Trepanning Tool Toolgrinding

I prefer carbide-inserted metal lathe tools for most turning work because they are convenient and cost-effective if you shop carefully for inserts. I've used them enough to achieve a good finish consistently. However, for certain tasks, HSS tools are ideal. This page highlights some of those tasks. If you have a tool grinder, it's worth learning to use it—it’s not difficult.

Trepanning Tool Toolgrinding

Trepanning is a useful operation that may be thought of as putting a groove in the face of a workpiece on the lathe. The groove may be narrow, a wide recess, or even all the way through to cut a disc out. Trepanning tools are available for mills and drill presses especially for the latter purpose. Here is a sequence Bobstandard published on HMEM showing how to trepan flywheels with a tool he has ground:

Here are a couple flywheels with trepanned recesses ground inside...

A look at the tool that did the work...

The tool in action...

General guidlines for grinding such a tool...

A commercially available treppaning tool for hole cutting: $29 apiece! You could grind this shape pretty easily too...

I've tried to grind my own trepanning tools for hole cutting on the mill with some success. I started with a dulled endmill and ground all but one flute off and tried to make that flute extend down as much as possible. I then installed the endmill in a boring head and went at it:

My trepanning tool ground from an endmill in action...

A commercially available trepanning tool of the type I show a cutter for above. It works a little better than the hand ground endmill, but not hugely better...

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