Manufacturing Technology -II Unit 2 PPT

1. Unit 2 - CENTRE LATHE AND SPECIAL
PURPOSE LATHES
G.Ravisankar, Asst Prof , Mechanical, Sri
Eshwar college of Engineering , Coimbatore .
1

2. UNIT II - CENTRE LATHE AND SPECIAL PURPOSE LATHES
2
Centre lathe, constructional features, specification,
operations – taper turning methods, thread cutting
methods, special attachments, machining time and
power estimation. Capstan and turret lathes- tool
layout – automatic lathes: semi automatic – single
spindle : Swiss type, automatic screw type – multi
spindle.
1. Hajra Choudhury, "Elements of Workshop Technology", Vol.II., Media
Promoters
2. Rao. P.N “Manufacturing Technology - Metal Cutting and Machine Tools",
Tata McGraw-Hill, New Delhi, 2003.

3. • Lathes are widely used machine tools in the mechanical
industries, factories, warehouses and manufacturing units.
• The main function of a lathe is to remove metal from a
piece of work to give it the required shape and size.
• Lathe rotates the object around the spindle for machining
the metal in desired form.
Lathe
3

4. • Based on the type of operation lathes are categorized in
manual and automatic CNC controlled (Computer
numerical control) machines.
• Lathes are designed for different industrial applications but
the basic features remains common.
• The main parts of lathes are headstock, bed, carriage and
tailstock.
• The various features and functionalities make the lathes
use for different types of applications.
Lathe
4

5. • Various types of lathes are available in the market based
on the machine tool functionality and technology used in
manufacturing the lathes.
 Center Lathe
 Tool room Lathe
 Turret Lathe
 Gang-tool Lathe
 Multi-spindle Lathe
 CNC Lathe
Types of Lathe
5

6. Center lathe
6

7. 7 7

8. • Head stock
• Tail stock
• Bed
• Carriage
• Feed rod
• Lead screw
• Feed change gear box
Centre lathe - constructional features
8

9. • Distance between centers : Maximum length of job that can be
turned
• Swing over the bed : Maximum diameter of the job that can be
turned
• Swing over the cross slide : Maximum diameter of the job that can
be turned with the job across the cross side
• Horse power of the motor
• Number of speeds
• Number of feeds
Lathe specifications
9

10. Lathe specifications
10

11. Lathe Accessories
• Divided into two categories
▫ Work-holding, supporting, and driving devices
 Lathe centers, chucks, faceplates
 Mandrels, steady and follower rests
 Lathe dogs, drive plates
▫ Cutting-tool-holding devices
 Straight and offset tool holders
 Threading tool holders, boring bars
 Turret-type tool posts
11

12. Lathe Centers
• 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
Work-holding, supporting, and driving devices cont.,
12

13. Chucks
• Used extensively for holding work for machining
operations
▫ Work large or unusual shape
• Most commonly used lathe chucks
▫ Three-jaw universal
▫ Four-jaw independent
▫ Collet chuck
Work-holding, supporting, and driving devices cont.,
13

14. Three-jaw Universal Chuck
• Holds round and hexagonal work
• Grasps work quickly and accurate
within few thousandths/inch
• Three jaws move
simultaneously when
adjusted by chuck wrench
▫ Caused by scroll plate into
which all three jaws fit
Work-holding, supporting, and driving devices cont.,
14

15. Four-Jaw Independent Chuck
• Used to hold round, square,
hexagonal, and irregularly shaped
workpiece.
• Has four jaws
▫ Each can be adjusted
independently by chuck wrench
• Jaws can be reversed to hold work
by inside diameter
Work-holding, supporting, and driving devices cont.,
15

16. • A collet is a holding device—
specifically, a subtype of chuck—that
forms a collar around the object to be
held and exerts a strong clamping force
on the object when it is tightened,
usually by means of a tapered outer
collar.
• It may be used to hold a workpiece or a
tool.
COLLET CHUCK
Work-holding, supporting, and driving devices cont.,
16

