Workshop Practice
By:
N. V. Sangade
PICT, Pune
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Lathe Machine
The first lathe machine that was ever developed was the
two-person lathe machine which was designed by the
Egyptians in about 1300 BC.
Primarily, there are two things that are achieved in this
lathe machine set-up. The first is the turning of the wood
working piece manually by a rope; and the second is the
cutting of shapes in the wood by the use of a sharp tool.
As civilizations progressed, there have been constant
modifications and improvements over the original twoperson lathe machine, most importantly on the production
of the rotary motion
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Working Principle- Lathe Machine
• The lathe is a machine tool which holds the
workpiece between two rigid and strong supports
called centres or in a chuck or face plate which
revolves. The cutting tool is rigidly held and
supported in a tool post which is fed against the
revolving work. The normal cutting operations are
performed with the cutting tool fed either parallel or
at right angles to the axis of the work.
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Basic Elements- Lathe Machine
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Basic Elements- Lathe Machine
1.
Machine bed: It usually made of cast iron. It holds or
supports all other parts of the lathe. The top of the machine
bed is flat and is machined to form guide ways on which
the carriage slides along the length of the lathe
2. Headstock: It is fixed at the extreme left hand of the bed
and contains shafts and gears immersed in lubricating oil.
The driving shaft inside is driven by an electric motor. The
driven shaft, which is in the form of a hollow spindle can
be driven at various r.p.m. by changing gears, projects out
of the headstock, A chuck (either three jaw or four jaw), is
screwed on this spindle. The work piece can be held in the
jaws of the chuck. When the spindle rotates, the chuck as
well as the work piece held also rotate about the
longitudinal axis of the spindle.
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Basic Elements- Lathe Machine
3.
4.
Tailstock: A tailstock is provided at the right hand end of the bed. It can
slide along the guide ways provided on the bed and may be brought
nearer to the headstock, if so desired. It can then be clamped or fixed on
the bed in that position. The tailstock has a spindle in the upper part of the
tailstock, the axis of which coincides with the axis of the headstock
spindle, both being at the same height above the bed. This spindle can be
moved forwards or backwards by rotating a hand wheel
Carriage: The carriage can slide along the length of the machine bed
from the tailstock end to the head stock end. This movement is controlled
by manually operating the hand traversing wheel. It can also be imparted
this traversing motion at different speeds automatically by engaging into
the feed rod or feed shaft. The carriage carries a cross slide, which can
independently move in a crosswise direction at right angles to the bed.
The cross slide can also be moved either manually through a smaller hand
wheel or through an automatic device. Mounted upon the cross slide is
another small slide, called the compound rest (or tool post slide) which
can be rotated in a horizontal plane. Its normal position at 0° rotation is
parallel to bed.
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Basic Elements- Lathe Machine
5. Feed Mechanism: Feed mechanism is the combination of
different units through which motion of headstock spindle
is transmitted to the carriage of lathe machine. Following
units play role in feed mechanism of a lathe machine : End
of bed gearing, Feed gear box, Lead screw and feed rod &
Apron mechanism
6. Thread Cutting Mechanism: The half nut or split nut is
used for thread cutting in a lathe. It engages or disengages
the carriage with the lead screw so that the rotation of the
leadscrew is used to traverse the tool along the workpiece
to cut screw threads. The direction in which the carriage
moves depends upon the position of the feed reverse lever
on the headstock.
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Block Diagram- Lathe Machine
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TYPES OF LATHE
1. Speed lathe
(a) Wood working
(b) Spinning
(c) Centring
(d) Polishing
4. Tool room Lathe
5. Capstan and Turret lathe
2. Centre or engine lathe
(a) Belt drive
(b) Individual motor drive
(c) Gear head lathe
3. Bench lathe
6. Special purpose lathe
(a) Whee1 lathe
(b) Gap bed lathe
(c) Dup1icating lathe
(d) T-lathe
7. Automatic lathe
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Types of operations- Lathe Machine
1.
2.
3.
4.
5.
6.
Turning
Facing
Boring
Parting
Drilling
Reaming
7.
8.
9.
10.
11.
12.
Knurling
Grooving
Threading
Forming
Chamfering
Filling and
Polishing
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Turning
• to reduce diameter of Job
• Feed: in direction parallel to work piece axis (Feed is
defined as the distance that a tool advances into the
work during one revolution of the headstock spindle.)
