A lathe rotates a workpiece about an axis to perform various operations such as cutting, sanding, knurling with tools. It consists of a headstock, bed, carriage, tailstock. The headstock powers the spindle and workpiece. The carriage moves the tool parallel to the axis of rotation. Turret and capstan lathes allow quick tool changes. Automatic lathes can produce identical pieces without operator attention after initial setup.

1. Lathe
By S K Mondal

4. Lathe
 A lathe is a large machine that rotates the work, and
cutting is done with a non-rotating cutting tool. The
shapes cut are generally round, or helical. The tool is
typically moved parallel to the axis of rotation during
cutting.
 head stock - this end of the lathe contains the driving
motor and gears. Power to rotate the part is delivered
from here. This typically has levers that let the speeds
and feeds be set.
 ways - these are hardened rails that the carriage rides
on.
 tail stock - this can be used to hold the other end of the
part.

5. Lathe
 Bed - this is a bottom pan on the lathe that catches chips,
cutting fluids, etc.
 carriage - this part of the lathe carries the cutting tool and
moves based on the rotation of the lead screw or rod.
 Lead screw - A large screw with a few threads per inch used
for cutting threads. It has ACME threads with included angle
of 29o for easy engagement and disengagement of half nut.
 Lead rod - a rod with a shaft down the side used for driving
normal cutting feeds.
 The critical parameters on the lathe are speed of rotation
(speed in RPM) and how far the tool moves across the work
for each rotation (feed in IPR)

6. General classifications used when describing lathes
 Swing - the largest diameter of work that can be rotated.
 Distance Between Centres - the longest length of
workpiece
 Length of Bed - Related to the Distance Between
Centres
 Power - The range of speeds and feeds, and the
horsepower available

7. Number of Spindle Speed
 Number of spindle speed is in a geometric progression.
 If n number of spindle speed is required with N1 is the
minimum speed then
 The values of step ratios are 1.06, 1.12, 1.26, 1.41, 1.58 and 2
 
1
1
min
max
max
1
1min1
1
1
3
1
2
111
RatioStepTherefore,
....,.........,,,











n
n
n
N
N
r
NrNandNN
rNrNrNrNN

8. IES - 2001
The spindle speed range in a general purpose lathe
is divided into steps which approximately follow
(a) Arithmetic progression
(b) Geometric progression
(c) Harmonic progression
(d) Logarithmic progression

9. IES - 1992
Feed gear box for a screw cutting lathe is designed
on the basis of
(a) Geometric progression
(b) Arithmetic progression
(c) Harmonic progression
(d) None.

10. Turning
 Turning - produces a smooth and straight outside radius
on a part.

11. Video

12. Threading
 Threading - The cutting tool is moved quickly cutting
threads.

13. Video

15. Threading
 In one revolution of the spindle, carriage must travel
the pitch of the screw thread to be cut.
    traingearcarriagetospindleofratiogear
screwleadtheofstartofNumber
cutbetothreadscrewtheofstartofNumber
screwleadtheofPitchL
cutbetothreadscrewtheofPitch
Lscg
L
s
LLss
NNi
z
z
P
LzNPzN







16. IES - 1998
A single start thread of pitch 2 mm is to be produced
on a lathe having a lead screw with a double start
thread of pitch 4 mm. The ratio of speeds between
the spindle and lead screw for this operation is
(a) 1 : 2 (b) 2: 1
(c) 1: 4 (d) 4: 1

17. IES – 1993, ISRO-2009
It is required to cut screw threads of 2 mm pitch on
a lathe. The lead screw has a pitch of 6 mm. If the
spindle speed is 60 rpm, then the speed of the lead
screw will be
(a) 10 rpm (b) 20 rpm
(c) 120 rpm (d) 180 rpm

18. Facing
 Facing - The end of the part is turned to be square.

19. Video

20. Tapering
 Tapering - the tool is moves so as to cut a taper (cone
shape).

21. Parting/Slotting/Grooving
 A tool is moved in/out of the work. shallow cut will leave
a formed cut, a deep cut will cut off the unsupported
part.

22. Video

23. Drilling/Boring
 Drilling/Boring - a cutter or drill bit is pushed into the
end to create an internal feature.

24. Video

25. Knurling
 Knurling is a manufacturing process whereby a
visually-attractive diamond-shaped (criss-cross)
pattern is cut or rolled into metal.
 This pattern allows human hands or fingers to get a
better grip on the knurled object than would be
provided by the originally-smooth metal surface.

