous fixtures which further are mounted on
magnetic chuck.
Other Grinding Operations.
Face grinding
• It is a method of grinding vertical flat surfaces. the
wheel spindle can be horizontal or vertical.
Set wheel grinding
•It is a method of grinding relatively short work
pieces without changing the cross setting of the
wheel once set.
Form grinding
•It is a method of producing formed surfaces through
grinding. The wheel face is given the desired shape
by dressing and then fed on to the work surface, as
in case of thread grinding and gear teeth grinding.
Other Grinding Operations.
Snagging
•It is an operation used for grinding the gates, sprues and
fins on castings, finishing forgings, and removing scale,
imperfections and excess metal from steel billets and
welded structures.
•Primary requirement, is removal of metal and not the
type of surface finish.
• work piece is not rigidly mounted or clamped in any
device.
• Feeding can be in two ways, i,e., either the work piece to
the grinding wheel or the wheel on to the work surface.
• feeding is done usually by hand.
Other Grinding Operations.
Off-hand grinding
•It is a rough grinding method in which the work is held in
hand and pressed against the rotating grinding wheel.
• method is commonly used for grinding of such items in
which accuracy and surface finish are not of primary
importance, such as in sharpening cutting edges of
chisels, etc.
Sharpening cutting tools
Several cutting tools, including single point tools, milling
cutters, drills, reamers, hobs, etc., need regrinding quite
often to provide them correct geometry, restore lost
geometry and sharpen their cutting edges.
Grinding Wheel Performance
• Wheel speed
• Work speed (in case of cylindrical grinding)
• Traverse feed of the wheel
• In feed, and
• Area of contact.
 Honing
• Honing is a low abrasing process using bonded abrasive
sticks for removing stock from metallic and non metallic
Surfaces.
• can be used for external cylindrical surfaces as well as flat
surfaces
• most commonly used for internal surfaces.
• performed as the final operation , to correct the errors
that resulted from the previous machining operations.
We Can perform
• Correction of geometrical accuracy
• Out -of-roundness
• Taper
• Axial distortion
• Dimensional accuracy
 Honing
• abrasive grains are bonded in the form of sticks by a resin
material
• sticks are presented to the work so that their full cutting
forces are in contact with the work surfaces.
• as large number of abrasive grains are presented to the
work surface simultaneously, substantial material removal
takes place.
For cylindrical surfaces,
• the abrasive grains are given a combination of two
motions-rotation and reciprocation
• The resultant motion of the grains is a cross-hatch lay
pattern with an included angle of 20° to 60°.
 Honing
• abrasive grains put more pressure on the high points.
• After the crest are removed ,bore is made straight.
• as large number of grains are in contact with the total
surface , a uniform surface finish is obtained.
• honing force and temperature never applied at anyone
point ,results in less surface damage compared to other
machining processes.
 Honing
Honing Conditions
• All materials can be honed.
• material removal rate is affected by the hardness of the
work material.
The typical rate are
• Soft material 1.15 mm/min on diameter
• Hard material 0.30 mm/min on diameter
• Maximum bore size that can be honed is about 1500 mm,
while the minimum size is 1.5 mm in diameter.
• Honing allowance should be small to be economical.
• depends upon the previous error to be corrected.
• Abrasives and the grain size to be selected depends upon
the work material and the resultant finish desired .
 Honing Conditions
Work Hardness Abrasive Grade Grain size for a Surface
material finish, m
BHN 0.01 0.025 0.3 0.4

Steel 200 - 300 Al2O3 R 600 500 400 320

330 - 470 O 600 500 400 320
50 - 65 RC J 500 400 320 280
Cast iron 200 - 470 SiC Q 500 400 280 280
50 -65 RC SiC J 400 280 220 150
Aluminium SiC R 600 500 400 320
Copper 120 - 140 SiC R 600 500 400 320
180 - 200 SiC R 600 500 400 320
Lapping
• Lapping is an operation used to generate extremely
high surface finish on flat surfaces using loose
abrasive.
• Lapping is generally the final finishing operation
done with loose abrasive grains.
• Extreme accuracy of dimension
• Correction of minor imperfection of shape
• Refinement of surface finish
• Close fit between mating surfaces
Lapping
• Lapping process is employed to get
• Extreme accuracy of dimension
• Correction of minor imperfection of shape
• Refinement of surface finish
• Close fit between mating surfaces
Lapping
• service life of component can be greatly increased by
the lapping process
• removes the valleys and hills present on the machined
surfaces
• stock-removal rates with silicon carbide are generally,
more compared to aluminium oxide.
• aluminium oxide gives better surface finish for the
same grain size.
• softer nonferrous materials require a finer grain size to
produce satisfactory finish in comparison to steel
Lapping
• Lapping is done by charging a lap made of soft material
with abrasive particles and rubbing it over the work piece
surface with a light pressure
• Lapping is done manually or by specially designed
machines.
• Pressure is applied on the lap and is moved with the loose
abrasive between the lap and the work removing the
material from the work till the work confirms to the profile
of the lap.
• Lap materials generally used are cast iron, soft wheel,
bronze and brass.
Lapping
• to achieve uniform abrasion of the work surface, all points
on the work are subjected to (the same amount of abrasing
by careful manipulation of the lap. For this purpose, the
manual lap is moved
• Special lubricants, generally called vehicles, are used during
the lapping process .
The desirable properties of fluids used as vehicle are the
following:
• Abrasive should be held in uniform suspension during the
operation.
• It should not evaporate easily.
• It should be non corrosive.
• It can be easily removed by normal cleaning.
Lapping
• Cutting fluids are water soluble cutting fluids. vegetable
oils, mineral oils and greases.
• Lapping speed is 100 to 250 m/min The material removed
depend upon the lapping speed.
• Higher lapping allowances require higher lapping speeds.
• The lapping pressure applied is 0.01 to 0.03 Mpa for soft
materials and 0.07 Mpa for hard materials.
• Higher pressure are likely to cause damaging of the work
surface. Lapping allowance depends on the previous
operation carried and the material hardness.
• Lapping can be carried out on flat surfaces as well as any
other forms such as cylindrical or any form surfaces. The
lap has to match the form surface required.
Polishing and Buffing
Polishing and Buffing
• Both these processes are used for making surfaces
smoother along with a glossy finish.
• Polishing and buffing wheels are made of cloth. felt
or such materials. which are soft and have a
cushioning effect.
• Polishing is done with a very fine abrasive in loose
form smeared on the polishing wheel. with the
work rubbing against the flexible wheel.
• very small amount of material is removed in
polishing.
Polishing and Buffing
• In buffing the abrasive grains, a suitable carrying
medium such as grease is applied at suitable
intervals to the buffing wheel.
• A negligible amount of material is removed in
buffing while a very high lustre is generated on the
buffed surface.
• The dimensional accuracy of the parts is not
affected by the polishing and buffing operations.
Grinding Wheel Designation and Selection

• Abrasive types
– Aluminium oxide (Al2O3),
– Silicon Carbide (SiC),
– Cubic Boron Nitride (CBN), and
– Diamond
• Grain size
Grinding Wheel Designation and Selection

• Bond
– Vitrified
– Silicate
– Synthetic resin
– Rubber
– Shellac, and
– Metal
Grinding Wheel Designation and Selection

• Grade
– Hard
– Soft