I've a used 1/2" MT2 end mill holder that I'd like to bore out to 3/4". The
problem is that the holder seems to be hardened throughout. A small file
won't scratch the bore of the holder. It seems that my options would be to
bore it out as-is with carbide or anneal it and bore. I suspect that
grinding would take forever and am not real thrilled with the idea of
grinding on the lathe, though I do have a decent toolpost grinder.

For annealing, I have available a toaster oven (500 °F) or gas barbecue, a
propane torch, or a 1-hour round trip to a friend with a small heat treating
oven. If scale is likely to be a problem with annealing, what is the best
way to deal with that? I don't much care about the appearance of the end
mill holder end, but don't want to screw up the MT2 end.

Does anyone have any thoughts on the best approach?