Unit 3A1 Lathe turning and related operations

Machining & Machining Tools
Unit-3A1
General Purpose and Special Purpose
Machine Tools
1
Lathe, Accessories, Attachments, Turning &
related operations

Overview
• Machine Tools Concept & Functions
• Machine Tools Classification & Types
• Lathe & Turning
• Lathe Operations
• Construction
• Attachments & Accessories
2

Machine Tools
Definition: A machine tool is a non-portable
power operated and reasonably valued device
or a system of devices in which energy is
expended to produce jobs of desired size,
shape and surface finish by removing excess
material from the preformed blanks in the form
of chips with the help of cutting tools moved
past the work surfaces.
3

Functions
Machine Tools produce desired geometrical surfaces on solid
bodies (preformed blanks) and for that they are basically
comprised of;
• Devices for firmly holding the tool and work
• Drives for providing power and motions to the tool and work
• Kinematic system to transmit motion and power from the sources
to the tool-work
• Automation and control systems including control systems for
machining parameters like speed, feed and depth of cut.
• Structural body to support and accommodate those systems with
sufficient strength and rigidity.
4

Tool work motions
 Various shapes are governed by movements of
Generatrix and Directrix (refer Unit-1 PPTS)
 For machining flat or curved surfaces the machine
tools need relative tool work motions, which are
categorized in following two groups:
 Formative motions namely
 Cutting motion (CM)
 Feed motion (FM)
 Auxiliary motions such as
 Indexing motion
 Additional feed motion
 Relieving motion
5

Machine tool drives
• For the desired tool work motions with power, machine tools are
driven by electric motors and use of some mechanisms like belt-
pulley, gears etc. In some machine tools, the tool-work motions are
provided by hydraulic drive also.
• Machine tools essentially need wide ranges of cutting speed and
feed rate to enable
• Machining different jobs (materials and size)
• Using different cutting tools (material, geometry and size)
• Various machining operations like high speed turning to low speed
thread cutting in lathes
• Degree of surface finish desired
6

Machine tool drives (Types)
Stepped drive
• Common in conventional machine tools where a discrete number of
speeds and feeds are available and preferably in G.P. (Geometric
progression) series.
• Stepped drive is attained by using gear boxes or cone pulley (old
method) along with the power source.
Stepless drive
• Modern CNC machine tools are provided with stepless drives
enabling optimum selection and flexibly automatic control of the
speeds and feeds.
• Stepless drive is accomplished usually by
Variable speed ac or dc motors
Stepper or servomotors
Hydraulic power pack
7

Broad classification of Machine Tools
• According to direction of major axis:
Horizontal -center lathe, horizontal boring machine etc.
Vertical – vertical lathe, vertical axis milling machine etc.
Inclined – special ( e.g. for transfer machines).
• According to purpose of use:
General purpose – e.g. center lathes, milling machines, drilling
machines etc.
Single purpose – e.g. facing lathe, roll turning lathe etc.
Special purpose – for mass production.
• According to degree of automation
 Non-automatic – e.g. center lathes, drilling machines etc.
Semi-automatic – capstan lathe, turret lathe, etc.
Automatic – e.g., single spindle automatic lathe, swiss type
automatic lathe, CNC milling machine etc. 8

• According to size:
 Heavy duty – e.g., Heavy duty lathes (e.g. ≥ 55 kw), boring mills,
planning machine, horizontal boring machine etc.
 Medium duty – e.g., Lathes – 3.7 ~ 11 kw, column drilling machines,
milling machines etc.
 Small duty – e.g., Table top lathes, drilling machines, milling machines.
 Micro duty – e.g., Micro-drilling machine etc.
• According to precision:
 Ordinary – e.g., Automatic lathes
 High precision – e.g., Swiss type automatic lathes
• According to number of spindles:
 Single spindle – center lathes, capstan lathes, milling machines etc.
 Multi-spindle – multispindle (2 to 8) lathes, gang drilling machines etc.
9

• According to blank type:
Bar type (lathes)
Chucking type (lathes)
Housing type
• According to type of automation:
Fixed automation – e.g., Single spindle and multispindle
lathes
Flexible automation – e.g., CNC milling machine
• According to configuration:
Stand-alone type – most of the conventional machine tools.
Machining system (more versatile) – e.g., Transfer
machine, machining center, FMS etc.
Power drive with speed and feed change mechanisms.
10

11
Turning & Related Operations

Turning and related operations
Turning
 Part is rotated while it is being machined.
 Axisymmetric jobs are produced
 Starting material is generally a workpiece made by other
processes, such as casting, forging, extrusion, drawing, or
powder metallurgy.
12

Lathe-Working Principle
 Workpiece hold between two rigid and strong supports called
centers or in a chuck or face plate which revolves.
 The cutting tool is rigidly held and supported in a tool post which is
fed against the revolving work.
 Cutting tool removes metal in the form of chips by shear action.
 The normal cutting operations are performed with the cutting tool fed
either parallel or at right angles to the axis of the work. The cutting
tool may also be fed at an angle relative to the axis of work for
machining tapers and angles.
13

