Hard Turning

First experiment with using cubic boron nitride cutting tools to machine hard steel.

I bought this gear to help cut a custom thread. It’s a metric module 1 gear with 24 teeth, which is the right count for a 0.6mm pitch threading feed, which the Proxxon PD 250/e can’t do with its standard change gear set. The width of the gear needs to be reduced, but when I tried to turn it with a carbide insert the cutting pressure was very high near the inside diameter and cutting produced some red hot chips. I tested the outer surface of the gear with a file, and found the file couldn’t mark it. It looks like it’s case hardened only, as the body of the metal turns easily.

I had just ordered a cubic boron nitride inside for interrupted cutting for another project, so I thought I’d give it a try. It turns out to work great.