Tool materials, rake and clearance angles and why each angle is needed.
A lathe tool has one cutting edge – it is a single point cutting tool. Common tool materials: high-speed steel (HSS), carbide tipped tools and inserts.
Tool angles
| Angle | Purpose |
|---|---|
| Top (back) rake | Slope of the top face towards the back; helps chips flow and reduces cutting force. |
| Side rake | Slope of the top face sideways; chip flow and easy cutting. |
| Front (end) clearance | Below the cutting edge at the front; stops the tool face rubbing on the job. |
| Side clearance | Below the side cutting edge; stops rubbing during feed. |
| Side cutting edge angle (approach) | Spreads the cut over a longer edge; protects the tip. |
| End cutting edge angle | Clearance between the end edge and the machined surface. |
| Nose radius | Strengthens the tip and gives better finish. |
Rake vs clearance Rake is on the top face – it is for cutting and chip flow. Clearance is below the cutting edge – it is to prevent rubbing.
Typical HSS tool angles for mild steel
Top rake about 12°–14°, side rake 10°–14°, clearance angles about 6°–8°. Soft materials (aluminium) need larger rake; brass and cast iron need small or zero rake.
Setting the tool
- Cutting edge exactly at the centre height of the job (check with tailstock centre).
- Overhang as short as possible.
Quick Revision
- Rake → chip flow, less force; clearance → no rubbing.
- HSS for MS: rake ~12–14°, clearance ~6–8°.
- Brass and cast iron: little or no rake.
- Tool at centre height, short overhang.
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