1. UNIT – II
TURNING MACHINES

2. Working Principle
• Fig. 9.3 shows the working
principle of a lathe.
• In a lathe, the workpiece is held
in a chuck or between centres
and rotated about its axis at a
uniform speed.
• The cutting tool held in tool
post is fed into the workpiece
for desired depth and in desired
direction (i.e., in linear,
transverse or lateral direction).

3. Centre lathe

4. • The Centre Lathe is used to manufacture cylindrical
shapes from a range of materials including; steels and
plastics.
• Components that assemble to make an car engine work
have been made using lathes.
• The Lathe may be operated by people (manual lathes)
or computer controlled lathes (CNC machines) that have
been programmed to carry out a particular task.

6. Parts of Lathe
1. Bed.
2. Headstock.
3. Tailstock.
4. Carriage.
5. Feed mechanism.

7. Lathe Bed
• Heavy, rugged casting
• Made to support working parts of
lathe
• On top section are machined
ways
• Guide and align major parts of lathe
8

8. Lathe parts
•Headstock
Holds lathe spindle and gears
Chuck is fitted to spindle
Spindle is hollow for long bars

9. Headstock
11

10. Lathe Parts
•Three Jaw Chuck
 Self centring
Holds round and hexagonal work
3 jaws are connected
Jaws are stamped 1,2 & 3 and
fitted in order
Chuck key used to open

11. 3 Jaw Chuck
Lathe
Chuck Key

12. Quick-Change Gearbox
15
Top View

13. Lathe parts
•Tailstock
Can be moved along
slideways
Can be clamped
in any location
Inside tapered
to hold drill chuck

14. Live (or Revolving) Centre
Tailstock
Lathe
Bed
Jacob’s Chuck
Centre drill

15. 4. Carriage

16. Carriage
• The carriage controls and supports the cutting tool.
• The carriage has the following five major parts :
• (i) Saddle. It is a H-shaped casting fitted over the bed. It moves
along the guideways.
• (ii) Cross-slide. It carries the compound slide and tool post ; can
be moved by power or by hand.
• (iii) Compound rest. It is marked in degrees ; used during taper
turning to set the tool for angular cuts.
• (iv) Tool post. The tool is clamped on the tool post.
• (v) Apron. It is attached to the saddle and hangs in front of the
bed. It has gears, levers and clutches for moving the carriage
with the lead screw for thread cutting.

17. Carriage
22

18. Carriage
23

19. Lathe parts
•Top Slide
(Compound slide)
Fitted to top of Cross slide
Carries tool post and cutting
tool
Can rotate to any angle
Is used to turn tapers

20. 5. Feed Mechanism
• It is employed for imparting various feeds (longitudinal,
cross and angular) to the cutting tool.
• It consists of feed reverse lever, tumbler reversing
mechanism, change gears, feed gear box, quick change
gear box, lead screw, feed rod, apron mechanism and
half nut mechanism.

21. Lathe Operations
• 1. Facing
• 2. Plain turning
• 3. Step turning
• 4. Taper turning
• 5. Drilling
• 6. Reaming
• 7. Boring
• 8. Undercutting or grooving
• 9. Threading
• 10. Knurling
• 11. Forming

22. Facing
• Facing is an operation of
machining the ends of a
workpiece to produce a flat
surface square with the axis.
• It is also used to cut the
work to the required length.
• The tool is moved at right
angles to the work using the
cross slide
• Flat surfaces are produced

23. Parallel Turning
• The tool moved parallel to the
work and cylindrical shapes are
formed

24. Parallel Turning
• The student can Parallel turn the work on the
lathe manually or use the automatic traverse
option

25. Lathe operations
Facing
Parallel Turning
Parallel Turning

26. 3. Step Turning
• In this type of lathe
operation various steps of
different diameters in the
workpiece are produced.
• It is carried out in the
similar way as plain
turning.

27. 4. Taper Turning

28. 4. Taper Turning

31. Fig. illustrates the method of turning taper 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. In this method the
tool angle should be properly checked before use. This method is limited to
turn short length of taper only. This is due to the reason that the metal is
removed by the entire cutting edge will require excessive cutting pressure,
which may distort the work due to vibration and spoil the work surface.

32. (iii) By using a taper turning attachment :
— This method provides a very wide range of taper.
— In this method of taper turning a tool is guided in a straight path set at an angle to the axis of rotation of the
workpiece, while the work is being revolved between centres or by a chuck aligned to the lathe axis.
As shown in Fig. , a taper turning attachment essentially consists of a bracket or frame which is
attached to the rear end of the lathe bed and supports a guide bar pivoted at the centre. The bar is provided with
graduations and may be swivelled on either side of the zero graduation and is set at the desired angle with the
lathe axis.

33. (iv) By manipulating the transverse and longitudinal feeds of the
slide tool simultaneously :
• Taper turning by manipulation of both feeds is inaccurate and requires
skill on the part of the operator.
• It is used for sharp tapers only.

