UNIT-II TURNING MACHINES Work Holding Devices And Thread Cutting Methods PREPARED BY SOUNDHAR.A
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
Thread Cutting Setup Producing helical groove on a cylindrical work piece Feed – lock nut, lead screw Longitudinal feed = pitch of the thread Pitch – ratio b/w spindle & longitudinal feed Lead screw & spindle – connected by change gears
Thread Cutting Operation Carriage lead screw by engaging half nut When spindle rotates, lead screw will be rotated at the same speed Pitch of work = pitch of lead screw
Thread Cutting Driver Headstock Spindle Work Tailstock Spindle Threading tool Changing gears Carriage Driven Lead screw Movement of carriage tool
Gear Trains Driver
Gear Trains Second stud First stud Driver A B Intermediate gears C Driven Lead screw
Lathe Attachment Milling attachment Copying attachment Grinding attachment Taper turning attachment
Grinding Attachment Attached to cross slide Work piece & grinding wheel rotate External grinding Work piece – b/w centers - & rotated Internal grinding Work piece – chuck & rotated Feed – moving carriage Depth – moving cross slide
Grinding Attachment Work Belt drive Head stock Chuck Grinder spindle
Milling Attachment 1st method 2nd method Milling cutter – chuck – rotated Work piece – cross slide Work fed against rotating milling cutter Depth – vertical adjustment of work piece Used to cut key ways & grooves 2nd method Milling mounted on carriage Work piece – held b/w centers – not rotated Cutter driven by motor vertically Feed given by carriage
Milling Attachment Vertical slide Clamping screw Packing piece Swivel base Cross slide Chuck End mill Work Carriage Bed