Just got my jointer knives sharpened for the first time & in setting them back up in the cutter head w/ a dial indicator, all three knives are about 3-4 thousandths of an inch less high in the middle. I'm guessing this is from being ground more in those spots, but not sure really why. Feel I should note that when I set them prior to sharpening they were flat across using the same methods, so I don't believe my technique is to blame. I've seen a method of sharpening them with a whet stone laid across the cutter head and the cutter head running. This is mentioned in the manual for my old model 60 jointer. I'm curious if any of you have tried this or any other methods for evening out the height discrepancy in your knives?