How is shank size chosen?

By what the tool post accepts: 8x8 mm and 10x10 mm are common on mini lathes. The tip also has to be set to centre height.

Why must the tool be set to centre height?

Above or below centre the rake changes: the surface suffers, facing leaves a pip in the middle, and a parting tool breaks its tip.

How is an HSS tool reground?

On a bench grinder, keeping the rake and clearance angles; if it heats, cool it in air rather than quenching. Check the cutting edge by eye afterwards.

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Lathe Tools

The lathe tool does the cutting, and its geometry decides the surface produced. Shank size follows the tool post; material is a choice between HSS and carbide.

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Geometry decides the surface

A straight tool turns the cylinder. An offset tool, left or right, can come square into a shoulder or a face and leaves the corner clean. A parting tool cuts a narrow deep groove and is what parts the work off.

Boring and internal threading tools work inside the hole, and the length of their shank governs chatter: a shank longer than it needs to be leaves a rippled surface.

HSS or carbide

HSS can be reground and is cheap; it works well in mild steel, aluminium, brass and plastic. Because it runs at a lower cutting speed it is the common choice on a small lathe.

Carbide is harder and takes more heat: it is what high cutting speeds and hard material call for, but it is brittle and does not take shock.

Frequently Asked Questions

How is shank size chosen?
By what the tool post accepts: 8x8 mm and 10x10 mm are common on mini lathes. The tip also has to be set to centre height.
Why must the tool be set to centre height?
Above or below centre the rake changes: the surface suffers, facing leaves a pip in the middle, and a parting tool breaks its tip.
How is an HSS tool reground?
On a bench grinder, keeping the rake and clearance angles; if it heats, cool it in air rather than quenching. Check the cutting edge by eye afterwards.