On May 25, 6:02*pm, Spehro Pefhany
wrote:
Sorry for the metal content, but there might be someone here who knows
the answer!

I would like to find the center of a 6" metal disk (center the mill
spindle precisely over it).

Here is my plan...

Use an edge finder and find 3 points at roughly 45 degrees to the
center by moving only the X axis, then only the Y axis (forming
a right triangle) with the hypoteneuse over the disk. Go halfway on
both X and Y between those pairs of X and Y numbers.

Does this sound like a reasonable plan?

Spehro,

Probes are kinda crappy for finding circles (CMMs aren't even good
with curved surfaces). Not sure about your tolerances, but indicating
the disk would likely be the best (indicator mounted to the spindle).

Why?
-Well, the edge finder prob may roll oddly along the curved edge of
the disk as you likely won't be on center the first try. I mean, you
have to have Y centered to make an accurate X measurement, and the
reverse. When you start, you'll have neither. If I had to do this, I'd
center one axis, center the other, then center the 1st again. You will
likely end up with a slightly different result.
-The disk may not be round. Depending on how it was made (turned,
punched, laser cut, plasma cut, waterjet, cylindrical ground, jig
ground, milled, etc, etc) your edge finder prob won't tell you
anything about its circularity and may touch a high or low point. An
indicator allows you to average highs and lows and find out the
location with the lowest deviation.

Just my $0.02 worth.

Regards,

Robin