Cutting the Commutator to make it smooth and round. This is done with a comm lathe, which cuts a small amount of metal off the comm, making it perfectly round and smooth, increasing performance. For the average backyard basher this should be done whenever the comm becomes blackened by the brushes. Chances are your LHS will do this for a small fee. For serious racers, this should be done avery 2-5 runs, depending on conditions and how much work you are willing to put in to gain maximum performance.