Milling & Grinding

13.505 MACHINE TOOLS
MODULE 3
1

MILLING MACHINE
 Milling is a process of removing metal by feeding the work
against a rotating multipoint cutter.
 The machine tool intended for this purpose is known as
milling machine.
 The surface obtained by this machine tool is superior in
quality and more accurate and precise.
 Eli Whitney designed a complete milling machine in 1818.
 In the year 1861 Joseph Brown, a member of Brown and
Sharp company developed the first universal milling
machine
2

TYPES OF MILLING MACHINES
1. Column and knee type
(a) Hand milling machine
(b) Plain Milling machine
(c) Universal milling machine
(d) Omniversal milling machine
(e) Vertical milling machine
2. Manufacturing of fixed bed type
(a) Simplex milling machine
(b) Duplex milling machine
(c) Triplex milling machine
3. Planer type
4. Special type
(a) Rotary table milling machine
(b) Drum milling machine
(c) Planetary milling machine
(d) Pantograph, profiling & tracer controlled milling machine
3

 Hand milling machine
 In hand milling machine the cutter is mounted on a
horizontal arbor and is rotated by power.
 The work is held in the table and is fed against the cutter.
 Used for cutting short keyways, grooving and keyway
cutting.
 Plain milling machine
 Plain milling machine with spindle on horizontal axis is
called horizontal milling machine.
 The work fitted on the table can be moved longitudinal,
transverse and vertical directions.
 Universal milling machine
 Similar to plain milling machines.
 In addition to three table movements the table can be
swiveled in horizontal plane.
 Used for cutting helical grooves.
4

 OMNIVERSAL MILLING MACHINE
 Used for tool room applications.
 In additional to the movement of the universal milling
machine, its knee can be swiveled in a horizontal plane.
 Suitable for cutting spiral grooves on angular jobs
 VERTICAL MILLING MACHINE
 Spindle is perpendicular to the worktable.
 Spindle head can be swiveled for angular cuts.
5

 BED TYPE MILLING MACHINE
 Larger and more robust than column and knee type milling
machines.
 According to the availability of spindles, the machines can be
classified as simplex, duplex and triplex.
 Used for heavy production work.
6

 PLANER TYPE MILLING MACHINE
 It consist of four spindles each with its own drive motor.
 Table movement provides the feed.
 Used where high MRR is the prime Concern.
7

 Special type milling machine
 Rotary table milling machine resembles the vertical
milling machine , but its work table can rotate about
vertical axis
 Suitable for machining flat surfaces with high
production rate.
 Planetary milling machine is used for machining
external or internal milling of circular surfaces.
 In this, the work is held stationary and milling cutter
moves in a planetary path to finish the part.
 Cam milling machine is used for milling disc cam.
 The work is mounted on face plate.
 Table movements are controlled by master cam.
 Profile milling is used to duplicate the template
attached to the machine.
 Movement of the cutter is controlled by a guide pin
which is in contact with the template.
8

COLUMN AND KNEE TYPE MILLING MACHINE
9

 Base
 It is made of cast iron and supports all
the other parts of the machine tool.
 A vertical column is mounted upon the
base.
 In some machines, the base serves as a
reservoir for cutting fluid.
 Column
 It is mounted upon the base and is box
shaped.
 It houses the mechanism for providing
drive for the spindle.
 The front vertical face of the column is
machined accurately to form dovetail
guide ways for the knee to move up and
down.
 The top of the column holds an
overhanging arm.
 Knee
 It slides up and down on the guide ways
of the column. An elevating screw
mounted on the base obtains this
movement.
 Saddle is mounted upon the knee and
moves in a cross direction
11

 Saddle
 It is mounted on the guideways of the knee and
moves towards or away from the face of the column.
 This movement can be obtained either by power or
by hand.
 The top of the saddle has guideways for the table
movement.
 Table
 The table is moved longitudinally either by power
or manually on the guideways of the saddle.
 The table of a universal milling machine can be
swiveled horizontally to perform helical works.
 The top surface of the table has got „T‟ – slots on
which the workpieces or other work holding devices
are mounted.
 Spindle
 It is located in the upper part of the column.
 It receives power from the motor through belt,
gears and clutches.
 The front end of the spindle has got a taper hole
into which the cutters are held with different cutter
holding devices
12

 Overhanging arm
 It supports the arbor from the top of the column.
 The arbor is supported by the bearing fitted within the arbor
support.
 It is also useful while using some special attachments.
 Arbor
 It supports the different types of cutters used in the machine.
 It is drawn into the taper hole of the spindle by a draw bolt.
 One or more cutters are mounted on the arbor by placing spacing
collars between them.
 The arbor is supported by an arbor support.
 The arbor is provided with a Morse taper or self-releasing taper
13

