Aluminum oxide is the traditional grit material. You’ll find it in less expensive khaki-color form, good if you need a disposable belt, and longer-lasting, dark brown premium belts.
However, for grits of 80 and coarser, many people now prefer zirconia belts (sometimes called “planer” belts). They have sharper, tougher cutting particles that cut more aggressively, last longer and don’t clog as easily. These belts are usually bright blue or purple. Zirconia belts cost slightly more than premium aluminum oxide belts.Belt Sander Reviews
Don’t push down on the sander; let its weight do the work. Go slowly, overlap passes and allow the tool to go past the end without dipping. Be careful not to tip the sander or change speed or direction. Put the cord over your shoulder so it’s out of the way.