27. Spinning
 Metal Spinning is a process by which circles of metal are
shaped over mandrels (also called forms) while mounted
on a spinning lathe by the application of levered force
with various tools.

28. Reaming
 A reamer enters the workpiece axially through the end
and enlarges an existing hole to the diameter of the
tool. Reaming removes a minimal amount of material
and is often performed after drilling to obtain both a
more accurate diameter and a smoother internal
finish.

29. Tapping
 A tap enters the workpiece axially through the end and
cuts internal threads into an existing hole. The
existing hole is typically drilled by the required tap
drill size that will accommodate the desired tap.

30. Work holding Devices for Lathes
 Held between centers
 3 jaw self centering chuck (Disc type jobs being held
in chucks )
 4 jaw independently adjusted chuck
 Held in a collet (Slender rod like jobs being held in
collets )
 Mounted on a face plate (Odd shape jobs, being held
in face plate)
 Mounted on the carriage
 Mandrels
 Magnetic chuck – for thin job

31. Lathe chucks
 Lathe chucks are used to support a wider variety of
workpiece shapes and to permit more operations to be
performed than can be accomplished when the work is
held between centers.
 Three-jaw, self-centering chucks are used for work that
has a round or hexagonal cross section.
 Each jaw in a four-jaw independent chuck can be moved
inward and outward independent of the others by means
of a chuck wrench. Thus they can be used to support a
wide variety of work shapes.
 Combination four-jaw chucks are available in which each
jaw can be moved independently or can be moved
simultaneously by means of a spiral cam.

32. 3 Jaw Chuck 4 Jaw Chuck

33. Collets Magnetic Chuck
Face Plate

34. Turning

35. Formula for Turning
 Depth of cut,
 Average diameter of workpiece
 Cutting Time,
 Metal Removal Rate
 Cutting Speed, V =

  1 2D D
d DOC mm
2

 1 2
avg
D D
D mm
2
 

L A O
CT
fN
   
  
2 2
1 2
avg
D D
MRR D dfN
4 / fN
 1D N
,m / min
1000

36. Example
How much machining time will be required to reduce
the diameter of a cast iron rod from 120 mm to 116 mm
over a length of 100 mm by turning using a carbide
insert. Cutting velocity is 100 m/min and feed rate = 0.2
mm/rev.

37. IES 2010
In turning a solid round bar, if the travel
of the cutting tool in the direction of
feed motion is 1000 mm, rotational
speed of the workpiece is 500 rpm, and
rate of feed is 0.2 mm/revolution, then
the machining time will be
(a) 10 seconds (b) 100 seconds
(c) 5 minutes (d) 10 minutes

38. IES - 2003
The time taken to face a workpiece of 72 mm
diameter, if the spindle speed is 80 r.p.m. and cross-
feed is 0.3 mm/rev, is
(a) 1.5 minutes (b) 3.0 minutes
(c) 5.4 minutes(d) 8.5 minutes

39. GATE-2013 (PI) Common Data
A disc of 200 mm outer and 80 mm inner diameter is
faced of 0.1 mm/rev with a depth of cut of 1 mm. The
facing operation is undertaken at a constant cutting
speed of 90 m/min in a CNC lathe. The main
(tangential) cutting force is 200 N.
Assuming approach and over-travel of the cutting
tool to be zero, the machining time in min is
(a) 2.93 (b) 5.86 (c) 6.66 (d) 13.33

40. IES - 2004
A medium carbon steel workpiece is turned on a
lathe at 50 m/min. cutting speed 0.8 mm/rev feed
and 1.5 mm depth of cut. What is the rate of metal
removal?
(a) 1000 mm3/min
(b) 60,000 mm3/min
(c) 20,000 mm3/min
(d) Can not be calculated with the given data

41. Turning Tapers on Lathes
Using a compound slide,
Using form tools,
Offsetting the tailstock, and
Using taper turning attachment.

42. Using a Compound Slide
 Limited movement of the compound slide
 Feeding is by hand and is non-uniform. This is
responsible for low-productivity and poor surface
finish.
 Can be employed for turning short internal and
external tapers with a large angle of (steep) taper.

