On Sun, 12 Dec 2010 09:35:37 GMT, "Harold & Susan Vordos"
wrote:

[...]

I'm in late on this conversation, and have not read all the responses.
However, a ready solution, if it hasn't been mentioned, is to run the part
in soft jaws. Turn the OD to size, then fashion pie shaped jaws that will
encompass the major portion of the diameter. By creating a step of the
proper depth, you'll be able to face the item parallel and bore the hole
concentric. Used properly, you shouldn't have any problem holding a half
thou in concentricity and parallelism. Facing should be the last
operation, and it should be done by taking equal amounts off each side, to
rough, then equal amounts off each side to finish, flipping the part over
for each pass. Leave a few thou only for the finish cuts


Jim Wilkins mentioned pie jaws.

A quick flit through Google turned up more questions than answers:

1) Pie jaws are available only for chucks with 2-part jaws, right?
2) The reason for soft jaws is ease of machining to fit the part?
3) What is the minimum size of the step that will hold a 3/16" part
securely (in aluminum)?
4) Should one be able to get pie jaws that will hold larger OD than
the regular external jaws in a 3-jaw chuck? The current 4" 3-jaw chuck
is just too small to hold the 4.5" piece on the outside (hence the
4-jaw use).

Michael Koblic,
Campbell River, BC