If you just want a couple done, I would leace the back end long by maybe 1/4" (6mm) and mill a good reference flat on it. Then clamp in a vise by holding on the faces. Indicate and drill.
If is a production part spend half a day and make a fixture.
You could also drill the 9/64 hole in your round blank first and then fixture that hole for to machine the square (this would be an easier set up) |