17. 46-17
Collet Chuck
• Most accurate chuck
• Used for high-precision work
• Spring collets available to hold round, square, or
hexagon-shaped workpieces
• Each collet has range of only few thousandths of
an inch over or under size stamped on collet
17

18. 46-18
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Collet Chuck
Special adapter fitted into taper of headstock spindle,
and hollow draw bar having internal thread inserted
in opposite end of headstock spindle. It draws collet
into tapered adapter causing collet to tighten on workpiece.
18

19. 46-19
Types of Lathe Dogs
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• Standard bent-tail lathe dog
▫ Most commonly used for round
workpieces
▫ Available with square-head
setscrews of headless setscrews
• Straight-tail lathe dog
– Driven by stud in driveplate
– Used in precision turning
19

20. 46-20
Types of Lathe Dogs
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• Safety clamp lathe dog
▫ Used to hold variety of work
▫ Wide range of adjustment
• Clamp lathe dog
– Wider range
than others
– Used on all shapes
20

21. Dog
21

22. Mandrels
• This used to holding hollow work pieces.
22

23. Lathe Bed
23

24. Cross Slide
24

25. Compound Rest
25

26. Tool post
26

27. Types of tool post
• Single Screw tool post
• Open Side tool post
• Four bolt tool post
• Four Way tool post
27

28. Single Screw tool post Open Side tool post
28

29. Four bolt tool post Four Way tool post
29

30. 46-30
Super Quick-Change Toolpost
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31. Left-Hand Offset Toolholder
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• Offset to the right
• Designed for machining work close to chuck or
faceplate and cutting right to left
• Designated by letter L
31

32. 46-32
Right-Hand Offset Tool holder
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• Offset to the left
• Designed for machining work close to the
tailstock and cutting left to right
▫ Also for facing operations
• Designated by letter R
32

33. 46-33
Straight Toolholder
• General-purpose type
• Used for taking cuts in either direction and for
general machining operations
• Designated by letter S
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33

34. Carriage
 In its simplest form the
carriage holds the tool
bit and moves it
longitudinally (turning)
or perpendicularly
(facing) under the
control of the operator
Work-holding, supporting, and driving devices cont.,
34

35. Tail stock
 It is usually used to apply support to
the longitudinal rotary axis of a
workpiece being machined.
 The spindle does not rotate but
does travel longitudinally under the
action of a lead screw and hand
wheel
 The spindle includes a taper to hold
drill bits, centres and other tooling.
 There is also provision to offset the tailstock from the spindles axis,
this is useful for turning small tapers, and when re-aligning the
tailstock to the axis of the bed.
Work-holding, supporting, and driving devices cont.,
35

36. Tail Stock
36

37. Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
37

38. Setting the tool height
• The cutting tool on the
lathe must be set to
the exact centre of the
work-piece
• We use the centre of
the tailstock to guide
us to the correct
height
38
38

39. Cutting tools
• We can put different shapes on the High speed tool bits to
cut different shapes on the workpiece
39
39

40. Lathe Operations
• Turning: produce straight, conical, curved, or grooved
workpieces
• Facing: to produce a flat surface at the end of the part or for
making face grooves.
• Boring: to enlarge a hole or cylindrical cavity made by a
previous process or to produce circular internal grooves.
• Drilling: to produce a hole by fixing a drill in the tailstock
• Threading: to produce external or internal threads
• Knurling: to produce a regularly shaped roughness on
cylindrical surfaces
40

41. Lathe Operations
41

42. Knurling
• A knurling tool is used to press a pattern onto a
round section.
• The pattern is normally used as a grip for a handle.
• This provide a grip for the round part
e.g. Screwdriver
42
42

43. Knurling
43
43

44. Parting off
• Parting-off is the operation of
cutting a workpiece after it has
been machined to the desired
size and shape.
• The process involves rotating the
workpiece on a chuck or
faceplate at half the speed to that
of turning and feeding by a
narrow parting off tool
perpendicular to the lathe axis by
rotating the cross slide screw by
hand.
44
44

45. Screw-cutting on the lathe
• Lathes are also used to cut
threads in round bars
• These threads take up
different profiles e.g iso
(60°) ACME etc.
• These threads can be seen
on bench vices, lathes etc.
45
45