• Depth of Cut: in direction perpendicular to workpiece axis
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Straight Turning
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Taper Turning
• in order to create a conical shape.
• Feed: a tool at an angle to the length of the work
piece
• Taper turning falls into three categories, short tapers
of relatively obtuse angles generally turned with the
top-slide, longer tapers of a more acute angle
produced either by setting the tailstock over or by use
of a taper turning attachment, and internal taper.
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Taper Turning
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Taper Turning
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Eccentric Turning
• The process of performing turning operations at
various axis in a single setting job is known as
eccentric turning.
• If a cylindrical workpiece has two separate axes of
rotating, one being out of centre to the other, the
workpiece is termed as eccentric and turning of
different surfaces of the workpiece is known as
eccentric turning.
• The distance between the axes is known as offset.
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Eccentric Turning
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Step Turning
• It is an operation of producing various steps of
different diameters of in the work piece. This
operation is carried out in the similar way as straight
turning.
• Also called as Shoulder turning.
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Step Turning
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Contour Turning
• Making a three-dimensional reproduction of the
shape of a template by controlling the cutting tool
with a follower that moves over the surface of a
template.
• Feed: tool follows contour that is other than straight,
thus creating a contoured shape
• Cutting tool has a simple shape, but the feed motion
is complex, special lathes or devices are required.
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Contour Turning
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Facing
• to reduce length of Job
• Feed: in perpendicular to
work piece axis
• Depth of Cut: in direction
parallel to work- piece axis
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Facing
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Parting
• In this operation, specific part of the work piece is
removed (detached) from the total length of the work
piece.
• The tool used for this operation is known as Parting Off
Tool.
• The tool moves specific lengthwise which is parallel to
the center line of the lathe machine with the help of
Carriage.
• The feed rate is provided with the help of Cross Slide.
• During this operation the work piece is rotated at lower
speed.
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Parting
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Drilling
• In this operation, a cylindrical hole is produced in a work piece, by cutting
edge of a cutter known as the drill.
• The drill bit is fitted into the barrel of the tailstock (drill is stationary).
• First the drill is bringing in contact to the work piece. In this position the
tailstock is locked on to the bed with the help of lever provided on the
tailstock, so as to avoid the backward movement of the tailstock.
• The feed is given to the drill with the help of hand wheel which is provided
on the tailstock.
• Before drilling operation, center is marked on the either face of the work
piece with the help of center drill. This is required so as to avoid the
eccentricity or taper of the hole into the work piece.
• During the operation the drill moves in longitudinal direction which is
parallel to the center line of the lathe machine. During this operation the
work piece is rotated at lower speed.
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Drilling
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Boring
• In this operation, the hole
is enlarged, which has
been produced previously
by drilling, casting or
forging
• Boring is used to correct
error in concentricity and
alignment
in
the
previously drilled hole.
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Reaming
• It provides sizing and finishing to the already drilled
hole.
• Operation of tool and movement of tool is same like
drilling operation. The tool used for reaming operation
is known as reamer, which has multiple cutting edges.
• Reamer cannot originate a hole. It simply follows the
path which has been previously drilled and removes a
very small amount of material.
• Two broad categories of commercial reamers are
generally available; these are hand reamers and
machine reamers.
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Reaming
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Knurling
• Knurling is the process of embossing a diamond shaped
pattern on the surface of the workpiece.
• The knurling tool holder has one or two hardened steel
rollers with edges of required pattern. The tool holder is
pressed against the rotating work. The rollers emboss the
required pattern. The tool holder is fed automatically to the
required length.
• Knurls are available in coarse, medium and fine pitches.
The patterns may be straight, inclined or diamond shaped.
• The purpose of knurling is:
o to provide an effective gripping surface
o to provide better appearance to the work
o to slightly increase the diameter of the work
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Knurling
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Knurling
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Grooving
• Grooving is the process of cutting a narrow groove on the
cylindrical surface of the workpiece.
• It is often done at end of a thread or adjacent to a shoulder
to leave a small margin. The groove may be square, radial
or bevelled in shape
• Grooving or recessing operations, sometimes also called
necking operations, are often done on workpiece shoulders
to ensure the correct fit for mating parts.
