For hole location you might want to investigate a co-axial indicator. Blake
makes a good one for around $150-200 or there are imports available at half
that price. They are also handy for aligning the TS on a lathe and can be
used to locate a cylidrical projection on a workpiece. They are graduated
to 0.0005" and probably accurate to 0.001-0.002", maybe a little better.

"David Anderson" wrote in message
gy.com...
Thanks to all for good comments - the link to the article by Mike Rehmis
entitled "Edge Finder" was right on target. Also, his comments about a
cheap tool being useless (which is what I was using) made perfect sense.
So,
I immediately bought a Starrett #827A which is much better. But, all these
comments evidently assume that we are locating a straight surface from the
spindle centerline. What about locating a curved, internal edge of a
hole?
Maybe that was my problem. I was attempting to locate the edge of a 0.402
inch diameter hole with the 0.200 tit on the finder. The "kick" now
depends
on the direction of rotation of the tool and whether the curved surface
being contacted is coming nearer or further away during the "kick".
Thanks
once again. Dave