lathe machine
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1.0 Introduction to Lathe Machine and Its Components
1.1 Lathe Machine
The lathe machine is a tool used principally for shaping articles of
materials especially metals by causing the work piece to be held and
rotated by the lathe while a tool bit is advanced into the work causing the
cutting action. The basic lathe that was designed to cut cylindrical metal
stock has been developed further to produce screw threads, tapered
work, drilled holes, knurled surfaces, and crankshafts. The typical lathe
provides a variety of rotating speeds and a means to manually and
automatically move the cutting tool into the work piece. Machinists and
maintenance shop personnel must be thoroughly familiar with the lathe
and its operations to accomplish the repair and fabrication of needed
parts. Figure 1 shows the engine lathe which is usually used for metal
lathing.
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Figure 1: Lathe Machine.
1.2 Type of Lathe Machine
There are many kinds of lathe machines available, the oldest
example being a pottery wheel, the origins of which date back to ancient
Egyptian civilization. In simple terms, a lathe machine is a machine which
spins the material or work piece, while a tool (hands in the case of the
pottery wheel) cuts or shapes the material. There are many kinds of
lathes available including wood lathes, engine lathes, tool room lathes,
turret lathes and more recently CNC lathe machines. However, the most
common type of lathe machine can be found nowadays is metal lathe.
1.2.1 Wood Lathe
The simplest lathe type is the wood lathe. As the name suggests, it
is designed for turning wood. Wood lathes are small machines consisting
of a bed, headstock, tailstock and tool rest. There are no precision ways
as are found on a metal-working machine, since the cutting tools are
moved by hand and not by machine power. Great skill is needed to
control the cutting tool to accurately turn smooth curves and complex
contours on the work piece.
The spindle is usually driven by a belt connected to a motor, and
speed changes are made by manually moving the belt to one of several
pulleys mounted to the back of the spindle. Lathe tools are held manually
against the work, with the support of the tool rest. The tool rest is
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adjustable and is clamped to the bed at a position convenient for the
operation at hand.
1.2.2 Engine Lathe
Engine lathes are the classic metal turning workhorses of the
production machine shop. They come in many sizes and are adaptable to
working virtually any material. These machines have a longitudinal bed
to which is mounted a headstock and tailstock.
As in the wood lathe, the headstock contains the spindle. However,
the spindle drive is more complex, including variable speed capability or
selectable gearing to provide a much wider range of speeds.
A carriage moves back forth on bed ways for longitudinal turning.
A cross-slide and compound rest is mounted to the top of the carriage to
provide cross and angular cutting capability.
The lathe cutting tools are moved against the work manually using
hand wheels or automatically under the power of a lead screw that is
driven by gears in the headstock.
1.2.3 Tool Room Lathe
The tool room lathe is a small- to medium-sized engine lathe
specially designed for high-precision work. These machines find use in
tool and die shops, where custom parts and precision fixtures are
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produced, often in support of production machining operations. Tool
room lathes are manufactured with special attention to spindle accuracy,
smooth operation and precise alignment of the carriage and cross slide.
A tool room lathe is capable of better accuracy and precision than a
standard engine lathe.
1.2.4 Turret Lathe
Turret lathes are used in production machine shops where several
sequential operations are needed on single work piece. It is costly and
time consuming to remove a work piece from one machine and hold it in
another. Removing and reholding a work piece also introduces errors in
work alignment and machining accuracy.
The turret lathe has a rotating turret mounted to the carriage so
that as soon as an operation with one tool is completed, the turret is
indexed to bring another tool into working position. The part is then
machined again without having to remove it from the chuck or collet.
Eight or more different operations can be performed on a work piece
using this type of machine.
1.2.5 CNC Lathe
Computer numerically controlled lathes have largely supplanted
engine lathes in production machining environments. CNC lathes offer
the advantages of greater powered axis drives, feedback control to
monitor and maintain tool positioning and high-speed repeatability of
complex machine motions. Once a program is verified, an operation can
be quickly set up again without the need for tedious manual adjustments.
