"DoN. Nichols" wrote in
:

On 2016-08-18, Doug Miller
wrote:
I needed to shorten the tailpiece for a bathroom sink drain:
chrome-plated brass tube 1.250 OD with 0.030" wall. Obviously
the tool of choice would be a tubing cutter, right? Except that
my tubing cutter has a maximum opening of 1.220", despite being
labeled as "1-1/4". Grrrr.

OK, no problem, I'll chuck it up in the metal lathe and part it
off. Should be easy, right?

No sooner does the parting tool start removing stock, than the
tube begins slowly but inexorably sliding out of the chuck. Not
crooked or anything like that, still concentric, just creeping
slowly in the direction of the tailstock. OK, maybe I didn't
tighten the chuck enough. Stop the lathe, reseat the tube in
the chuck, make sure it's darn good and tight, try again.

[ ... ]

After 45 minutes, I finally got it turned down far enough to
slip it into the tubing cutter, after which it took about 45
seconds to complete the cut.

Why is this happening? And, more importantly, how can I prevent
it? This was number 1 of two pieces that I have to shorten by
the same amount.

The tubing is rather thin -- and is flexing as you try to
cut
it.

First thing is to turn a plug to fit inside the tubing to
support it before tightening the jaws on the OD of it. A collet
(if you had one large enough) might work, but support the ID and
you can get a much better grip on it. Hardwood or aluminum
depending on what you have available.

Depending on the length of the tube, perhaps also a plug
with a
shoulder in the other end, and support that with a live (ball
bearing) center.

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.