 It is very similar to a horizontal milling machine in
construction as it has the same parts of base, column, knee,
saddle and table.
 The spindle of the machine is positioned vertically.
 The cutters are mounted on the spindle.
 The spindle is rotated by the power obtained from the
mechanism placed inside the column.
 Angular surfaces are machined by swiveling the spindle head.
15

ADVANTAGES AND DISADVANTAGES
Advantages Disadvantages
1. The metal is removed at a
faster rate as the cutter has got
multiple cutting edges and
rotates at a higher speed.
2. It is possible to perform
machining by mounting more
than one cutter at a time.
3. The table of the machine can
be moved to an accuracy of
0.02mm.
4. It is very useful since various
cutters and precise tools can be
machined.
5. Special attachments can be
mounted on the machine to
perform operations that are
performed in other machine
tools.
6. The quality of the shop is
enhanced with the presence of
this machine.
1. The cost of the milling
machine is high.
2. As milling cutters cost high,
the investment for procuring
tools is more.
3. The production cost will
increase if we carry out the
operations performed in a shaper
or a drilling machine with a
milling machine.
16

ELEMENTS OF PLAIN MILLING CUTTER

 Body of cutter: It is the part of
the cutter left after exclusion of
the teeth.
 Face: The portion of the teeth
next to the cutting edge is known
as face.
 Land: The relieved back portion
of the tooth adjacent to the
cutting edge. It is relieved to
avoid interference between the
surface being machined and the
cutter.
 Outside diameter: The diameter
of the circle passing through the
peripheral cutting edges.
 Central hole: It refers to the
hole present at the centre of the
cutter. A keyway is cut inside the
hole.

Gash or chip space: it is the
space between back of one tooth
and face of next tooth.
Relief angle: It is angle the
between the land of the tooth and
the tangent to the outside
diameter of the cutter at the
cutting edge of the particular
tooth. (approx 7.5 °).
Primary clearance angle: It is
the angle between the back of the
tooth and the tangent drawn to
the outside diameter of the cutter
at the cutting edge. (approx. 5 -
15°)

 Secondary clearance angle:
It is the angle formed by the
secondary clearance surface and
the tangent to the periphery of
the cutter at the cutting edge.
 Rake angle: The angle between
the face of the cutter and a
radial line passing through the
tooth of the cutting edge.
 The rake angles may be
positive, negative or zero.
 10 to 20°.
 If the radial line and the tooth
face coincide in the diameter
plane the rake angle is zero.
 Larger rake angles are used for
cutting softer material.

TYPES OF MILLING CUTTERS
1. Plain milling cutter
 Light duty plain milling cutter
 Heavy duty plain milling cutter
 Helical plain milling cutter
2. Side milling cutter
 Plain
 Staggered
 Half side
 Interlocking
3. Metal Slitting Saw
 Plain
 Staggered
21

4. Angle milling cutter
 Single
 Double
5. End mill
 Taper shank
 Straight
 Shell
6. T-slot milling cutter
7. Woodruff key slot milling cutter
8. Fly cutter
9. Formed cutter
 Convex milling cutter
 Concave milling cutter
 Corner rounding milling cutter
 Gear cutter
 Thread milling cutter
10. Tap and reamer cutter
22

 Plain milling cutter
 Plain milling cutters are cylindrical in shape and have teeth on
the circumferential surface only.
 They are used for producing flat surfaces parallel to the axis of
rotation of the spindle.
 The teeth of the cutter may be straight or helical according to
the size.
 If the width of the cutter is more, it is called as slabbing cutter
or cylindrical milling cutter.
 Helical plain milling cutters are superior to a straight plain
milling cutter
23

 Side milling cutter
 Side milling cutters have teeth on its periphery and also on one
or both of its sides.
 They are intended for removing metal from the sides of the
workpiece.
 There are different types of side milling cutters namely face
and side milling cutter, half side milling cutter, staggered teeth
side milling cutter, and interlocked side milling cutter.
 Machining is performed by selecting a proper milling cutter.
24

 Metal slitting saw
 It is intended for cutting narrow, deep slots and for parting off
operation.
 The teeth are cut on the circumference of the cutter.
 The width of the cutter is limited.
 The outside diameter of the cutter will be upto 200mm and
width of the cutter ranges from 0.75mm to 7mm.
 The side of the cutter is relieved so that the side may not rub
against the work.
25

