- Practice · 6 marks
Work holding and tool mounting on lathe
Short answer
Work holding: three-jaw chuck for rounds, four-jaw for irregular, collet for precision, face plate for odd shapes, between centres with driver for long shafts, mandrel for bored parts, steady and follower rests for support. Tools are clamped in a tool post at centre height with minimal overhang and set square to the workpiece.
Describe the devices used to hold work on a centre lathe. How are cutting tools mounted and set on the lathe?
Work holding devices
| Device | Description and use |
|---|---|
| Three-jaw self-centring chuck | Jaws move together by a scroll; holds round and hexagonal bars quickly; accuracy is moderate |
| Four-jaw independent chuck | Each jaw moves separately; holds square, irregular or eccentric jobs; can be set accurately with a dial indicator |
| Collet chuck | Split sleeve gripping small bars of exact size; very accurate, used in production |
| Face plate | Large disc with slots; irregular jobs are bolted to it with clamps and angle plates |
| Between centres | A job with centre holes is supported between the headstock (live) centre and the tailstock (dead) centre and driven by a lathe dog and driver plate; for long shafts |
| Mandrel | A tapered rod pressed into a bored job so that the outside is turned concentric with the bore |
| Steady rest and follower rest | Support long, slender jobs to prevent bending; the steady rest is fixed on the bed, the follower rest travels with the carriage |
Mounting and setting of tools
- The tool is clamped in the tool post (four-way turret post or quick-change post); the overhang is kept as small as possible for rigidity.
- The cutting tip is set exactly at the height of the job's centre line, by checking against the tailstock centre, with a steel rule held against the job, or by a trial cut. A tool set above centre has less clearance and rubs; a tool set below centre has less effective rake and the work tends to climb over the tool.
- Packing (shims) is placed under the tool to raise it; the tool must be firmly clamped.
- The tool is set at right angles to the job for turning and facing; for threading, the tool is set square to the job with a thread gauge (centre gauge).
- The depth of cut is set with the cross-slide dial, whose graduations show the tool movement; the reduction in diameter is twice the depth of cut.
✓ Answer checked by Claude Opus 5.5 (high effort)
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