I can't turn between centers yet cause i lack the stuff. But i still turn only one tube at a time on my mandrel. It is WAY more accurate even on the mandrel when it is shortened.
Yeah, I am with you. Whenever I turn two blanks on the mandrel the rightmost one is always vibrating a little bit. The skew does not cut as well either.
And folks, think about it. When you are turning two blanks at a time, while you are turning one blank the other one is just spinning there, idle. So the only time you are losing is the time it takes to switch out. Not that much time when you think about it and I suspect next to nothing with TBC.
Now finishing is a different story. I prefer to finish both blanks at once since there are gains in applying CA to both blanks and waiting for it to cure. But by this stage I am already turned down to size and there doesn't seem to be any drawbacks to doing both on the mandrel with Johnny's delrin blanks, but I am always open to new and better ways.