either way works... as long as you indicate in the bore not the o.d. ... circular interp. is the term. you were looking for on the cnc mill... most cnc mills now have a good canned cycle to do it for you all it needs to know is where to do it...
i set up with a 4 jaw and a jig to indicate the bore and single point them... or just for ***** ans giggles you can put it in a turn mill and turn it while you circular interp. it by using polar cords. or you can burn them on a e.d.m. if your just looking for something to keep you on your toes