1. TOPIC:CENTRE LATHE,CONSTRUCTIONAL FEATURES
PREPARED BY
SOUNDHAR.A

2. Types of Lathe
Classified according to size, design, method of drive & purpose
Speed lathe
Engine lathe
Bench lathe
Tool room lathe
Semi automatic lathe
Automatic lathe
Special purpose lathe
Copying lathe

3. Types of Lathe Speed lathe Head stock, tail stock & adjustable slide
Lead screw, feed box & apron mechanism not provided
Spindle - driven by high speed motor & stepped cone pulley
Tool – fed by hand
Suitable for wood turning, spinning & polishing work.
Types are:
Wood working lathe
Metal spinning lathe
Metal turning lathe
Polishing lathe

4. Types of Lathe Engine Lathe Head stock, tail stock, carriage & bed
Lead screw, feed box & apron mechanism are provided
Tool fed cross wise or longitudinally by hand or automatically
Types are:
Step cone pulley drive lathe
Geared lathe
Variable speed lathe

5. Types of Lathe Bench Lathe Lathe mounted on a bench
Has all parts like centre lathe
Used for machining small parts

6. Types of Lathe Tool room lathe
Necessary attachments for accurate & precision machining
More range of speeds & feeds obtained
Used in high precision works

7. Types of Lathe Semi – automatic lathe
Operations - both manually & automatically
Machining - carried out in proper sequence
Turret head - number of tools are fitted
Tail stock not used
Used for mass production
Speed & feed is high
Types:
Capstan lathe
Turret lathe

8. Types of Lathe Automatic Lathe All works done automatically
Cams are used for speed , feed & tool changes
Initial setting of jobs & tools is enough – works carried out automatically
Used for mass production

9. Types of Lathe Special purpose lathe
Used to carry out specific operations only
Types of lathe:
Crank shaft lathe
Wheel lathe – special purpose lathe
Used for finishing the journals
Turning the thread on rail road car & locomotive wheels
Duplicating lathe

10. Types of Lathe Copying Lathe
Tool follows a template through a stylus or tracer
Tracer connected with cutting tool by hydraulic device
Tools move according to tracer movement & do machining operations

11. Head Stock Mechanism Two types Back geared head stock
All geared head stock

12. Back geared head stock Lever downward position Indirect Speed
Lever upward position
Direct Speed
Lever downward position
Indirect Speed
Lock Pin
Back gears
Pinion
Cone Pulley
Bull gear

13. https://www.youtube.com/watch?v=34xmgMHjmY0 – Back geared

14. Back geared head stock
 Reduces spindle speed - thread cutting & knurling operations
Stepped cone pulley & Pinion gear P1 form one unit
Mounted on spindle – rotates freely
Bull gear  to lathe spindle
Lock pin – lock or unlock bull gear G1 with cone pulley
Back shaft – 2 gears B1, B2 – engaged or disengaged by lever L
Speed can be adjusted by changing the flat belt on the steps of cone pulley
Cont..

15. Back geared head stock Lever upward position Lever downward position
Step cone pulley locked with main spindle
Back gear not engaged
4 Direct speeds (high speed)
Shifting the belt on 4 different cone pulleys
Lever downward position
Step cone pulley not locked with main spindle
Back gear engaged
4 Indirect speed (low speed) -
Power transmitted - P1  B1, B1  B2 , B2  G1 , G1 spindle
Speed  at B1 (B1 > P1 )
B1, B2 – have same speeds
Again Speed  at G1 (G1 > B2)
Thus speed reduced by engaging back gear

16. All geared head stock Loose Pulley Fast Pulley 1 2 Intermediate Shaft
Spindle Shaft
Loose Pulley
Fast Pulley 1 2
Intermediate Shaft 3 4
Head stock Casting 5 6
Splined head stock spindle
Live Center 9 8 7

17. All geared head stock Better compared to other types
Spindle rotates – constant speed motor – thru belt
Various speeds – diff gear combination - change lever position – diff spindle speeds
Head stock has 3 main parts
Splined shaft – rotated by motor
3 gears G1, G2, G3 - shifted by lever along shaft
Intermediate shaft
3 gears G4, G5, G6 - cannot be moved axially
Splined spindle
3 gears G7, G8, G9 - can be moved axially
Nine diff speeds can be obtained
Contd..