 Angle milling cutter
 The teeth of the angle milling cutter are not parallel to the
axis but are at an angle to it.
 By using angle milling cutter, inclined surfaces, bevels and
helical grooves are machined.
 There are two types of angle milling cutter
 Single angle milling cutter and
 double angle milling cutter.
26

 „T‟ – Slot milling cutter
 It is a special form of end mills intended for machining „T‟-
slots.
 It looks like a side milling cutter with a shank.
 The cutters have cutting teeth on the periphery as well as on
both sides of the cutter.
27

 End mill
 These cutters have cutting teeth on the end as well as on the
periphery of the cutter.
 It is made of two parts – body and shank.
 The shanks of the cutter may be straight or taper.
 If the cutter doesn‟t have a shank it is called shell end milling
cutter.
 These cutters are useful in machining long narrow slots, holes
and flat surfaces
28

 Fly cutter
 Fly cutter is the simplest form of cutter.
 It consists of a single point cutting tool attached to the end of
the arbor.
 The cutting edge may be formed to reproduce a contoured
surface.
 They are used when standard cutters are not available.
 The work is done very slowly because of a single cutting edge
29

 Formed cutter
 Formed cutters have irregular profiles on their cutting edges to
produce required outlines on the work.
 Concave and convex milling cutters are used to produce convex
and concave surfaces respectively.
 Using gear milling cutters, gears are machined.
 Corner round milling cutters are used for cutting a radius on
the edges of the work.
 With the help of thread milling cutters threads are milled to a
specific form and size.
 Tap and reamer cutters are used for producing grooves or flutes
in taps and reamers
30

 Woodruff Key Slot Milling Cutter
 They are small standard cutters similar in construction to a
thin small diameter plain milling cutter
 Used for production of woodruff key slots
 Cutter is provided with a shank and may have straight or
staggered teeth
31

Fundamental milling processes
 The various milling processes may be grouped under two
headings:
1. Peripheral milling 2. Face milling
 Peripheral milling
 The machining is performed by the cutting edges on the
periphery of the milling cutter.
 It is classified under two headings
1. Up milling 2. Down milling
32

 Up milling
 In this method, the workpiece mounted on the table is fed
against the direction of rotation of the milling cutter.
 The cutting force is minimum during the beginning of the cut
and maximum at the end of cut.
 The thickness of chip is more at the end of the cut. As the
cutting force is directed upwards, it tends to lift the workpiece
from the fixtures.
 A difficulty is felt in pouring coolant on the cutting edge. Due
to these reasons the quality of the surface obtained by this
method is wavy.
 This processes being safer is commonly used and sometimes
called conventional milling
33

 Down milling
 The workpiece mounted on the table is moved in the same
direction as that of the rotation of the milling cutter.
 The cutting force is maximum at the beginning and minimum
at the end of cut.
 The chip thickness is more at the beginning of the cut.
 The workpiece is not disturbed because of the bite of the cutter
on the work.
 The coolant directly reaches to the cutting point.
 So the quality of surface finish obtained is high. Because of the
backlash error between the feed screw of the table and the nut,
vibration is setup on the workpiece.
44

MILLING MACHINE OPERATIONS
The following operations are performed using suitable
milling cutters.
1.Plain milling
2. Face milling
3. Side milling
4. Straddle milling
5. Angular milling
6. Gang milling
7. Form milling
8. End milling
9. Flute milling
10. Keyway milling
11. Drilling & reaming
12. Boring
13. Gear cutting
14. Thread milling
15. Cam milling
57

 Plain milling
 It is the operation of production of a flat surface parallel to the
axis of rotation of the cutter.
 It is also called as slab milling.
 Plain milling cutters and slab milling cutters are used to
perform this operation
58

 Face milling
 The face milling is the operation performed by the face milling
cutter rotated about an axis at right angles to the work
surface.
 End mills and side & face milling cutter are also used at times
to perform this operation.
 The depth of cut is provided to the table.
59

 Side milling
 Side milling is the operation of machining a vertical surface
on the side of a workpiece by using a side milling cutter.
60

 Straddle milling
 It is the operation of production of two vertical surfaces on
both sides of the work by two side milling cutters mounted on
the same arbor.
 By using suitable spacing collars, the distance between the two
cutters is adjusted correctly.
 The straddle milling is commonly used to produce square or
hexagonal surfaces.
61

 Angular milling
 Production of an angular surface on a workpiece other than
at right angles to the axis of the milling machine spindle is
known as angular milling
 Example of angular milling is the production of the „V‟ blocks
62

 Gang milling
 It is the operation of machining several surfaces of work
simultaneously by feeding the table against a number of
cutters (either of same type or of different type) mounted on
the arbor of the machine.
 This method saves much of machining time and mostly used
in production work.
63

