un,
I use a drill press drum sander to rough them out- with 80 grit, then 120 grit sleeves.
Then its on to my Grizzly grinder...I use a 320 belt, then an 800 belt - I push the belt off the edge of my 8 inch wheel and soften the 320 up with a piece of steel, to make it pliable, then holding the knife sideways you run the edge of the belt across the grooves...the 800 grit is very soft already, so you dont need to break it down.
I then use a dremel type tool with buffing wheels and buff them shiny, then finish on my clean wheels on big buffer motor.