On 05/25/2010 03:02 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?

Yes, but...

Why not start by eyeballing one axis -- say the Y axis. Then use the
edge finder to find the X dimension each way, and split that. Then set
your X axis to that center point, and do the same with the Y axis. If
you really want to be anal, repeat with the X axis, just to assure
yourself that any error is lost in the noise.

That way you'll be finding an edge that's more or less perpendicular to
the travel of the edge finder, which should lead to more accuracy.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com