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How to Grind a Lathe Tool Bit
Guide · Updated October 28, 2026
A hand-ground high-speed steel tool bit is still the most flexible tool on a manual lathe. Get the clearance (relief) angles right so the tool cuts instead of rubbing, add rake for a free cut, and finish with a small nose radius and a hone.
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Step by step
- Dress the wheel: A true, clean aluminum oxide wheel; keep water nearby to cool the bit.
- Grind the end relief: Grind the end clearance first, leaving the end cutting edge angled back from square.
- Grind the side relief: Grind the side clearance below the side cutting edge.
- Grind the side rake: Grind the top surface sloping away from the side cutting edge.
- Add back rake if needed: A little back rake for steel and aluminum; none for brass.
- Form the nose radius: Round the point slightly.
- Hone: Hone the cutting edges on a fine stone.
Worked example: right-hand turning tool for mild steel
Published HSS tables (LittleMachineShop and the Metal Arts Press tool-bit table) list machine steel at side relief 10–12°, front (end) relief 8°, side rake 12–18° and back rake 8–15°. A good middle start is 10° side relief, 8° end relief, 14° side rake and 10° back rake, with end cutting edge angle about 15°, side cutting edge angle about 10–15°, nose radius about 1/64–1/32 in. The same tables give brass and bronze 0° back rake and 5° to −4° side rake, cast iron 12° side and 5° back rake, and aluminum 15° side and 35° back rake. Angles are not critical; most tools cut, just less well. With 1/32 in nose radius, keep finishing feed well under the radius, for example 0.004 in/rev.
Relief vs rake
Relief (clearance) lets the tool cut without rubbing; rake controls how the chip curls and the cutting force. Too much relief weakens the edge; too little rubs.
Cooling
Do not let HSS turn blue repeatedly; cool it in water often. Never quench carbide.
Common problems
Rubbing or squealing: not enough relief, or tool above center. Chipped edge: too much relief or rake for the material. Poor finish: no nose radius or dull edge. Tool digging in: too much rake on brass.
Tips
- Height: set tool height.
- Drills: sharpen a drill.
- Carbide: carbide inserts.
FAQ
What angles for a lathe tool bit?
For machine steel: 10–12° side relief, 8° end relief, 12–18° side rake and 8–15° back rake.
What wheel?
Aluminum oxide.
Rake for brass?
Little or none.
Should I hone?
Yes, for a better finish and edge life.
Why does my tool rub?
Not enough relief or it is above center.
Related guides and calculators
- How to Set Tool Height on a Lathe
- How to Sharpen a Drill Bit
- Carbide Insert Basics for Turning
- Turning Speeds and Feeds
- How to Face on a Lathe
- How to Use a Center Gage (Fishtail)
- How to Use an Arbor Press
- How to Use a Form Tool on a Lathe
- All free machinist calculators
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