43. Using a Compound Slide contd..
 The angle is determined by
l
dD
2
tan


tapertheoflengthl
diametersmallerd
stockofDiameterD
angletaperHalf





44. IES - 2006
For taper turning on centre lathes, the method of
swiveling the compound rest is preferred for:
(a) Long jobs with small taper angles
(b) Long jobs with steep taper angles
(c) Short jobs with small taper angles
(d) Short jobs with steep taper angles

45. Example
Find the angle at which the compound rest should
be set up to turn taper on the workpiece having a
length of 200 mm, larger diameter 45 mm and the
smaller 30 mm.

46. Offsetting the tailstock
 It is necessary to measure the tailstock offset when using
this method.
 This method is limited to small tapers (Not exceeding 8o
) over long lengths.
 By offsetting the tailstock, the axis of rotation of the job
is inclined by the half angle of taper.

47. Offsetting the tailstock Contd..
 Tailstock offset (h) can be determined by
  tan
2
Lhor
l
dDL
h 



48. IES - 1992
Tail stock set over method of taper turning is
preferred for
(a) Internal tapers
(b) Small tapers
(c) Long slender tapers
(d) Steep tapers

49. IAS - 2002
The amount of offset of tail stock for turning taper
on full length of a job 300 mm long which is to have
its two diameters at 50 mm and 38 mm respectively
is
(a) 6 mm (b) 12 mm
(c) 25 mm (d) 44 mm

50. IES - 1998
A 400 mm long shaft has a 100 mm tapered step at
the middle with 4° included angle. The tailstock
offset required to produce this taper on a lathe
would be
(a) 400 sin 4° (b) 400 sin 2°
(c) 100 sin 4° (d) 100 sin 2°

51. Form tool
 Special form tool for generating the tapers is used. The
feed is given by plunging the tool directly into the work.
This method is useful for short external tapers, where
the steepness is of no consequence, such as for
chamfering.

52. Taper Turning Attachment
 Additional equipment is attached at the rear of the lathe.
 The cross slide is disconnected from the cross feed nut.
 The cross slide is then connected to the attachment.
 As the carriage is engaged, and travels along the bed, the
attachment will cause the cutter to move in/out to cut
the taper.
 For turning tapers over a comprehensive range is the use
of taper turning attachment.

54. Errors in tool settings
 Setting the tool below the centre decrease actual rake angle,
while clearance angle increases by the same amount. Thus
cutting force increased.
 Setting the tool above the centre causes the rake angle to
increase, while clearance angle reduces. More rubbing with
flank.

55. IES 2010
The effect of centering error
when the tool is set above the
center line as shown in the figure
results effectively in
1. Increase in rake angle.
2. Reduction in rake angle.
3. Increase in clearance angle.
4. Reduction in clearance angle.
Which of these statements is/are
correct?
(a) 1 only (b) 1 and 4 only
(c) 2 and 4 only (d) 1, 2, 3 and 4

56. Turret Lathe
A turret lathe, a number of tools can be set up on the
machine and then quickly be brought successively into
working position so that a complete part can be
machined without the necessity for further adjusting,
changing tools, or making measurements.

57. Turret Lathe

58. Capstan Lathe

59. Video

60. Capstan lathe Turret lathe
Short slide, since the saddle is
clamped on the bed in position.
Saddle moves along the bed,
thus allowing the turret to be of
large size.
Light duty machine, generally for
components whose diameter is
less than 50 mm.
Heavy duty machine, generally
for components with large
diameters, such as 200 mm.
Too much overhang of the turret
when it is nearing cut.
Since the turret slides on the
bed, there is no such difference.
Ram-type turret lathe, the ram and
the turret are moved up to the
cutting position by means of the
capstan Wheel. As the ram is
moved toward the headstock, the
turret is automatically locked into
position.
Saddle-type lathes, the main
turret is mounted directly on the
saddle, and the entire saddle
and turret assembly
reciprocates.

