In article , Dave Hinz says...

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

The drop-dead "works any time" approach to this is to turn the
polar coordinates into cartesian coordinates.

Basically you just center the part on the milling machine's
spindle axis, and then dial in X and Y to get points which are
all at the same radius from the center, but at different angles.

So for your example of a five hole BC, you need to put one hole
at X=0, and Y=R.

Then you just need two other paired coordinates, because the
thing is symmetric about the X=0 line.

One of pair, for example, will be X= +/- RSin 72, and Y = RCos 72 deg

Jim


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