We always took them off the car to do it at Richmond Ford. No clue what they charged but it wasnt much. I'd say to get a nice clean surface you'd be better off putting it on a true lathe OFF the car.

Also, just from my experience...its always a good idea to buy some extra rotors to have sitting around all clean and straight so you can swap them and get the others turned at your leisure. I have 2 sets of the SHO and rotate them whenever they get warped...no down time

-Kevin