Thoughts on HSS Toolgrinding

I prefer carbide inserted tools for most lathe work--they're very convenient, cost effective if you shop carefully for inserts, and I have used them enough that I know how to get a good finish from them on my lathe. However, there are tasks where HSS tools are ideal. This page captures some of those I've come across over time.

Trepanning Tool

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...