Turning Processes
 Turning: to produce straight, conical, curved, or grooved work pieces
such as shafts, spindles, and pins.
 In this process the tool is fed along the axis of the spindle. Turning is the
removal of metal from the outer diameter of a rotating cylindrical
work piece.
14

Turning Processes
Facing: to produce a flat surface at the end of the part and
perpendicular to its axis , useful for parts that are assembled
with other components. Face grooving produces grooves for
applications such as O-ring seats
15

Turning Processes
Cutting with form tools: to
produce various axisymmetric
shapes for functional or
aesthetic purposes
Boring: to enlarge a hole or
cylindrical cavity made by a
previous process or to produce
circular internal grooves
16

Turning Processes
Drilling: to produce a hole , which
may be followed by boring to
improve its dimensional accuracy and
surface finish.
Parting: also called cutting off, to
cut a piece from the end of a part, as
is done in the production of slugs or
blanks for additional processing into
discrete products
17

Turning Processes
Threading: to produce
external or internal threads
Knurling: to produce a
regularly shaped roughness
on cylindrical surfaces, as in
making knobs and handles
18

Operations On Lathe-Detailed
Straight turning: The work is turned straight when it is made
to rotate about the lathe axis and the tool is fed parallel to the
lathe axis. The straight turning produces a cylindrical surface
by removing excess metal from the workpieces
19

Shoulder turning/Step Turning:
 Process of turning different surfaces having different
diameters.
 The work is held between centres and the tool is moved
parallel to the axis of the lathe.
 Also called shoulder turning.
20

Taper & Taper Angle
A taper may be defined as an uniform increase or decrease in
diameter of a piece of work measured along its length.
21

Taper turning: An operation performed on a lathe
that feeds a tool at an angle to the length of the
work piece in order to create a conical shape or
gradual reduction in diameter.
 There are four methods
 Tailstock set over method
 By Swiveling the Compound rest method
 Taper turning attachment method
 Form tool method
 All these methods are discussed in detail.
22

Tailstock Set over Method of Taper Turning
23

24

25

Swiveling the Compound Rest Method
of Taper Turning
26

Swiveling the Compound Rest Method
of Taper Turning
27

Taper turning
attachment Method
of Taper Turning
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Taper turning attachment Method
of Taper Turning
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Taper turning attachment Method
30

Chamfering:
 Operation of beveling the extreme end of a work piece.
 For removing burrs, to protect the end of the work piece
from being damaged and to have a better look.
 Essential before thread cutting so that the nut may pass
freely on the threaded work piece.
33

Eccentric turning
 If a cylindrical workpiece has two separate axes of rotating, one
being out of centre to the other, the workpiece is termed as
eccentric and turning of different surfaces of the workpiece is known
as eccentric turning. The distance between the axes is known as
offset.
 If the offset between the centres is small, two sets of centers are
marked on the faces of the work. The work is held and rotated
between each set of centers to machine the eccentric surfaces.
 For more offset distance special machines are used
34

Facing:
 Facing is the process of making flat surfaces on a lathe.
 The job is held on a faceplate or chuck and the tool is fed at
right angles to the bed to obtain flat surfaces.
 using a 4- jaw chuck you can face rectangular or odd-shaped
work to form cubes and other non-cylindrical shapes.
35

Forming: A forming tool having cutting edges conforming to the shape
required is fed straight into the work for turning a convex, concave or any
irregular shape
Filing: finishing operation that removes burrs, sharp corners and
feed marks from the workpiece.
Polishing: After filing, the surface quality is improved by the polishing
operation with the help of emery cloth of fine grades.
36

Grooving/Recessing/Necking:
 cutting a narrow groove on the cylindrical surface
 often done at the end of thread or adjacent to a shoulder to leave a
margin.
 The groove may be square, radial or beveled in shape.
37

Knurling
 Process of embossing a diamond shaped pattern on the surface of a work
piece by making a series of indentations or depressions
 The knurling tool holder has one or two hardened steel rollers with edges of
required pattern.
 The tool holder is pressed against the rotating work. The rollers emboss the
required pattern.
 Knurls are available in coarse, medium and fine pitches. The patterns may
be straight, inclined or diamond shaped.
 to provide an effective gripping surface, better appearance, to slightly
increase the diameter of the work
38

Spinning :
 also known as spin forming or spinning or metal turning
 a disc or tube of metal is rotated at high speed and formed into
an axially symmetric part.
 This process is covered in detail in sheet metal forming processes.
Spring winding:
 Method of springs winding performed on lathe. Not in our scope to
discuss here.
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Undercutting:
 Done at the end of a hole
 Near the shoulder of stepped cylindrical surfaces
 At the end of the threaded portion in bolts
 Enlarging the diameter if done internally and
reducing the diameter if done externally over a
short length.
 Mainly to make fits perfect. Boring tools and
parting tools are used

• Parting-off: The parting or cutting off is the operation of
cutting away a desired length of the workpiece, i.e., dividing
the workpiece in two or more parts.
40

Drilling
 Making holes generally in the centre of the workpiece with the help
of drills.
 The drill is held in the tailstock and the drilling operation is carried out
by advancing the drill in the workpiece by rotating the handle of the
tail stock.
 First face the end, then drill hole using a center drill and then
perform drilling.
 Hole become oversized and misaligned without use of centre drill.
41