46. Thread cutting Formula
• Driver teeth/Driven teeth
= Pitch of the work/ pitch of lead screw
Ex ;
Pitch of the work= 2
pitch of lead screw=4
No of driver teeth = 20
20/? = 2/4
No of driven teeth = 40
46

47. 55-47
Thread
Terminology
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Permission required for reproduction or display.
47

48. 55-48
Thread Terminology
• Screw thread
▫ Helical ridge of uniform section formed on inside
or outside of cylinder or cone
• External thread
▫ Cut on external surface or cone
• Internal thread
▫ Produced on inside of cylinder or cone
48

49. 55-49
• Major diameter
▫ Largest diameter of external or internal thread
• Minor diameter
▫ Smallest diameter of external or internal thread
• Pitch diameter
▫ Diameter of imaginary cylinder that passes
through thread at point where groove and thread
widths are equal
▫ Equal to major diameter minus single depth of
thread
▫ Tolerance and allowances given at pitch diameter
line
49

50. 55-50
• Number of threads per inch
▫ Number of crests or roots per inch of threaded
section (Does not apply to metric threads)
• Pitch
▫ Distance from point on one thread to
corresponding point on next thread, measured
parallel to axis
▫ Expressed in millimeters for metric threads
• Lead
▫ Distance screw thread advances axially in one
revolution (single-start thread, lead = pitch)
50

51. 55-51
• Root
▫ Bottom surface joining sides of two adjacent
threads
▫ External thread on minor diameter
▫ Internal thread on major diameter
• Crest
▫ Top surface joining two sides of thread
▫ External thread on major diameter
▫ Internal thread on minor diameter
• Flank
▫ Thread surface that connects crest with root
51

52. 55-52
• Depth of thread
▫ Distance between crest and root measured
perpendicular to axis
• Angle of thread
▫ Included angle between sides of thread measured
in axial plane
• Helix angle
▫ Angle that thread makes with plane
perpendicular to thread axis
52

53. • Chamfering is the operation of beveling the extreme end of
a workpiece.
• This is done to remove the burrs, to protect the end of the
workpiece from being damaged and to have a better look.
• The operation may be performed after knurling, rough
turning, boring, drilling.
Chamfering
 Chamfering is an essential operation
before thread cutting so that the nut
may pass freely on the threaded
workpiece.
53

54. TAPER TURNING
54

55. • In ordinary straight turning, the cutting tool moves along a line parallel to
the axis of the work, causing the finished job to be the same diameter
throughout.
• When the diameter of a piece changes uniformly, from one end to the
other, the piece is said to be tapered. Taper turning as a machining
operation is the gradual reduction in diameter from one part of a
cylindrical workpiece to another part.
• Tapers can be either external or internal. If a workpiece is tapered on
the outside, it has an external taper; if it is tapered on the inside, it has
an internal taper.
INTRODUCTION
55

56. INTRODUCTION
56

57. • The method used for turning a taper depends on the
degree, length, location of the taper (internal or
external), and the number of pieces to be done.
▫ Taper Turning by a form tool
▫ By swivelling the compound rest
▫ By offsetting the tail stock
▫ By taper turning attachment
• With any of these methods, the cutting tool must be
set exactly on centre with the axis of the workpiece
or the workpiece will not be truly conical, and the
rate of taper will vary with each cut.
Methods of Taper Turning
57

58. Taper Turning by a form tool
• A broad nose tool having straight cutting edge is set on
to the work at half taper angle, and is fed straight into
the work to generate a tapered surface.
• The half angle of taper will correspond to 90 minus
side cutting edge angle of the tool. In this method the
tool angle should be properly checked before use.
Methods of Taper Turning cont.,
58

59. Methods of Taper Turning cont.,
59

60. By swivelling the compound rest
• This method is used to produce short or steep tapers.
• The principle of this compound rest is that axis of
workpiece rotates parallel to the bed axis and the
cutting tool moves at the desired angle where the
compound rest is already swivelled.
• We can calculate the swivelled angle of compound rest
in respect of lathe axis by following formula :
Methods of Taper Turning cont.,
60