18. All geared head stock
Nine diff speeds obtained by meshing the gears individually
Gears G1, G2, G3 with G4, G5, G6
Gears G7, G8, G9 with G4, G5, G6
When G1 meshed with G4, same time G7 meshed with G4 speed of __ x __
Contd.. G1 G4 G4 G7

19. All geared head stock
__ x __
__ x __ G7 G1 G4 G2 G5 G3 G6 G8 G9

20. Feed Mechanism Feed – Movement of tool relative to work piece
Transmit motion - spindle  carriage
Rotary motion  linear motion
Longitudinal feed – moving carriage - automatic
Cross feed – moving cross slide - automatic
Angular feed – moving compound slide
Mechanisms for automatic feed:
Tumbler gear reversing mechanism
Quick change gear box
Tumbler gear quick change gear box
Apron mechanism

21. Tumbler Gear Reversing Mechanism

22. Tumbler Gear Reversing Mechanism

23. Tumbler Gear Reversing Mechanism
Change the direction of lead screw & feed rod while cutting thread – moving carriage
Two same sized pinions – mounted in bracket
Bracket pivoted – move up & down by lever L
A, B – tumbler gears
C – spindle gear – attached to lathe spindle
D – stud gear – attached to lead screw through set of intermediate gear (E)
E-Intermediate gear
F- Lead Screw gear
Cont..

24. Tumbler Gear Reversing Mechanism
Lever upward
A engaged with C
Motion transmitted through C, A, D, E, F gears
Lead screw & spindle – rotate – anti-clock wise
Carriage moves towards head stock – L  R
Lever downward
B engaged with C
Motion transmitted through C, B, A, D, E, F gears
Lead screw– rotate –clock wise
Carriage moves towards tail stock – L  R
Lever neutral
Tumbler gears wont engage with spindle
No motion transmitted
Lead screw will not rotate

25. Quick change gear box Different feeds
Power from lathe spindle  feed shaft through
tumbler gear
change gear
quick change gear box
Shaft A (diff sizes of gears) – keyed with cone gear
Shaft B ( one gear) – receives 9 diff speeds from shaft A thru sliding gear
Shaft B - shaft C thru 4 cone gears
Hence shaft C gets 9x4 = 36 diff speeds
Shaft C – lead screw thru clutch
Shaft C – feed rod thru gear train

26. Quick Change Gear box

27. Quick change gear box Spindle Tumbler Gear Cone gear Shaft A
Sliding key
Clutch handle
Lead screw
Shaft B
Feed Shaft
Sliding gear
Shaft C

28. Apron Mechanism
Transforming rotary motion of feed rod & lead screw into motion of carriage
Power - spindle  Lead screw & feed rod thru tumbler gear
Power - feed rod  worm wheel thru gears A, B, C & worm wheel
Worm wheel attached with splined shaft
Splined shaft always engage with F & G
F & G – keyed to feed check shaft
Feed check shaft fitted to knob E – 3 positions

29. Apron

30. Apron Mechanism Knob E – neutral position Knob E – Push in position
No power transmitted - Hand feed given
Longitudinal feed – rotate longitudinal feed hand wheel
Cross feed – rotate cross slide hand wheel
Half nut engaged for thread cutting by half nut lever
Knob E – Push in position
Rotating gear G – engage with H
Power  pinion
Automatic longitudinal feed takes place
Knob E – Pull out position
Rotating gear F – engage with K
Power  cross feed screws
Automatic cross feed takes place

31. Apron Mechanism - Neutral
Cross slide
Cross slide screw
Bed
Rack
Pinion
Lead Screw
Half nut A C
Lever
Worm wheel H B
Feed shaft G
worm D K
Splined shaft F
Longitudinal feed hand wheel
Feed check shaft E
Cross slide hand wheel

32. Apron Mechanism – Push in Longitudinal feed
Cross slide
Cross slide screw
Bed
Rack
Pinion
Lead Screw
Half nut A C
Lever
Worm wheel H B
Feed shaft G H
worm D
Splined shaft K F
Longitudinal feed hand wheel
Feed check shaft E
Cross slide hand wheel

