Lathe Machine

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.

1

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

2

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

3

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.

4

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.

5

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

6

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..

7

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

8

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.

9

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.

10

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

11

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

12

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

13

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

14

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

15

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.

16

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

17

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.

18

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

19

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:

20

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.

21

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

22

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

23

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

24