61. Methods of Taper Turning cont.,
61

62. Methods of Taper Turning cont.,
62

63. Methods of Taper Turning cont.,
63

64. Methods of Taper Turning cont.,By Taper turning attachment
• The taper attachment is used for turning and boring tapers. It is bolted to
the back of the carriage saddle. In operation, it is connected to the cross-
slide so that it moves the cross-slide laterally as the carriage moves
longitudinally.
• This action causes the cutting tool to move at an angle to the axis of the
workpiece to produce a taper.
• The angle of the desired taper is set on the guide bar of the attachment,
and the guide bar support is clamped to the lathe bed. Since the cross-
slide is connected to a shoe that slides on this guide bar, the tool follows
along a line that is parallel to the guide bar and hence at an angle to the
workpiece axis corresponding to the desired taper.
64

65. Methods of Taper Turning cont.,
65

66. THREAD CUTTING METHODS
66

67. • Thread of any pitch, shape and size can be cut on a lathe
using single point cutting tool.
• The job is held in between centres or in a chuck and the
cutting tool is held on tool post.
• The cutting tool must travel a distance equal to the pitch
(in mm) as the work piece completes a revolution.
• The definite relative rotary and linear motion between
job and cutting tool is achieved by locking or engaging a
carriage motion with lead screw and nut mechanism and
fixing a gear ratio between head stock spindle and lead
screw.
Method of thread cutting
67

68. THREAD CUTTING METHODS ON A LATHE
68

69. SPECIAL ATTACHMENTS IN A
CENTER LATHE
69

70. SPECIAL ATTACHMENTS
▫ Each general purpose conventional machine tool is designed
and used for a set of specific machining work on jobs of limited
range of shape and size.
▫ But often some unusual work also need to be done in a specific
machine tools, e.g. milling in a lathe, tapping in a drilling
machine, gear teeth cutting in shaping machine and so on.
▫ Under such conditions, some special devices or systems are
additionally used being mounted in the ordinary machine tools.
70

71. • Some attachments being used in the general
purpose conventional machine tools are
• In centre lathes :
▫ Taper turning attachment
▫ Copy turning attachments
▫ Milling and cylindrical grinding attachments
▫ Spherical turning attachments
▫ Relieving attachment
SPECIAL ATTACHMENTS
71

72. Taper turning attachment
72

73. COPY TURNING ATTACHMENTS
73
For Complex contours, the tool should be feed in two axis (X & Y)
simultaneously

74. MILLING AND CYLINDRICAL GRINDING
ATTACHMENTS
74

75. Milling Attachments
75

76. Grinding Attachments
76

77. SPHERICAL TURNING ATTACHMENTS
77

78. RELIEVING ATTACHMENT
78

79. THREAD PITCH CORRECTING ATTACHMENT
79

80. GEAR ARRANGEMENT IN A
LATHE
80

81. • There are mainly two types of gear arrangements
used in headstock of lathe machine.
▫ All geared headstock
▫ Back geared headstock
GEAR ARRANGEMENT
81

82. • In this type, constant motor speed is provided to
the gear arrangement but depending upon the
requirement of speed, it changes using gear
arrangement which is controlled by levers.
• These levers change their position to generate
different combinations to acquire different speed.
ALL GEARED HEADSTOCK - GEAR ARRANGEMENT
82

83. ALL GEARED HEADSTOCK - GEAR ARRANGEMENT
83

84. • In this type, power is transmitted to the spindle via
two step cone pulleys and requires the use of belt
drive to connect them.
• A pinion gear is mounted with small end of cone
pulley.
• In this type, a bull gear is also used which can be
locked or in unlocked position through lock pin and
is keyed to spindle.
BACK GEARED HEADSTOCK - GEAR ARRANGEMENT
84

85. • Back gears are
mounted eccentric
shaft and used to
reduce speed.
• There are further two
types to obtain
variation in speed.
▫ Direct speed
▫ Indirect speed
BACK GEARED HEADSTOCK - GEAR ARRANGEMENT
85