Reaming
 process of enlarging holes to accurate sizes.
 always carried out after drilling.
 similar to drilling -reamer is held in tailstock
 Two broad categories :hand reamers and machine
reamers.
42

Boring
 Enlarging a hole produced by drilling, casting, punching or forging
with the help of a single point tool.
 Boring cannot originate a hole.
 Job is held in a chuck or face plate and a boring tool held on the tool
post are fed into it.
 The operation is similar to external turning in that the feed and depth of
cut are given by the longitudinal and cross motions of the tool
respectively.
43

Counter boring
 Process of boring a hole to more than one diameter on the same
axis
 Needed for receiving the head of a socket head cap screw.
 Carried out with a boring tool.
Taper boring: Process of making angular or tapered bores
Tapping: Process of making internal threads by using a tool called
tap. Detailed discussion will be in unit-4 of thread manufacturing. 44

Milling
 Operation of removing material from a work piece with multi point
rotating cutter generally on milling machines
 In absence of milling machine, can be performed on lathe by milling
attachment
45
On a lathe, the milling cutter
is held in the headstock and
the work piece is clamped in
movable vice.
cutter revolving against the
work piece.
used for milling small work
pieces only, where a milling
machine cannot be used.

Grinding
 Removing material by means of rotating abrasive wheel for
finishing operations.
 work piece is held between the centres and the grinding operation is
carried out by mounting the tool post grinder on the compound slide.
 carried out after rough turning, to provide an accurate finish by
removing a small amount of material.
46

Thread Cutting on Lathe Machine
• By various cutting tools made of HSS or often cemented
carbide tools.
• Centre lathes to single spindle automats are used
• Special purpose lathes and CNC lathes including turning
centers used
• Threads are produced in centre lathes by various methods
• By single point cutting tool
• By thread chasing (covered later)
• By attachments of die threading and tapping
(covered later)

Cutting with Single Point Tool on Lathe
• A single-point cutting tool is used to produce a thread form on a
cylinder or cone.
• The tool moves linearly while the precise rotation of the
workpiece determines the lead of the thread.
• The process can be done to create external or internal threads
(male or female).
• In external thread cutting, the piece can either be held in a chuck
or mounted between two centers.
• With internal thread cutting, the piece is held in a chuck. The tool
moves across the piece linearly, taking chips off the workpiece
with each pass.

a) Operator should be fully conversant with different terms, types, starts and
shape of threads.
b) External or internal threads may be cut on lathe either with the help of a
die or tap respectively or a thread cutting tool may be used.
c) A certain relation is needed between job revolutions and revolutions of
lead screw to control the linear movement of the tool, parallel to the job
length when half nut is engaged with lead screw.
d) The tool should be ground to the proper shape and profile of the thread
to be cut.
e) Many lathes are provided with quick-change gearbox in which
different ratios of spindle and lead screw revolutions can be readily
obtained by simply shifting the gear change lever. In other lathes,
for cutting different pitches of threads, every time gears are
changed.
f) For cutting threads on a lathe, headstock spindle is connected with the
lead screw through gears in such a way that positive carriage feed is
obtained and the lead screw is driven at a predetermined speed in
relation to the spindle speed.

It includes only three gears,
driver, driven and some suitable
intermediate gear. The
intermediate gear has no effect
on the ratio. It simply acts as a
connection that is used to fill up
the distance gap between the
driver, and the driven gear and
makes the lead screw rotate in
the same direction of the
machine spindle.
When cutting a screw thread, the tool is moved along the bed and is
driven by a nut engaging with the lead screw. The lead screw is driven by
a train of gears from the machine spindle. The gear train may be arranged
in one of the following ways:
A. Simple gear train.

B. Compound gear train. Sometimes driver and driven gear ratio becomes so
typical that the selection of gears to arrange in a simple train becomes difficult.
For example Dr and Dn ratio is 4/26, and then a set of gears, which can give this
ratio in the simple train, may become difficult. In such cases the solution is
obtained with the use of compound wheel train, the gear ratio become
Gears supplied with lathes, generally, range from 20 to 120 teeth in steps of 5 teeth
with two 40s or two 60s. The lead screw on lathes is always single-threaded and of
a pitch varying from 5 to 10 mm depending on the size of the machine. For English
lathes, the most common screw threads have 2, 4, or 6 tpi.

Example
Calculate suitable gear trains for the following cases :
a. 2.5 mm pitch on a 6 mm lead screw
b. 11 tpi on a 4 tpi lead screw
c. 7 threads in 10 mm on 6 mm lead screw
d. 7/22 in. pitch, 3 start on a lathe with 2 tpi
e. 2.5 mm pitch on a 4 tpi lead screw
f. 12 tpi on a lathe having 6 mm pitch lead screw

Thread Catching
 Required depth of a thread cannot be obtained in a single
cut of tool and several successive cuts are needed.
 In the first cut, tool travels up to the job length, and then it
is to be taken to the starting position for giving the second
cut.
 Now if tool is not fed exactly in the previous groove, it may
form a new groove thus wastage of the job.
 Modern machines are provided with facilities to reverse the
rotation of job, which will bring the tool to original position
without disengaging the half-nut.
 But few machines are not equipped with such facilities. In
those machines tool is to be brought back by some other
means.

