The centre lathe

THE CENTRE LATHETHE CENTRE LATHEPARTSPARTS

OPERATIONSOPERATIONSACCESSORIESACCESSORIES

SAFETY SAFETY PRECAUTIONSPRECAUTIONS

• Always know the quickest way to stop the machine.

• Never leave the chuck key in the chuck• Clean the machine after every use.• Oil the necessary parts before use.• Never make any adjustment while the

machine is running.• Never leave tools or scrap metals on the

machine.

Diagram used for illustrationDiagram used for illustration

LATHE TOOLSLATHE TOOLS

Lathe tools maybe made of any of the following materials:

• Plain carbon steel• High speed steel• Stellite • Cemented carbide• Diamond

TOOL FORMSTOOL FORMS

BUTT BRAZED TOOLSThese are made by brazing or welding a

piece of H.S.S. to a high tensile steel shank.

TOOL FORMSTOOL FORMS

TIPPED TOOLThese have a hip of cemented carbide, etc.

brazed to a blank of high steel. They are very economical.

TOOL FORMSTOOL FORMS

TOOL BITSThese fit in a special holder that grips the

tool at an angle of 15 degrees. This provides easy height adjustment.

TOOL SHAPESTOOL SHAPES

The shape of the tool and the angles of its ground faces will depend on;

• The operation to be performed.• The material which has to be machined.• The power and rigidity of the lathe• The amount of material to be removed.• The quality of finish desired.

TYPICAL TOOL TYPICAL TOOL SHAPESSHAPES

TYPICAL TOOL TYPICAL TOOL SHAPESSHAPES

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TYPICAL TOOL TYPICAL TOOL SHAPESSHAPES

TOOL ANGLESTOOL ANGLES

A large tool angle• Gives maximum strength.• Helps heat dissipation.• Increases the power needed to force the

tool into the work.

TOOL ANGLESTOOL ANGLES

A small tool angle• Weakens the cutting edges.

• Gives a good finish.• Gives little tearing.• Gives easy cutting.

TOOLSTOOLS

NB. The harder and tougher the material, the more it will be for the cutting edge of the tool to penetrate the metal, and at the same time retain its sharpness.

Tool Angles.Tool Angles.

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PARTING OFF TOOLPARTING OFF TOOL

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STRAIGHT TOOL HOLDERSTRAIGHT TOOL HOLDER

This carries one tool which is held in position by two or three set bolts. It is locked in position by one large nut or lever. Adjustment is made for height by means of parallel packing pieces.

STRAIGHT TOOL HOLDERSTRAIGHT TOOL HOLDERAdvantages• Sturdy and reliable• The rake and clearance angles are not

affected when adjusting to center height.

Disadvantages• Needs packing pieces for height adjustment.• Will carry only one tool at a time

TOOL HOLDERTOOL HOLDERThis is a multi-tool post and holds four tools

at the same time. It is locked in by a single hand lever. The holder swivels about its centre bolt so that each tool in turn can be brought into position.

THE MULTI-TOOL HOLDERTHE MULTI-TOOL HOLDER

Advantages• Carries four tools at the same time.• Height adjustment does not affect tool

angles.

Disadvantages• Needs packing for height adjustment.

AMERICAN TYPE HOLDERAMERICAN TYPE HOLDER

This is usually on small lathes. Adjustment for height is made by swiveling the boat or rocker.

Advantages• Height adjustment is easily made.

Disadvantages• Only one relatively small bolt to lock the

tool box in position.• The size of the tool that can be used is

limited by the width of the slot.

AMERICAN TYPE HOLDERAMERICAN TYPE HOLDER

CENTERING THE WORKCENTERING THE WORK

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ACCESSORIESACCESSORIES

TOOLS THAT ARE USED ON THE CENTRE LATHE TO ENHANCE SOME PROCESSES.

