Mike Henry wrote:
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 =B0F) 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?

I would avoid annealing and the potential of scale ruining the MT2. My
approach would be to try tempering it back to about 600 degrees F (pale
blue) and then bore it out with a carbide tool. If you try this, let us
know if this works.