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CNC lathes excel at cutting curved contours without the need for
specially shaped tools. This is done by programmed variation of the
speed of two motion axes and the spindle simultaneously there it is an
operation that is impossible with an engine lathe.
1.2.6 Special Purpose Lathe
As the name implies, these lathes are used for special purposes
such as heavy-duty production of identical parts. In addition, these lathes
also perform specific functions that cannot be performed by the standard
lathes. Some examples of special purpose lathes include the bench-type
jewelers lathes, automatic lathes, crankshaft lathes, duplicating lathes,
multi spindle lathes, brake drum lathes, and production lathes among
others.
1.3 Components of a Lathe Machine
Generally, the lathe is mainly composed of the bed, headstock,
tailstock, and the carriage. Figure 2 shows the structure of a typical
engine lathe.
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Figure 2: Structure of a typical engine lathe.
1.3.1 Bed
The bed is the foundation of the working parts of the lathe to
another. The main feature of lathe machine construction is the ways
which are formed on its upper surface and run the full length of the bed.
The ways provide the means for holding the tailstock and carriage, which
slide along the ways, in alignment with the permanently attached
headstock. The bed allows the carriage and the tailstock to be in parallel
with the axis of the spindle. Moreover, the bed also serves as the base of
the lathe and is connected to the headstock.
1.3.2 Headstock
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The headstock is located on the operator’s left end of the lathe
bed. It contains the main spindle and oil reservoir and the gearing
mechanism for obtaining various spindle speeds and for transmitting
power to the feeding and threading mechanism. The headstock
mechanism is driven by an electric motor connected either to a belt or
pulley system or to a geared system. The main spindle is mounted on
bearings in the headstock and is hardened and specially ground to fit
different lathe holding devices. The spindle has a hole through its entire
length to accommodate long workplaces. The hole in the nose of the
spindle usually has a standard Morse taper which varies with the size of
the lathe. Centers, collets, drill chucks, tapered shank drills and reamers
may be inserted into the spindle. Chucks, drive plates, and faceplates
may be screwed onto the spindle or clamped onto the spindle nose.
1.3.3 Tailstock
The tailstock is located on the opposite end of the lathe from the
headstock. It supports one end of the work when machining between
centers, supports long pieces held in the chuck, and holds various forms
of cutting tools, such as drills, reamers, and taps. The tailstock is
mounted on the ways and is designed to be clamped at any point along
the ways. It has a sliding spindle that is operated by a hand wheel and
clamped in position by means of a spindle clamp. The tailstock may be
adjusted laterally by adjusting screws..
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1.3.4 Carriage
The carriage includes the apron, saddle, compound rest, cross
slide, tool post, and the cutting tool. It sits across the lathe ways and in
front of the lathe bed. The function of the carriage is to carry and move
the cutting tool. It can be moved by hand or by power and can be
clamped into position with a locking nut. The saddle carries the cross
slide and the compound rest. The cross slide is mounted on the dovetail
ways on the top of the saddle and is moved back and forth at 90° to the
axis of the lathe by the cross slide lead screw. The lead screw can be
hand or power activated. A feed reversing lever, located on the carriage
or headstock, can be used to cause the carriage and the cross slide to
reverse the direction of travel. The compound rest is mounted on the
cross slide and can be swiveled and clamped at any angle in a horizontal
plane. The compound rest is used extensively in cutting steep tapers and
angles for lathe centers. The cutting tool and tool holder are secured in
the tool post which is mounted directly to the compound rest. The apron
contains the gears and feed clutches which transmit motion from the
feed rod or lead screw to the carriage and cross slide.
2.0 How Lathe Machine Fails
2.1 Lathe Machine Failure Statistic
According to Saravanan (2003), all failures of lathe machine have
been grouped into four-failure modes viz., component damage, fuse
burnt, circuit fault and looseness. It can be observed that the dominant
failure mode is because of component damage. The components are
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electrical, electronics and of mechanical categories. The most of the
components are standard and bought-in components. Figure 2 shows the
histogram of lathe failure mode.