33. Apron Mechanism – Pull Out Cross feed
Cross slide
Cross slide screw
Bed
Rack
Pinion
Lead Screw
Half nut A C
Lever
Worm wheel H B
Feed shaft G
worm D K
Splined shaft F
Longitudinal feed hand wheel
Feed check shaft E
Cross slide hand wheel

34. Work Holding Devices Chuck Centers Face Plates Angle plate Mandrel
Steady & follower rest

35. Work Holding Devices

36. Chuck Attached to head stock spindle
Hold small length work pieces & irregular shape work pieces
Work pieces are held in jaws of the chuck
Types
Three jaw chuck or self centering
Four jaw chuck or independent chuck
Magnetic chuck

37. Chuck - Types
Three jaw chuck or self centering (hold regular shaped work piece)
Has 3 jaws – move in equal distance – radial direction – chuck key
9 circular discs
Front – Spiral scroll
Back – bevel teeth – 3 bevel pinions fitted
Chuck key turned – bevel pinion & disc rotate
Four jaw chuck or Independent chuck (hold regular or irregular shaped work piece)
Has 4 jaws – each moved individually
Each jaw fitted to screw with the help of slots at backside
The screws have square hole at the top to receive chuck key & can be rotated
When chuck key turned in the slot, the particular jaw will only move
So, irregular shape work piece & large work piece can be held
Magnetic chuck
Has a flat surface
Chuck has magnetic power – electromagnet
Work piece held on chuck by magnetic power
Only magnetic material can be held on the chuck

38. Three jaw chuck or self centering
Has 3 jaws – move in equal distance – radial direction – chuck key
9 circular discs
Front – Spiral scroll
Back – bevel teeth – 3 bevel pinions fitted
Chuck key turned – bevel pinion & disc rotate
Used to hold regular shaped work piece – round & hexagonal

39. Three jaw chuck
back

40. Four jaw chuck or Independent chuck
Hold regular / irregular shaped work piece
Has 4 jaws – each moved individually
Each jaw fitted to screw - slots at backside
Screws - square hole at the top to receive chuck key & can be rotated
When chuck key turned in the slot, the particular jaw will only move
So, irregular shape work piece & large work piece can be held

41. Four jaw chuck
back

42. Magnetic Chuck Has a flat surface
Chuck has magnetic power – electromagnet
Work piece held on chuck by magnetic power
Only magnetic material can be held on the chuck

43. Centers Hold & centering the work pieces Conical end - machined to 60º
Shank – made by taper turning
Live center - Center in head stock
Dead center - Center in tail stock

44. Dog Carrier or Catch Plate
Hold job & work piece in b/w the centers
Catch plate – circular disc – screwed on spindle
Tail part  catch plate
When spindle rotates, work pieces also rotate thru catch plate & carrier arrangement

45. Dog Carrier or Catch Plate

46. Face Plate Hold irregular shaped work pieces
Screwed – spindle – when spindle rotates, face plate too rotates
It’s a circular disc – has 4 T-slots & a number of plain radial slots
Slots –hold work pieces

47. Face Plates

48. Angle Plate
Made of cast iron- has 2 machined right angle to each other
Has holes & slots
One face - work piece
Other face - face plate
When spindle rotates, face plate with angle plate & work piece will also rotate
Angle plate used for holding elbow pieces

49. Mandrel Hold hollow work pieces
Mandrel inserted into the hollow work pieces – held b/w live center & dead center
Different types of mandrels are used for diff types of jobs

50. Plain Mandrel

51. Mandrel

52. Mandrel

53. Steady Rest Has a cast iron base – rest on guide ways of lathe bed
Top – one end for removing job without disturbing steady rest
Work piece – held b/w 3 jaws – move radially & separately
Turning operation - 2 stages - carriage will not pass
So, work piece turned to 1st half , then reversing it to second half

54. Follower Rest Has a C type casting
2 adjustable jaws – support work piece
Follower rest mounted on saddle – move together with tool
Used to give continuous support to work piece

55. Lathe Operations Centering Straight Turning Grooving Parting Off
Rough Turning
Finish Turning
Shoulder Turning
Facing
Chamfering
Knurling
Forming
Grooving
Parting Off
Eccentric Turning
Drilling
Reaming
Boring
Milling
Grinding

