Replacing a Gear, Part IV

Sherline makes a single-point gear cutter for their mill. I've got a Taig mill, which uses a different setup in the spindle. This means I couldn't use the Sherline part, and I couldn't find one for the Taig. So, I built one.

I followed the Sherline design with a few key changes: I made the cutter with a 3/8" shaft so I could grip it in the Taig collet. Since I was making my gear out of Delrin, I used W1 tool steel instead of a HSS bit. The mill had no problem cutting the W1 (once I figured out speeds and feeds) and was used to put the correct profile on the tool. For reference, I put about a 5 degree relief on the tool so the back of the tool wouldn't cut as the tool spins.

Size caused a few issues trying to cut this gear. Since the holder was 1 1/2", and the tool bit stuck out about 1/2", there was a 2" diameter circle that had to be traversed freely in order for the tool to cut. This meant working at the end of a piece of 9mm Delrin, which resulted in lots of chatter. There wasn't enough room for the tailstock to support the work, so I had to turn a much longer center for the tailstock. Were I to do this over again, I'd try to keep the overall diameter of the cutter down to prevent this issue.

At the end, though, I had a pair of gear-shaped objects that ran together quite nicely. Not perfect, but enough to keep the process going.