2. Lathe A lathe is a large machine that rotates the work, and
cutting is done with a non-rotating cutting tool. The shapes cut
are generally round, or helical. The tool is typically moved
parallel to the axis of rotation during cutting. head stock - this
end of the lathe contains the driving motor and gears. Power to
rotate the part is delivered from here. This typically has levers
that let the speeds and feeds be set. ways - these are hardened
rails that the carriage rides on. tail stock - this can be used to
hold the other end of the part.
3. Lathe Bed - this is a bottom pan on the lathe that catches
chips, cutting fluids, etc. carriage - this part of the lathe
carries the cutting tool and moves based on the rotation of the
lead screw or rod. Lead screw - A large screw with a few threads
per inch used for cutting threads. It has ACME threads with
included angle of 29o for easy engagement and disengagement of half
nut. Lead rod - a rod with a shaft down the side used for driving
normal cutting feeds. The critical parameters on the lathe are
speed of rotation (speed in RPM) and how far the tool moves across
the work for each rotation (feed in IPR)
4. General classifications used when describing lathes Swing -
the largest diameter of work that can be rotated. Distance Between
Centres - the longest length of workpiece Length of Bed - Related
to the Distance Between Centres Power - The range of speeds and
feeds, and the horsepower available
5. Number of Spindle Speed Number of spindle speed is in a
geometric progression. If n number of spindle speed is required
with N1 is the minimum speed then The values of step ratios are
1.06, 1.12, 1.26, 1.41, 1.58 and 2 1 1 min max max 1 1min1 1 1 3 1
2 111 RatioStepTherefore, ....,.........,,, n n n N N r NrNandNN
rNrNrNrNN
6. IES - 2001 The spindle speed range in a general purpose
lathe is divided into steps which approximately follow (a)
Arithmetic progression (b) Geometric progression (c) Harmonic
progression (d) Logarithmic progression
7. IES - 1992 Feed gear box for a screw cutting lathe is
designed on the basis of (a) Geometric progression (b) Arithmetic
progression (c) Harmonic progression (d) None.
8. Turning Turning - produces a smooth and straight outside
radius on a part.
9. Video
10. Threading Threading - The cutting tool is moved quickly
cutting threads.
11. Video
12. Threading In one revolution of the spindle, carriage must
travel the pitch of the screw thread to be cut.
traingearcarriagetospindleofratiogear screwleadtheofstartofNumber
cutbetothreadscrewtheofstartofNumber screwleadtheofPitchL
cutbetothreadscrewtheofPitch Lscg L s LLss NNi z z P LzNPzN
13. IES - 1998 A single start thread of pitch 2 mm is to be
produced on a lathe having a lead screw with a double start thread
of pitch 4 mm. The ratio of speeds between the spindle and lead
screw for this operation is (a) 1 : 2 (b) 2: 1 (c) 1: 4 (d) 4:
1
14. IES 1993, ISRO-2009 It is required to cut screw threads of
2 mm pitch on a lathe. The lead screw has a pitch of 6 mm. If the
spindle speed is 60 rpm, then the speed of the lead screw will be
(a) 10 rpm (b) 20 rpm (c) 120 rpm (d) 180 rpm
15. Facing Facing - The end of the part is turned to be
square.
16. Video
17. Tapering Tapering - the tool is moves so as to cut a taper
(cone shape).
18. Parting/Slotting/Grooving A tool is moved in/out of the
work. shallow cut will leave a formed cut, a deep cut will cut off
the unsupported part.
19. Video
20. Drilling/Boring Drilling/Boring - a cutter or drill bit is
pushed into the end to create an internal feature.
21. Video
22. Knurling Knurling is a manufacturing process whereby a
visually-attractive diamond-shaped (criss-cross) pattern is cut or
rolled into metal. This pattern allows human hands or fingers to
get a better grip on the knurled object than would be provided by
the originally-smooth metal surface.
23. Spinning Metal Spinning is a process by which circles of
metal are shaped over mandrels (also called forms) while mounted on
a spinning lathe by the application of levered force with various
tools.
