engine lathe

7/31/2019 Engine Lathe

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Engine Lathe

Functions and ControlsIntroduction

WARNING:

Machine tools present a safety hazard.

Improper operation can result in severeinjury. These topics are for non-laboratorystudy only and are not to be used inconjunction with the operation of any tool or

machine described herein. Never use amachine tool without the supervision of aqualified instructor.


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This topic discusses thevarious FUNCTIONSandPARTSof the engine latheincluding its SIZEandMOVEMENTS. The WAYS,MOTOR, HEADSTOCK,

SPINDLE, CARRIAGE, andTAIL STOCKare introducedand the HEADSTOCKADJUSTMENTSand itsSPEEDand FEED RATESareexplained. Use of theCENTER, DOG, FACEPLATE,STEADY REST, FOLLOWERRESTand TAPERATTACHMENTSare alsomentioned.


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1: The Function of the Lathe

The main function of theengine lathe is to holdand rotate the work pieceto perform a machiningoperation. Machining

operations include facing,turning, drilling, reaming,form threading, boring,multiple diametersturning, knurling and

more. This silent videoshows a few boring,facing, and turningoperations
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2: The Parts of the Lathe

Many topics will refer tothe parts of the lathe.Therefore it is importantto be able to identify the

basic parts of an enginelathe; the headstock,spindle, tail stock, quill,ways, bed, carriage,

apron, saddle, crossslide, compound slide,tool post, feed rod, andlead screw.
http://www.jjjtrain.com/vms/Media/lathe_functions/lathe_parts_E320.wmv


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3: Movements of the Lathe

The lathe has many moving partsall with a special functions. Youshould understand the names andmovements of the parts of thelathe.

The spindle rotates in both

directions. The tail stock can bepositioned along the ways and thequill moves within the tail stock.The carriage also moves along theways. The cross slide movesperpendicular to the ways. Thecompound slide moves at anypreset angle over the saddle. Thelead screw and feed rod alsorotate and are reserved for certainautomatic functions.
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4: Ways, Motor, and Headstock

To keep some of the mechanisms moving longitudinally straight and true, ways aremachined on the top surface of the bed. Ways are ground and often hardened . Theycan be shaped like an inverted "V", flat, or other shapes that the manufacturerdecides to use. The carriage and tail stock mechanisms are aligned on the ways.(figure 1).

Modern machines are called gear-head lathes because the entire system of speedand feed adjustments are gears just like the transmission of an automobile. The

headstock contains the heart of the lathe and includes the motor and gear train(figure 2). The motor is normally below the headstock and connected by a belt orgears (figure 3) to the spindle and lead screws.
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5: The Spindle

which facilitate turning, boring, facing,etc. The spindles have variousconfigurations that you should beaware of.

The Threaded type spindle nose(figure 1) is the oldest type and has notaper to assist in mounting a chuck or

attachment and is screwed on thespindle until the end bears on thespindle flange.

The tapered key type spindle (figure 2)is assisted by a taped nose, a key onthe nose and secured with a threadedcollar.

The cam-lock type spindle nose (figure

3) has a short taper that accuratelypositions the spindle mounting and hascam studs that fit into a ring of holesand cam-locked by turning a chuckkey. This is the most common spindlenose found on lathes today.
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6: Spindle RPM

The headstock levers on amodern gear head lathe allowquick changes in speeds and feed(figure 1). Index plates areavailable on or below theheadstock noting where variouslevers must be positioned toachieve the proper speed or feedor thread turning. Index platesusually show positions for bothinch and metric threads. Moreabout this on page 8.

In the past spindle speed werechanged manually by movingdrive belts from pulley to pulley asshown in the image of this oldLogan lathe (figure 2)
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7: Starting and Stopping the

Spindle To start or stop the spindle a non-rotating

starting/stopping shaft runs from theheadstock for the full length of the bed. It willhave at least one handle attached like theone shown in the photo. On the machineshown, pulling up on the handle from theneutral position starts the spindle in thecounterclockwise direction (the correctdirection for 99% of lathe operations). Forthe same handle, in the neutral position, aslight shift to the right and pushing down onthe handle will cause the spindle to rotateclockwise. For both scenarios a movementback to the neutral position will turn off themotor. The spindle will then coast down to astop. This lever actuated starting andstopping of the spindle is very common.