Figure 3: Histogram of lathe failure mode.
2.2 Cause of Lathe Machine Failure
There are so many situations where the lathe machine is working
improperly or fail. The operator should always do inspections on the
operation of lathe machine to ensure it is functioning in good condition.
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There are many reasons will cause failure case of lathe machine
occurs. Below is the some of the failures which commonly occurs in lathe
machine and their causes.
i. There is harmonic chatter in the work
The work is too thin for the length.
Bearings have failed or have insufficient preload.
ii. The knob or control is hard to turn
There are wood chips and dust in the thread.
The thread is stripped.
iii. The motor will not run
The motor is not plugged in.
A circuit breaker or fuse has blown.
The thermal switch in the motor has tripped.
A fuse has blown in the AC or DC variable-speed drive.
There is brownout or no electricity.
The motor winding has burned out.
iv. The tailstock or tool rest slides on the bed during turning
operations
The bed has grease or finish on it.
The hold-down mechanism needs adjustment.
v. The tool does not move smoothly on the rest
The tool rest is dry.
The tool rest needs dressing.
vi. Work slows down when apply a tool
The tailstock is loose.
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The belt is loose.
The key has come out of the motor or headstock pulley
vii. There is vibration
The work is out of balance.
A part is loose.
A belt is loose.
The motor or headstock pulleys are dirty or not concentric.
The pulleys are not in alignment.
The pulleys are out of balance.
There is a defective motor or a bent motor shaft.
The stand resonates.
3.0 Type of Maintenance for Lathe Machine
The engine lathe is a precision machine tool and must be treated
with great care. Regular cleaning and maintenance will help to assure
that the lathe will maintain its service life and accuracy for many years.
This unit will cover basic lathe maintenance. The procedures you find
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within this document should be able to be performed by apprentice or
beginning machine tool students. Lathe maintenance that requires more
extensive disassembly should only be done by, or under the supervision
of, qualified personnel.
3.1 Routine Maintenance
A lathe doesn't require a great deal of maintenance and even
thrives in an environment of downright neglect. There are some habits
operator can form and some things operator can do that will greatly add
to the life of the machine and to operator’s enjoyment of using it. The
first habit is to unplug the machine when you perform most maintenance.
Other habits follow different schedules. Routine maintenance will keep
the lathe machine running smoothly for years. Table 1 shows the routine
maintenance of a lathe machine.
Frequency Task ReasonEvery time you use a Morse-taper accessory
Wipe dust out of the taper socket with your finger and wipe the taper accessory.
The biggest cause of spindle damage is damaged tapers or taper seats due to dirt.
Every turning session Sweep or vacuum chips from the machine, then wax. All unpainted metal parts such as the bed, spindles, and tool rest. Oil plane bearings. If your machine has oil holes or cups, you should apply a few drops of high viscosity machine oil. Some older motors also have oil cups, which should be lubricated.
Wood is hygroscopic and even dry wood can promote rusting in the right conditions. If you turn green wood, this action is an absolute must. Plane bearings will run forever if lubricated. They require a film of oil; if they don’t have it, they will quickly fail.
Monthly Grease any zerk fittings. Some older
Grease is required on a regular basis to keep
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machines may have grease fittings for the headstock bearings and possibly the motor. They should be given one shot of grease. Do not overgrease. This should be a habit.
such bearings healthy.
Annually Clean all belt pulleys. Dirt and rubber buildup on pulleys causes vibration.
Every one to five years Check the belt for wear and the bearings for endplay and lubrication. On most lathes that are used a reasonable amount, this check should be done more frequently. Since the spindle has to be removed on most lathes to replace the belt, you might as well replace the bearings. On variable-width sheave machines, belt replacement will be required every year or two, so replacing the bearings may not make sense in this case.
A worm or loose belt causes vibration and poor power transmission. Dry bearings will soon fail.
Every decade regardless of use
Replace the belt and bearings.
