In article , Harold & Susan Vordos says...

Yes, they do, and in the process the shaft is constantly creating more and
more clearance between the centers as it cold flows to achieve the form. .
Look closely at centers that have been run offset to see how badly they are
deformed from the center drilled configuration. Further, if, when turning
between centers, if the face on either end of a part is not perfectly
square, it has the effect of creating an out-of-round (oval) turn. This
very concept has been the subject of endless debate, with almost no one in
agreement, but all it takes is a little experience in precision grinding to
put it directly into focus. Be certain to maintain right angles on the
ends of offset turned parts unless you don't mind oval turns.

Your memory is incorrect in this regard. Under normal conditions,
the centers don't open up, and in the case I tested, the end of
the part *wasn't* square to the machine axis, and it *did* turn
a round, not oval piece. To remind folks of the tests that were
done:

http://www.metalworking.com/DropBox/_2001_retired_files/offcenters.txt
http://www.metalworking.com/DropBox/_2001_retired_files/offcenters1.jpg
http://www.metalworking.com/DropBox/_2001_retired_files/offcenters2.jpg
http://www.metalworking.com/DropBox/_2001_retired_files/offcenters3.jpg
http://www.metalworking.com/DropBox/_2001_retired_files/offcenters4.jpg

One of the regulars here at that time tested the roundness of the
turned part, it showed no systematic deviation from round to the
limit of the tallyrond tester.

Jim


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