I use a screwdriver shaft through the central hole in the bar blade for balance, and a 14" flat disk (36 grit size) for grinding, because the very coarse grinding material reduces the heating of the steel. An angle grinder will also do the job properly if you are careful and go slowly. However in essence the rule is, you use what you've got. Just don't let the blade get hot. If it's gone blue, it's gone soft. Grinding off the blue doesn't grind off the softened part, the blue is just the oxide layer on the surface of the metal.
