TOPIC:CENTRE LATHE,CONSTRUCTIONAL FEATURES PREPARED BY SOUNDHAR.A

Types of Lathe Classified according to size, design, method of drive & purpose Speed lathe Engine lathe Bench lathe Tool room lathe Semi automatic lathe Automatic lathe Special purpose lathe Copying lathe

Types of Lathe Speed lathe Head stock, tail stock & adjustable slide Lead screw, feed box & apron mechanism not provided Spindle - driven by high speed motor & stepped cone pulley Tool – fed by hand Suitable for wood turning, spinning & polishing work. Types are: Wood working lathe Metal spinning lathe Metal turning lathe Polishing lathe

Types of Lathe Engine Lathe Head stock, tail stock, carriage & bed Lead screw, feed box & apron mechanism are provided Tool fed cross wise or longitudinally by hand or automatically Types are: Step cone pulley drive lathe Geared lathe Variable speed lathe

Types of Lathe Bench Lathe Lathe mounted on a bench Has all parts like centre lathe Used for machining small parts

Types of Lathe Tool room lathe Necessary attachments for accurate & precision machining More range of speeds & feeds obtained Used in high precision works

Types of Lathe Semi – automatic lathe Operations - both manually & automatically Machining - carried out in proper sequence Turret head - number of tools are fitted Tail stock not used Used for mass production Speed & feed is high Types: Capstan lathe Turret lathe

Types of Lathe Automatic Lathe All works done automatically Cams are used for speed , feed & tool changes Initial setting of jobs & tools is enough – works carried out automatically Used for mass production

Types of Lathe Special purpose lathe Used to carry out specific operations only Types of lathe: Crank shaft lathe Wheel lathe – special purpose lathe Used for finishing the journals Turning the thread on rail road car & locomotive wheels Duplicating lathe

Types of Lathe Copying Lathe Tool follows a template through a stylus or tracer Tracer connected with cutting tool by hydraulic device Tools move according to tracer movement & do machining operations

Head Stock Mechanism Two types Back geared head stock All geared head stock

Back geared head stock Lever downward position Indirect Speed Lever upward position Direct Speed Lever downward position Indirect Speed Lock Pin Back gears Pinion Cone Pulley Bull gear

https://www.youtube.com/watch?v=34xmgMHjmY0 – Back geared

Back geared head stock  Reduces spindle speed - thread cutting & knurling operations Stepped cone pulley & Pinion gear P1 form one unit Mounted on spindle – rotates freely Bull gear  to lathe spindle Lock pin – lock or unlock bull gear G1 with cone pulley Back shaft – 2 gears B1, B2 – engaged or disengaged by lever L Speed can be adjusted by changing the flat belt on the steps of cone pulley Cont..

Back geared head stock Lever upward position Lever downward position Step cone pulley locked with main spindle Back gear not engaged 4 Direct speeds (high speed) Shifting the belt on 4 different cone pulleys Lever downward position Step cone pulley not locked with main spindle Back gear engaged 4 Indirect speed (low speed) - Power transmitted - P1  B1, B1  B2 , B2  G1 , G1 spindle Speed  at B1 (B1 > P1 ) B1, B2 – have same speeds Again Speed  at G1 (G1 > B2) Thus speed reduced by engaging back gear

All geared head stock Loose Pulley Fast Pulley 1 2 Intermediate Shaft Spindle Shaft Loose Pulley Fast Pulley 1 2 Intermediate Shaft 3 4 Head stock Casting 5 6 Splined head stock spindle Live Center 9 8 7

All geared head stock Better compared to other types Spindle rotates – constant speed motor – thru belt Various speeds – diff gear combination - change lever position – diff spindle speeds Head stock has 3 main parts Splined shaft – rotated by motor 3 gears G1, G2, G3 - shifted by lever along shaft Intermediate shaft 3 gears G4, G5, G6 - cannot be moved axially Splined spindle 3 gears G7, G8, G9 - can be moved axially Nine diff speeds can be obtained Contd..

