https://youtu.be/ccAbc_dYHoU
Printable View
If you want your bolt circle to be concentric with the outside edge, I just use my center finder from the combination square. (The "V" shaped part) and use that to set for the depth of my inner circle and run a scribe around the disk using the end of the rule to guide me.
I felt like the casting was just a bit out of round to do that. It turned out that is was not that bad and I could have probably done that. Thanks