 Form milling
 The form milling is the operation of production of
irregular contours by using form cutters.
 Machining convex and concave surfaces and gear cutting
are some examples of form milling.
64

 End milling
 It is the operation of producing a flat surface which may be
vertical, horizontal or at an angle to the table surface.
 The end milling is performed by a cutter known as an end mill.
 End milling is mostly performed in a vertical milling machine.
65

 Keyway milling
 The operation of production of keyways, grooves and slots of
different shapes and sizes can be performed in a milling
machine by using a plain milling cutter, a metal slitting saw,
an end mill or by a side milling cutter
66

 Gear cutting
 Gear cutting operation is performed in a milling machine by
using a form cutter.
 The work is held between centers on a universal dividing head.
 A proper gear cutter is selected and the teeth are cut by DP,
module method
67

INDEXING
 Indexing is the operation of dividing the periphery of
the work piece into any number of equal divisions by
using a special attachment called Indexing head or
dividing head.
 It involves the rotation of workpiece through required
angle between two successive cuts.
 Different method of indexing are
 Direct indexing
 Simple indexing
 Compound indexing
 Differential indexing.
 Angular indexing
68

Indexing (Dividing) Head
 The dividing head is an important part of a universal
milling machine.
 Its main purpose is to divide the workpiece into equal
divisions.
 Different types of indexing head are
 Direct indexing head
 Simple indexing head
 Universal indexing head
 Optical indexing head
69

 Swiveling block
 Mounted in base enables
headstock to be tilted from 5º
below horizontal to 10º beyond
vertical
 Spindle
 Mounted in swiveling block with
40-tooth worm wheel, meshes
with worm
 Worm
 Right angle to spindle, connected
to index crank
 Direct indexing plate
 Engaged by pin and attached to
front of spindle
70

 Direct indexing
 It is rapid indexing method for dividing very small number of
equal divisions on a large number of identical parts.
 It uses an indexing head with no gearing arrangement.
 Index plate has 24 equally space holes
 Indexing is done by rotating the spindle by hand and after
required position is reached the spindle is locked by the pin.
 When the spindle turn through required angle the work piece
also turned through same part of revolution.
 With a direct indexing plate having 24 holes it is possible to
divide the work into equal divisions of 2,3,4,6,8,12 and 24
 Number of holes to be moved = (24/N)
 N – number of divisions required
71

 Simple or Plain indexing
 This type of indexing is more accurate and permits more number
of divisions on the circumference than direct indexing.
 Rotation of the crank turns the worm meshing with worm wheel.
 Work positioned by means of crank, index plate, and sector arms
 Worm attached to crank must be engaged with worm wheel on dividing
head spindle
 40 teeth on worm wheel
 One complete turn on index crank cause spindle and work to
rotate one-fortieth of a turn (ratio of 40:1)
72

 Index plate circular holes are needed when number of
turns of crank has a fractional value.
 Types of indexing plates
 BROWN AND SHARPE (3 standard plates available )
 Plate 1 – 15,16,17,18,19,20
 Plate 2 -21,23,27,29,31,33
 Plate 3 – 37,39,41,43,47,49
 CINCINNATI AND PARKINSON TYPE (a large plate with holes on
double side)
73

 Rules
 With 3 Brown and sharpe indexing plates, simple index can be
done up to 50 and also even divisions up to 100 except 96.
 Calculating the index movement or number of turns of crank
for most divisions, simply divide 40 by number of divisions to
be cut or
 If 40/N gives a whole number, the crank should turn equal to
the whole number.
 If it gives a whole number with fraction, the numerator and
denominator may be multiplied (if necessary) with a common
factor, so that the denominator equal to the number of holes in
index plate circle and numerator indicates the number of hole
to be moved.
74

75
 The indexing required to cut eight teeth
 Indexing required for 19 teeth
 19 hole circle may be used for dividing the work.
 19 hole circle need 2 completes revolution of crank plus
2 holes on a 19 hole circle
crankindexofturnsfull5
8
40

crankindexofturns
19
2
219/40 

 Compound indexing
 This type of indexing is used for the divisions beyond simple
indexing.
 The word compound indexing is an indicative of compound
movements of indexing crank and then plate along with crank.
 In this case indexing plate is normally held stationary by a lock
pin.
 First we rotate the indexing crank through a required number
of holes in a selected hole circle, then crank is fixed through pin.
 It is followed by another movement by disengaging the rear lock
pin, the indexing plate along with indexing crank is rotated in
forward or backward direction through predetermined holes in
a selected hole circle, then lock pin is reengaged.
 +ve sign if the index crank and plate rotate in same direction.
 -ve sign if the index crank and plate rotate in opposite direction
76
crankindexofturns
B
b
A
a
/40 N

