Hello, after several passes with 24G abrasive sleeve on a drum sander the hardwood floor is mostly but not completely stripped of the old varnish. Some patches still retain traces of the finish. I was wondering if this is something to expect? I thought that the combination of a drum sander and a 24G sleeve would make one extra careful not to damage hardwood floor as opposed to applying extra force to the drum. Or should I have been pushing the handle down all the time, which would be exausting?