you need to get some real coarse sandpaper and a board that you can hold the sandpaper against. lay the board under the wheel at an angle and lightly touch the wheel but dont press hard. let the sandpaper gradually sand the glue and old grit away. move to a clean spot frequently and make sure to keep square to the wheel.
when you are done cleaning up the wheel, you should be able to hold your thumbnail close to the wheel (-1/32") spinning it by hand and never have it touch. apply the glue like it says in the instructions and you'll be ready to go.
Richard,
Do you take it all the way down to white paper?
Thanks!