34. 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

35. Knurling

36. SPECIAL ATTACHMENT
• Most of the details discussed so far allow for general purpose
machining operations to be carried using a centre lathe. In addition, it
is possible to provide special enhancements to the capability of a
lathe whereby it could be used for special applications using special
attachments. One such attachment discussed earlier is the taper
turning attachment for obtaining cylindrical tapers or conical surfaces.
• Milling attachment
Milling is the process of removing metal by moving the work against
a rotating cutter, that cutter is mounted on the tool holder is called
arbor.

37. • Milling attachment
1. for cutting groove or keyways
• Work is held on the cross slide
milling cutter is held by a chuck
using special attachment.

38. 2.For cutting multiple grooves and gear wheel
• Work piece is held stationary b/w centres. The attachment on the
cross slide on the carriage which driven by separate electrical motor
• For cutting gears, a universal driving head is fitted on the rear end of
the head stock spindle to divide the work equally.

39. 2. Grinding attachment
• It is the operation of removing metal in the form of
chip. It is done by moving the work against rotating
abrasive wheel. It is the finishing operation process.

40. 3. Copy Turning Attachment
• Many a times the need exists for machining complex
contours, which require the feeding of the tool in two
axes (X and Y) simultaneously, similar to taper turning.
For such purposes copy turning is to be used. In this,
the cross slide is directly driven by a stylus which can
trace a master for the actual contour to be produced.
• The cross slide is made similar to the taper turning
attachment.

42. Capstan lathe
• Turret head is mounted on
a ram which slides over
the saddle
• Turret movement is
limited
• Sorter work pieces can be
machined.
• It is not provide rigidity
due to overhanging of ram
Turret lathe
• It is directly mounted on
saddle, But it slides on the
bed.
• It moves on the entire
length of the bed
• Long work piece can be
machined
• It provide rigidity and
strong

43. Capstan lathe
• Light duty application
• Turret head moved
manually
• 60mm dia work can be
machined
• No cross wise movement
• Overhung type of slide is
not used
Turret lathe
• Heavy duty application
• Cant be moved manually
• 125mm – 200mm
• Facing & turning done by
cross wise movement
• It is used for specific
operation

44. AUTOMATIC LATHES
• These are machine tools in which components are
machined automatically.
• The working cycle is fully automatic that is repeated to
produce duplicate parts with out participation of operator.
• All movements of cutting tools, their sequence of
operations, applications, feeding of raw material, parting
off, un loading of finished parts all are done on machine.
• All working & idle operations are performed in definite
sequence by control system adopted in automatic which is
set up to suit a given work.
• Only operation reqd to be performed manually is loading
of bar stock/ individual casting/ forged blanks.
• These machines are used when production requirements
are too high for turret lathes to produce economically.

45. Advantages
• Greater production over a given period.
• More economy in floor space.
• More consistently accurate work than turrets.
• More constant flow of production.
• Scrap loss is reduced by reducing operator error.
• During machine operation operator is free to operate
another machine/ can inspect completed parts.

46. SEMI AUTOMATICS
• These are turning machines used for chucking work.
• In this type of lathes although all movements of w/p (or)
tools are automatically controlled, but w/p has to be loaded
into & removed from chuck at beginning & end of each
cycle of operation.
• Machine cycle is automated, but direct participation of
operator is reqd to start subsequent cycle, i.e., to machine
each w/p.
• Operator work is to load w/p or blank into machine, start
the ma/c, checks the work, & removes the completed part
by hand.

47. AUTOMATICS & SEMI AUTOMATICS are designed to perform
following operations:
• Centering, cylindrical turning, tapered, formed surfaces,
drilling, boring, reaming, facing, knurling, thread cutting,
facing, milling, grinding, cut off.
• With help of special attachments additional operations like
slotting can be done on this m/c.
Selection of lathe : same job can be machined on engine,
capstan, turret, automatic lathes . Main considerations are:
• Quantity of production reqd.
• Number of machining operations to be done on job,
number of tools reqd to employed.
• Over all dimensions of that portion of job which is to be
machined.

48. CLASSIFICATION OF AUTOMATIC LATHES
• Depending up on type of work machined these machines
are classified as:
1. Magazine loaded Automatics:
• Machines used for producing components from separate
blanks.
• Also called as automatic checking machines.
2. Automatic Bar Machines:
• designed for machining components from bar/ pipe
stock.
• M/c’s are used for manufacture of high quality fasteners
(screws, nuts), bushings, shafts, rings, rollers, handles
which are usually made of bar / pipe stock.

