On Jul 31, 2:18 pm, "Spamlet" wrote:

Trust me: sugar does the job well. In the days before cheap Chinese masonry
drills, I used iron water pipe to make holes in brick walls, by dunking in
sugar at red heat after cutting a few rough teeth in the end.

Thanks, I shall try that.
I needed to make an inverse drill, to trim the outside of a rough
brass casting so that I could put a thread on it. I made a steel tube
and cut some teeth on it and put it in the drill press. It worked OK
but next time I will harden the teeth.
The casting would not fit in the lathe or I would have used that of
course.