 Differential indexing
 Compound indexing is not in practice due to the complications in
calculating index crank movement.
 Principle of differential indexing is same as that compound
indexing except that the rotation of index plate is achieved by
suitable gear arrangement.
 Gear set 1 – 24,28,32, 40,44,48,56,72,86,100 teeth.
 With above divisions and3 brown and sharpe plate it is possible
to divide/index up to 382 divisions.
 Gear set 2 – 46,47,52,58,68,70,76,84 teeth – with these teeth it is
possible to divide up to 383to 1008 divisions.
77

 Rotation of spindle crank causes rotation of the work spindle in
the ratio40 : 1.
 Rotary motion of the work spindle is communicated to the index
plate through the gears (A,B,C and two equal bevel gears and
two equal spur gears).
 The index plate is rotated in one direction or other , depending
upon the gearing.
 In this way differential movement of the crank relative to the
plate is obtained.
 The net movement is obtained by the combination of crank
movement with the movement of the plate.
79

 RULES
 Index crank movement =
 A – a selected number.
 The change of gears may be obtained by the relation.
 When (A-N) is +ve , the index plate must be rotate in same
direction of the crank.
 When (A-N) is -ve , the index plate must be rotate in opposite
direction of the crank
80
A
40
)(
A
40
Driven
Driver
NA

GRINDING
 Grinding is a process of removing material by abrasive action of a
revolving wheel on the surface of a work-piece in order to bring it
to required shape and size
 Grinding is a surface finishing operation where very thin layer of
material is removed in the form of fine dust particles. (thickness
0.25-0.5mm)
 The wheel used for performing the grinding operation is known
as grinding wheel
 It consists of sharp crystal called abrasive held together by a
binding material or bond.
 The accuracy of grinding process is up to 0.000025mm
83

 The grinding machine consists of a power driven grinding
wheel spinning at the required speed and a bed with a fixture
to guide and hold the work-piece.
 Coolant is placed to cool the work piece so that it does not
overheat and go outside its tolerance.
 Principle
 Work piece is fed against the rotating abrasive wheel.
 Due to action of rubbing or friction between the abrasive
particles and work piece material is removed
84

TYPES OF GRINDING MACHINE
According to the accuracy of the work to be done on a grinding
machine, they are classified as
1. Rough grinding machines
2. Precision grinding machines
 Rough grinding machines
 The rough grinding machines are used to remove stock with no
reference to the accuracy of results.
 Excess metal present on the cast parts and welded joints are
removed by rough grinders.
85
1. Hand grinding machine
2. Bench grinding machine
3. Floor stand grinding machine
4. Flexible shaft grinding machine
5. Swing frame grinding machine
6. Abrasive belt grinding machine

Belt grinder:
 It is suitable for all kind of applications like finishing,
deburring and stock removal.
Floor stand and bench grinders
 Used for grinding of various materials and cutting tools in tool
rooms, foundries and general repair shops
 It carries a horizontal spindle having grinding wheels mounted on
both ends
SWINGING FRAME GRINDER

 It can be suitably bolted on a
bench at convenient height
 The floor or pedestal grinder
is nothing but a bench
grinder of the above type
mounted on a steel stand or
pedestal of suitable height
 The horizontal spindle
carrying the grinding wheel
is normally an extension on
both side of the armature
shaft of the motor
 These grinder are also be
used for polishing by
replacing the grinding wheel
by polishing wheel.

 Precision grinding machines
 Precision grinders are used to finish parts to very accurate
dimensions.
 The main types of precision grinders are
88
1. Cylindrical grinding machines
2. Internal grinding machines
3. Surface grinding machines
4. Tool and cutter grinding machines
5. Special grinding machines

CYLINDRICAL GRINDING MACHINE
 Cylindrical grinders are generally used to grind external
surfaces like cylinders, taper cylinders, faces and shoulders of
work.
 There are two types of cylindrical grinding machines and they
are
1. External cylindrical grinding machines
2. Internal cylindrical grinding machines
89

 External cylindrical grinding machine
 Cylindrical centre type grinders are intended primarily for grinding plain
cylindrical parts. Fig.4.1 illustrates a cylindrical grinder.
Base
 The base is made of cast iron and rests on the floor.
 It supports the parts mounted on it.
 The top of the base is accurately machined and provides guideways for
the table to slide on.
Tables
 The tables are mounted on top of the base.
 There are two tables namely lower table and upper table.
 The lower table slides on the guideways on the bed.
 It can be moved by hand or by power within required limits.
 The upper table can be swiveled upto ±10 degree and clamped in
position.
Headstock
 The headstock is situated at the left side of upper table.
 It supports the workpiece by means of a centre and drives it by means
of a dog.
 It may hold and drive the workpiece in a chuck.
 It houses the mechanism meant for driving the work.
 The headstock of a universal grinding machine can be swiveled to any
required angle.
90

