Surface grinders have an abrasive grinding wheel that produces a smooth finish on flat surfaces. They're used on cast iron, steel, brass, and aluminum workpieces as well as some plastic workpieces. These large machines have a reciprocating table that holds a workpiece and moves it against the wheel. The workpiece is held in place on the table with a workholding device as the table moves underneath the grinding wheel. Grinding wheels of different shapes can be used to create custom workpiece geometries.