Most free standing lathes (not bench lathes)

have a foot brake like the one shown.Pressing on the foot brake turns off themotor and applies a braking pressure to thespindle. The advantage of the foot brake isinstant stopping and, therefore, addedsafety.


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8: Setting Speeds and Feeds

To machine various types of materials, hold tight tolerances andproduce good surface finish , the spindle RPM must be properlyselected. Selection of spindle speed is accomplished by

manipulating the appropriate levers. Speeds are calculated byformulas. It is important for the operator to know the horsepower ofthe lathe's motor to select speeds and feeds within the machine'slimits.
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As with spindle speeds, correct feed rates must also be calculated.

Feed rates can be set by locating the settings panel (index plate) on the lathe. In thisvideo 0.002 per revolution is selected. Four levers and one dial must be set to A E V3 X. The next feed rate selected is 0.040 per revolution which requires a setting of BE R 7 X. Both feedrates were with the same spindle RPM. Changing spindle RPMdoes not change the feed rate.

Nearly every gear head engine lathes use a method similar to this video for settingspindle speeds. First you will have to locate the spindle speed read out on themachine. Now select an RPM from those available. In the video 370 RPM is selectedwhich requires the two levers shown to be in the correct position. The next speedselected is 36 RPM

The correct RPM is calculated from a known cutting speed (CS) in Feet Per Minute(FPM). The CRS is dependent on he material and should be looked up in theMachinery's Handbook. The formula is RPM = (CSx4)/diameter. Typical CS foraluminum is 250 and for mild steel it is 80. Therefore a 6" dia bar of mild steel shouldbe turned at (80x4)/6= 53 RPM.

The correct feed rate in Inches Per Revolution (IPR) is calculated from chipload.Chipload is the amount the cutter is buried into the part and varies from tool to tool.R.S.

Do not confuse feed "speed" with feed "rate". Feed rate is the amount the tool movesfor each revolution of the spindle. If the spindle is turning very slowly the tool feedspeed will be slow. If the spindle is turning very fast the tool feed speed will be very

fast. In both cases the tool feed rate is identical. R.S.
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9: The Carriage

The carriage is a combination offive main parts; the saddle, thecross-slide, the apron, thecompound rest and the tool rest(left top). The purpose of thiscombination is to hold a cutting

tool securely while at the sametime moving it (feeding) towhatever position is necessary tomachine the work piece.

The Apron is the front vertical faceof the carriage. It is a covering

plate or a casting that housesgears, clutches and levers. Theapron has an autofeed knob, ashift-feed knob (left middle), and athreading nut engagement handle(left bottom).
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The autofeed handle willengage or disengage allfeed motions. The shift-

feed handle will changethe feed from the carriageto the cross slide or visaversa. Somewhere on theheadstock there will be a

feed-reversing handle.This handle changes thedirection of rotation of thefeed rod, thus reversingthe feed direction of the

cross slide and thecarriage. The threadengagement handleengages the threading nut.


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10: The Tail Stock

The tail stock and the headstock areopposite one another and in normalconditions are aligned on the same center(figure 1 ). For cutting a taper the tail stockcan be adjusted off center. The tail stock ispositioned behind the carriage and mountedon the same ways as the saddle. It can belocked in any position on the ways (figure 2).There are two units to a tail stock; the base

and the head (figure 3). To set the tail stock;on or off center there are offsetting adjustingscrews on the base. The head consist of thequill (ram or spindle are also names used),quill lock, hand wheel, and a clamp lever ornut. A clamp lever or nut is used to tightenthe tail stock in position on the ways (thelonger handle in figure 2 is the clamp leverthat pulls upward against the clamp barely

visible below the tail stock in figure 4.). Thequill has a standard Morse internal taper forholding a center, Jacobs chuck or any othertool that has a standard external Morsetaper (figure 5). Graduations have beenengraved on the quill spindle to measure thelength that the ram has project from thehead.

