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.