Finding Edge of Finished Surface

[Lavcat]

Thanks. A centering scope could meet the need, but it would have to be small, both in the shank diameter and overall length. The MSC one you linked has a 3/8 inch shank and might be small enough for me to use in a chuck. Have you seen any that are smaller?

Here is another one that might be the same model:
Opt-CenterScope

For many years I made my living building cameras, so I like the idea of optical methods! So far from what I have read of the microscopes, even the cheap ones are a lot more expensive than a laser though.

A lot of my google searches for machining questions turn up hits on Practical Machinist.

As to how precise, for the current project I'd be happy for 0.1 mm, so let's say 5 mils. I don't have a DRO device on my table however.