the set screw hole and allow it to penetrate for a few minutes. in particular stubborn cases, after removing the screw, you may also have to put a couple of drops into the hole in order to loosen the collar on the shaft. there is no harm in using a wrench such as a channel lock to rock the collar back and forth in order to break it free of the glass dust. be careful not to use so much force that you bend the steel shaft. you should be able to pull the wheel off of the shaft at this point. if you have trouble grabbing the upper wheel 