PRINCIPLE OF LATHE MACHINE

THE LATHE IS A MACHINE TOOL WHICH HOLDS THE W/P B/W TWO RIGID & STRONG SUPPORTS CALLED CENTRES OR IN A CHUCK OR IN FACE PLATE WHICH

REVOLVES. THE CUTTING TOOL IS HELD AND FED AGAINST THE REVOLVING WORK.CUTTING TOOL FED EITHER PARALLEL OR AT RIGHT ANGLES TO THE AXIS

OF W/P. OR MAY ALSO AT AN ANGLE

LATHE SPECIFICATION• A-SWING• B-DISTANCE B/W CENTERS• C-LENGTH OF BED• D-RADIUS(ONE HALF OF SWING

PRINCIPLE PARTS OF LATHE

PRINCIPLE PARTS OF LATHE

1-BED AND WAYSBED IS THE MAIN BODY OF THE LATHE MADE FROM STURDY CAST IRON. THE WAYS ARE

GROUND SURFACES ON THE TOP SIDE OF BED ON WHICH THE CARRIAGE AND TAILSTOCK RIDE

HEADSTOCK & SPINDLE• THE HEADSTOCK COMPRISES THE RECTANGULAR METAL CASTING AT THE LEFT END

OF THE LATHE .• IT CONTAINS THE SPINDLE SHAFT AND IT SUPPORTS BEARINGS AND HIGH/LOW

SPEED SHIFT LEVER AND GEARS.• SPINDLE IS THE MAIN ROTATING SHAFT ON WHICH THE CHUCK IS MOUNTED IT

SUPPORTED BY PRECISION THRUST BEARINGS.

CARRIAGE AND SADDLE• THE CARRIAGE SUPPORTS THE CROSS-SLIDE, COMPOUND AND TOOL POST.• MOVES ALONG THE WAYS UNDER MANUAL OR POWER FEED.• SADDLE RIDES ACROSS THE TOP OF THE WAYS AND THE APRON• SADDLE SUPPORTS THE CARRIAGE HAND WHEEL• CARRIAGE HAND WHEEL MOVES THE CARRIAGE ALONG THE WAYS BY MEANS OF A RACK AND

PINION DRIVE .

CROSS-SLIDE AND COMPOUND • THE CROSS SLIDE IS A DOVETAILED SLIDE THAT MOVES AT A RIGHT ANGLE TO THE WAYS.• THE COMPOUND SITS ON THE TOP OF THE CROSS SLIDE AND CAN BE ROTATED TO SET THE

TOOL TO ADVANCE AT AN ANGLE TO THE W/P.

TOOLPOST AND TOOLS• THE TOOLPOST CAN HOLD UP TO 4TOOLS AT ONCE ,EACH LOCKED IN PLACE BY HEXAGONAL

HEAD CAP SCREWS.• THE TOOLPOST ROTATE ALONG A LARGE BOLT ON THE TOP OF THE COMPOUND SLIDEAND IS

LOCKED IN PLACE BY CLAMPING LEVER.• TOOL CAN BE READYMADE CARBIDE TIP TOOLS.

TYPES OF LATHE

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

toolrooms, and job shops– Primarily for single piece or short runs– Manually operated

Special Types of 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

Special Types of Lathes

• Single- and multiple-spindle automatic lathes– Six or eight different operations may be performed on

many parts at the same time– Will produce parts for as long as required

• Tracer lathes– Used where a few duplicate parts required– Hydraulically operated cross-slide controlled by stylus

bearing against round or flat template

Special Types of Lathes• Conventional/programmable lathe

– Operated as standard lathe or programmable lathe to automatically repeat machining operations

– 2-axis (DRO) so can see exact location of cutting tool and workpiece in X and Z axes

• Computerized numerically controlled lathes– Cutting-tool movements controlled by computer-controlled program to

perform sequence of operations automatically

Work Holding Devices

THREE JAWS CHUCK- For holding cylindrical stock centered.- For facing/center drilling the end of your aluminum stock

FOUR JAWS CHUCK- This is independent chuck generally has four jaws , which are adjusted individually on the chuck face by means of adjusting screws

• Thin jobs can be held by means of

magnetic chucks.

Collet Chuck

Magnetic Chuck

Collet chuck is used to hold small workpieces

Thin jobs can be held by means of magnetic chucks.

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

LATHE DOGS• LATHE DOGS ARE CAST METAL DEVICES USED TO PROVIE A FIRM

CONNECTION BETWEEN THE HEADSTOCK SPINDLE AND THE W/P MOUNTED BETWEEN CENTRES.

Tail

Tail

MANDRELS• MANDRELS IS USED TO HELD THE HOLLOW/DRILLED W/P.•

Workpiece Mandrel

RESTS

• LONG W/P NEED EXTRA SUPPORT THAT TEND TO SPRING AWAY FROM THE TOOL BIT. WE USE THE REST FOR PROVIDE SUPPORT.

Jaws

HingeWork Work Jaws

Lathe bed guideways

Carriage

FACE PLATES• A LATHE FACE PLATE IS A FLAT ROUND PLATE THAT THREADS TO THE

HEADSTOCK SPINDLE TO THE LATHE.• THE FACEPLATE IS USED FOR IRREGULARLY SHAPED W/P THAT CANNOT

SUCCESFULLY HELD BY CHUCKS.

Work

piece

Lathe Operations• Turning: produce straight, conical, curved, or grooved workpieces

• Facing: to produce a flat surface at the end of the part or for making face grooves.

• • Boring: to enlarge a hole or cylindrical cavity made by a previous process

or to produce circular internal grooves.• • Drilling: to produce a hole by fixing a drill in the tailstock • • Threading: to produce external or internal threads• • Knurling: to produce a regularly shaped roughness on cylindrical surfaces

Lathe Operations

CUTTING PARAMETERS IN LATHE

CUTTING SPEED V=ΠDN/1000• Where D= diameter of w/p in mm N= r.p.m.MACHINING TIME T= l/Fn• Where l=length of w/p f=feed in mm/rev. N=r.p.m. DEPTH OF CUT t= (D-d)/2, where d=diameter of w/p after machiningMETAL REMOVAL RATE(MRR) = ΠDtfN

REFERENCES

• Book• Manufacturing Science-II BY- K.M. MOEED

• Website• www. engbasics.com • www. efunda.com