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