"Ed Huntress" wrote in message
...
On Fri, 19 Aug 2016 21:42:00 -0000 (UTC), Doug Miller
wrote:

Jon Elson wrote in
newsbCdnZFnEIR3ySrKnZ2dnUU7-S-
:

Doug Miller wrote:



Many thanks to all who responded -- I now have multiple solutions
for the next time I'm in this situation. I'm a very experienced
woodworker, but I'm sure you all realize that I'm just a beginner
in the metal shop, and I learned a lot from reading your
responses.
Well, we pretty much guessed that, as this is actually a VERY
common problem
in turning operations. Any time you are turning a tube, unless
the wall is
REALLY thick, it will happen to some extent.

And turning a tube isn't a real common operation on a wood lathe, so
this was completely
outside my experience.

There are all sorts of ways to deal with it, up to even wire EDM.

Where SWMBO works, they have a plasma cutter, but I figured that was
overkill.

FWIW, when I have to cut off thin tubes, I pad the tube in my
four-jaw
with some pieces of wood (I have even bored a piece of wood to the
approximate size, and then bandsawed it to make a "collet") and turn
the tube slowly against a hacksaw.

Crude, but it works, without crushing the tube.

--
Ed Huntress

I made a collet-like hub for a 10" solar tracker pulley by boring the
center of a piece of 2x4 to slip over the water pipe support, drilling
stress relief holes a few inches out on the centerline on either side
and slitting between them with a handsaw. A screw on either side of
the center hole closes it tight on the pipe. Other than the center
hole that I bored on a lathe face plate it was bench vise and battery
drill work.

I could have bored the hole to size after cutting the slots to hold a
large piece of thin-walled tubing in the lathe.

If you have a metal ring, perhaps cut from leftover scrap at the Home
Depot pipe threader, one of my old-time lathe books mentions using it
to close a custom wooden collet like Ed mentioned, by tapping it onto
a taper on the OD.

Usually I hacksaw with the lathe off and the drive engaged, which
keeps the work from spinning too easily unless I bear down hard on the
saw to advance the cutting area.

It's a leather-belt-drive lathe, which has both advantages and
disadvantages. An advantage is that the spindle stops almost instantly
(if the tool is cutting) when I raise the tension lever, so I can
thread right up to a shoulder or stop in a drilled hole.

--jsw