Thread Catching
The process of setting the tool repeatedly in the
previously formed groove is called thread catching or
thread chasing. Few methods of thread chasing are given
below
(a) At the end of each travel of the tool, take it back from the job surface
and stop the machine. Disengage half-nut from lead screw and return it
by hand to the starting point of the cut. By trial method, set the tool in
right groove, start the machine to have the fresh cut after giving a
certain feed to the tool.
(b) Do not disengage half-nut from lead screw at the end of each cut.
By reversing the direction of lead screw, bring the carriage to the
starting position of the cut. A mark may be given on the bed by the side
of the carriage; this will help in setting the carriage immediately. This
method is useful for cutting threads on short lengths or in blind holes or
for threads of odd pitches, which are difficult to cut even with the help of
chasing dial method.

Procedure for External Threads
 Hold the job between the lathe centres or in chuck as required and turn
it to the size of the major diameter of thread to be cut.
 Select suitable change gear set for cutting required pitch of thread and
arrange them. At the end of job, which will be starting end for every cut
while threading, turn a very small step of diameter equal to the minor
diameter to be cut i.e. recessing.
 Set the tool properly, swivel and clamp the compound rest at an angle if
required as discussed already. Adjust the spindle speed for threading.
 Bring the tool at the starting point, take a certain depth of cut and
engage the half nut with lead screw. This will move the tool along the job
length forming a thread groove.
 Have few successive cuts to obtain the required depth of thread. That
small step turned at the job and will guide you to feed the tool up to a
required depth.
 When threading is complete, stop the lathe and measure the depth of
the threads with a thread pitch gauge.

Procedure for Internal Threads
 Hold the job in a chuck. Make a hole equal to the minor diameter
of the thread. A common practice is to make the hole slightly
larger than minor diameter of thread for providing a clearance
between the mating parts.
 Turn a small groove at the end of the thread length equal to the
major diameter of the thread to guide the operator for maintaining
the correct depth of thread.
 Rest of the procedure is the same as for cutting external threads.
Special care is needed while threading a blind hole
• By moving carriage, bring the tool to the job front and let it go
inside the hole till it reaches the point at, which the last thread will
terminate.
• At this position, make a line on the bed to guide the operator that
he is not to allow the carriage to come towards the left ahead of
this mark

Cutting Right hand & Left Hand Threads
Cutting Right Hand Threads
 Direction of rotation of job and lead screw should be same
i.e. towards the operator (counter clock wise).
 For threading on job, start the cut from tail stock side.
 After engaging half nut, see that the tool moves from the
tail stock side to headstock side.
Cutting Left Hand Threads
 Reverse the direction of rotation of lead screw with the
direction reversing mechanism lever.
 Start the cut on job from headstock side so that when half
nut is engaged tool should move from headstock to tail
stock side.

Cutting Multistart Threads
 Cutting procedure of multi start threads is similar to that of
cutting single start threads.
 In multi start thread, circumference of the job should be divided
in to as many parts as the starts of the threads and thus every
part of the divisions of the circumference of job becomes the
starting point for the new start.
 Several methods are given below to divide the job circumference
to take cuts for different starts
(a) Faceplate of lathe may be divided and marked in as many parts
as the starts are to be had on the job. Every mark will give the
starting position for new start of the thread.
(b) Indexing faceplate of typical construction for cutting multi start
threads are usually available. On the plate, means are
provided to rotate the job through whatever fractional part of
the job circumference is needed.

Cutting Multistart Threads
(c) Compound rest is also used for adjusting the tool to have
the correct spacing while cutting multi start threads. Set the
compound rest parallel to work axis. When one start of the
thread is cut, then the tool is moved a distance equal to the
pitch to be cut. This method is mostly used for cutting internal
threads. Make sure that there is no backlash in the compound
rest screw.
The rest of the procedure is to get the lines of different starts
inscribed on the job surface along the length with a thread
cutting tool, cut rough profiles of different starts. For finishing
the threads, finish first start completely and then one after the
other.

Tapered Threads
• The only precaution used for cutting threads on a
tapered surface is that the threading tool is set
perpendicular to the lathe axis and not to the tapered
surface. Rests of the procedure is same. Only taper
turning attachment is employed for taper turning and
thread cutting.

65

Typical Lathe and Its Various Components
67

Typical Lathe and Its Various Components
68

Bed
 Bed is mounted on the legs of the lathe which are
bolted to the floor.
 It is made of cast iron and its top surface is
machined accurately and precisely.
 Cast iron possesses better lubricating property due
to presence of free graphite , has high compressive
strength, better shock absorption capacity, In order
to increase its hardness and reduce the effect of
residual stresses, can be easily alloyed with nickel,
chromium and molybdenum and easily cast and
machined, If required, hard surface can also be
produced by induction hardening process.
 Headstock of the lathe is located at the extreme left
of the bed and the tailstock at the right extreme.
 The top of the bed has flat or V shaped guideways
that are precision machined parallel to assure
accuracy of movement.
69

