GS, SCTCE

LATHE

GS, SCTCE

GS, SCTCE

• Probably the oldest machine tool• Removes undesired material from a

rotating w/p in the form of chips with the help of a tool

• Tool can be traversed across the w/p• Can fed into the w/p• Produce cylindrical & plane surfaces• Also produce tapers• Parts as small as that used in

watches to huge parts

GS, SCTCE

Lathe Specification• Height of the centres measured above lathe bed• Maximum dia that can be rotated above the bed ways• Dia over carriage• Distance between two centres• Bed length• Range of spindle speed• Range of metric threads that can be cut• Gear ratio• Power rating of electric motor

GS, SCTCE

IMPORTANT PARTS1) BED

• Base or foundation of lathe• Rigid casting made in one piece• Holds and supports all other parts of lathe• Top portion is planed to form guide ways for the

carriage & tail stock• Usually made of cast iron

GS, SCTCE

2) HEAD STOCK• Permanently fastened to the inner ways at left hand end of

the bed• Serves to support spindle and driving arrangements• Lathes receive their power through the head stock

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3)TAIL STOCK

•T2:reduction gear box (optional) •T3:body •T4:adjustable base •T5:spindle •T1:feed screw •T6:locking lever

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• Situated right end of the bed• Support right end of work• Also used for holding and feeding tools such as

drill, reamers, taps etc.• Body is adjustable on the base & can be moved

to and fro

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4) CARRIAGE

1: Tool post,2: top-slide,2a: top-slide feed screw and dial,2b: Compound portion of top-slide (protractor),3: cross-slide,3a: cross-slide scale,3b: cross-slide feed screw and dial,4: saddle,5: apron,5a: carriage hand wheel,5b: half-nuts lever,5c: feed lever

GS, SCTCE

• Carriage controls & supports the cutting tool• Located between head stock & tail stock• Moved manually or with power• SADDLE :-• H-shaped casting fitted over bed• it moves along guide ways• CROSS SLIDE :-• Carries compound rest & tool post• COMPOUND REST :-• Supports tool post• May be swiveled on the cross slide to any angle in the horizontal plane• Used during taper turning • TOOL POST :-• Hold various cutting tools• APRON :-• Fastened to the saddle• Hangs over the front of the bed• Has gears, levers & clutches to move the carriage• Converts rotary motion of the feed shaft or the lead screw to translatory motion

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WORK HOLDING DEVICES

• 1:- CHUCK

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• Hold w/p of short length, large dia or irregular shape

• a) 4 JAW CHUCK• Also called independent chuck• Each jaw can be independently actuated• Used for irregular shapes and if we have to drill a hole at

the centre• b) 3 JAW CHUCK• Also called universal chuck• All the 3 jaws move simultaneously• Used for holding round, hexagonal and symmetrical w/p

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6 JAW CHUCK

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• C) COLLET CHUCK• Used for holding bars of small size• Available in square, round, hexagonal etc.

GS, SCTCE

GS, SCTCE

GS, SCTCE

• d) MAGNETIC CHUCK• Electrically operated or permanent magnetic type• Not having wide spread use

GS, SCTCE

2:- LATHE CENTRES• Used during turning operations• Made of very hard materials to take-up the thrust during machining• a) Ordinary centre• Used for most general works• b) Tipped centre• Carbide or hard alloy tip• Wear resistant• c) Ball centre• Offers minimum strain & wear• Used for taper turning• d) Revolving centre• Friction less• It is supported in the bearings housed in the body• Supports heavy jobs & jobs that revolve at high speed• e) Pipe centre• For supporting pipes & hollow end w/p• f) Insert type centre• Economical

GS, SCTCE

GS, SCTCE

GS, SCTCE

3:- CARRIERS• Also called driving dogs• Used to drive the w/p when it is held btwn

two centres• Attached to the end of w/p by a set screw4:- FACE PLATE• Mounting w/p on face plate provides an ideal

way of supporting certain type of works• Either screwed or bolted to the threaded stock

spindle

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GS, SCTCE

GS, SCTCE

GS, SCTCE

5:- MANDREL• Hardened piece of round bars with centres at each ends

• Used for holding & obtaining a hollow piece of work• Made of high carbon steel to avoid distortion & wear

GS, SCTCE

GS, SCTCE

Types of Mandrels• a) plain• Suitable for one size bore• b) Stepped• Having steps of different diameter• c) Screwed• Used for mounting w/p with internal threads• d) Cone • Used for w/p of different hole diameter• e) Expansion• Mandrels with slots• f) Taper shank

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6:- STEADY REST• Used when long w/p is machined by holding it in the

chuck• Avoids undue deflection of the job at the other end

• 7:- FOLLOWER REST• Performs same function as that of steady rest• But it moves along the w/p as it is attached to the saddle• It supports the work opposite to the tool and counteracts

the cutting force

GS, SCTCE

GS, SCTCE

GS, SCTCE

GS, SCTCE

GS, SCTCE

GS, SCTCE

LATHE OPERATIONS

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TURRET & CAPSTON LATHE• They are the natural evolution of engine lathe• Advantage of this type is the multiple tool holders which

enable the setting up of all the tools for a job• Simple tailstock is replaced by with a rotating or indexing

hexagonal or capstan head on which several tools can be mounted

• 14 tools can be mounted at a time• Movement of tool can be adjusted by stops• In turret lathe, turret is mounted directly onto the auxiliary

slide• In capstan lathe, turret is carried on a separate ram which

can be moved to and fro

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GS, SCTCE

GS, SCTCE

TURRET : -• Six sided block• Carried on the bed for holding and moving the tools• Each face of hexagonal turret is provided with tapped holes for

various attachments• In capstan, turret is not hexagonal but circular with six holes

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LIMITATIONS OF CENTRE LATHE• NOT SUITABLE FOR BATCH AND MASS PRODUCTION• Increased tool change over time• Skilled labour requirement• Only one tool can be used in normal case• Proper care is needed for accuracy

GS, SCTCE

ADVANTAGES OF CAPSTON & TURRET LATHES

• Multiple tool availability• Different work holding methods• Automatic feeding of tools• Automatic stopping of the tools at precise location• Automatic control in operation• Head stock has more & heavier range of speeds• High production rate• Semi skilled labors can do the work• More rigid in holding works and tools• Two or more operations can be done at a time

GS, SCTCE

GS, SCTCE

GS, SCTCE

GS, SCTCE

GS, SCTCE

GS, SCTCE

AUTOMATIC LATHES

• Lathes that have their tools automatically fed to work and withdrawn after the cut is complete are known as automatic lathes

• used when repeated operations have to be done• Produce identical parts without operator• Increased productivity• Reduce unit cost• Better utilization of resources• High accuracy• Reduced inventory• Opportunity of unattended production• Less labour requirement

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• can be used continuously 24 hours a day, • only need to be switched off for occasional maintenance. • Less skilled/trained people can operate• can be updated by improving the software • can be programmed by advanced design software enabling the

manufacture of products that cannot be made by manual machines

• Modern design software allows the designer to simulate the manufacture of his/her idea.

• There is no need to make a prototype or a model. This saves time and money.

• One person can supervise many CNC machines• Sometimes only the cutting tools need replacing occasionally.

GS, SCTCE