CENTERSCENTERS

These are machined with a morse taper, fit into the morse taper sockets of the head stock and tail stock spindles. Work to be turned may be held between the two centers or with chuck and tail stock in center. They are usually made of H.C.S but H.S.S, though expensive, is sometimes used for heavy or high speed work.

DEAD OR LIVE CENTERSDEAD OR LIVE CENTERS

The dead center fits into the tail stock and the live center fits into the head stock. Both have a 60 degree included angle at the point, although this is sometimes increased to 90 degrees for heavy work.

LIVE CENTRELIVE CENTRE

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HALF CENTERHALF CENTER

This is used in the tailstock to allow the tool to clear the center and give more room for facing up after the work has been mounted between centers.

BALL CENTERBALL CENTER

This is sometimes used for tapering by the “set-over tail stock” method. The standard centers cannot sit squarely in the center hole when the tail stock is set over.

THE LUBRICATION OF CENTERSTHE LUBRICATION OF CENTERS

Centers can be lubricated using the following:

• Tallow • Granite• Grease

COLLET CHUCKSCOLLET CHUCKS

These are used to hold work to be turned very firmly and will rotate it with a high degree of accuracy.

COLLET CHUCKSCOLLET CHUCKS

CHUCKS AND KEYSCHUCKS AND KEYS

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FACE PLATEFACE PLATEThis is a circular slotted casting which

screws onto the spindle nose. It is used for holding work that cannot be held conveniently in the 3 or 4 jaw chucks or by centers. Sometimes an angle plate has to be used in the set-up, particularly when two faces have to be machined at right angles to each other.

FACE PLATEFACE PLATE

TRAVEL STEADYTRAVEL STEADY

This is bolted to the cross slide or carriage of the lathe and is used to support long slender work to stop the metal from bending under the pressure of the cut.

TRAVEL STEADYTRAVEL STEADY

FIXED STEADYFIXED STEADYThis is bolted to the lathe bed and is used to

support work that projects a long way out of the chuck. It is often used as an end support for long bars too big in diameter to go through the head of the machine, so that end of the bar may be machined. Grease is necessary where the jaws make contact with the work.

FIX STEADYFIX STEADY

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FIXED STEADYFIXED STEADY

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FIX STEADY IN USEFIX STEADY IN USE

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FIXED STEADY AT WORKFIXED STEADY AT WORK

PARTS OF THE LATHEPARTS OF THE LATHE

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THETHE BEDBEDThis is a casting, supported on rigid legs and very accurately machined on the top faces. Different lathes have differently spaced beds.

THE GAP BEDTHE GAP BEDMany lathes are provided with a

gap in the bed at the headstock end to accommodate work that is short and larger in diameter than can be swung over the bed.

THE GAP BEDTHE GAP BED

BACK GEARBACK GEARWhere a belt drive is used, a range

of low speeds is given often by means of a back gear. If the lathe has three pulleys, thus giving a range of three spindle speeds, back gear will provide three lower speeds.

BACK GEARBACK GEAR

THE CARRIAGETHE CARRIAGE

This is a casting machined on the underside to fit the bed and along which it slides. Fixed to the front of the carriage is the apron, behind which lies the mechanism for controlling the movement of the carriage and the cross slide.

CARRIAGECARRIAGE

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THE RACKTHE RACK

This is fitted to the underside of the bed front. The carriage handle and spindle are linked to the rack by gears so that when the handle is turned the carriage moves along the bed.

THE HEADSTOCKTHE HEADSTOCK

This is the casting fixed to the left hand end of the bed.

THE HEADSTOCKTHE HEADSTOCK

THE CROSS SLIDETHE CROSS SLIDE

This is mounted on the carriage and can be moved at right angles to the bed by means of a hand wheel at the front.

COMPOUND SLIDE OR COMPOUND SLIDE OR TOPSLIDETOPSLIDE

This is mounted on the cross slide. It is located by heavy dowel pin, on which it swivels. The top of the cross slide is marked in degrees so that the compound slide can be turned and locked at any desired angle.