Time alone will take its toll. Grease in sealed bearings will dry out, and rubber in belts gets hard and cracks.
Table 1: Routine maintenance of lathe machine.
3.2 Bearing Replacement
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With plane bearings, the lathe can run smoothly by oiling the
bearings on a daily basis. Most lathes today, even those found on the
used market, are equipped with ball bearings that are lubricated and
sealed for life. These bearings don't require any regular maintenance, but
they do need to be replaced every few years. The sides of ball bearings
are generally sealed with plastic, which retains the grease packed into
the bearing during assembly. Age and use take their toll on any grease,
even in a sealed-f or-life bearing. Eventually, the grease fails and the
bearing fails shortly thereafter.
3.3 Lubrication Application
If the operator is ever in doubt, always know that there is never a
time where the operator can use too much lubrication. Amongst the
gears and the pulleys, there is always can be added a bit of grease. This
will simply help keep the gears and pulleys running smoothly while also
ensuring that the gears don't break down to fast by being exposed to the
air and feel the effects of oxygenation. Eventually your gears and pulleys
are going to have to be replaced, because at some point they are going
wear away due to rust.
3.4 Drive Belts Inspection
The drive belts supply power from the motor to the spindle. Access
to the drive belts is gained by removing the end guard on the headstock.
Make sure that all power is locked out before removing any guards. Drive
belts come in matched sets and should only be replaced with a matched
set of belts. Visually inspect the drive belts for excessive wear and
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cracking. If notice that one or more of the drive belts appear to be
excessively worn or cracked, bring this to the attention of the instructor.
Check the belt tension by applying finger pressure to each belt at a point
midway between the two pulleys. For correct tension a deflection of
about 3/8 of an inch should be evident in each belt. If the amount of
deflection is more than 3/8 of an inch in any one or more of the belts,
bring this to the attention of the instructor.
3.5 Gib Adjustment
All lathes employ precision slide ways. The saddle, cross slide, and
the compound slide all ride along a box slide way or dovetail slide way.
After time the parts that ride along the slide ways begin to wear. To
compensate for this wear, machine tools are equipped with adjustable
parts called gibs that allow operator to eliminate the space that has been
created by the wear between the slide ways. There are two types of gibs,
which are straight gibs and tapered gibs. Straight gibs are adjusted by
screws spaced out along the length of the gib. The screws push the gib in
to create more contact with the sliding mechanisms. Tapered gibs use
two screws. The screws are located in each end of the tapered gib. One
screw acts as an adjustment while the other screw acts as a locking
mechanism. Because tapered gibs are wider on one end than the other,
they slide in or out creating more or less contact between the sliding
mechanisms.
3.6 Cross Slide Gib Adjustment
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Wear in the cross slide ways must be adjusted by using the screw
on the front face of the cross slide. The procedure is to first loosen the
similar gib screw on the rear face of the cross slide, then re-tighten the
front screw to lock or adjust the gib in its new position. After the
adjustment, traverse the cross slide over its entire travel to be sure of
smooth, even operation.
3.7 Compound Slide Gib Adjustment
Wear in the compound slide ways must be adjusted by using the
screw on the front face of the compound slide. The procedure is to first
loosen the similar gib screw in the rear face of the tool slide, then re-
tighten the front screw to lock or adjust the gib in its new position. After
making the adjustment, traverse the compound slide over its entire
travel to be sure of smooth, even operation.
3.8 Wipers Pads Cleaning
Most lathes are equipped with wiper pads. Wiper pads are typically
made of felt that will hold oil. Wipers are designed to keep out small
chips and dirt between the slides and the ways. Wipers are saturated
with oil to catch the fine particles of dirt or debris before they get
between the two sliding surfaces. The wipers should be removed,
cleaned, and re-saturated with oil regularly. You should never use
compressed air for cleaning a lathe. Compressed air will push the fine
particles trapped in the wiper between the mating surfaces of the slides,
causing premature wear on these precision surfaces.
