Harold & Susan Vordos wrote:
"Ken Grunke" wrote in message
...
snip--------

That's because the contact of the center's cone with the

cone-shaped hole varies between the outer, larger diameter of the hole
and the smaller diameter of the hole's cone shape at the workpiece end's
slanted face.


I have to correct myself before I go to bed, or else I won't be able to
sleep. I was wrong about a slanted end resulting in an egg shape.
Actually, the tool pressure would push the workpiece against the cone
center as I said before, but the contact would only be at the bottom of
the centerhole's cone shape.
I hope a picture is worth a thousand words:

http://www.ken.crwoodturner.com/offsetcenters/

These are closeup top views of a workpiece offset between centers. The
end is cut at 10 degrees to illustrate the hypothetical situation I
mentioned in my previous post.

In view A, the tailstock center is all the way into the center hole but
in view B, you see what happens when the workpiece is turned 180
degrees--there's interference at point X. So the tailstock center has to
back out a bit, resulting in a sloppy fit when the shaft turns back
around to the view A position.

I could have just let this go, but nooooooooooo--I had to spend over a
frickin' hour preparing this message and the pics to explain a
hypothetical situation that would probably never occur for 99% of all
machinists. Oh well, it was kinda fun.

Moral of the story: face off the ends of a shaft you're offset turning
between centers, or something wierd might happen!


Give that man a cigar!

Harold


I could use a beer instead! ;-)

Ken Grunke




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take da "ma" offa dot com fer eemayl