Try replacing the original tiny, hex-head set screw with something more stout and easier to tighten. I use a standard brass, 3/8" long, 440 treaded, slot-head screw and it works many times better than the original set screw. It is much easier to tighten and won't strip like the original hex-head screw. Any good hardware store will have a wide selection of brass 440 treaded screws.