by process include tapered rolls, piston pins, shock absorber rods, shafts, and needles. Plunge This type is used to finish irregularly shaped surfaces. The workpiece is rotated while the abrasive plunges onto the desired surface. Wheels Abrasive cups or wheels are used to superfinish flat and spherical surfaces. The wheel and workpiece are rotated in opposite directions, which creates the cross-hatching. If the two are parallel then the result if a flat finish, but if the wheel is tilted slightly a convex or concave surface will form. Abrasives Common abrasives used for superfinishing include aluminum oxide, silicon carbide, cubic boron nitride (CBN) and diamond. Aluminum oxide is used for "roughing" operations. Silicon carbide, which is harder than aluminum oxide, is used for "finishing" operations. CBN and diamond are not as commonly used, but find use with specialized materials such as ceramics and M50 tool steel. Note that graphite may be mixed with other abrasives to add lubricity and to enhance the appearance of the finish. Abrasive grains must be very fine to be used with superfinishing; usually 5–8 μm. Advantages and disadvantages Advantages of superfinishing include: increasing part life, decreasing wear, closer tolerances, higher load bearing surfaces, better sealing capabilities, and elimination of a break in period. The main disadvantage is that superfinishing requires grinding or a hard turning operation beforehand, which increases cost. Superfinishing has a lower cutting efficiency because of smaller chips and lower material removal rate. Superfinishing stones are softer and wear more quickly, however they do not need to be dressed. Applications Common applications include: steering rack components, transmission components, fuel injector components, camshaft lobes, hydraulic cylinder rods, bearing races, needle rollers, and sharpening stones and wheels. It has been proven that superfinishing certain parts makes them more durable. For example, if the teeth in a gear are superfinished they will last up to four times as long. See also Abrasive machining Honing Lapping References Notes Bibliography . . Grinding and lapping