I am trying my hand at my first Wobbler Steam Engine. I made the Cylinder from 25mm Alu and drilled a 13mm hole for the piston about 6mm off center. Now I would like to mill a flat on the side of the Cylinder for the Inlet and Exhaust ports as well as the pivot point. I have to line the Cylinder up in the Milling Vice that the Flat and the 13mm hole are perpendicular. I tried eyeballing it in the vice but I would like to do it more accurately, but for the death of me I cannot find a way to do it. What would be the easiest?