• When a thread is required to run the full length of the part to
a shoulder, a groove is usually machined to allow full travel
of the nut.
• Grooving the workpiece prior to cylindrical grinding
operations allows the grinding wheel to completely grind
the workpiece without touching the shoulder.
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Grooving
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Grooving
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Threading
• Thread of any pitch, shape and size can be cut on a lathe using
single point cutting tool.
• Thread cutting is operation of producing a helical groove on
spindle shape such as V, square or power threads on a
cylindrical surface.
• 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.
• To make or cut threads, the cutting tool is brought to the start
of job and a small depth of cut is given to cutting tool using
cross slide.
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Threading
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Threading
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Forming
• Cutting tool has a shape that is imparted to the
workpiece by plunging the tool into the workpiece.
• In form turning, cutting tool is complex and
expensive but feed is linear and does not require
special machine tools or devices.
• Forming is a process of turning a convex, concave or
any irregular shape.
• For turning a small length formed surface, a forming
tool having cutting edges conforming to the shape
required is fed straight into the work.
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Forming
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Forming
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Chamfering
• Chamfering is the operation of bevelling the extreme
end of the workpiece.
• The form tool used for taper turning may be used for
this purpose.
• Chamfering is an essential operation after thread
cutting so that the nut may pass freely on the threaded
workpiece.
• This is done to remove the burrs, to protect the end of
the work piece from being damaged and to have a
better look.
• The operation may be performed after knurling, rough
turning, boring, drilling.
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Chamfering
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Filling and Polishing
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Mill files are generally considered best for lathe filing.. Other types such as the
round, half-round, and flat hand files may also be used for finishing irregular
shaped workplaces. Never use a file without a handle.
For filing ferrous metals, the lathe spindle speed should be four or five times greater
than the rough turning speed. For filing nonferrous metals, the lathe spindle speed
should be only two or three times greater than the roughing speed.
Too slow a speed may cause the workpiece to be filed out of round, while too high
a speed will cause the file to slide over the workpiece, dulling the file and glazing
the piece.
NOTE: When filing, file left-handed if at all possible to avoid placing your arm
over the revolving chuck or lathe dog.
The file is held at an angle of about 10° to the right and moved with a slow sliding
motion from left to right so that the teeth will have a shearing action.The direction
of stroke and angle should never be the opposite, as this will cause chatter marks on
the piece.
The file should be passed slowly over the workpiece so that the piece will have
made several revolutions before the stroke is completed.
The pressure exerted on the file with the hands should be less than when filing at
the bench. Since there are less teeth in contact with the workpiece, the file must be
cleaned frequently to avoid scratching.
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Filling and Polishing
• Polishing with either abrasive cloth or abrasive paper is desirable to
improve the surface finish after filing. Emery abrasive cloth is best
for ferrous metals while abrasive paper often gives better results on
nonferrous materials.
• The most effective speed for polishing with ordinary abrasives is
approximately 5,000 feet per minute. Since most lathes are not
capable of a speed this great for an average size workpiece, it is
necessary to select as high a speed as conditions will permit.
• In most cases the abrasive cloth or paper is held directly in the hand
and applied to the workpiece, although it may be tacked over a piece
of wood and used in the same manner as a file. Improvised clamps
may also be used to polish plain round work.
• To produce a bright surface, polish the work dry. To produce a dull
satin finish, apply oil as the polishing operation is in progress.
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Filling and Polishing
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Safety Precautions while Working on
Lathe Machine
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
One should always be sure that all guards are in place before running the
machine. (Machine guarding is a safety feature on or around manufacturing or
other engineering equipment consisting of a shield or device covering hazardous
areas of a machine to prevent contact with body parts or to control hazards like
chips or sparks from exiting the machine)
Always clamp the work and tool properly with correct size of work and tool
holding device.
Always keep the machine clear of tools.
Machine should be stopped before making measurements or adjustments.
Wear an apron or a properly fitted shop coat. Goggles should also be used.
One should remove necktie, wrist watch and jewellery while working.
One should not operate the lathe until he knows the proper procedure.
One should check the work frequently when it is being machined.
One should check the face-plate or chuck by hand to be sure that there is no
danger of the work striking any part of the lathe.
Stop the machine and remove chips with pliers. One should not remove the chips
by hand
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