Bed
70
Lathe bed cross section :
Saddle rests on a-a and tailstock
rests on b-b
Two basic types of ribbing are as follows:
(a) Box ribbing.
(b) Diagonal ribbing.
 The box formation (Box ribbing is
convenient to produce, apertures in the
walls permitting the positioning and
extraction of cores.
 Diagonal ribbing provides greater
torsional stiffness and permits swarf to
fall between the sections.
Lathe bed cross section of a cast iron
bed for a heavy lathe

Headstock
 Headstock is mounted permanently on the inner guide ways at the left
hand side of the leg bed.
 The headstock houses a hollow spindle to which bar stock can be fed
and the mechanism for driving the spindle at multiple speeds. Using
a chuck or collets, spindle rotates the work
71
The headstock will have any of the following
arrangements for driving and altering the spindle
speeds
(i) Stepped cone pulley drive
(ii) Back gear drive
(iii) All gear drive

Spindle
 The spindle rotates on two large bearings housed on the
headstock casting
 Hole extends through the spindle so that a long bar
stock may be passed through the hole.
 The front end of the spindle is threaded on which
chucks, faceplate, driving plate and catch plate are
screwed.
72

Tailstock
 Fits on the inner ways of the bed and can slide towards headstock
to fit the length of the work piece.
 optional taper turning attachment can be mounted to it.
 It is equipped with a center that may be fixed (dead center), or it may
be free to rotate with the workpiece (live center).
 Situated at right end of bed, used for supporting right end of WP
 Used for holding and feeding the tools such as drills, reamers, taps
etc.
73

Carriage
 Carriage is located between the headstock and tailstock on the lathe
bed guideways.
 It can be moved along the bed either towards or away from the
headstock.
 It has several parts to support, move and control the cutting tool.
74
The parts of the carriage are :
a) saddle
b) apron
c) cross-slide
d) compound rest
e) compound slide
f) tool post

Saddle
75
 It is an “H” shaped casting.
 It connects the pair of bed guideways like a bridge.
 It fits over the bed and slides along the bed between
headstock and tailstock.
 The saddle or the entire carriage can be moved by providing
hand feed or automatic feed.

Cross Slide
76
 Cross-slide is situated on the saddle and slides on the
dovetail guide ways at right angles to the bed guide ways.
 It carries compound rest, compound slide and tool post.
 Cross slide hand wheel is rotated to move it at right angles to
the lathe axis.

Compound Rest
77
 Compound rest is a part which connects cross slide and compound slide.
 It has a circular base on which angular graduations are marked.
 The compound rest can be swiveled to the required angle while turning
tapers.
 A top slide known as compound slide is attached to the compound rest
by dove tail joint.

Tool Post
78
 This is located on top of the
compound slide.
 It is used to hold the tools rigidly.
 Tools are selected according to the
type of operation and mounted on
the tool post and adjusted to a
convenient working position.
 There are different types of tool
posts and they are:
1. Single screw tool post
2. Four bolt tool post
3. Four way tool post
4. Open side tool post

Leadscrew
 The lead screw is a long threaded shaft used as master screw.
 It is brought into operation during thread cutting to move the carriage to
a calculated distance.
 Mostly lead screws are Acme threaded.
 The lead screw is held by two bearings on the face of the bed.
 A half nut lever is provided in the apron to engage half nuts with
the lead screw.
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Feed rod
 Feed rod is placed parallel to the lead screw on the front side of the
bed.
 It is a long shaft which has a keyway along its length.
 The power is transmitted from the spindle to the feed rod through
tumbler gears and a gear train.
 It is useful in providing feed movement to the carriage except for
thread cutting and to move cross-slide.
81

Lathe Specifications
• The height of the centres measured from the lathe bed. (r )
• The swing diameter over bed. This is the largest diameter of work that
will revolve without touching the bed and is twice the height of the
centre measured from the bed of the lathe. (d)
• The length between centres. This is the maximum length of work that
can be mounted between the lathe centres. (C)
• The swing diameter over carriage. This is the largest diameter of work
that will revolve over the lathe saddle, and is always less than the swing
diameter over bed.
• The maximum bar diameter. This is the maximum diameter of bar
stock that will pass through hole of the headstock spindle.
• The length of bed. This indicates the approximate floor space occupied
by the lathe. (b)
83

Lathe Classification & Types
84

Classification of Lathes
• According to configuration
• Horizontal
• Most common for ergonomic conveniences
• Vertical
• Occupies less floor space, only some large lathes are of this type.
Useful in heavy workpiece with d>>>l
• According to purpose of use
• General purpose
• Very versatile where almost all possible types of operations are
carried out on wide ranges of size, shape and materials of jobs;
example: centre lathes
• Single purpose
• Only one (occasionally two) type of operation is done on limited
ranges of size and material of jobs; example – facing lathe, roll
turning lathe etc.
• Special purpose
• Where a definite number and type of operations are done
repeatedly over long time on a specific type of blank; example:
gear blank machining lathe etc. 85

• According to size or capacity
• Small (low duty)
• In such light duty lathes (up to 1.1 kW), only small and
medium size jobs of generally soft and easily machinable
materials are machined
• Medium (medium duty)
• These lathes of power nearly up to 11 kW are most
versatile and commonly used
• Large (heavy duty)
• Mini or micro lathe
• These are tiny table-top lathes used for extremely small
size jobs and precision work; example: swiss type
automatic lathe
86

