"David Todtman" wrote in message
news:AOg9f.361787$1i.338638@pd7tw2no...
I broke a tap today. There was not enough protruding for me to get a grip
and twist it out. I thought I would anneal the tap in situ and drill it
out. So I heated it red hot with my TIG torch and let it air cool.

When I tried to drill, I found it was still way hard and I abandoned the
idea of drilling out the broken tap. I had the flexability to drill and
tap
beside the original hole so there was really no great loss. But, what if
I
really needed that particular spot?

Would I have had better luck drilling had I cooled the part more slowly
(e.g., buried the part in a bucket of ash)?

Is my thinking nuts or is this a way to get at an offending broken tap?

TIA,
David Todtman



Unlike carbon steel, HSS requires a long soak time (hours) at approximately
1500 F, then very slow cooling in order to anneal. It is often permitted to
cool down with the furnace to avoid air quenching. Heating with your TIG
torch and then allowing it to cool as you did is highly unlikely to have had
a softening effect on it. HSS can be successfully silver soldered or TIG
brazed with silicon bronze rod to shanks with no negative effects, which
makes it possible to make custom tools for those rare occasions when you
can't otherwise machine an object. .

Aside from the tips you've already received, you could always EDM the center
out of the broken tap. Years ago, long before EDM's were on the market as
we know them, Elox sold a tap burner that used tubing as an electrode, and
that was the prescribed procedure. Burn the center out of the tap, then pick
the teeth out of the existing threads. Working carefully, most broken
taps could be removed successfully. As I recall, it required a little
skill on the part of the operator to avoid burning the threads.

Harold