The champagne cork and valve grinding compound is the traditional way but I've seen it done with a wire cup wheel if you have a hard alloy. I've used a plywood disc with firm sponge and leather glued to it for big swirls.
You can use a yard stick like piece of wood with notches cut into it for a guide if you don't have a drill press or are doing something that won't fit in one, clamp it to the part with shims under it and sit the mandrel shaft of your drill in a notch, don't forget to shift it a half notch over for the next row down.
