Lathe

History• Lathe forerunner of all machine tools

• First application was potter's wheel– Rotated clay and enabled it to be formed into

cylindrical shape

• Very versatile (many attachments)– Used for turning, tapering, form turning, screw

cutting, facing, drilling, boring, spinning, grinding and polishing operations

• Cutting tool fed either parallel or right angles

Special Types of Lathes

• Engine lathe– Not production lathe, found in school shops,

toolrooms, and jobbing shops– Basic to all lathes

• Turret lathe– Used when many duplicate parts required– Equipped with multisided toolpost (turret) to

which several different cutting tools mounted• Employed in given sequence

Engine Lathe

• Accurate and versatile machine• Operations

– Turning, tapering, form turning, threading, facing, drilling, boring, grinding, and polishing

• Three common– Toolroom– Heavy-duty– Gap-bed

Lathe Size and Capacity

• Designated by largest work diameter that can be swung over lathe ways and generally the maximum distance between centers

• Manufactured in wide range of sizes– Most common: 9- to 30- in. swing with

capacity of 16 in. to 12 feet between centers– Typical lathe: 13 in. swing, 6 ft long bed, 36 in.– Average metric lathe: 230-330 mm swing and

bed length of 500 – 3000 mm

Indicated by the swing and the length of the bed

Lathe Size

Parts of the Lathe

Bed

Headstock

QuickChangeGearbox

Tailstock

Carriage

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Setting Speeds on a Lathe

• Speeds measured in revolutions per minute– Changed by stepped pulleys or gear levers

• Belt-driven lathe– Various speeds obtained by changing flat belt

and back gear drive

• Geared-head lathe– Speeds changed by moving speed levers into

proper positions according to r/min chart fastened to headstock

Safety Note!! NEVER change speeds when lathe is running.

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Lathe Accessories

• Divided into two categories– Work-holding, -supporting, and –driving devices

• Lathe centers, chucks, faceplates

• Mandrels, steady and follower rests

• Lathe dogs, drive plates

– Cutting-tool-holding devices• Straight and offset toolholders

• Threading toolholders, boring bars

• Turret-type toolposts

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Lathe Centers

• Work to be turned between centers must have center hole drilled in each end – Provides bearing surface

• Support during cutting

• Most common have solid Morse taper shank60º centers, steel with carbide tips

• Care to adjust and lubricate occasionally

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Chucks

• Used extensively for holding work for machining operations– Work large or unusual shape

• Most commonly used lathe chucks– Three-jaw universal– Four-jaw independent– Collet chuck

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Three-jaw Universal Chuck• Holds round and hexagonal work• Grasps work quickly and accurate within

few thousandths/inch• Three jaws move

simultaneously whenadjusted by chuck wrench– Caused by scroll plate into

which all three jaws fit

• Two sets of jaw: outside chucking and inside chucking

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Four-Jaw Independent Chuck

• Used to hold round, square, hexagonal, and irregularly shaped workpieces

• Has four jaws– Each can be adjusted independently by chuck

wrench

• Jaws can be reversed to hold work by inside diameter

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Headstock Spindles

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Universal and independent chuck fitted to three types of headstock spindles

1. Threaded spindle nose– Screws on in a

clockwise direction

2. Tapered spindle nose– Held by lock nut

that tightens on chuck

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Headstock Spindles

3. Cam-lock spindle nose• Held by tightening cam-locks using T-wrench• Chuck aligned by taper

on spindle nose

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Registration lines on spindle nose

Registration lines on cam-lock

Cam-locks

Cam-lock mating stud on chuck or faceplate

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Collet Chuck

• Most accurate chuck

• Used for high-precision work

• Spring collets available to hold round, square, or hexagon-shaped workpieces

• Each collet has range of only few thousandths of an inch over or under size stamped on collet

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Collet Chuck

Special adapter fitted into taper of headstock spindle, and hollow draw bar having internal thread inserted in opposite end of headstock spindle. It draws collet into tapered adapter causing collet to tighten on workpiece.

