Dave Hinz wrote:
On Tue, 05 Jul 2005 13:16:04 -0500, Rex B wrote:

Get the two marked with a sharp punch, then use a compass to scribe the
other two.


I thought of that...right after I drilled & tapped the first two holes.

That makes it a little harder. I suppose if your tapped holes were
tight, you could chuck a bolt into the lathe and center drill a small
hole, then screw one into each hole flush to locate the compass.

So, that would really work with any number of holes; once I have the
circle diameter known and marked, pick a point, determine the spacing,
and walk it around the circle. If I didn't screw something up, it'll
all line up to the original hole when I get all the way around - yes?

With just 4 holes it's actually easier than that. Quick trial & error
until both arcs intersect at the circle scribed earlier.