M and I frequently have problems with
overexpanding flute head joint tenons. It's an especially frequent
problem on Armstrongs, which have a pretty narrow diameter on the
head joint tenon. Our shrinker is just a bit too big to properly
shrink an Armstrong once it's overexpanded and that means we have to
spend a lot of time lapping. The shrinker will grab then tenon, it
just can't be closed far enough to press the diameter to a narrower
size. Even with a tenon die that's supposedly sized to Armstrong head
joints (.777” I think), I've still expanded a few head joints to
the point that they don't fit, though I suspect that has more to do
with problems in the socket.
Mike came up with a trick today,
though, that seems to shrink these tenons a little bit when they're
overexpanded, which at least makes for less time spent lapping. Like
I said, the shrinker grabs the tenon tightly but just doesn't shrink
far enough to permanently collapse the diameter. Mike put the
shrinker on the tenon, then chucked it in a vise sideways (so the
vise wasn't exerting any more shrinking force), then drew the tenon
through the shrinker. It seems to have worked, and I think with a
little paraffin added in to the mix for lubrication and
space-filling, it could be a reasonably effective technique.
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