METAL CUTTING: Lathe

METAL CUTTING: Lathe

1. Lathe components

   • BED
     • Gray cast for vibration dampening
   • HEADSTOCK ASSEMBLY
     • Includes:
       • spindle
       • Transmission
       • Drive motor
   • TAILSTOCK ASSEMBLY
     • Includes
       • Longitudinal way clamp
       • Transverse way clamp
       • Quill for cutting tools
       • Live centers or dead centers
   • QUICK CHANGE GEARBOX
     • Powers carriage assembly movement with lead screw
   • CARRIAGE ASSEMBLY
     • Fixed to cross slide, holds tool post at variable orientations. Provides longitudinal and transverse movement of tooling
   • WAYS
     • Provides precise guidance to carriage assembly and tailstock
   • TOOL FEED MECHANISMS
     • cause the cutting tool to move when engaged
   • lead screw cause the apron and cutting tool to advance quickly
     • used for cutting threads
   • Feed rod moves the apron and cutting tool slowly forward
     • used for most turning
   • chuck is self centering
     • 3 locator pieces or 4 independent magnetic

2. TYPES OF LATHE MACHINES

   • engine
     • simplest and most versatile. Manually operated and requires skilled operators
     • Suitable for low and medium production and for repair work
   • turret
     • capable of carrying our multiple cutting operations on the same workpiece
     • Several cutting tools are mounted and rapidly used against to the workpiece one by one by indexing the turret.
     • For high production work
   • CNC
   • Specialised
     • multiple spindles
     • multiple fixed tools
     • copying lathes
     • vertical lathes

3. TURNING PARAMETERS

   • REVOLUTION SPEED
     • Rotating speed of the spindle and the workpiece
     • N- rpm or rev/min
   • CUTTING SPEED
     • Surface speed of the work piece at the cutting point
       • every piece has a different cutting speed
     • V - mm/rev
   • DIAMETER
     • size of the workpiece at the cutting point
     • D - mm
   • V=N*PI()*D(ave.)
   • DEPTH OF CUT
     • the thickness of the layer being removed from the workpiece
     • d - mm
   • FEED
     • Movement of tool per revolution
     • f - mm/rev
   • FEED RATE
     • Linear speed of tool along the workpiece
     • fr - mm/min
   • MATERIAL REMOVAL RATE (MRR)
     • Volume of material removed from workpiece per unit of time
     • MRR - mm^3/min
   • CUTTING TIME
     • Time taken to complete cutting process
     • T - min
   • LENGTH OF CUTTING
     • cutting distance
     • L - mm
   • MMR = V*f*d
   • T = L/fr = L/N*f

4. CUTTING CONICAL SHAPES

   • called a taper
   • use a form tool
     • specifically designed for one cut
   • compound slide method
     • compound slide is set to travel at half of the taper angle
     • tool is fed across the work by hand
   • Off-set tail stock
     • normal rotating part of the lathe still drives the workpiece but the centre at the tailstock is off-set
     • limited to small tapers
     • tailstock off-set h = L*sin(alpha)
       • alpha is the half of the taper angle
       • L is the workpiece length
   • Using Lathe Copying Attachments
     • attaches to the compound rest and moves along side of a template

5. CUTTING SCREW THREADS

   • cut with a single-point cutting tool
   • for large threads
   • in radial cutting, the tool is fed directly into the workpiece

Images and files in the map