56. Lathe Operations

57. Centering
Producing conical shape holes – ends of work piece (Longer work pieces)
Centers marked at the ends - centre punch
Work piece - chuck & rotated
Drill bit - tail stock – fed into the work piece by turning the hand wheel

58. Straight Turning
Producing cylindrical surface by removing the material from outside diameter of the work piece
Work piece held b/w live & dead centers
Right hand turning tool clamped on tool post
Work piece rotated
Tool fed parallel to lathe axis also depth of cut given to tool
Two types of turning
Rough Turning
Finish Turning

59. Straight Turning - Types
Rough Turning
Feed rate – fast (0.3 mm – 1.5 mm per revolution)
Depth of cut – heavy (2 mm – 5 mm)
Finish Turning
Feed rate – slow (0.1 mm – 0.3 mm per revolution)
Depth of cut – small (0.5 mm – 1 mm)

60. Shoulder Turning Operation - shoulder of stepped diameter work piece
Right hand facing tool – square shoulder
Round nose tool – radius shoulder
Types of shoulders
Square
Bevelled
Filleted
Grooved

61. Facing Making flat surface at the end of work piece
Work piece held in chuck or b/w centers
Work piece rotated
Facing tool fed perpendicular to lathe axis

62. Chamfering
Making bevelled surface or to turn a slope at the end of the work piece
It is done after knurling, rough turning & thread cutting
Remove burrs & sharp edges
Work piece rotated – tool fed perpendicular to the lathe axis

63. Knurling
Produce impression (any shape) on the outer surface of work piece
Give good gripping surface
Knurling tool - two hardened steel rollers with cutting teeth
Tool held in tool post & pressed against the rotating work piece – moved parallel to lathe axis
Speed & feed should be very low

64. Forming
Making concave, convex or any other irregular shape on the work piece
Cutting tool should be made to the required form
Work piece held b/w centers & form tool moved perpendicular to the revolving work piece

65. Grooving
Reducing the diameter of work piece over a very narrow surface
Also called recessing, undercutting or necking
Work piece held in chuck
Grooving tool fed against revolving work piece

66. Parting Off
Process of cutting of work piece after the completion of all machining operations
Parting tool is used
Work piece held in chuck & rotated
Carriage locked at the required position
Spindle speed reduced
Tool fed slowly perpendicular to lathe axis

67. Eccentric Turning Making of eccentric Set up Operation
Center of one cylinder is out of the center of other cylinder – crank shaft, cam shaft, eccentric on a shaft
Two set of center holes (offset from the normal axis of the work piece) are drilled – end of work piece
Amount of offset = half of eccentricity required
Operation
Work piece - one axis of rotation – in b/w centers
One cylindrical surface turned
Work piece removed & held in other axis of rotation for turning the other cylindrical surface

68. Drilling Producing cylindrical hole in a work piece
Methods used for making a drill
First method
Work piece - chuck or face plate
Drill bit - tail stock spindle
Tail stock clamped near work piece
Work piece rotated & drill bit fed into the work piece – turning tail stock hand wheel
Second method
Drill held in chuck
Work piece - pad supported by tail stock spindle
Work piece fed by tail stock hand wheel while the drill bit is revolving

69. Drilling

70. Reaming
Operation of finishing & sizing of already drilled hole – dimensionally more accurate
Tool – Reamer – has multiple cutting edges
Work piece - chuck & revolves slowly
Reamer – tail stock – fed into the work piece for reaming

71. Reaming & Remears

72. Boring Enlargement of hole
Done when correct size drill bit not available
Work piece - chuck/face plate - rotated
Boring tool - tool post - fed parallel to lathe axis
Boring tool - smaller holes
Boring bar - larger holes

73. Milling Removing metal – rotating cutter (multiple cutting edges)
Work piece - vice
Vice - compound rest
Milling cutter rotated
Work piece fed by moving carriage

74. Slab Milling & Face Milling

75. End Milling

76. Grinding Removing metal – grinding wheel External grinding
Work piece revolved b/w centers
Grinding wheel – compound rest – tool post – fed against the work piece
Internal grinding
Work piece – chuck or face plate
Grinding wheel – tool post – compound rest
Feed - carriage
Depth of cut given by cross slide