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3.9 Tailstock Clamp Adjustment
The lock position of the bed clamp lever on the tailstock is
adjustable and should be located before top dead center. The lever is
adjusted by a self-locking bolt located on the underside of the tailstock
front clamp plate and between the bed way. Turn the bolt clockwise to
increase the clamping action. Lathes may also be equipped with an
auxiliary bolt on the tailstock. This bolt is used to give additional
clamping action when required. It does not require any adjustment.
3.10 End Gearing and Backlash Inspection
The end gearing on the lathe connects the spindle rotation with
the feed and threading rods. The gears supplied with a lathe allow the
operator to obtain an extensive range of feeds, metric threads, threads
per inch, module and diametral pitch threads. To cut threads over a
broad range, the lathe operator will need to make changes to the end
gear train. Basic lathe setup and operation includes being able to
properly change the gears in the train. Most lathes are equipped with
charts that explain the gear positioning for certain types and ranges of
threads. When the proper gears have been selected and set in the gear
train, the mounting or clamping bolts should be lightly snugged in place
with a strip of paper or feeler stock placed between the gears. The gears
should then be pushed together against the paper shim. The clamping
bolts should then be tightened. Remove the shim. The space left
between the gears, where the shim was placed, is known as backlash. On
most lathes the backlash amount should be between 0.007 and 0.011
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inches. If the gears are noisy, more backlash space should be made
between the gears. Finish the backlash adjustment by placing a small
amount of lubricant on the gear train.
4.0 Critical Parts and Troubleshooting
Problems with a lathe can be related to the motor, including it not
starting, and the machine slowing, tool chattering and broken work
pieces. These kinds of issues can be identified and corrected with some
troubleshooting. Table 2 shows the troubleshooting for lathe machine.
Problem Cause SolutionThere is harmonic chatter in the work.
The work is too thin for the length.
Bearings have failed or have insufficient preload.
Cradle the work in hand, use a heel cut with skew, use a gauge, or employ a steady rest.
Adjust the preload or replace the bearings.
The knob or control is hard to turn.
There are wood chips and dust in the thread.
The thread is stripped.
Clean the threads. If necessary, run a tap into the internal thread and run a die over the external thread.
Replace parts, helicoil the internal thread.
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The motor will not run.
The motor is not plugged in.
A circuit breaker or fuse has blown.
The thermal switch in the motor has tripped.
A fuse has blown in the AC or DC variable-speed drive.
There is brownout or no electricity.
The motor winding has burned out.
Plug in the motor.
Reset the breaker or replace the fuse.
Reset the thermal switch.
Replace the fuse.
Check with electric company.
Rewind or replace the motor.
The tailstock or tool rest slides on the bed during turning operations.
The bed has grease or finish on it.
The hold-down mechanism needs adjustment.
Clean with the appropriate solvent.
Adjust the hold-down mechanism.
The tool does not move smoothly on the rest.
The tool rest is dry.
The tool rest needs dressing.
Wax the too rest.
Dress and wax the tool rest.
Work slows down when apply a tool.
The tailstock is loose.
The belt is loose. The key has
come out of the motor or headstock pulley.
Tighten the tailstock.
Tighten the belt. Replace the key
and tighten the grub screw which locks it.
There is vibration. The work is out of balance.
A part is loose. A belt is loose. The motor or
headstock pulleys are dirty or not concentric.
The pulleys are not in alignment.
Round the work better with a band-saw or drawknife and change speed.
Find and tighten the loose part.
Replace the belt. Clean or replace
the pulleys. Adjust the
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The pulleys are out of balance.
There is a defective motor or a bent motor shaft.
The stand resonates.
pulleys. Have the pulleys
balanced. Repair or
replace the motor.
Put sand bags in or on the stand.
Table 2: Troubleshooting for lathe machine.
5.0 Safety
In machining operations, there is one sequence of events that one
must always follow: SAFETY FIRST, ACCURACY SECOND, AND SPEED
LAST. With this in mind, let's look at some of the more important safety
precautions that should be observed before and during lathe operations.
