Not to "mill" a head but to "true" it up. The crucial part is to be sure you have a flat surface. A very flat surface. Though granite (and other materials) are used as surfaces in the machining world for flat surfaces, that doesn't mean any and every granite counter top is flat. Very thick glass can also be used, if its flat. Once you are sure you have a flat surface, the next important thing is your technique. Use figure 8 motion while sanding. Count the number of passes, turn it quarter turn and repeat, turn quarter turn repeat, turn quarter turn repeat. Don't use back and forth scrubbing action. Only time I have done this was just to true up a head or determine if the head is truly flat. I use much finer paper than the fella in the video. Some feel having a flat but rougher finish is better than a super smooth shiny surface like 600 grit can produce. I've never had issues. I also use some super lite oil or water. Works much better than dry. All JMO. Good luck