61. IES - 2012
Lathe machine with turret can turn a work piece of
limited length only because,
(a) Cross slide motion is obstructed by turret
(b) Turret cannot work on a long job
(c) Chuck cannot be replaced by a face plate
(d) Turret replaces the loose centre

62. Turret indexing mechanism
 The hexagonal turret is rotated (for indexing) by a
Geneva mechanism where a Geneva disc having six
radial slots is driven by a revolving pin. Before starting
rotation, the locking pin is withdrawn by a cam lever
mechanism. The single rotation of the disc holding the
indexing pin is derived from the auxiliary shaft with the
help of another single revolution clutch as indicated.
 For automatic lathe: Ratchet and Pawl mechanism

63. Automatic Lathe
 The term automatic is somewhat loosely applied, but is
normally restricted to those machine tools capable of
producing identical pieces without the attention of an
operator, after each piece is completed. Thus, after
setting up and providing an initial supply of material,
further attention beyond replenishing the material
supply is not required until the dimensions of the work
pieces change owing to tool wear.
 A number of types of automatic lathes are developed
that can be used for large volume manufacture
application, such as single spindle automatics, Swiss type
automatics, and multi-spindle automatics.

64. Video

65. Swiss type Automatic Lathe Or Sliding Headstock Automatics
 Headstock travels enabling axial feed of the bar stock
against the cutting tools.
 There is no tailstock or turret
 High spindle speed (2000 – 10,000 rpm) for small job
diameter
 The cutting tools (upto five in number including two on
the rocker arm) are fed radially
 Used for lot or mass production of thin slender rod or
tubular jobs, like components of small clocks and wrist
watches, by precision machining.

67. Multi Spindle Automatic Lathe
 For increase in rate of production of jobs usually of
smaller size and simpler geometry.
 Having four to eight parallel spindles are preferably used.
 Multiple spindle automats also may be parallel action or
progressively working type.

68. Video

69. Norton type Tumbler-gear quick-change Gear box

70. Norton type Tumbler-gear quick-change Gear box
 It comprises a cone of gears 1 to 8 mounted on shaft S2.
 The tumbler gear can slide on shaft S1. It can mesh with any
gear on shaft S2 through an intermediate gear which is
located on a swinging and sliding lever so that it can engage
gears 1 to 8 of different diameters, on shaft S2.
 The lever can be fixed in any desired ratio position with the
help of a stop pin.
 The drive is usually from the driving shaft S1 to the driven
shaft S2.

72. GATE – 2008
The figure shows an incomplete schematic of a
conventional lathe to be used for cutting threads
with different pitches. The speed gear box Uv, is
shown and the feed gear box Us, is to be placed. P, Q.
R and S denote locations and have no other
significance. Changes in Uv, should NOT affect the
pitch of the thread being cut and changes in Us,
should NOT affect the cutting speed.
Contd…..

73. GATE -2008 Contd….
The correct connections and the correct placement of Us are
given by
(a) Q and E are connected. Us, is placed between P and Q.
(b) S and E are connected. Us is placed between R and S.
(c) Q and E are connected. Us, is placed between Q and E.
(d) S and E are connected. Us, is placed between S and E.

75. IES - 2009
Which one of the following methods should be used
for turning internal taper only?
(a) Tailstock offset
(b) Taper attachment
(c) Form tool
(d) Compound rest

76. IES - 1997
Consider the following operations:
1. Under cutting 2. Plain turning
3. Taper turning 4. Thread cutting
The correct sequence of these operations in machining a
product is
(a) 2, 3, 4, 1 (b) 3, 2, 4, 1
(c) 2, 3, 1, 4 (d) 3, 2, 1, 4

78. IAS - 2001
Consider the following operations and time
required on a multi spindle automatic machine to
produce a particular job
1. Turning …1.2 minutes
2. Drilling …1.6 minutes
3. Forming …0.2 minute
4. Parting …0.6 minute
The time required to make one piece (cycle time) will be
(a) 0.6 minutes (b) 1.6 minutes
(c) 3.6 minutes (d) 0.9 minute

80. IES 2011
In Norton type feed gearbox for cutting Whitworth
standard threads with a standard TPI Leadscrew, power
flows from:
(a) Spindle to Tumbler gear to Norton cone to Meander
drive to Leadscrew
(b) Spindle to Norton cone to Tumbler geat to Meander
drive to Leadscrew
(c) Spindle t o Tumbler gear to Meander drive to Norton
cone to Leadscrew
(d) Spindle to Norton cone to Meander drive to Tumbler
gear to Leadscrew

82. Q. No Option Q. No Option
1 C 6 A
2 A 7 B
3 D 8 B
4 B 9 D
5 B 10 C
Ch – 2: Lathe