All geared head stock Nine diff speeds obtained by meshing the gears individually Gears G1, G2, G3 with G4, G5, G6 Gears G7, G8, G9 with G4, G5, G6 When G1 meshed with G4, same time G7 meshed with G4 speed of __ x __ Contd.. G1 G4 G4 G7

All geared head stock __ x __ __ x __ G7 G1 G4 G2 G5 G3 G6 G8 G9

Feed Mechanism Feed – Movement of tool relative to work piece Transmit motion - spindle  carriage Rotary motion  linear motion Longitudinal feed – moving carriage - automatic Cross feed – moving cross slide - automatic Angular feed – moving compound slide Mechanisms for automatic feed: Tumbler gear reversing mechanism Quick change gear box Tumbler gear quick change gear box Apron mechanism

Tumbler Gear Reversing Mechanism

Tumbler Gear Reversing Mechanism

Tumbler Gear Reversing Mechanism Change the direction of lead screw & feed rod while cutting thread – moving carriage Two same sized pinions – mounted in bracket Bracket pivoted – move up & down by lever L A, B – tumbler gears C – spindle gear – attached to lathe spindle D – stud gear – attached to lead screw through set of intermediate gear (E) E-Intermediate gear F- Lead Screw gear Cont..

Tumbler Gear Reversing Mechanism Lever upward A engaged with C Motion transmitted through C, A, D, E, F gears Lead screw & spindle – rotate – anti-clock wise Carriage moves towards head stock – L  R Lever downward B engaged with C Motion transmitted through C, B, A, D, E, F gears Lead screw– rotate –clock wise Carriage moves towards tail stock – L  R Lever neutral Tumbler gears wont engage with spindle No motion transmitted Lead screw will not rotate

Quick change gear box Different feeds Power from lathe spindle  feed shaft through tumbler gear change gear quick change gear box Shaft A (diff sizes of gears) – keyed with cone gear Shaft B ( one gear) – receives 9 diff speeds from shaft A thru sliding gear Shaft B - shaft C thru 4 cone gears Hence shaft C gets 9x4 = 36 diff speeds Shaft C – lead screw thru clutch Shaft C – feed rod thru gear train

Quick Change Gear box

Quick change gear box Spindle Tumbler Gear Cone gear Shaft A Sliding key Clutch handle Lead screw Shaft B Feed Shaft Sliding gear Shaft C

Apron Mechanism Transforming rotary motion of feed rod & lead screw into motion of carriage Power - spindle  Lead screw & feed rod thru tumbler gear Power - feed rod  worm wheel thru gears A, B, C & worm wheel Worm wheel attached with splined shaft Splined shaft always engage with F & G F & G – keyed to feed check shaft Feed check shaft fitted to knob E – 3 positions

Apron

Apron Mechanism Knob E – neutral position Knob E – Push in position No power transmitted - Hand feed given Longitudinal feed – rotate longitudinal feed hand wheel Cross feed – rotate cross slide hand wheel Half nut engaged for thread cutting by half nut lever Knob E – Push in position Rotating gear G – engage with H Power  pinion Automatic longitudinal feed takes place Knob E – Pull out position Rotating gear F – engage with K Power  cross feed screws Automatic cross feed takes place

Apron Mechanism - Neutral Cross slide Cross slide screw Bed Rack Pinion Lead Screw Half nut A C Lever Worm wheel H B Feed shaft G worm D K Splined shaft F Longitudinal feed hand wheel Feed check shaft E Cross slide hand wheel

Apron Mechanism – Push in Longitudinal feed Cross slide Cross slide screw Bed Rack Pinion Lead Screw Half nut A C Lever Worm wheel H B Feed shaft G H worm D Splined shaft K F Longitudinal feed hand wheel Feed check shaft E Cross slide hand wheel