24. Reaming A reamer enters the workpiece axially through the
end and enlarges an existing hole to the diameter of the tool.
Reaming removes a minimal amount of material and is often performed
after drilling to obtain both a more accurate diameter and a
smoother internal finish.
25. Tapping A tap enters the workpiece axially through the end
and cuts internal threads into an existing hole. The existing hole
is typically drilled by the required tap drill size that will
accommodate the desired tap.
26. Work holding Devices for Lathes Held between centers 3 jaw
self centering chuck (Disc type jobs being held in chucks ) 4 jaw
independently adjusted chuck Held in a collet (Slender rod like
jobs being held in collets ) Mounted on a face plate (Odd shape
jobs, being held in face plate) Mounted on the carriage Mandrels
Magnetic chuck for thin job
27. Lathe chucks Lathe chucks are used to support a wider
variety of workpiece shapes and to permit more operations to be
performed than can be accomplished when the work is held between
centers. Three-jaw, self-centering chucks are used for work that
has a round or hexagonal cross section. Each jaw in a four-jaw
independent chuck can be moved inward and outward independent of
the others by means of a chuck wrench. Thus they can be used to
support a wide variety of work shapes. Combination four-jaw chucks
are available in which each jaw can be moved independently or can
be moved simultaneously by means of a spiral cam.
28. 3 Jaw Chuck 4 Jaw Chuck
29. Collets Magnetic Chuck Face Plate
30. Turning
31. Formula for Turning Depth of cut, Average diameter of
workpiece Cutting Time, Metal Removal Rate Cutting Speed, V = 1 2D
D d DOC mm 2 1 2 avg D D D mm 2 L A O CT fN 2 2 1 2 avg D D MRR D
dfN 4 / fN 1D N ,m / min 1000
32. Example How much machining time will be required to reduce
the diameter of a cast iron rod from 120 mm to 116 mm over a length
of 100 mm by turning using a carbide insert. Cutting velocity is
100 m/min and feed rate = 0.2 mm/rev.
33. IES 2010 In turning a solid round bar, if the travel of the
cutting tool in the direction of feed motion is 1000 mm, rotational
speed of the workpiece is 500 rpm, and rate of feed is 0.2
mm/revolution, then the machining time will be (a) 10 seconds (b)
100 seconds (c) 5 minutes (d) 10 minutes
34. IES - 2003 The time taken to face a workpiece of 72 mm
diameter, if the spindle speed is 80 r.p.m. and cross- feed is 0.3
mm/rev, is (a) 1.5 minutes (b) 3.0 minutes (c) 5.4 minutes(d) 8.5
minutes
35. GATE-2013 (PI) Common Data A disc of 200 mm outer and 80 mm
inner diameter is faced of 0.1 mm/rev with a depth of cut of 1 mm.
The facing operation is undertaken at a constant cutting speed of
90 m/min in a CNC lathe. The main (tangential) cutting force is 200
N. Assuming approach and over-travel of the cutting tool to be
zero, the machining time in min is (a) 2.93 (b) 5.86 (c) 6.66 (d)
13.33
36. IES - 2004 A medium carbon steel workpiece is turned on a
lathe at 50 m/min. cutting speed 0.8 mm/rev feed and 1.5 mm depth
of cut. What is the rate of metal removal? (a) 1000 mm3/min (b)
60,000 mm3/min (c) 20,000 mm3/min (d) Can not be calculated with
the given data
37. Turning Tapers on Lathes Using a compound slide, Using form
tools, Offsetting the tailstock, and Using taper turning
attachment.
38. Using a Compound Slide Limited movement of the compound
slide Feeding is by hand and is non-uniform. This is responsible
for low-productivity and poor surface finish. Can be employed for
turning short internal and external tapers with a large angle of
(steep) taper.