Tailstock
 The tailstock is situated at the right
side of the table.
 It can be adjusted and clamped in
various positions to accommodate
different lengths of workpieces.
Wheelhead
 The wheelhead may be moved at right
angles to the table ways.
 It is operated by hand or by power to
feed the wheel to the work.
 The wheelhead carries a grinding
wheel.
 Its driving motor is mounted on a
slide at the top and rear of the base.
 The grinding wheel rotates at about
1500 to 2000 r.p.m.
Internal cylindrical grinding machines
 Internal grinders are useful in
grinding cylindrical holes and taper
holes.
91

Surface grinding machines
 Surface grinding machines are employed to finish plain or flat
surfaces horizontally, vertically or at any angle.
 There are four different types of surface grinders. They are
92
1. Horizontal spindle and reciprocating table type
2. Horizontal spindle and rotary table type
3. Vertical spindle and reciprocating table type
4. Vertical spindle and rotary table type

Horizontal spindle surface grinding
machine
 The majority of surface grinders are of
horizontal spindle type.
 In the horizontal type of the machine,
grinding is performed by the abrasives on
the periphery of the wheel.
 Though the area of contact between the
wheel and the work is small, the speed is
uniform over the grinding surface and the
surface finish is good.
 The grinding wheel is mounted on a
horizontal spindle and the table is
reciprocated to perform grinding operation.
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Base
 The base is made of cast iron. It is a box like
casting which houses all the table drive
mechanisms.
 The column is mounted at the back of the base
which has guideways for the vertical
adjustment of the wheelhead.
Saddle
 Saddle is mounted on the guideways provided
on the top of the base.
 It can be moved at cross towards or away from
the column.
Table
 The table is fitted to the carefully machined
guideways of the saddle.
 It reciprocates along the guideways to provide
the longitudinal feed. .
Wheelheead
 An electric motor is fitted on the wheelhead to
drive the grinding wheel.
 The wheelheed is mounted on the guideways
of the column, which is secured to the base.
 It can be raised or lowered with the grinding
wheel to accommodate workpieces of different
heights and to set the wheel for depth of cut.
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Vertical spindle surface grinding
machine
 The face or sides of the wheel are used
for grinding in the vertical type surface
grinders.
 The area of contact is large and stock can
be removed quickly. But a criss-cross
pattern of grinding scratches are left on
the work surface.
 Considering the quality of surface finish
obtained, the horizontal spindle type
machines are widely used.
 The grinding wheel is mounted on the
vertical spindle of the machine. The work
is held on the table and grinding is done.
 The base of the machine is a box like
casting. The base is very similar to the
one of the horizontal spindle type.
 It houses all the table drive mechanisms.
95

Tool and cutter grinding machines
 Tool and cutter grinders are used mainly to
sharpen the cutting edges of various tools
and cutters.
 They can also do surface, cylindrical and
internal grinding to finish jigs, fixtures, dies
and gauges.
 Base
 The base of the machine gives rigidity and
stability to the machine.
 It is bolted rigidly to the floor of the shop by
bolts and nuts.
 It supports all the other parts of the
machine.
 It is box type and houses all the mechanisms
for the saddle movements.
 Saddle
 The saddle is mounted directly on the top of
the base and slides over it.
 The column is mounted on the saddle.
 It can be moved up and down and swivelled
to either side.
96

Table
 The table moves on the top of the base,
which is mounted over the saddle.
 The table has two layers.
 The worktable is mounted on the sub
table which has „T‟ slots for mounting the
work and attachments used on the
machine.
 The worktable can be swiveled while
grinding tapers.
Headstock and tailstock
 The headstock and tailstock are mounted
on either side of the table.
 The workpieces are positioned between
centres and driven exactly as in a
cylindrical grinder.
Wheelhead
 The wheelhead is mounted on a column
on the back of the machine.
 It can be swiveled and positioned in the
base for different set-up.
 A straight wheel and a cup wheel are
mounted on either sides of the wheelhead.
97

Centreless grinding
 Centreless grinding is a method of grinding external
cylindrical, tapered and formed surfaces on workpieces that
are not held and rotated between centres or in chucks.
 There are two types of centreless grinding and they are
1. External centreless grinding
2. Internal centreless grinding
98

