On Fri, 18 Jul 2014 11:00:59 -0700, wrote:

snip

Greetings Michael,
I've been thinking about your problem and how I would cut lots of
rings from thinwall brass tubing. What I would try is putting a plug
into the tubing so that it could be held tightly in the lathe chuck.
Then I would use an aluminum mandrel held in the tail stock to support
the tubing while cutting. I would make the mandrel about 15 thousandts
of an inch under the ID of the tube. Spin the tubing and apply the
cutting wheel. The tubing must stick out from the chuck enough so that
the tubing can flex against the mandrel when the cutting wheel is
applied. Since the tubing would only need to flex about .0075" you
could cut pretty close to the chuck. I envision a mandrel that extends
into the tubing about 3 or 4 inches. Use some oil on the mandrel. Then
cut off a ring, advance the carriage toward the chuck, cut a ring, and
so on. Then after enough rings are cut to lose the support of the
mandrel, loosen the tailstock and slide it towards the chuck until it
once again supports the tubing. Cutting against the mandrel should
lessen the amount the ring shrinks at the cut, and when the cutting
wheel touches the aluminum mandrel it won't be dulled.
Cheers,

You have hit the core of the problem which is the deformation of a
thin-walled conduit while cutting. Following on from your thoughts I
suspect I should get much better results even using a hand cutter if I
put a mandrel through the conduit first. Maybe even a wooden one.

Thanks.

Michael Koblic,
Campbell River, BC