I have in the past tried resharpening jointer knives on a stone by hand, but without much luck. The steel is too hard, and too much material had to be removed for the stone to make much of a difference within a reasonable amount of time spent sharpening.
My dad however, living in Northern Ontario, far away from a good sharpening service, has been resharpening his jointer and planer blades himself using a high speed grinder with a vertical axis, similar to the one shown at left, but bigger.
I found this grinder for cheap at a yard sale, so I decided that I should take another stab at resharpening jointer knives myself.
This time, with a fast running grinder, I had much better luck. The grinder is actually a wet wheel, but it runs at 1700 rpm. The water pump on it is dead, so I always wet it with my fingers. It’s a very fine grit stone, so it’s safe to touch while spinning.