External centreless grinding
 Two wheels - a grinding and a
regulating wheel are used in
external centreless grinding.
 Both these wheels are rotated in the
same direction.
 The work is placed upon the work
rest and rotated between the wheels.
 The feed movement of the work
along its axis past the grinding
wheel is obtained by tilting the
regulating wheel at a slight angle
from the horizontal.
 An angular adjustment of 0 to 10
degrees is provided in the machine
for this purpose.
99

Internal centreless grinding
 The principle of external centreless
grinding is applied to internal
centreless grinding also.
 Grinding is done on the inner
surfaces of the holes.
 In internal centreless grinding, the
work is supported by three rolls - a
regulating roll, a supporting roll
and a pressure roll.
 The grinding wheel contacts the
inside surface of the workpiece
directly opposite the regulating roll.
 The distance between the contours
of these two wheels is the wall
thickness of the work.
100

Advantages of centreless grinding
1. As the workpiece is supported throughout the entire length ,
grinding is done very accurately.
2. Small, slender and fragile workpieces can be ground easily.
3. No chucking or mounting of the work on mandrels & other
holding devices are required.
4. As the process is continuous, it is best adapted for production
work.
5. The size of the work can easily be controlled.
6. A low order of skill is needed in the operation of the machine.
Diadvantages of centreless grinding
1. In hollow work, there is no certainity that the outer diameter
will be concentric with the inside diameter.
2. Works having multiple diameters are not handled easily
101

Grinding machine operations
 The process of grinding is the operation of removing
excess material from metal parts by a grinding wheel
made of hard abrasives.
 The following operations are generally performed in a
grinding machine.
1.Cylindrical grinding
2. Taper grinding
3. Gear grinding
4. Thread grinding
102

Cylindrical grinding
 Cylindrical grinding is performed by mounting and rotating the
work between centres in a cylindrical grinding machine.
 The work is fed longitudinally against the rotating grinding wheel to
perform grinding.
 The upper table of the grinding machine is set at 0° during the
operation.
Taper grinding
 Taper grinding on long workpieces can be done by swiveling the
upper table.
 If the workpiece is short, the wheelhead may be swiveled to the
taper angle.
 Another method of grinding external taper is to true the face of the
grinding wheel by a diamond tool dresser to the required angle.
 In this case, the table and the wheelhead are not swiveled.
103

Gear grinding
 The teeth of gears are ground
accurately on gear grinding machines
for their shape.
 Gear grinding is done by the
generating process or by using a form
grinding wheel.
 The generating process makes use of
two saucer shaped grinding wheels.
 These wheels are used to grind two
faces of successive teeth.
 This is a very precise method of
performing gear grinding.
Thread grinding
 Thread grinding machines are used to
grind threads accurately.
 The grinding wheel itself is shaped to
the thread profile. These formed
grinding wheels have one or multi
threads on them.
104

Grinding wheel
 A grinding wheel is a multi-tooth cutter made up of many hard
particles known as abrasives having sharp edges.
 The abrasive grains are mixed with a suitable bond, which acts as a
matrix to manufacture grinding wheels.
 According to construction, grinding wheels are classified under three
categories.
1. Solid grinding wheels
2. Segmented grinding wheels
3. Mounted grinding wheels
Abrasives
 Abrasives are used for grinding and polishing operations.
 It should have uniform physical properties of hardness, toughness and
resistance to fracture.
 Abrasive may be classified into two principal groups.
1. Natural abrasives
2. Artificial abrasives
105

 Natural abrasives
 The natural abrasives are obtained from the Earth‟s crust.
 They include sandstone, emery, corundum and diamond.
 Sandstone is used as abrasive to grind softer materials only.
 Emery is natural alumuna.
 It contains greater percentage of aluminium oxide than emery.
 Diamond is the hardest available natural abrasive.
 It is used in making grinding wheels to grind cemented
carbide tools.
106

 Artificial abrasives
Artificial abrasives are of two types.
1. Silicon carbide abrasives
2. Aluminium oxide abrasives
Silicon carbide
 Silicon carbide is manufactured from 56 parts of silica, 34 parts of
powdered coke, 2 parts of salt and 12 parts of sawdust .
 There are two types of silicon carbide abrasives
- green grit and black grit.
 Silicon carbide is next to diamond in the order of hardness.
 It is denoted by the letter „S‟
Aluminium oxide
 Aluminium oxide is manufactured by heating mineral bauxite, silica,
iron oxide, titanium oxide, etc., mixed with ground coke and iron
borings in arc type electric furnace.
 This is denoted by the letter „A‟. 108

