Manufacturing Technology -II Unit 2

Manufacturing Technology -II Unit 2 PPT

1. Manufacturing Technology II 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. | 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 30

31. Left-Hand Offset Toolholder Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. 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 incorpo r ated in a mach i ne 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 li k e tool – work mounting, bar feeding, tool indexing etc. repeatably with minimum human interventi o n but with the help of spe c ial or additional mechan i sm and control systems. 97

98. General Purpose Semiautomatic And Automatic Lathes. According to degree of automation machine tools are classified as, Non auto m atic where most of t he handling operations irrespective of processing operations, are done manually, like centre lathes etc. Semiautomatic Automatic where all the handling or auxiliary operations as well as the processing opera t ions a r e carried out automatically. 98

99. The conventional general purpo s e automated lathes can be classified as, a) Semi automatic capstan lathe (ram type turret lathe) turret lathe multiple spindle turret lathe copying (hydraulic) lathe b) Aut o matic Aut o matic cutti n g off lathe Single spindle automatic lathe Swiss type automatic lathe Multiple spi n d l e automatic lathes 99

100. The conventional general purpo s e automated lathes can be classified as, The other categories of semiautomatic and automatic lathes are : Vertical turret lathe Special pu r pose lathes Non conventional type, i.e., flexi b ly automatic CNC la t hes, turning centre etc. 100

101. Semi a utomatic lathes The characteristic features of such lathes ar e, some major auxilia r y motions and handling opera t ions like bar feeding, speed change, tool change etc. are done quickly and consistently with lesser human involvement the operators need lesser skill and putting lesser effort and attention 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. F i g. schematically shows the basic configuration of capstan lathe . Sche m atic configura t ion of capstan lathe. 102

103. Pictorial view of a capstan lathe 103

104. In contrast to centre la t hes, capstan and turret lathes are semiautomatic Possess an axially movable ind e xable turret (mostly hexago n al) 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 producti v e for qu i ck enga g ement 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 la t hes, capstan and turret lathes are Semiautomatic Enable repetitive production of s ame job requiring less involvement, effort and attention of the operator for pre-setting of work–speed and feed rate and length of t r avel of the cutting tools are relatively costlier Are suitable and economically v iable for batch production or s mall 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 caps t an and turret lathes such as, Turret lathes are relatively more robust and heavy duty machines Capstan lathes gene r ally deal with short or long rod type blan k s held in collet, whereas turret lathes mostly work on c hucking t yp e jobs held in the quick acting chucks In capstan lathe, the turret travels with limited stroke length within a saddle type guide block, called au x iliary bed, which is clamped on the main bed as indi c ated in Fig. whereas in turret lathe, the heavy turret being mounted on the sad d le which directly slides wi t h larger stroke length on the main bed as indi c ated in Fig. 108

109. There are some differences in between caps t an and turret lathes such as, One additional guide rod or pilot bar is provided on the headstock of the turret lathes as shown in F ig . 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 cha s ing 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 s pindle and horizontal axis type. Turret lathes are also mostly single horizontal type but it may be also s pindle and Vertical type and Multispindle type Turret lathes are mostly horizontal a x is s i ngle spindle type. T he multiple spindle vertical turret l athes are characterised by : Suitably u s ed for large lot or m a ss production of jobs of generally chucking type relatively large size requiring limited number of machining ope r ations Machine axis – vertical for lesser floor space occupied easy loading and unloading of blanks and finished jobs relieving the spindles of bending loads due to job – wei g ht. Number of spindle – four to eight. Mul t iple s pindle Vertical Turr e t lathe 110

111. Basic configuration of multi spindle automatic vertical lathe Fig ure visualise the basic c onfiguration of multiple spindle vertical turret lathes whi c h 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 : Parallel processing type : Progress i ve l y processing t y pe : Continuous l y w orking t y pe : Parallel processing type : The spindle carrier remains stationary. Only the tool slides move with cutting tools radially and axially. 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 : The spindle carrier with the blanks fitted in the chucks on the rotating spindle is indexed at regular interval by a Geneva mechanism. At each station the job undergoes a few preset machining work by the axially and / or radially fed cutting tools. 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. This type of lathes are suitable for jobs requiring large number of operations. 113

114. Continuously working type : Like in parallel processing type, here also each job is finished in the respective station where it was loaded. 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. 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. Such system is also suitable for jobs requiring very few and simple machining operations. 114

115. Hydraulic copying (tracer controlled) lathes Jobs ha v ing steps, tapers and / or curved profiles, as typically s hown in Fi g. are conveniently and economically produced in bat c h or lot in semiautomatically operated tracer controlled hydraulic cop y ing lathe. Th e movement of the sty l us along t he template provided with the same desired job-profile) is hydraulically tran s mitted to the cutting tool tip which replica t es 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 di stinguished categories based on constructional fea t ures, operational characteristics, number of spindles and appli c ati o ns as follows Single spindle Automatic cutting off l athes Automatic ( screw cutting) lathe Swiss type automatic lathe 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 60 o (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 Through study of the job to be produced. Selection of machine tool (after studying the job): Selection of blank (based on job and machine selected): Identification and listing of the elementary machining operations required, depending upon the product configuration Combine elementary machining operations as much as possible for saving time Sequence the operations (after combining) Select cutting tools: 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 φ 12) and drilling and centering (for the next job) 3 Finish turning ( φ 10) 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

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137. Thank You 137