A belt sander is a machine used to sand down wood and other materials for finishing purposes. Belt sanders can be either hand-held, where the sander is moved over the material, or stationary (fixed), where the material is moved to the sanding belt. Stationary belt sanders are sometimes mounted on a work bench, in which case they are called bench sanders. Belt sanders can have a very aggressive action on wood and are normally used only for the beginning stages of the sanding process, or used to rapidly remove material. Sometimes they are also used for removing paints or finishes from wood. Fitted with fine grit sand paper, a belt sander can be used to assure a completely smooth surface. Sanding wood produces a large amount of sawdust. Therefore, belt sanders employed in woodworking are usually equipped with some type of dust collection system. It may be as simple as a cloth filter bag attached to a portable sander or a large vacuum system to suck dust particles away into a central collector.