On Jun 8, 4:08*am, Wes wrote:
"Roger Shoaf" wrote:

I use the finger nail method. *Tapped holes are going to be a problem though.

Turning a tight pin to stick in tapped hole and indicating that might be more accurate.
Usually when you are tring to pick up such a hole, there is something broken in it though


Wes

Usually when I've had to measure a tapped hole pattern it was to drill
a mounting plate to match. I just put setscrews or Phillips heads in
and visually pick up the center, or for better accuracy chuck a
matching screw in a collet and turn a point or center hole on it. Two
little flats ground on the sides make it removeable with tweezers.

When I asked the machine shop to measure one particularly critical
pattern they used a height gage to measure snug-fitting pin gages in
the holes, but I still had to open up the resulting mounting holes a
little to make the screws fit. I think the tap may have raised an
uneven burr on the ID of the threads.

If I really really had to be accurate I'd single-point a thread that
fits snugly and make my own center plug. A small 5C-mount chuck works
well for a part that has to be removed to check the fit.

Jim Wilkins