"jim rozen" wrote in message
...
In article , Harold & Susan Vordos says...

Yep, I remember, and I commend you for the great pictures, but that's not
what we're talking about. My point is turning a taper with an offset
*tailstock* center, although it's possible I never made that clear in my
original argument. It's not the same thing. The degree of error in
drilling offset centers remains constant and there is no movement of the
part as it relates to the fixed, but *in line* centers in the test you
performed. The machine centers, in your specimen, would pick the high
spots and run there, likely not fully seated, but with enough area of
contact to perform without distorting. When you offset the tailstock,
everything changes. You didn't prove your point originally, I simply
quit
talking about it because I had quit following RCM (sort of like not
talking
to your family, I discovered).

That's not what it seemed to me. The centers were non-axial, and
the part *was* round. Case closed. You could argue that the test
wasn't extreme enough. I thought it proved the point.

Try that same test, this time offset the tailstock, and for purpose of
proving whether you're right, or I am, turn a much shorter piece, with a
large offset, so it's exaggerated. Be certain that the faces are not
at
right angles to the center, which is a part of my argument. You'll not
only
mush the centers, you'll detect an oval. Grinders (the machines, not
the
operators) don't lie. By the way, you shouldn't need any special
machine
to learn what I'm talking about. Simply measuring the part will disclose
the oval. It will be fairly obvious.

Well, the HLVH that was used for the other test can't offset the
tailstock.
But my SB at home can. So the features should be:

1) the end of the stock should be cut at an angle

2) the centers should be drilled in the correct way, ie, coaxial

3) the tailstock should be well offset

4) the part should not be that long.

I could ship it to you when it's done, for your inspection. :^)

Jim

Cool! That's it. Because you'll be turning a taper, it might not be
real easy to detect the out of round condition with a micrometer. I may
have made it sound like you'd be making an egg, but it's not quite that
extreme. By moving your tailstock back on center and running an indicator
on the now taper machined surface, I can't imagine that you won't be able to
detect some degree of out of round. Should also be able to see some
small amount of center deformation, too. I'm keenly interested in your
findings, Jim.

Harold