[HELP] Centering on a rotary table

[Maxiice]

I would just clamp a piece of metal in the rotary table. that is bigger than the piece you are gonna mill o-ring groove on. Then clean it up in the mill and mill a pocket while turning the rotary table. make a snug fit pocket to hold you piece and make four holes, thread them up and bolt your piece to the piece in the rotary table. Then you would be in center on every piece until you remove the big piece from the rotary table