So did centering the set screw work??? In case you don't know, There is a little anvil in the center of the set screw and the thumb screw that is replaceable. When mine just won't hold a blade well anymore, I replace it. I always keep a couple of new sets around. If you cut with the same size blades most of the time and then try to cut with a different sized blade, the wear pattern on those anvils are minutely worn and have a tough time holding much larger or smaller blade.