Yes, X and Y Zero is on the part center and generally Z zero on the top surface.
I machine all of the "round parts" Barrel Plate, Recoil Plate, Carrier Block, Front Plate, etc. on 3/8" Shoulder Bolts of varing length. When the part is in the lathe, I will drill, bore and ream the center hole to 3/8" so that it is dead true to the OD and turned features. Then for the milling operation I attach a plate to the mill table and face it plate. In the center I again drill, bore and ream a 3/8" hole about 3/8" deep and then drill and tap a 5/16-18 hole in the bottom, this becomes X and Y Zero for all future operations. Directly above this hole on the fixture I will drill and ream a 3/16" hole at X=0.0, Y=0.625. this becomes the index pin for all parts.
To setup a part to be milled, the 3/8" hole in the fixture is indicated and zeros set. The blank is then bolted into place with the 3/8" shoulder bolt. Next I drill and ream a 3/16" index hole through the part on thin pieces and 3/8" deep on thick parts. For the thick parts I turn the part over reclamp and put the index hole in the second side after locating the first hole with a 3/16" dowel pin to the fixture.
This approach keeps all the features on the pieces "timed" to each other and allows the part to be removed or put back on the fixture easily and without having to worry about rotation.
This approach works for me.
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HI nitewatchman, I am still drawing with Bobcad and I will have to admit that there are a lot of miracles that will have to happen when I am finished. I studied your G codes and have gained a lot especially from your mill rim reliefs file. The Robotool controller is capable of entering G codes right on the machine. So maybe if my drawings don't work out very well I will try to enter just the G codes from one of your files on a piece of wood or wax to see what happens. Did you zero the tool on the top surface of your material on center? Thanks, bruski