On Fri, 25 Feb 2005 00:25:41 -0600, "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 °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?
Mike,
I can only speak to the annealing question, Harold gives
excellent advise as to the other considerations. He and others also
cautioned me about annealing a MT2/J33 adapter so that I could remove
the tang and drill and tap for a drawbar for use on my Clausing 8520
mill. I never heat treated the adapter after finishing it and it seems
to be holding up well under my light use. I annealed as follows:
I put the adapter in a piece of copper pipe with one end pinched off
and the other sealed with a
brass plug. Put the whole thing into a charcoal fire and let it burn
until the coarcoal was gone. Perhaps an hour total burn time as I
added charcoal at one point. Fished it out when cool and it had turned
a nice blue-grey color and was well annealed. There was virtually no
scale except where air had leaked in a little at the crimped end of
the pipe. I finished drilling and tapping and can now use my new Rohm
chuck. I haven't tried to reharden and temper it as it seems to work
well as it is. For my hobby use I doubt it will matter. YMMV. If I had
thought of it at the time I'd have put some paper in the pipe with the
adapter to burn up the oxygen in the pipe. Better yet would have been
to seal the pipe better in the first place.
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