On Fri, 10 Dec 2010 13:07:29 GMT, Doug White
wrote:

[...]


4) After facing both sides the piece was only 0.154" thick and as such
thin enough to flex in the chuck jaws.

4) is a possibility. Another is that the material had internal stresses
which were released by the machining, resulting in distortion. I've seen
this happen big time with plastics like Delrin, but not so much with
steel.

If it was me, I'd turn the OD, and then use a "Step collet" for the rest.
They can machined in place to fit the part precisely, so are guaranteed
concentric. They also apply very even force to the OD of the part,
unlike the high point pressure of a bunch of chuck jaws.

http://travers.com/skulist.asp?Reque...&q=block%20id%
20114899



I have never seen one of those so I had a look around the Google to
see how they work.

If I understand it correctly for a work piece like mine one would get
a 5" step collet and machine it closely to fit the OD of the work
piece. Presumably the clamping range of these collets is the same as
ordinary 5C collets - rather small. The recess would have to be deep
enough to accommodate the work piece and a spacer to allow boring of
the central hole.

Even at $172 it would be a good investment if one were to make more of
these pieces. Unfortunately I do not think I can use 5C collets on my
lathe.

Michael Koblic,
Campbell River, BC