49. • Depending upon number of work spindles, automatic
lathes are classified as:
1. Single Spindle Automatics.
2. Multi Spindle Automatics.
• Depending upon purpose & arrangement of spindle also
automatics are classified as:
1. Purpose General & single purpose m/c.
2. Arrangement of spindle Horizontal & vertical

50. I) Type of Single Spindle Automatics:
a) Automatic Cutting Off Machine:

51. • These machines produce short w/p’s of simple form by means
of cross sliding tools. Machines are simple in design.
• Head stock with spindle is mounted on bed.
• 2 cross slides are located on bed at front end of spindle.
• CAMS on cam shaft actuate movements of cross slide through
system of levers.
Operation:
• The reqd length of work(stock) is fed out with a cam
mechanism, up to stock stop which is automatically advanced
in line with spindle axis at each end of cycle.
• Stock is held in collet chuck of rotating spindle.
• Machining is done by tolls that are held in slides operating only
in cross wise direction.
• Typical simple parts (3 to 20 mm dia) machined on such a
machine is shown in fig.

52. b) Single spindle Automatic Screw m/c:

53. • Used for producing small screws(12.7 to 60 mm dia) generally, but
also in production of all sorts of small turned parts.
• These are completely automatic bar type turret lathes, designed for
machining complex internal & external surfaces on parts made of
bar stock/separate blanks.
• Up to 10 different cutting tools can be employed at one time in
tooling of this kind of screw machine.
• 2 cross slides(front & rear) are employed for cross feeding tools.
• Vertical tool slides for parting off operation may also be provided .
• Head stock is stationary & houses the spindle.
• Bar stock is held in collet chuck & advanced after each piece is
finished & cut off.
• All movements of machine units are actuated by cams mounted on
cam shaft.

54. • Bar stock is pushed through stock tube in a bracket & its
leading end is clamped in rotating spindle by means of collet
chuck.
• By stock feeding mechanism bar is fed out for next part.
• Machining of central hole is done by tools that are mounted on
turret slide.
• Parting off/ Cutting off, form tools are mounted on cross slide.
• At end of each cut turret slide is with drawn automatically &
indexed to bring next tool to position.

55. c) Swiss type automatic screw/Sliding head screw:

57. • As name implies in this m/c head stock is movable & tools are fixed.
• These machines are used for machining long accurate parts of small
diameter.(2 to 25mm).
• Bar stock is held in rotating collet in head stock & all longitudinal
feeds are obtained by cam which moves entire head stock as unit.
• Rotating bar stock is fed through hard bushing in centre of tool head.
• Tool head consists of 5 single point tools is placed radially around
bushing.
• Mostly diameter turning is done by 2 horizontal slides, other 3 slides
used for operations such as knurling, chamfering, cutoff.
• Tools are controlled & positioned by cams that bring tool in as
needed to turn, face, form, cutoff w/p from bar as it emerges from
bushing. Close tolerances 0.005 to 0.00125 mm are obtained.

58. II) Multi Spindle Automatics:
• These are fastest type of production machines and are
made in a variety of models with 2,4,5,6,8 spindles.
• In contrast with single spindle m/c where one turret face at
a time is working on one spindle, in multi spindle m/c all
turret faces works on all spindles at same time.
• Production capacity is higher, machining accuracy is lower
compared to single spindle.
• Because of longer set up time, increased tooling cost this
machines are less economical than other on short runs,
more economical for longer runs.

59. a) Parallel Action Automatics/ Multiple Flow m/c:

60. • In this type of machine same operation is performed on each spindle, w/p
is finished in each spindle in one working cycle.
• It means that
No. of components being machined== No. of spindles in machine.
• Rate of production is high & machine can be used to machine simple parts
only since all the machining processes are done at one position.
• These machines are usually automatic cutting off bar type machines, used
to perform same work as single spindle automatic cut off machines.
• Machine consists of frame with head stock at right end.
• Horizontal work spindles that are arranged one above the another
are housed in this head stock.
• Cross slides are located at right & left hand sides of spindles & carry cross
feeding tools. All working & auxiliary motions of machine unit are
obtained from CAM mounted on cam shaft.

61. b) Six Spindle Progressive Action Multi Spindle:

62. • In this design of machine, the w/p is machined in states &
progressively in station after station.
• Head stock is mounted on left end of base of machine.
• It carries spindle carrier which rotates about a horizontal
axis through centre of machine.
• Working spindles are mounted on this spindle carriers.
• Spindles carry collets & bars from which w/p’s are
machined.
• Bar stock is fed through each spindle from rear side.
• On face of spindle carrier support are mounted cross slides
which carry tools for operations such as cutoff, turning,
facing, forming, chamfering.

63. • No. of slides === No. of spindles.
• Main tool slide (end tool slide) extends from middle of
this support.
• Fed of each tool, both cross slide & end tool slides is
controlled by its own individual cams.
• In this diagram spindle carrier indexes on its own axis by
60° at each cutting tool retraction.
• As spindle carrier indexes, it carries work from one station
to another station where different tolls operate on work.
• Stock moves round the circle in counter clock wise
direction & returns to station no. 6 for cutting off.