86. FEED MECHANISM IN A
LATHE
86

87. • There are number of feed mechanisms used in lathe
machine in which each has unique function.
• Feed mechanisms comprises of reverse mechanism,
change gear quadrant, quick change gearbox, lead
screw, feed rod and apron.
GEAR ARRANGEMENT
87

88. • Reverse mechanism is used to change the direction of
carriage either from headstock to tailstock or vice versa.
• Change gear quadrant with quick change gear box is
used to provide us different feed rates to lead screw and
feed rod
REVERSE MECHANISM
88

89. • The sole purpose to use tumbler gear mechanism is to reverse
the direction of lead screw and feed rod automatically
TUMBLER GEAR MECHANISM
89

90. • The construction of tumbler gear mechanism,
• E gear is attached to the spindle and known as spindle gear.
The purpose of this gear is to rotate feed rod and lead screw
in clockwise direction.
• A and B are tumbler gears and are fitted in a bracket.
• The lever M placed in the bracket can move upward or
downward.
TUMBLER GEAR MECHANISM
90

91. For position 1,
• the lever M is in upward position and gear A connects with
stud gear D and spindle gear E.
• This arrangement will move carriage towards headstock. On
the otherhand,
In position 2,
• lever will be in the horizontal position and gear E will connect
with gear B, then B to A and A to D.
• With this arrangement, lead screw direction will reverse and
this time, it will move in the anti-clockwise direction and
carriage will move towards tailstock.
TUMBLER GEAR MECHANISM
91

92. • In quick change gear box, the motion is transmitted from
spindle to the shaft A through tumbler gear and change gears.
• On the otherside of shaft A, the 12 cone gears and can provide
us 12 different speeds
QUICK CHANGE GEAR BOX
92

93. Quick change gear box
93

94. • Apron mechanism is used to move carriage on the lead screw
and also for automatic thread cutting operation.
APRON MECHANISM
94

95. • Bevel gear feed reversing mechanism is actually the modified
form of tumbler gear mechanism.
BEVEL GEAR FEED REVERSING MECHANISM
95
Source: http://www.bestinnovativesource.com/2013/01/05/feed-mechanism-in-lathe-machine/

96. Semiautomatic &
Automatic Lathes.
96

97. General Purpose Semiautomatic And Automatic Lathes.
Automation is incorporated in a machine tool or machining system
as a whole for higher productivity with consistent quality aiming
meeting the large requirements and overall economy.
Such automation enables quick and accurate auxiliary motions, i.e.,
handling operations like tool – work mounting, bar feeding, tool
indexing etc. repeatably with minimum human intervention but
with the help of special or additional mechanism and control
systems.
97

98. General Purpose Semiautomatic And Automatic Lathes.
According to degree of automation machine tools are classified as,
1.Non automatic where most of the handling operations
irrespective of processing operations, are done manually, like
centre lathes etc.
2.Semiautomatic
3.Automatic where all the handling or auxiliary operations as
well as the processing operations are carried out automatically.
98

99. The conventional general purpose automated lathes can be
classified as,
a) Semi automatic
1. capstan lathe (ram type turret lathe)
2. turret lathe
3. multiple spindle turret lathe copying (hydraulic) lathe
b) Automatic
1. Automatic cutting off lathe
2. Single spindle automatic lathe
3. Swiss type automatic lathe
4. Multiple spindle automatic lathes
99

100. The conventional general purpose automated lathes can be
classified as,
The other categories of semiautomatic and automatic lathes
are :
1. Vertical turret lathe
2. Special purpose lathes
3. Non conventional type, i.e., flexibly automatic CNC
lathes, turning centre etc.
100

101. Semiautomatic lathes
The characteristic features of such lathes are,
1. some major auxiliary motions and handling operations
like bar feeding, speed change, tool change etc. are
done quickly and consistently with lesser human
involvement
2. the operators need lesser skill and putting lesser
effort and attention
3. suitable for batch or small lot production costlier
than centre lathes of same capacity.
101

