"Doug Miller" wrote in message
. ..
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.

Same thing. I get maybe 0.0005" (that's right, half a thou) removed,
before the tube begins
sliding again.

I tried low rpm, high rpm, slow feed, rapid feed, lots of oil, no oil --
no difference that I could
see.

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.

Which way was it creeping? If out, then just set the lip on the tube up
against the back of the chuck jaws, and use a bullnose center in the end.
If slipping in, put a block of wood inside the chuck behind it, and tighten
down the screws of your spider to keep the block from moving. If you don't
have spider bolts on the back of your lathe spindle it might be time to add
them. Never know when you might need to do some turning on a rifle barrel
next.

I would suspect it was slipping in because the end with the lip would be
more rigid effectively making your tube into a cone with the large end at
the lip when you clamp down.

Personally I would have probably cut it on the bandsaw or with a hacksaw,
and then debuirred it with a file, or deburring tool depending on what was
handy. There is a huge amount of overlap in the joints of that type of
fitting, and it doesn't have to be very precise at all.

Lots of tools could have done the job. Tail pipe cutter. Pipe cutter.
Tubing cutter. Hacksaw. Bandsaw. Abbrassive saw. Dremel tool. Jigsaw.
Sawzall.

That style fitting and assembley is designed with ease of use in mind.
Hence the huge overlap. As long as it reaches past the geasket, and doesn't
have any burrs to catch hair and clog its fine.