grinding, process by which surface material is removed from an object, usually metal, by the abrasive action of a rotating wheel or a moving belt that contains abrasive grains. A grinding wheel can be made by mixing a bonding material, usually clay, with abrasive grains of such substances as silicon carbide or aluminum oxide. The mixture is then shaped into a wheel and hardened. A grindstone is a grinding wheel made by shaping naturally occurring sandstone, which contains abrasive quartz grains. Grinding is used in many manufacturing processes to produce a fine surface finish on an object and to bring the size of an object to within very fine tolerances. A grinding machine has devices that hold an unfinished object and move it past the machine's abrasive wheel or belt, which is driven by a motor. For less exacting work, such as sharpening cutting tools, objects can be hand held and ground by a machine consisting mainly of an abrasive wheel or belt. For many products grinding is only one step in a finishing process that involves additional similar operations such as honing, lapping, polishing, and buffing.