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Types of Lathe Dogs

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• Standard bent-tail lathe dog– Most commonly used for round

workpieces– Available with square-head

setscrews of headless setscrews

• Straight-tail lathe dog– Driven by stud in driveplate– Used in precision turning

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Types of Lathe Dogs

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• Safety clamp lathe dog– Used to hold variety of work– Wide range of adjustment

• Clamp lathe dog– Wider range

than others– Used on all shapes

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Left-Hand Offset Toolholder

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• Offset to the right

• Designed for machining work close to chuck or faceplate and cutting right to left

• Designated by letter L

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Right-Hand Offset Toolholder

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• Offset to the left• Designed for machining work close to the

tailstock and cutting left to right– Also for facing operations

• Designated by letter R

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Straight Toolholder

• General-purpose type

• Used for taking cuts in either direction and for general machining operations

• Designated by letter S

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Toolholders for Indexable Carbide Inserts

• Held in holder by cam action or clamps

• Types available– Conventional

– Turret-type

– Heavy-duty toolposts

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Cutting-Off (Parting) Tools

• Used when work must be grooved or parted off

• Long, thin cutting-off blade locked securely in toolholder by either cam lock or locking nut

• Three types of parting toolholders– Left-hand– Right-hand– Straight

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Threading Toolholder

• Designed to hold special form-relieved thread-cutting tool

• Has accurately ground 60º angle– Maintained throughout life of tool

• Only top of cutting surface sharpened when becomes dull

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Super Quick-Change Toolpost

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Depth of Cut

• Depth of chip taken by cutting tool and one-half total amount removed from workpiece in one cut

• Only one roughing and one finishing cut – Roughing cut should be deep as possible to

reduce diameter to within .030 to .040 in. (0.76 to 1 mm) of size required

– Finishing cut should not be less than .005 in.

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Example: Depth of cut on a lathe

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Safety

• Be aware of safety requirements in any area of shop

• Always attempt to observe safety rules

• Failure results in:– Serious injury– Resultant loss of time and pay– Loss of production to company

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Safety Precautions

• Lathe hazardous if not operated properly

• Important to keep machine and surrounding area clean and tidy

• Accidents usually caused by carelessness

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Safety Precautions

• Always wear approved safety glasses

• Rollup sleeves, remove tie and tuck in loose clothing

• Never wear ring or watch

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Safety Precautions

• Do not operate lathe until understand controls• Never operate machine if safety guards

removed• Stop lathe before measure work or clean, oil

or adjust machine• Do not use rag to clean work or machine

when in operation– Rag can get caught and drag in hand

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Safety Precautions

• Never attempt to stop a lathe chuck or driveplate by hand

• Be sure chuck or faceplate mounted securely before starting– If loose, becomes dangerous missile

• Always remove chuck wrench after use– Fly out and injure someone– Become jammed, damaging wrench or lathe

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Safety Precautions

• Move carriage to farthest position of cut and revolve lathe spindle one turn by hand– Ensure all parts clear without jamming– Prevent accident and damage to lathe

• Keep floor around machine free from grease, oil, metal cuttings, tools and workpieces– Oil and grease can cause falls– Objects on floor become tripping hazards

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Safety Precautions

• Avoid horseplay at all times

• Always remove chips with brush– Chips can cause cuts if use hands– Chips become embedded if use cloths

• Always remove sharp toolbit from toolholder when polishing, filing, cleaning, or making adjustments

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Objectives

• Mount and/or remove lathe centers properly

• Align lathe centers by visual, trial-cut, and dial-indicator methods

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Lathe Centers

• Work machined between centers turned for some portion of length, then reversed, and other end finished

• Critical when machining work between centers that live center be absolutely true– Concentric work

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To Mount Lathe Centers

• Remove any burrs from lathe spindle, centers, or spindle sleeves

• Clean tapers on lathe centers and in headstock and tailstock spindles

• Partially insert cleaned center in lathe spindle• Force center into spindle• Follow same procedure when mounting

tailstock center• Check trueness of center

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To Remove Lathe Centers

• Live center– Use knockout bar pushed through headstock

spindle (slight tap)– Use cloth over center and hold to prevent damage

• Dead center– Turn tailstock handwheel to draw spindle back

into tailstock• End of screw contacts end of dead center, forcing it

out of spindle

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Grinding Lathe Cutting Tool

• Wide variety of cutting tools for lathe– All have certain angles and clearances regardless

of shape

Shape and Dimensions of General-purpose Lathe Toolbit

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To Grind a General-Purpose Toolbit

