I have machined a collar for my machine like the one in the article at the top of this page

http://www.floridaame.org/HowTo2.htm

so I can add a simple digital readout to my rig. I want to drill holes to mount the collar and to add a point for mounting calipers. So I need three holes 90 degrees spacing from each other.

When I normally want to drill through something round I place it in the vice and use an edge finder and measure the gap in the jaws to find center. Problem is the collar will only fit in the vice sideways so that will not help me fine the true edge/highest point of the collar.

How can I set this up in the machine ?

Thanks for all the replies, all good workarounds. I actually had a thought myself, I could just mount a DTI in the chuck and run it over the work to find the highest reading. I dont think my edge finder is long enough unfortunately Les. Good idea Jason with Tri square I like that, in fact if I could put a block of anything true against the work I could find the edge of that and take my calculations from there.

many thanks,

Ady.