Apron Mechanism – Pull Out Cross feed Cross slide Cross slide screw Bed Rack Pinion Lead Screw Half nut A C Lever Worm wheel H B Feed shaft G worm D K Splined shaft F Longitudinal feed hand wheel Feed check shaft E Cross slide hand wheel

Work Holding Devices Chuck Centers Face Plates Angle plate Mandrel Steady & follower rest

Work Holding Devices

Chuck Attached to head stock spindle Hold small length work pieces & irregular shape work pieces Work pieces are held in jaws of the chuck Types Three jaw chuck or self centering Four jaw chuck or independent chuck Magnetic chuck

Chuck - Types Three jaw chuck or self centering (hold regular shaped work piece) Has 3 jaws – move in equal distance – radial direction – chuck key 9 circular discs Front – Spiral scroll Back – bevel teeth – 3 bevel pinions fitted Chuck key turned – bevel pinion & disc rotate Four jaw chuck or Independent chuck (hold regular or irregular shaped work piece) Has 4 jaws – each moved individually Each jaw fitted to screw with the help of slots at backside The screws have square hole at the top to receive chuck key & can be rotated When chuck key turned in the slot, the particular jaw will only move So, irregular shape work piece & large work piece can be held Magnetic chuck Has a flat surface Chuck has magnetic power – electromagnet Work piece held on chuck by magnetic power Only magnetic material can be held on the chuck

Three jaw chuck or self centering Has 3 jaws – move in equal distance – radial direction – chuck key 9 circular discs Front – Spiral scroll Back – bevel teeth – 3 bevel pinions fitted Chuck key turned – bevel pinion & disc rotate Used to hold regular shaped work piece – round & hexagonal

Three jaw chuck back

Four jaw chuck or Independent chuck Hold regular / irregular shaped work piece Has 4 jaws – each moved individually Each jaw fitted to screw - slots at backside Screws - square hole at the top to receive chuck key & can be rotated When chuck key turned in the slot, the particular jaw will only move So, irregular shape work piece & large work piece can be held

Four jaw chuck back

Magnetic Chuck Has a flat surface Chuck has magnetic power – electromagnet Work piece held on chuck by magnetic power Only magnetic material can be held on the chuck

Centers Hold & centering the work pieces Conical end - machined to 60º Shank – made by taper turning Live center - Center in head stock Dead center - Center in tail stock

Dog Carrier or Catch Plate Hold job & work piece in b/w the centers Catch plate – circular disc – screwed on spindle Tail part  catch plate When spindle rotates, work pieces also rotate thru catch plate & carrier arrangement

Dog Carrier or Catch Plate

Face Plate Hold irregular shaped work pieces Screwed – spindle – when spindle rotates, face plate too rotates It’s a circular disc – has 4 T-slots & a number of plain radial slots Slots –hold work pieces

Face Plates

Angle Plate Made of cast iron- has 2 machined surfaces @ right angle to each other Has holes & slots One face - work piece Other face - face plate When spindle rotates, face plate with angle plate & work piece will also rotate Angle plate used for holding elbow pieces

Mandrel Hold hollow work pieces Mandrel inserted into the hollow work pieces – held b/w live center & dead center Different types of mandrels are used for diff types of jobs

Plain Mandrel

Mandrel

Mandrel

Steady Rest Has a cast iron base – rest on guide ways of lathe bed Top – hinged @ one end for removing job without disturbing steady rest Work piece – held b/w 3 jaws – move radially & separately Turning operation - 2 stages - carriage will not pass So, work piece turned to 1st half , then reversing it to second half

Follower Rest Has a C type casting 2 adjustable jaws – support work piece Follower rest mounted on saddle – move together with tool Used to give continuous support to work piece

Lathe Operations Centering Straight Turning Grooving Parting Off Rough Turning Finish Turning Shoulder Turning Facing Chamfering Knurling Forming Grooving Parting Off Eccentric Turning Drilling Reaming Boring Milling Grinding