• According to degree of automation
• Non-automatic
• Almost all the handling operations are done manually;
example: centre lathes
• Semi-automatic
• Nearly half of the handling operations, irrespective of the
processing operations, are done automatically and rest
manually; example: capstan lathe, turret lathe, copying
lathe relieving lathe etc.
• Automatic
• Almost all the handling operations (and obviously all the
processing operations) are done automatically; example –
single spindle automat (automatic lathe), swiss type
automatic lathe, etc. 87

• According to type of automation
• Fixed automation
• Conventional; example – single spindle automat, swiss type
automatic lathe etc.
• Flexible automation
• Modern; example CNC lathe, turning centre etc.
• According to configuration of the jobs being handled
• Bar type
• Slender rod like jobs being held in collets
• Chucking type
• Disc type jobs being held in chucks
• Housing type
• Odd shape jobs, being held in face plate
88

• According to precision
• Ordinary
• Precision (lathes)
• These sophisticated lathes meant for high accuracy and
finish and are relatively more expensive.
• According to number of spindles
• Single spindle
• Common
• Multispindle (2, 4, 6 or 8 spindles)
• Such uncommon lathes are suitably used for fast and
mass production of small size and simple shaped jobs.
89

Types of Lathes
• Bench Lathe
• Speed Lathe
• Engine Lathe/Center Lathe
• Tool Room Lathe
• Capstan & Turret Lathe
• Automatic Lathe
• Special Purpose Lathe
90

Bench Lathe
 very small lathe on bench
or cabinet.
 It is used for small and
precision work for light
jobs and it is very
accurate. Production of
gauges, punches etc
 It is usually provided with
all the attachments, which
a larger lathe carries, and
is capable of performing
almost all the operations
which a larger lathe can
do.
91

Speed Lathes
• In this lathe spindle can rotate at a very high speed with the help of a
variable speed motor built inside the head stock of lathe.
• Bench type or can have supporting legs cast and fitted to the bed.
• most of the attachments like other lathes but no provision for power
feed.
• No gear box, carriage and the lead screw. tool is fed and actuated
by hand.
92
employed for wood turning,
polishing, centering and
metal spinning, etc.

Engine Lathe/Centre Lathe
• Its headstock is bigger in size and more robust, incorporating suitable
mechanism for providing multiple speeds to the lathe spindle.
• The headstock spindle receives power from a lathe shaft or an
individual motor through belts. In that case, it will have a cone pulley
with back gears in the headstock to provide different speeds to the
spindle.
• If it carries a combination of gears, instead of the cone pulley and
back gears combination, the lathe is known as geared head lathe and
the headstock as all geared head stock.
93
 Most widely used type of lathe
 Driven by a steam engine in past
so the name is engine lathe
 Now driven by an individual motor
drive
 Resembles a speed lathe, but its
construction is relatively more
robust.

Tool Room Lathe
 Used for precision components,
dies, tools, jigs etc.
 engine lathe equipped with some
extra attachments for obtaining
accuracy
 attachments provided are taper
turning attachment, follower
rest, collets, chucks, etc.
 comparatively smaller bed
length than engine lathe. The
most commonly used lengths are
135 to 180 cm.
94

Capstan & Turret Lathe
• In Tanks turret refers to a sort of
arrangement used to hold several weapons
which can fire the particular shot depending
on exact requirement
• In ships Capstan is a spinning vertical
cylinder used for pulling heavy objects
with a rope
• semiautomatic and fitted with multi tool
holding devices, called capstan and turret
heads.
• different types of operations can be
performed on a workpiece without
resetting of work or tools.
• With the turret lathes, sequential
operations can be done on the work
piece, eliminating errors in work alignment.
• used for mass production of identical
parts in the minimum time.
95

Automatic Lathe
• For enhancing the quality as well as the
quantity of production
• Used for mass production of identical
parts
• All the working and job handling
movements of job are automatic. No
participation of operator
• In semi-automatic lathes, mounting and
removal of work is done by operator
whereas all the operations are performed
by the machine automatically.
• available having single or multi spindles.
• They fall in the category of heavy duty,
high speed lathes
96

Special Purpose Lathes
• The Gap bed lathe which has a
removable section in the bed in front
of the headstock to provide a space
or gap is used to swing extra large
diameter jobs.
• The Wheel lathe is made for
finishing the journals and turning the
tread on railroad car and locomotive
wheels.
• Number and types of special
purpose lathes are very big. Only
a few are covered above
97

Lathe Accessories
and
Attachments
99

Lathe Accessories
Additional elements or devices essentially required for that
machine’s general functioning, mainly for properly holding and
supporting the workpiece and the cutting tool
• Centers
• Chucks
• Lathe dogs
• Drive plates
• Face plate
• Mandrels
• Steady and follower rests
100

Centres
• There are two types of centres i.e., live centre and dead centre.
• A centre which fits into the headstock spindle and revolves with the work is
called live centre.
• The centre which is used in a tailstock spindle and does not revolve is called
dead centre.
• Work to be turned between centers must have center hole drilled in each end
• Provides bearing surface
• Support during cutting
• Most common have solid Morse taper shank 60º centers, steel with carbide tips
• Care to adjust and lubricate occasionally
101

