A bench grinder is a benchtop type of grinding machine used to drive abrasive wheels. A pedestal grinder is a similar or larger version of grinder that is mounted on a pedestal, which may be bolted to the floor or may sit on rubber feet. These types of grinders are commonly used to hand grind various cutting tools and perform other rough grinding. Depending on the bond and grade of the grinding wheel, it may be used for sharpening cutting tools such as tool bits, drill bits, chisels, and gouges. Alternatively, it may be used to roughly shape metal prior to welding or fitting. A wire brush wheel or buffing wheels can be interchanged with the grinding wheels in order to clean or polish workpieces. Stiff buffing wheels can also be used when deburring is the task at hand. Some buffing machines (buffers) are built on the same concept as bench grinders except for longer housings and arbors with buffing wheels instead of grinding wheels. Bench grinders are standard equipment in metal fabrication shops and machine shops, as are handheld grinders (such as angle grinders and die grinders). Operation (including safety standards) Wheel speed Wheels come with maximum RPM ratings printed on the label (paper blotter). The grinder's RPM must be equal or lower; "the maximum operating speeds indicated on the wheel's tag must never be exceeded". Greatly overspeeding a grinding wheel makes it explode, which can injure or kill the operator. Workpiece material suited to wheel grade The typical wheels on most bench grinders are vitreous-bond wheels. They work best to do their intended task, but they inherently have a risk of cracking. Grinding wheels designed for steel are not to be used for grinding softer metals, like aluminum. The soft metal gets lodged in the pores of the wheel and later expands with the heat of grinding. This can dislodge pieces of the grinding wheel, causing injury. Sides of wheel versus periphery Grinding is prohibited on the side of a typical (disk-shaped) bench grinder wheel, which is designed for grinding on the periphery only. Risk of wheel explosion otherwise threatens. Some tool and cutter grinders have cup-shaped wheels designed to do grinding on the side. Tool rest and spark arrester placement The tool rest needs to be tight and within 2 to 3 mm of the wheel (" to "). This prevents the workpiece from slipping down between