I have indexed various parts on my mill/drill by clamping the piece down firmly. Then I use a piece of stock that is the same diameter of the work piece(You may have to make this). Insert the index piece in the drill. Run the table up, centering the piece to be worked on. Clamp everything in place. Run the table down, remove the index piece, insert the tool you want to use. It should be centered. A real machinest could probably explain this much better...