From dressing and shaping metal to squaring and sharpening bits, plane irons, and chisel blades, the bench grinder is an invaluable workshop maintenance tool. Grinders are classified according to their wheel diameter. The 5-to 7-inch benchtop models, with 1/4- to 1/2-horsepower motors, are the most popular home workshop sizes. They can be mounted on a work surface or fastened to a seoarate stand.
Grinding wheels come in many grits and compositions. Medium 36- and 60-grit aluminum oxide wheels will handle most tasks adequately, but you may need a finer wheel, with either 100 or 120 grit, for delicate sharpening jobs. Buffing wheels for polishing metal, and wire wheels for removing rust and cleaning metal, are also worth owning.
Most grinders operate at one speed, or allow a choice of two speeds-typically 2950 and 3600 rpm. Some newer models offer variable speeds, a particularly valuable option for polishing and cleaning, and for grinding with speeds low enough to maintain the temper of a steel tool.
No grinder should be used without lowering the guard mounted above each wheel; the tool should also come equipped with adjustable tool rests and wheel covers sheathing 75 percent to 80 percent of the wheels. More expensive grinders may have other features, such as spark arresters, a water tray for cooling tool tips, and exhaust outlets.
Check your grinder wheels regularly for fractures and, as the wheel wears, adjust the distance between the tool rest and the grinding wheel to about 1/4 inch. A grinding wheel will eventually become dull and clogged with metal particles, and its edges may go out-of-square. A wheel dresser is a special tool that is used to true the working face of a grinding wheel and square its edges.
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