Nicked blades definitely need changed. But,. . . .maybe a blade isn't dull, just needs some "help". I found my blades get a minutely thin layer of lint, same as a sewing machine. It just needs a careful wipe. Also found the nut can loosen after a while. So now if it skips I loosen the nut, wipe and tighten then test. If it skips, off it goes and a new blade is in order.