Lathe Operations

Centering Producing conical shape holes – ends of work piece (Longer work pieces) Centers marked at the ends - centre punch Work piece - chuck & rotated Drill bit - tail stock – fed into the work piece by turning the hand wheel

Straight Turning Producing cylindrical surface by removing the material from outside diameter of the work piece Work piece held b/w live & dead centers Right hand turning tool clamped on tool post Work piece rotated Tool fed parallel to lathe axis also depth of cut given to tool Two types of turning Rough Turning Finish Turning

Straight Turning - Types Rough Turning Feed rate – fast (0.3 mm – 1.5 mm per revolution) Depth of cut – heavy (2 mm – 5 mm) Finish Turning Feed rate – slow (0.1 mm – 0.3 mm per revolution) Depth of cut – small (0.5 mm – 1 mm)

Shoulder Turning Operation - shoulder of stepped diameter work piece Right hand facing tool – square shoulder Round nose tool – radius shoulder Types of shoulders Square Bevelled Filleted Grooved

Facing Making flat surface at the end of work piece Work piece held in chuck or b/w centers Work piece rotated Facing tool fed perpendicular to lathe axis

Chamfering Making bevelled surface or to turn a slope at the end of the work piece It is done after knurling, rough turning & thread cutting Remove burrs & sharp edges Work piece rotated – tool fed perpendicular to the lathe axis

Knurling Produce impression (any shape) on the outer surface of work piece Give good gripping surface Knurling tool - two hardened steel rollers with cutting teeth Tool held in tool post & pressed against the rotating work piece – moved parallel to lathe axis Speed & feed should be very low

Forming Making concave, convex or any other irregular shape on the work piece Cutting tool should be made to the required form Work piece held b/w centers & form tool moved perpendicular to the revolving work piece

Grooving Reducing the diameter of work piece over a very narrow surface Also called recessing, undercutting or necking Work piece held in chuck Grooving tool fed against revolving work piece

Parting Off Process of cutting of work piece after the completion of all machining operations Parting tool is used Work piece held in chuck & rotated Carriage locked at the required position Spindle speed reduced Tool fed slowly perpendicular to lathe axis

Eccentric Turning Making of eccentric Set up Operation Center of one cylinder is out of the center of other cylinder – crank shaft, cam shaft, eccentric on a shaft Two set of center holes (offset from the normal axis of the work piece) are drilled – end of work piece Amount of offset = half of eccentricity required Operation Work piece - one axis of rotation – in b/w centers One cylindrical surface turned Work piece removed & held in other axis of rotation for turning the other cylindrical surface

Drilling Producing cylindrical hole in a work piece Methods used for making a drill First method Work piece - chuck or face plate Drill bit - tail stock spindle Tail stock clamped near work piece Work piece rotated & drill bit fed into the work piece – turning tail stock hand wheel Second method Drill held in chuck Work piece - pad supported by tail stock spindle Work piece fed by tail stock hand wheel while the drill bit is revolving

Drilling

Reaming Operation of finishing & sizing of already drilled hole – dimensionally more accurate Tool – Reamer – has multiple cutting edges Work piece - chuck & revolves slowly Reamer – tail stock – fed into the work piece for reaming

Reaming & Remears

Boring Enlargement of hole Done when correct size drill bit not available Work piece - chuck/face plate - rotated Boring tool - tool post - fed parallel to lathe axis Boring tool - smaller holes Boring bar - larger holes

Milling Removing metal – rotating cutter (multiple cutting edges) Work piece - vice Vice - compound rest Milling cutter rotated Work piece fed by moving carriage

Slab Milling & Face Milling

End Milling

Grinding Removing metal – grinding wheel External grinding Work piece revolved b/w centers Grinding wheel – compound rest – tool post – fed against the work piece Internal grinding Work piece – chuck or face plate Grinding wheel – tool post – compound rest Feed - carriage Depth of cut given by cross slide