Figur

e1

Figure 1
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Figure 2 Figure 3

Figure 4 Figure 5


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11: Centers, Dogs, and Faceplate

To hold a work piece directly in the center of the spindle and be true to (in line with)the spindle a center can be used. There are three types of centers; the live center(figure 1), the dead center (figure 2), and the half center (discussed below). A livecenter rotates on internal bearings. A dead center does not rotate. A dead center

creates friction and must be lubricated (the live center rotates with the part and doesnot create friction). All centers are 60 degrees at the tip. To assure that the center isholding the work piece correctly, a special hole is center drilled at the end of the workpiece that matches the shape of the center. Faceplates (figure 3) are also calledDriver Plates. They are circular with a slot or a series of slots for bolts or to hold thebent-tail of a lathe dog (figure 4). To turn a shaft that is being held by centers a dog isused with a faceplate. Faceplates are also available with T-slots for clamping.

Figure 1 Figure 2
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Special circumstances require special tools. The half center is justsuch a tool. It is used to provide special clearance for lathe tooling.With this setup you can see how the live center in the tail stockinterferes with the tool bit. With the half center installed the tool bithas clearance. Half centers are always dead centers. Remember tokeep them greased as they do not turn freely like a live center.
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12: Threading, Steady Rest, Follower Rest, and TaperAttachment

Forming threads by singlepointing on the lathe requiresrepetitive cutting. To assurerecurring cuts in the samelocation, a thread-chasing dial

or a high-speed threadingattachment is used. Theseattachments are normally onthe side of the apron (imageright). The thread-chasing dialengages with the leads crew

and is used to indicate when toengage the half nut to permitthe cutting tool to follow exactlyin the original cut.
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Steady Rest

A steady rest is used when a long work

piece must be supported during amachining operation. Specifically amachining operation at he end of the workpiece. The steady rest is clamped to the

ways of the lathe and adjustable restpoints are adjusted to perfectly center thepart while, at the same time, supportingthe part during machining.
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Follower Rest

A follower rest performs somewhat like a steady

rest except that the follower rest attaches to thesaddle. This allows the follower rest to "follow"along with the carriage during automatic feed.The front side of the rest is open and the top

rear and bottom has adjustable rest points (thebottom rest point is not visible in this video).This type of rest is especially useful for

machining along the length of a long bar.Without the follower rest the bar would bepushed inward and away from the cutting tool(more at the center of the length than at either

end).
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Note: it is important to realizethat removing stock on the barremoves contact by the restpoints and they will have to be

readjusted after each pass.

Taper Attachment

The taper attachment is used tocreate a taper on a work piece.The taper attachment isattached to the back ways of thelathe. An adjustable block isclamped to the cross slide andthe block moves at a fixed rateaccording to the desired taperthat has been set. The taper is

turned as the longitudinal feed isengaged.


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13: Sizing a Lathe

Engine lathes vary in size. Their size is identified by the largest workpiece diameter that can be turned without hitting some part of thelathe. This diameter is referred to as the "swing". Size is also

determined by the longest part that can fit between centers. So a13x72 lathe has a 13" swing and can accommodate a 72" long workpiece. (figure 1). A typical lathe has a 13 inch swing, 6 foot long bed,and capacity to turn work 36 inches between centers. Small benchengine lathes have a 9 inch or less swing and have a 20 to 40 inchbetween centers.


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Many lathes have a removable section of the ways thatprovides for turning lager diameters near the head.These are commonly called "gap lathes". There isanother unique lathe that is also called a "gap lathe"

(figure 2). This lathe can turn larger diameter work than astandard engine lathe of comparable size. The gap lathehas a bed which slides aft (right in the picture), opening agap near the head. Distance between centers when thebed is fully retracted is 50 percent more than when the

bed is in its normal position.

engine lathe

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