Trepanning Tool 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.  If you have a Tool Grinder, it’s worth learning to use it, and it isn’t hard.

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…