39. Using a Compound Slide contd.. The angle is determined by l
dD 2 tan tapertheoflengthl diametersmallerd stockofDiameterD
angletaperHalf
40. IES - 2006 For taper turning on centre lathes, the method
of swiveling the compound rest is preferred for: (a) Long jobs with
small taper angles (b) Long jobs with steep taper angles (c) Short
jobs with small taper angles (d) Short jobs with steep taper
angles
41. Example Find the angle at which the compound rest should be
set up to turn taper on the workpiece having a length of 200 mm,
larger diameter 45 mm and the smaller 30 mm.
42. Offsetting the tailstock It is necessary to measure the
tailstock offset when using this method. This method is limited to
small tapers (Not exceeding 8o ) over long lengths. By offsetting
the tailstock, the axis of rotation of the job is inclined by the
half angle of taper.
43. Offsetting the tailstock Contd.. Tailstock offset (h) can
be determined by tan 2 Lhor l dDL h
44. IES - 1992 Tail stock set over method of taper turning is
preferred for (a) Internal tapers (b) Small tapers (c) Long slender
tapers (d) Steep tapers
45. IAS - 2002 The amount of offset of tail stock for turning
taper on full length of a job 300 mm long which is to have its two
diameters at 50 mm and 38 mm respectively is (a) 6 mm (b) 12 mm (c)
25 mm (d) 44 mm
46. IES - 1998 A 400 mm long shaft has a 100 mm tapered step at
the middle with 4 included angle. The tailstock offset required to
produce this taper on a lathe would be (a) 400 sin 4 (b) 400 sin 2
(c) 100 sin 4 (d) 100 sin 2
47. Form tool Special form tool for generating the tapers is
used. The feed is given by plunging the tool directly into the
work. This method is useful for short external tapers, where the
steepness is of no consequence, such as for chamfering.
48. Taper Turning Attachment Additional equipment is attached
at the rear of the lathe. The cross slide is disconnected from the
cross feed nut. The cross slide is then connected to the
attachment. As the carriage is engaged, and travels along the bed,
the attachment will cause the cutter to move in/out to cut the
taper. For turning tapers over a comprehensive range is the use of
taper turning attachment.
49. Errors in tool settings Setting the tool below the centre
decrease actual rake angle, while clearance angle increases by the
same amount. Thus cutting force increased. Setting the tool above
the centre causes the rake angle to increase, while clearance angle
reduces. More rubbing with flank.
50. IES 2010 The effect of centering error when the tool is set
above the center line as shown in the figure results effectively in
1. Increase in rake angle. 2. Reduction in rake angle. 3. Increase
in clearance angle. 4. Reduction in clearance angle. Which of these
statements is/are correct? (a) 1 only (b) 1 and 4 only (c) 2 and 4
only (d) 1, 2, 3 and 4
51. Turret Lathe A turret lathe, a number of tools can be set
up on the machine and then quickly be brought successively into
working position so that a complete part can be machined without
the necessity for further adjusting, changing tools, or making
measurements.
52. Turret Lathe
53. Capstan Lathe
54. Video
55. Capstan lathe Turret lathe Short slide, since the saddle is
clamped on the bed in position. Saddle moves along the bed, thus
allowing the turret to be of large size. Light duty machine,
generally for components whose diameter is less than 50 mm. Heavy
duty machine, generally for components with large diameters, such
as 200 mm. Too much overhang of the turret when it is nearing cut.
Since the turret slides on the bed, there is no such difference.
Ram-type turret lathe, the ram and the turret are moved up to the
cutting position by means of the capstan Wheel. As the ram is moved
toward the headstock, the turret is automatically locked into
position. Saddle-type lathes, the main turret is mounted directly
on the saddle, and the entire saddle and turret assembly
reciprocates.
56. IES - 2012 Lathe machine with turret can turn a work piece
of limited length only because, (a) Cross slide motion is
obstructed by turret (b) Turret cannot work on a long job (c) Chuck
cannot be replaced by a face plate (d) Turret replaces the loose
centre
57. Turret indexing mechanism The hexagonal turret is rotated
(for indexing) by a Geneva mechanism where a Geneva disc having six
radial slots is driven by a revolving pin. Before starting
rotation, the locking pin is withdrawn by a cam lever mechanism.
