When I grind valve seats and want a nice finish when I get done, I take a strip of abrasive cloth about 1/4 inch wide and 4 inches long. I place it between the seat and stone with the abrasive side facing the stone. I hold the cloth with one hand and then turn on the driver for just a second or two. It makes the stone a lot smoother and leaves the seats with a very nice finish.
The Parts Bin