KDX, make some marks with a magic marker down the bevel to use as a guide. Then using your jig, adjust the angle used so the cut is toward the edge, not the spine. Gently do a bit more grinding - this should allow you to remove metal from edge without touching the spine. "IF" you do touch the spine a bit too much, just do a flat grind on platen which will flatten nicely removing any marks on the spine.
Ken H>