I recall reading about this technique in on old book (reprinted by
Lindsay). In that account, it was suggested that the die be
heat-treated before removing the mild steel plugs. It was claimed that
the quench will loosen these plugs so that they will almost fall out.

It seems to me that leaving the plugs in would also help protect the
cutting edges from overheating, as well as keep them from cooling off
too quickly on the way to the quench tank. I always have trouble
heat-treating tiny stuff.

Dave


Robert Swinney wrote:
Tim,
You musta missed something. Usu. 2 or 3 relief holes are made in the proper
locations and then those holes are filled in with close fitting plugs of
mild steel, preferably hammered in so they will expand into a tight fit.
The heads formed, if any, when hammering in the relief-hole plugs need to
ground off so the plugs can be driven out. Next, the center hole is drilled
and threaded with your new tap. Finally, the relief hole plugs are driven
out with a punch. Viola! New die, ready for final shaping, if desired,
(square is good, here) and heat treating.

I have made several tap and die combos; some custom for really strange
threads but most just for the experience and being able to say, "I can do
it". The largest I have is a 3/4 - 10,

Bob Swinney