Large Sanding Drums

Yes, you need to have some back ground not to want to pull your hair out on the "getting it centered issue", But it really isn't that hard to resolve. You only put the first set screw in {1 is plenty for this application}, then eyeball the drum centered and tighten the drum down to hold your sleeve, turn the 1 set screw down just touching. Speed your machine up as high as possible and it will center it's self. Tighten the set screw down tight without hitting the drum. The second set screw is needed as it is a locking set screw, simular to double nutting a bolt that you don't want to vibrate loose. I have to confess I dropped mine into the sawdust and couldn't find them but from experience I know that the first one in should be a cupped end set screw and the second a flat nose set screw. This takes a touch, if you have problems with this then snug the first one and turn the machine on and hold a roller caster to the center of the sleeve with the nut snug and with a good eye you very soon will have it as close as humanly possible. Follow the same steps in the final tightenings. Trying to move it this way then that and tightening and loosening it each try will drive you loooney and I think the combination of probabilities are infinite. You have moved it to far, not far enough, to much left and not enough up etc.. Give this a try. I think it will help you using one way or the other depending on how used to setting machines of all types. I am not a writer so I probably typed in a circle and left out things so that it doesn't work for you and if I did I'm sorry. I  just saw this and wanted to help you all out.