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With this simple jig, a drill press and a cup grinder, I can sharpen any jointer or planer knife. First I make a hardwood block and cut it to 1/16 in. less than the length of the knives. Then I add a retaining piece at each end, as shown. Install a medium-grit cup grinder in the drill press and set the speed at the high end of its range. Lower the grinding wheel until it just touches the blade, then lock the quill. Continue grinding until all the nicks in the knife are removed. Use the same procedure to grind the remaining knives, then hone them on an oil or waterstone in the usual way.