102. CAPSTAN AND TURRET LATHES
The semiautomatic lathes, capstan lathe and turret lathe are very similar in
construction, operation and application. Fig. schematically shows the basic
configuration of capstan lathe.
Schematic configuration of capstan lathe.
102

103. Pictorial view of a capstan lathe
103

104. In contrast to centre lathes, capstan and turret lathes are
semiautomatic
• Possess an axially movable indexable turret (mostly
hexagonal) in place of tailstock holds large number of cutting
tools; upto four in indexable tool post on the front slide, one in
the rear slide and upto six in the turret (if hexagonal) as
indicated in the schematic diagrams.
• Are more productive for quick engagement and overlapped
functioning of the tools in addition to faster mounting and
feeding of the job and rapid speed change.
104

105. In contrast to centre lathes, capstan and turret lathes are
Semiautomatic
• Enable repetitive production of same job requiring less
involvement, effort and attention of the operator for pre-
setting of work–speed and feed rate and length of travel of the
cutting tools are relatively costlier
• Are suitable and economically viable for batch production or
small lot production.
105

106. Schematic configuration of turret lathe.
106

107. Pictorial view of a turret lathe.
107

108. There are some differences in between capstan and turret lathes
such as,
1. Turret lathes are relatively more robust and heavy duty machines
2. Capstan lathes generally deal with short or long rod type blanks
held in collet, whereas turret lathes mostly work on chucking type
jobs held in the quick acting chucks
3. In capstan lathe, the turret travels with limited stroke length within
a saddle type guide block, called auxiliary bed, which is clamped
on the main bed as indicated in Fig. whereas in turret lathe, the
heavy turret being mounted on the saddle which directly slides
with larger stroke length on the main bed as indicated in Fig.
108

109. There are some differences in between capstan and turret lathes
such as,
• One additional guide rod or pilot bar is provided on the
headstock of the turret lathes as shown in Fig. to ensure
rigid axial travel of the turret head
• External screw threads are cut in capstan lathe, if required,
using a self opening die being mounted in one face of the
turret, whereas in turret lathes external threads are
generally cut, if required, by a single point or multipoint
chasing tool being mounted on the front slide and moved by
a short lead screw and a swing type half nut.
109

110. Ram type turret lathes, i.e., capstan lathes are usually single spindle and horizontal axis type.
Turret lathes are also mostly single horizontal type but it may be also spindle and
1. Vertical type and
2. Multispindle type
Turret lathes are mostly horizontal axis single spindle type. The multiple spindle vertical turret
lathes are characterised by :
Suitably used for large lot or mass production of jobs of generally
1. chucking type
2. relatively large size
3. requiring limited number of machining operations
Machine axis – vertical for
1. lesser floor space occupied
2.easy loading and unloading of blanks and finished jobs relieving the spindles of bending
loads due to job – weight.
Number of spindle – four to eight.
Multiple spindle Vertical Turret lathe
110

111. Basic configuration of multi spindle automatic vertical lathe
Figure visualise the basic
configuration of multiple spindle
vertical turret lathes which are
comprised mainly of a large disc
type spindle carrier and a tool
holding vertical ram as shown.
111

112. Such vertical turret lathes are of three categories :
1. Parallel processing type :
2. Progressively processing type :
3. Continuously working type :
Parallel processing type :
1. The spindle carrier remains stationary. Only the tool slides
move with cutting tools radially and axially.
2. Identical jobs (say six) are simultaneously mounted and
machined in the chucks parallely at all stations each one
having same set of axially and / or radially moving cutting
tools.
112

113. Progressively processing type :
1. The spindle carrier with the blanks fitted in the chucks on the
rotating spindle is indexed at regular interval by a Geneva
mechanism.
2. At each station the job undergoes a few preset machining work by
the axially and / or radially fed cutting tools.
3. The blank getting all the different machining operations
progressively at the different work stations is unloaded at a
particular station where the finished job is replaced by another
fresh blank.
4. This type of lathes are suitable for jobs requiring large number of
operations.
113