Carelessness and ignorance are two great menaces to personal
safety. Other hazards can be mechanically related to working with the
lathe, such as proper machine maintenance and setup.
5.1 Major Hazards
The major hazards in the operation of lathe include:
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Eyes injuries from flying pieces of metal.
Hand or foot injuries from dropping heavy objects such as chucks
or stock.
Catching clothing, shop rags, gloves, hands or arms in the lathe
parts or in the work.
Cutting hands on chips or sharp edges of the work.
Injuries from being struck by flying work or chips.
Back injuries from failure to use work handling equipment for
heavy chucks and stock.
Skin disease from coolant or cutting oils.
Reaching over or under rotating parts.
Lathe accidents are usually caused by:
Loose clothing snagging on the revolving work piece, the chuck, or
the work piece.
Flying chips entering the eye when turning cast iron or nonferrous
metals.
Contact of the hands or arms with the lathe dog, chuck or work
piece.
5.2 Safety Guidelines
All lathe operators must be constantly aware of the safety hazards
that are associated with using the lathe and must know all safety
precautions to avoid accidents and injuries.
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The operator should prepare himself by rolling up his shirt sleeves
and removing watches, rings, and other jewelry that might become
caught while he is operating the machine.
The operator should be sure to wear safety glasses or a face shield
of the approved type at all times when operating a lathe or when in the
area of lathes that are in operation.
The operator should be sure that the work area is clear of
obstructions that one might fall over or trip on.
On turret lathes, care must be taken not to catch loose or torn
clothing on a stock that is supported in the collet with chucks and
extends beyond the headstock of the lathe.
If a coolant or cutting oil is used, the operator should take care
when adjusting the splash pans to prevent the liquid from splashing on
the floor. The cutting oil or coolant can make the floor beneath the lathe
slippery and cause the operator to lose his balance and suffer injury.
The operator will keep the floor around the machine clear of oil or
grease to prevent anyone from slipping and falling into the machine.
The operator should use assistance when handling heavy or
awkward parts, stock, or machine accessories. Never remove chips with
your bare hands; a pair of pliers, a hook, or a brush should he used.
(Stop the machine while removing the chips.)
The operator should prevent long chips from being caught in the
chuck by using good chip control procedures. The operator should never
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try to stop the machine with his hands or body. The operator will turn the
machine off before talking to anyone. The operator should know how to
stop the machine quickly if an emergency arises. The operator must be
attentive, not only to the operation of the machine, but the events going
on around it.
The operator should be alert to the location of the cutting tool
while taking measurements or making adjustments to the machine. He
should see that the work and the cutting tools clear each other and that
they are clamped securely before starting the machine.
The operator will remove the centers and the cutting tools when
not being used, and always observe the specific safety precautions
posted for the machine in which you are operating.
6.0 Conclusion
Lathe machine is an extremely useful piece of equipment that can
be used in workshop. For those who do extensive lathing work, owning a
working lathe is very important. However, having said that, it is also
important to note that this piece of equipment is as dangerous as it is
useful. It may increase the range of jobs that you can do, but it can also
cause accidents. Thus, users should follow the safety guidelines when
using lathe machine. Besides that, there are many different lathe
problems that can occur while you are using this tool. Fortunately, most
of these problems can be avoided by following troubleshooting
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guidelines. A part of that, a lathe machine can perform more efficient and
longer by having suitable maintenance.
7.0 Reference
AIPD (1988) Lathe Operations – Subcourse OD1645. Edition 8.
Conover E. (2001) The Lathe Book: A Complete Guide to the Machine and Its Accessories. USA: The Taunton Press
Saravanan S., Yadava G. S., Rao P. V. (2003) Machine Tool Failure Data Analysis for Condition Monitoring Application. In: Proceedings of the 11th National Conference on Machine and Mechanism, 18-20 December, HT Delhi, New Delhi. Allied Publishers Pvt. Limited, pp 552-558
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