On Sun, 25 Sep 2011 18:43:04 +0930, "Kevin(Bluey)"
wrote:

On 9/25/2011 6:00 PM, Harold & Susan Vordos wrote:

wrote in message
...
snip--
Many set screws actually harden with heating - from my experience

I'm having more than a little trouble believing that. I'm not aware of
any set screws being made from precipitation hardening steels, although
I do suppose they could be. Beyond that, the only way the screw would be
harder is if it was heated rapidly, heating only the screw, so the
surrounding material behaved as a heat sink and quenched the material
while the carbon was still converted. Sort of like a chilled iron
casting. I'm having a problem with the idea that that happens,
especially when heating by torch.

I'd suggest that a fast heating to a dull red heat would anneal the
screw. Once annealed, whether it backs out or not (it may, for the heat
will have also disrupted the rust that has formed), it will be dead
simple to drill out. Drilling to the minor diameter of the screw should
result in a clean hole with threads entrapped, like half a heli-coil.

Harold


Im with you Harold . Never had a set screw harden when heated .

The vast majority of cup end set screws are either A2 or A4 steel -
which is by definition an air hardening steel - and WILL harden when
heated. Just like most exhaust studs. They are hard enough to start
with, but if you heat them trying to get them out they end up as hard
as glass. Very hard to anneal, particularly when jammed into a
casting.
The advice regarding spot heating the screw is good advice , I have used
this procedure a number of times and it works .
Works particularly well in maleable iron pullies etc, as it enlarges
(in) the hole, then shrinks back, leaving a looser fit

Soaking in a good penetrating agent is also good , in conjuction with
the spot heating

If you can get a left hand drill the minor diameter of the screw thread
, some times the drill will grab and screw the screw out for you .