1. Dress face of grinding wheel2. Grip toolbit firmly, supporting hands on grinder

toolrest3. Hold toolbit at proper

angel to grind cuttingedge angle

• Tilt bottom of toolbittoward wheel and grind 10º side reliefor clearance angle

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Cutting edge ~ ½ In long and extend over ¼ width of toolbit

10º side relief or clearance angle

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4. While grinding, move toolbit back and forth across face of wheel

• Prevents grooving wheel

5. Toolbit must be cooled frequently during grinding

• Never overheat toolbit!• Never quench stellite or cemented-carbide

tools• Never grind carbides with aluminum oxide

wheel

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6. Grind end cutting edge so it forms angle of a little less than 90º with side cutting edge

– Hold tool so that end cutting edge angle and end relief angle of 15º ground at same time

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70º to 80º Point Angle

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7. Using toolbit grinding gage, check amount of end relief when toolbit is in toolholder

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Knurling

• Process if impressing a diamond-shaped or straight-line patter into the surface of the workpiece– Improve its appearance– Provide better gripping surface– Increase workpiece diameter when press fit

required

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Knurling

• Diamond- and straight-pattern rolls available in three styles– Fine

– Medium

– Course

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Knurling Tool

• Toolpost-type toolholder on which pair of hardened-steel rolls mounted

Knurling tool withone set of rolls inself-centering head

Knurling tool with three sets of rollsin revolving head

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Universal Knurling Tool System

• Dovetailed shank and as many as seven interchangeable knurling heads that can produce wide range of knurling patterns

• Combines in one tool– Versatility– Rigidity– Ease of handling– Simplicity

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Procedure to Knurl in a Lathe

1. Mount work between centers and mark required length to be knurled

• If work held in chuck for knurling, right end of work should be supported with revolving tailstock center

2. Set lathe to run at one-quarter speed required for turning

3. Set carriage feed to .015 to .030 in.

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4. Set center of floating head of knurling tool even with dead-center point

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5. Set knurling tool at right angles to workpiece and tighten it securely

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6. Start machine and lightly touch rolls against work to check tracking

7. Move knurling tool to end of work so only half the roll face bears against work

8. Force knurling tool into work approximately .025 in. and start lathe

OR

Start lathe and then force knurling tool into work until diamond pattern come to point

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9. Stop lathe and examine pattern10. Once pattern correct, engage automatic

carriage feed and apply cutting fluid to knurling rolls

11. Knurl to proper length and depth• Do not disengage feed until full length has

been knurled; otherwise, rings will be formed on knurled pattern

12. If knurling pattern not to point after length has been knurled, reverse lathe feed and take another pass across work

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Grooving

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Square

Round

V-shaped

• Done at end of thread to permit full travel of nut up to a shoulder or at edge of shoulder for proper fit

• Also called recessing, undercutting, or necking

• Rounded grooves used where there is strain on part

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Procedure to Cut a Groove

1. Grind toolbit to desired size and shape of groove required

2. Lay out location of groove

3. Set lathe to half the speed for turning

4. Mount workpiece in lathe

5. Set toolbit to center height

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6. Locate toolbit on work at position where groove is to be cut

7. Start lathe and feed cutting tool toward work using crossfeed handle until toolbit marks work lightly

8. Hold crossfeed handle in position and set graduated collar to zero

9. Calculate how far crossfeed screw must be turned to cut groove to proper depth

10. Feed toolbit into work slowly using crossfeed handle

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11. Apply cutting fluid to point of cutting tool• To ensure cutting tool will not bind in

groove, move carriage slightly to left and to right while grooving

• Should chatter develop, reduce spindle speed

12. Stop lathe and check depth of groove with outside calipers or knife-edge verniers

Safety note: Always wear safety goggles when grooving on a lathe

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Threads

• Used for hundreds of years for holding parts together, making adjustments, and transmitting power and motion

• Art of producing threads continually improved

• Massed-produced by taps, dies, thread rolling, thread milling, and grinding

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Threads

• Thread– Helical ridge of uniform section formed on

inside or outside of cylinder or cone

• Used for several purposes:– Fasten devices such as screws, bolts, studs, and

nuts– Provide accurate measurement, as in micrometer– Transmit motion– Increase force

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Thread Terminology

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