The single rotation of the disc holding the indexing pin is derived
from the auxiliary shaft with the help of another single revolution
clutch as indicated. For automatic lathe: Ratchet and Pawl
mechanism
58. Automatic Lathe The term automatic is somewhat loosely
applied, but is normally restricted to those machine tools capable
of producing identical pieces without the attention of an operator,
after each piece is completed. Thus, after setting up and providing
an initial supply of material, further attention beyond
replenishing the material supply is not required until the
dimensions of the work pieces change owing to tool wear. A number
of types of automatic lathes are developed that can be used for
large volume manufacture application, such as single spindle
automatics, Swiss type automatics, and multi-spindle
automatics.
59. Video
60. Swiss type Automatic Lathe Or Sliding Headstock Automatics
Headstock travels enabling axial feed of the bar stock against the
cutting tools. There is no tailstock or turret High spindle speed
(2000 10,000 rpm) for small job diameter The cutting tools (upto
five in number including two on the rocker arm) are fed radially
Used for lot or mass production of thin slender rod or tubular
jobs, like components of small clocks and wrist watches, by
precision machining.
61. Multi Spindle Automatic Lathe For increase in rate of
production of jobs usually of smaller size and simpler geometry.
Having four to eight parallel spindles are preferably used.
Multiple spindle automats also may be parallel action or
progressively working type.
62. Video
63. Norton type Tumbler-gear quick-change Gear box
64. Norton type Tumbler-gear quick-change Gear box It comprises
a cone of gears 1 to 8 mounted on shaft S2. The tumbler gear can
slide on shaft S1. It can mesh with any gear on shaft S2 through an
intermediate gear which is located on a swinging and sliding lever
so that it can engage gears 1 to 8 of different diameters, on shaft
S2. The lever can be fixed in any desired ratio position with the
help of a stop pin. The drive is usually from the driving shaft S1
to the driven shaft S2.
65. GATE 2008 The figure shows an incomplete schematic of a
conventional lathe to be used for cutting threads with different
pitches. The speed gear box Uv, is shown and the feed gear box Us,
is to be placed. P, Q. R and S denote locations and have no other
significance. Changes in Uv, should NOT affect the pitch of the
thread being cut and changes in Us, should NOT affect the cutting
speed. Contd..
66. GATE -2008 Contd. The correct connections and the correct
placement of Us are given by (a) Q and E are connected. Us, is
placed between P and Q. (b) S and E are connected. Us is placed
between R and S. (c) Q and E are connected. Us, is placed between Q
and E. (d) S and E are connected. Us, is placed between S and
E.
67. IES - 2009 Which one of the following methods should be
used for turning internal taper only? (a) Tailstock offset (b)
Taper attachment (c) Form tool (d) Compound rest
68. IES - 1997 Consider the following operations: 1. Under
cutting 2. Plain turning 3. Taper turning 4. Thread cutting The
correct sequence of these operations in machining a product is (a)
2, 3, 4, 1 (b) 3, 2, 4, 1 (c) 2, 3, 1, 4 (d) 3, 2, 1, 4
69. IAS - 2001 Consider the following operations and time
required on a multi spindle automatic machine to produce a
particular job 1. Turning 1.2 minutes 2. Drilling 1.6 minutes 3.
Forming 0.2 minute 4. Parting 0.6 minute The time required to make
one piece (cycle time) will be (a) 0.6 minutes (b) 1.6 minutes (c)
3.6 minutes (d) 0.9 minute
70. IES 2011 In Norton type feed gearbox for cutting Whitworth
standard threads with a standard TPI Leadscrew, power flows from:
(a) Spindle to Tumbler gear to Norton cone to Meander drive to
Leadscrew (b) Spindle to Norton cone to Tumbler geat to Meander
drive to Leadscrew (c) Spindle t o Tumbler gear to Meander drive to
Norton cone to Leadscrew (d) Spindle to Norton cone to Meander
drive to Tumbler gear to Leadscrew
71. Q. No Option Q. No Option 1 C 6 A 2 A 7 B 3 D 8 B 4 B 9 D 5
B 10 C Ch 2: Lathe