114. Continuously working type :
1. Like in parallel processing type, here also each job is
finished in the respective station where it was loaded.
2. The set of cutting tools, mostly fed only axially along a face of the
ram continuously work on the same blank throughout its one
cycle of rotation along with the spindle carrier.
3. The tool ram having same tool sets on its faces also rotate
simultaneously along with the spindle carrier which after each
rotation halts for a while for unloading the finished job and loading
a fresh blank at a particular location.
4. Such system is also suitable for jobs requiring very few and
simple machining operations.
114

115. Hydraulic copying (tracer controlled) lathes
1. Jobs having steps, tapers and / or curved profiles, as
typically shown in Fig. are conveniently and economically
produced in batch or lot in semiautomatically operated tracer
controlled hydraulic copying lathe.
2. The movement of the stylus along the template provided
with the same desired job-profile) is hydraulically transmitted
to the cutting tool tip which replicates the template profile.
A typical job suitable for copy turning.
115

116. General Purpose Automatic lathes
• Automatic lathes are essentially used for large lot or mass production of
small rod type of jobs.
• Automatic lathes are also classified into some distinguished categories based
on constructional features, operational characteristics, number of spindles
and applications as follows
1. Single spindle
 Automatic cutting off lathes
 Automatic (screw cutting) lathe
 Swiss type automatic lathe
2. Multi spindle automatic lathe
116

117. SINGLE SPINDLE AUTOMATIC LATHE
The general purpose single spindle automatic lathes are widely used for quantity
or mass production (by machining) of high quality fasteners; bolts, screws, studs
etc., bushings, pins, shafts, rollers, handles and similar small metallic parts from
long bars or tubes of regular section and also often from separate small blanks.
Unlike the semiautomatic lathes, single spindle automats are :
 Preferably and essentially used for larger volume of production i.e., large lot production and mass
production
 used always for producing jobs of rod, tubular or ring type and of relatively smaller size.
 Run fully automatically, including bar feeding and tool indexing, and continuously over a long duration
repeating the same machining cycle for each product
 Provided with upto five radial tool slides which are moved by cams mounted on a cam shaft of
relatively smaller size and power but have higher spindle speeds
117

118. A typical single spindle automatic lathe
118

119. The characteristics and applications of these single spindle
automatic lathes are :
• In respect of application :
• Used for lot or mass production of thin slender rod or tubular
jobs, like components of small clocks and wrist watches, by
precision machining;
o Job size (approximately)
⎯ Diameter range – 2 to 12 mm
⎯ Length range – 3 to 30 mm
Swiss type automatic lathe
119

120. Dimensional accuracy and surface finish – almost as good as provided by
grinding
• In respect of configuration and operation
ο The headstock travels enabling axial feed of the bar stock against the
cutting tools
ο There is no tailstock or turret
ο High spindle speed (2000 – 10,000 rpm) for small job diameter
ο The cutting tools are fed radially
ο Drilling and threading tools, if required, are moved axially using
swivelling device(s)
ο The cylindrical blanks are prefinished by grinding and are moved
through a carbide guide bush as shown.
Swiss type automatic lathe
120

121. Basic principle of Swiss type automatic lathe.
121

122. Multispindle Automatic lathes
 For further increase in rate of production of jobs usually of smaller size and
simpler geometry.
 Multispindle automatic lathes having four to eight parallel spindles are
preferably used.
 Unlike multispindle turret lathes, multispindle automatic lathes ;
 Are horizontal (for working on long bar stocks)
 Work mostly on long bar type or tubular blanks
 Multiple spindle automats also may be parallel action or progressively working
type.
 Machining of the inner and outer races in mass production of ball bearings are,
for instance, machined in multispindle automatic lathes.
122

123. Kinematic system and working principle of capstan lathe
Like general configurations and applications, the basic kinematic systems
are also very similar in capstan lathes and turret lathes (particularly single
spindle bar and horizontal types) in respect of their major functions, i.e.,
ο Bar feeding mechanism
ο Turret moving and indexing
ο Speed and feed drives
123

124. Bar feeding mechanism of capstan lathe
 The bar stock is held and tightly clamped in the push type spring collet
which is pushed by a push tube with the help of a pair of bell-crank levers
actuated by a taper ring as shown in Fig.
 Bar feeding is accomplished by four elementary operations;
 Unclamping of the job – by opening the collet
 Bar feed by pushing it forward
 Clamping of the bar by closing the collet
 Free return of the bar-pushing element
124

