a. Grindstones. Most bench grinders found in carpentry shops are equipped with two grinding wheels: one of coarse grit and one with fine grit. Grinding wheels are held to the shaft by nuts, which squeeze the wheel between two special side washers. Grinding wheels are also rated by the turning speed they can withstand. Be sure you use stones made to withstand the rated revolutions per minute of the grinder electric motor. A tool rest is attached to the grinder frame and is adjustable for height as well as for distance from the stone. Most grinders are equipped with heavy-duty glass guards to permit watching as you grind. If there is no eye guard, you must wear safety goggles to protect your eyes. It is considered poor practice to use the side of the wheel for grinding. When the surface of the stone becomes irregular or filled with metal particles, use a stone dressing tool (Figure 2-49) to restore a good grinding surface. A water container, attached to the base of the grinder, is used for cooling parts being ground. Always cool the blades of tools you are sharpening to prevent destroying the temper of the metal with the excess heat generated from grinding. Heavy grinding is done on the coarse wheel, and light or finish-type grinding is done on the fine grit stone. Most cutting edges should be finished by hand, using a fine oilstone.

b. Oilstones. Oilstones are used after the grinding operation to give a tool the keen, sharp edge required for smooth cutting (Figure 2-50).

c. Artificial Stones. These stones have coarse, medium, or fine grades. Coarse stones are used for general work where fast cutting is required. Medium stones are used for sharpening tools that do not require a keen edge. They are recommended for sharpening tools that are used for working softwoods. Fine stones are used where a keen edge is desired. Cabinetmakers whose tools require a very fine, keen edge use the fine type of stone.

d. Files and Rasps. A file is a steel instrument used for cutting and smoothing metal and wood. A rasp is a very coarse file that differs from an ordinary file in teeth size and shape. Figure 2-51 shows the types of files. Wood files are usually tempered to work lead or brass; they should not be used on any harder surface. When using a file, never allow it to drag on the backward stroke; it cuts only on the forward stroke. When using a rasp, fix the work firmly in a vise and grasp the rasp in both hands, with one hand holding and the other applying a light pressure to the rod (Figure 2-52).