Types of bonds
 A bond is an adhesive substance that is employed to hold
abrasive grains together in the form of grinding wheels.
 There are several types of bonds.
 Different grinding wheels are manufactured by mixing hard
abrasives with suitable bonds.
 The table containing the types of wheels manufactured using
different types of bonds and their symbols is given below
109

Grain size (Grit)
 The grinding wheel is made up of thousands of abrasive grains.
 The grain size or grit number indicates the size of the abrasive
grains used in making a wheel, or the size of the cutting teeth.
 Grain size is denoted by a number indicating the number of
meshes per linear inch of the screen through which the grains
pass when they are graded.
 There are four different groups of the grain size namely coarse,
medium, fine and very fine.
 If the grit number is large, the size of the abrasive is fine and a
small grit number indicates a large grain of abrasive.
110

Grade
 The grade of a grinding wheel refers to the hardness with
which the wheel holds the abrasive grains in place.
 It does not refer to the hardness of the abrasive grains.
 The grade is indicated by a letter of the English alphabet.
 The term „soft‟ or „hard‟ refers to the resistance of a bond offers
to disruption of the abrasives.
 A wheel from which the abrasive grains can easily be dislodged
is called soft whereas the one, which holds the grains more
securely, is called hard.
 The grade of the bond can be classified in three categories
111

Sturcture
 The relative spacing occupied by the abrasives and the bond is
referred to as structure.
 It is denoted by the number and size of void spaces between
grains.
 It may be „dense‟ or „open‟.
 Open structured wheels are used to grind soft and ductile
materials.
 Dense wheels are useful in grinding hard & brittle materials.
112

Standard marking system of grinding
wheels
 The Indian standard marking system for grinding
wheels has been prepared with a view of establishing a
uniform system of marking of grinding wheels to
designate their various characteristics.
Prefix - Manufacturer‟s abrasive type symbol
First element (letter) -Type of abrasive
Second element (number)- Size of abrasive
Third element (letter) - Grade of bond
Fourth element (number) - Structure of the
grinding wheel
Fifth element (letter) - Type of bond
Suffix Manufacturer‟s symbol
113

Selection of Grinding Wheel
1.Properties of the material to be machined i.e
hardness, toughness, strength
2. Quality of surface finish required.
3. Grinding allowance provided on the work-piece i.e the
amount of stock to be removed
4. Dimensional accuracy required
5. Method of grinding i.e wet or dry
6. Rigidity, size and type of machine
7. Relative sizes of wheel and job
8. Type of grinding to be done
9. Speed and feed of wheel
116

Glazing
 It is the condition of the grinding wheel in which the cutting
edges or the face of the wheel takes a glass-like appearance.
 Glazing takes place if the wheel is rotated at very high speeds
and is made with harder bonds.
 Rotating the wheel at lesser speeds and using soft bonds are the
remedies.
 The glazed wheels are dressed to have fresh, sharp cutting
edges.
Loading
 The wheel is loaded if the particles of the metal being ground
adhere to the wheel.
 The openings or pores of the wheel face are filled up with the
metal.
 It is caused by grinding a softer material or by using a very
hard bonded wheels and running it very slowly.
 It may also take place if very deep cuts are taken by not using
the right type of coolant.
117

Dressing
 If the grinding wheels are loaded or gone out of shape, they can
be corrected by dressing or truing of the wheels.
 Dressing is the process of breaking away the glazed surface so
that sharp particles are again presented to the wheel.
 The common types of wheel dressers known as “Star” -dressers
or diamond tool dressers are used for this purpose.
 A star dresser consists of a number of hardened steel wheels on
its periphery.
118

 The dresser is held against the face of the revolving wheel and
moved across the face to dress the wheel surface.
 Star type of dresser is used particularly for coarse and rough
grinding wheels.
 For precision and high finish grinding, small industrial
diamonds known as „bort‟ are used.
 The diamonds are mounted in a holder.
 The diamond should be kept pointed down at an angle of 10-15°
and a good amount of coolant is applied while dressing.
 Very light cuts only may be taken with diamond tools.
119

Truing
 The grinding wheel becomes worn from its original shape because
of breaking away of the abrasive and bond.
 Sometimes the shape of the wheel is required to be changed for
form grinding.
 For these purposes the shape of the wheel is corrected by means of
diamond tool dressers.
 Truing is done to make the wheel true and concentric with the bore
or to change the face contour of the wheel.
 This is known as truing of grinding wheels.
 Diamond tool dressers are set on the wheels at 10-15° and moved
across with a feed rate of less than 0.02mm.
 A good amount of coolant is applied during truing.
120

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