SPEED CHANGINGSPEED CHANGING

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TAILSTOCK OR LOOSETAILSTOCK OR LOOSEHEADSTOCKHEADSTOCK

This is a casting that can be moved along the bed and locked in any desired position by means of a locking nut or lever.

TAILSTOCKTAILSTOCK

TAILSTOCK OR LOOSE TAILSTOCK OR LOOSE HEADSTOCKHEADSTOCK

LEAD SCREW LEAD SCREW AND AND

FEED SHAFTFEED SHAFT

Running the length of the bed is the lead screw, a threaded rod which can be turned at different speeds by means of a gear box or gear train.

This screw has threads of either square or acme.

LATHE OPERATIONSLATHE OPERATIONS• Facing• Parallel turning• Tapering• Knurling• Screw threading• Drilling • Boring • Parting off

TAPER TURNING.TAPER TURNING.

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DRILLING ON THE LATHEDRILLING ON THE LATHE

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BORING ON THE LATHEBORING ON THE LATHE

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KNURLINGKNURLING

Knurling may be defined as the process of checking the surface of a piece by rolling depressions into the surface.

KNURLING TOOLKNURLING TOOL

Most knurled jobs in machine-shop are of the pattern as fine, medium, coarse, straight, and diamond. The knurls are small wheels with the marking cut in their faces and all are hardened.

KNURLSKNURLS

(1) and (4) coarse pattern, (2) and (5) medium, (3) and (6) fine, (1), (2), and (3) diamond, (4), (5), and (6) straight.

KNURLING OPERATIONKNURLING OPERATION

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Lathe Operations.Lathe Operations.• .

Lathe Tools At WorkLathe Tools At Work

Cutting Speed.Cutting Speed.• All materials have an optimum All materials have an optimum

Cutting Speed and it is defined Cutting Speed and it is defined as the speed at which a point on as the speed at which a point on the surface of the work passes the surface of the work passes the cutting edge or point of the the cutting edge or point of the tool and is normally given in tool and is normally given in meters/min.meters/min.

Cutting Speed.Cutting Speed.

Where: Where: N = Spindle Speed (RPM)N = Spindle Speed (RPM)CS = Cutting Speed of Metal CS = Cutting Speed of Metal (m/min)(m/min)d = Diameter of Work piece. d = Diameter of Work piece.

Recommended Cutting Recommended Cutting Speeds.Speeds.

MaterialMaterial Cutting SpeedCutting Speed

Mild steelMild steel 18 to 2518 to 25

stainless steelstainless steel 12 to1812 to18

aluminiumaluminium Up to 300Up to 300

Cutting fluids in Cutting fluids in common use.common use.

• WaterWater• It has a high specific heat but is It has a high specific heat but is

poor in lubrication and also poor in lubrication and also encourages rusting. It is used as a encourages rusting. It is used as a cooling agent during tool grinding. cooling agent during tool grinding.

• They are used for heavier cutting operations because of their good lubricating properties and are commonly found in production machines where high rates of metal removal are employed. Mineral oils are very suitable for steels but should not be used on copper or its alloys since it has a corrosive effect.

Mineral Oils.Mineral Oils.

• Oil will not dissolve in water but Oil will not dissolve in water but can be made to form an intimate can be made to form an intimate mixture or emulsion by adding mixture or emulsion by adding emulsifying agents. The oil is then emulsifying agents. The oil is then suspended in the water in the form suspended in the water in the form of tiny droplets. These fluids have of tiny droplets. These fluids have average lubricating abilities and average lubricating abilities and good cooling properties.good cooling properties.

Soluble Oils.Soluble Oils.

Vegetable Oils.Vegetable Oils.• They are good They are good lubricants but are of lubricants but are of little used since they little used since they are liable to decompose are liable to decompose and smell badly.and smell badly.