Chucks
• It is an important device used for holding and rotating the
workpiece in lathes.
• The work pieces which are too short to be held between
centres are clamped in a chuck.
• The internal threads in the chuck fit on to the external
threads on the spindle nose.
• It is attached to the lathe spindle by means of two bolts with
the back plate screwed on to the spindle nose.
• Chucks can be power or manually actuated with a chuck
wrench.
102

Chucks
Three jaw universal chuck
The three jaw universal chuck, as
shown in Fig. is also called self-
centering chuck or scroll
chuck. Thus chuck is used for
holding round and hexagonal
work.
Four jaw independent chuck
four reversible jaws, each of which
may be independently adjusted
to accommodate the work it
supports.
This type of chuck can hold
square, round and irregular
shape of work in either a
concentric or eccentric position.
103

Chucks
Collet chuck
• Used to hold small workpieces
• A collet is basically a longitudinally-split, tapered bushing. The workpiece
(generally with a maximum diameter of 25 mm) is placed inside the collet,
and the collet is pulled (draw-in collet; Figs. a and b) or pushed (push
out collet) mechanically into the spindle.
• The tapered surfaces shrink the segments of the collet radially,
tightening onto the workpiece. Collet grips nearly the entire circumference
of the part, making the device well suited particularly for parts with small
cross sections. Because the radial movement of the collet segments is small,
workpieces generally should be within 0.125 mm of the nominal size of the
collet.
104

Chucks
Other chucks
Other chucks are magnetic chuck (Used to hold thin jobs by magnetic
forces), combination chucks (combination of self-centering and
independent chucks), drill chucks for drills & air or hydraulic chuck
105

Drive Plate
• A circular plate which is bored out and threaded so that it
can be attached to the spindle nose.
• It also carries a hole for the pin which is used only when the
work is held in a lathe dog having straight tail.
• When bent-tail dog is used, this pin is
taken out and the bent portion of the tail is inserted into the
hole
106

Face Plate
 Similar to drive plate but is larger in diameter.
 It contains more open slots or T-slots so that bolts may be
used to clamp the workpiece to the face of the plate.
 The face plate is used for clamping irregularly shaped
workpieces which cannot be conveniently held in a chuck.
107

Angle Plate
• An angle plate is simply a cast iron plate with to faces planed at right
angles to each other and having slots in various positions for the clamping
bolts.
• It is always used with the face plate for holding such parts which cannot
be clamped against the vertical surface of the face plate.
108

Lathe Dog or Carrier
• The work placed on a mandrel or held between centres is
rotated positively by clamping the dog or carrier to the end of the
work.
• This is engaged with a pin attached to the drive plate or face
plate.
• The lathe dog or carrier may be of straight type or bent type
109

Mandrels
• The lathe mandrel is a
cylindrical bar with centre
hole at each end. It is
used to hold hollow
work pieces to machine
their external surface.
• The work revolves with
the mandrel which is
mounted between the
centres of the lathe.
110

Mandrels
111
a. Plain Mandrel b. Expanding Mandrel c. Nut type mandrel

Rests
Long workpieces often need to be
supported in the middle, as cutting tools
can push (bend) the work piece away from
where the centers can support them,
because cutting metal produces
tremendous forces that tend to vibrate or
even bend the workpiece.
Steady rest :
It stands stationary from a rigid mounting
on the bed, and it supports the
workpiece at the rest’s center, typically
with three contact points 120° apart.
Follower rest:
it is mounted to the carriage rather than
the bed, which means that as the tool bit
moves, the follower rest “follows
along”
112

Rests
113
a. Steady Rest b. Follower Rest

Centre Lathe Machine Attachments
• To perform some unusual or specific work, some special
devices or systems are additionally used and mounted in
the ordinary machine tools. Such additional special devices,
which augment the processing capability of any ordinary
machine tool, are known as Attachments
• Taper turning attachment
• Copy turning attachments
• Milling and cylindrical grinding attachments
• Grinding Machine attachment For Lathe
• Spherical turning attachments
• Relieving attachment
• Thread Pitch Correction Attachment For Lathe
• Thread chase dial attachment
• Eccentric Turning attachment
114

Taper Turning Attachments
 Cross slide is delinked from the saddle and is moved crosswise
by the guide block which moves along the guide bar preset at the
desired taper angle.
 Thus, the cutting tool, which is fitted on the cross slide through
the tool post and the compound slide, also moves along with the
guide block in the same direction resulting the desired taper
turning.
115

Mechanical Type Copy Turning Attachment
 The stylus is fitted in the spring loaded tool slide and while
travelling longitudinally along with saddle moves in
transverse direction according to the template profile enabling
the cutting tool produce the same profile on the job
116
 The entire attachment
is mounted on the
saddle after
removing the cross
slide from that.
 The template
replicating the job-
profile desired is
clamped at a suitable
position on the bed.