125. Typical bar feeding mechanism in capstan lathe
125

126.  After a job is complete and part off, the collet is opened by moving the lever
manually rightward to withdraw the push force on the collet.
 Further moving of the lever in the same direction causes forward push of the
bar with the help of the ratchet – paul system shown.
 After the projection of the bar from the collet face to the desired length
controlled by a pre-set stop – stock generally held in one face of the turret or
in a separate swing stop, the lever is moved leftward resulting closing of the
collet by clamping of the bar stock.
 Just before clamping of the collet, the leftward movement of the lever
pushes the bar feeder (ratchet) back freely against the paul
Bar feeding mechanism of capstan lathe
126

127. Turret indexing mechanism in capstan and turret lathes
The turret (generally hexagonal) holding the axially moving cutting tools have the
following motions to be controlled mechanically and manually ;
 Forward axial traverse comprising;
 quick approach – manually done by rotating the pinion as shown
 slow working feed – automatically by engaging the clutch
 stop at preset position depending upon the desired length of travel of
the individual tools
 Quick return – manually done by disengaging the clutch and moving the
turret back
 Indexing of the turret by 60o (or multiple of it) – done manually by further
moving the turret slide back.
127

128. Turret indexing in capstan and turret lathe.
128

129. Tool Layout For Machining A Product In Semi-Automatic And Automatic
Lathes.
The procedural steps to be followed in sequence for lot or batch production of a
job by machining in semi-automatic and automatic general purpose machine
1. Through study of the job to be produced.
2. Selection of machine tool (after studying the job):
3. Selection of blank (based on job and machine selected):
4. Identification and listing of the elementary machining operations
5. required, depending upon the product configuration
6. Combine elementary machining operations as much as possible for saving
time
7. Sequence the operations (after combining)
8. Select cutting tools:
9. work scheduling or preparation of the instruction sheet or operation chart
giving column-wise :
129

130. A typical tool layout for a particular job being machined in a single spindle
automatic lathe is schematically shown
130

131. Case Study : As An Example
Task (say) : 2500 pieces of hollow hexagonal headed mild steel bolts,
as shown in Fig. are to be produced by machining.
Shape and dimension of the specific job
131

132. Machine tool selected :
Single spindle automatic lathe for
• Lot production (for smaller volume of production capstan lathe is
better)
• Circular bar type job
• Common machinable material
• Simple machining operations required
Blank selected :
Hot rolled hexagonal section mild steel bars for;
• saving machining of the hexagonal head portion
• the hexagonal head is of standard size which is available
• job size – reasonable for single spindle automatic
• not being precision job
132

133. Elementary machining operations – identified and listed :
• Facing
• Centering
• Chamfering (1) – front
• Chamfering (2) – middle portion
• Chamfering (3) – bolt head
• Rough turning (1) – to make circular from hexagon
• Rough turning (2) – to reduce diameter to 12 mm
• Finish turning – to φ10
• Drilling
• Grooving (forming)
• Thread cutting
• Initial parting
• Parting
133

134. Combining elementary operations
• combining operations to be done by a compound tool in a single travel from one
tool position
• paralleling or overlapping operations to be done by different tools moving in
different directions.
The listed elementary operations can be combined and sequenced as follows
1 Rough turning (1), initial parting and rear chamfering (3)
2 Rough turning (to φ12) and drilling and centering (for the next job)
3 Finish turning (φ10)
4 Spot facing and front chamfering (1)
5 Grooving and central chamfering (2)
6 Thread cutting
7 Parting
134

135. Table – 1 : Scheduling; operation chart
Scheduling – operation chart indicating tools and tool positions and
machining conditions.
N = spindle speed (rpm), s = feed (mm/rev), L = tool travel, CF = cutting fluid
HT (1) = hexagonal vertical slide turret face 1, RS = Rear slide, FS = front slide, VS
= Vertical slide
135

136. 136

137. 137