Hydraulic type Copy Turning Attachment
 In mechanical system the heavy cutting force is
transmitted at the tip of the stylus, which causes
vibration, large friction and faster wear and tear.
 In hydraulic copying, where the stylus works simply as
a valve – spool against a light spring and is not
affected by the cutting force.
 Here also, the stylus moves along the template
profile to replicate it on the job.
 Costlier than the mechanical type but works much
smoothly and accurately.
117

Hydraulic Type Copy Turning Attachment
118
 The cutting tool is rigidly
fixed on the cross slide
which also acts as a valve –
cum – cylinder.
 If stylus remains on a
straight edge parallel to the
lathe bed, the cylinder does
not move transversely and
the tool causes straight
turning.
 If stylus starts moving along a slope or profile, i.e., in cross feed
direction the ports open and the cylinder starts moving accordingly
against the piston fixed on the saddle.
 Again the movement of the cylinder i.e., the slide holding the tool,
is by same amount travelled by the stylus, which closes the ports.
 Repeating of such quick incremental movements of the tool, Δx and Δy
result in the profile with little surface roughness.

Milling Attachment
This is a milling head,
comprising a motor, a small
gear box and a spindle to
hold the milling cutter,
mounted on the saddle after
removing the cross slide etc.
Milling attachments are
generally used for making
flat surfaces, straight and
helical grooves, splines,
long and deep screw
threads, worms etc. in centre
lathes by using suitable milling
cutters.
119

Grinding
Attachment
 Similar to milling attachment, but no gear box and the spindle speed is
much higher as needed for grinding operation.
 Employed for external and internal cylindrical grinding, finishing
grooves, splines etc. And also for finish grinding of screw threads in
centre lathe.
 Cannot provide high accuracy and finish.
 Called tool post grinder.
 It is mounted on the compound rest in place of tool post.
 Consists of a base plate, grinding wheel and a motor.
 The job is held in a chuck or between centres.
 It is extensively used for grinding lathe centres in position.
120

Spherical/Ball Turning Attachment
 These simple attachments are used in centre lathes for machining spherical;
both convex and concave surfaces and similar surfaces.
 the desired path of the tool tip is controlled by the profile of the template
which is pre-made as per the radius of curvature required.
 The saddle is disconnected from the feed rod and the leadscrew.
 When the cross slide is moved manually in transverse direction, the tool
moves axially freely being guided by the template only.
Spherical Turning with template

Spherical/Ball Turning Attachment
the distance R can be set according to the radius of curvature desired.
Spherical Turning without template

Relieving Attachment
 The teeth of form relieved milling cutters like gear milling cutters, taps, hobs
etc. are provided with flank having Archimedean spiral curvature.
Machining and grinding of such curved flanks of the teeth need relieving
motion to the tool (or wheel) .
 It is comprised of a spring loaded bracket which holds the cutting tool and is
radially reciprocated on the saddle by a plate cam driven by the feed rod as
indicated
123

Thread Pitch Correction Attachment
While cutting screw thread in centre lathes by single point chasing tool, often the
actual pitch, pa deviates from the desired (or stipulated) pitch, ps by an error (say ±
Δp) due to some kinematic error in the lathe. Mathematically,
ps – pa = ± Δp
Therefore for correct pitch, the error ± Δp need to be compensated and this may be
done by a simple differential mechanism, namely correcting bar attachment as
schematically indicated in Fig.
Pa = 1 x UC x L
± Δp = pstan(±α).L/(πmZ)
where, UC = transmission ratio, L = lead of the leadscrew, m, Z = module and no. of
teeth of the gear fixed with the nut and is additionally rotated slightly by the
movement of the rack along the bar.
Such differential mechanism of this attachment can also be used for intentionally
cutting thread whose pitch will be essentially slightly more or less than the standard
pitch, as it may be required for making differential screws having threads of slightly
different pitch at two different locations of the screw.
124

Thread Pitch Correction Attachment
125

Thread Chasing Dial Attachment
 Cutting of threads is done in several passes and after each pass tool is
brought back to the initial start position for next pass
 If the tool does not follow the path, the threads will be spoiled.
 The chasing dial overcomes the difficulty of catching the threads at
correct start.
 It consists of graduated dial that is connected to a worm wheel - The
worm is in mesh with the lead screw, so that if the saddle is
stationary, the lead screw acts as a worm and rotates the chasing
dial.
 When the half nut is engaged, the tool starts travelling but the dial
remains stationary with one of the graduations opposite to the
arrow.
 When the cut is completed the saddle is returned to the starting
point. When the nut is disengaged and the dial remains rotating as
soon as the graduated line comes opposite to the arrow, the half
nut can be engaged and the tool will follow its original cut.
126

Thread Chasing Dial Attachment
.
127

Eccentric Turning Attachment
.
 It refers to the turning of certain diameters at different
lengths on the same shaft or jobs whose axis is not falling
in line with the main axis. A crank shaft of an engine is the
example of such job.
 This type of attachment is equipped with the provision of shifting
the centres of the work away from the lathe spindle axis.
 An accurate marking and truing is of prime important in the
sequence of operation of jobs of this nature.
128

Turning Mathematics
.
Detailed Explanation covered in Unit-1 PPTs
130

Turning Mathematics
MATERIAL-REMOVAL RATE: The material-removal rate (MRR) in turning is
the volume of material removed per unit time, with the units of
mm3/min.
Detailed Explanation in Unit-1 ppts
131

Unit 3A1 Lathe turning and related operations

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