Superfinishing

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Superfinishing is a metalworking process which produces a very fine, mirror-smooth finish. After a metal piece is ground to an initial finish, it is superfinished with a finer grit solid abrasive stone or abrasive lapping compound in the form of a paste.

After any machining operation, peaks and valleys are left behind in the surface.^[1] These variations, typically a few millionths of an inch in magnitude, can be seen under high magnification. This surface is further smoothed by rubbing with a very fine abrasive stone or paste. During this process, the pressure applied between the abrasive and the work piece is very light and has a short stroke. Its motion on the work piece is controlled, such that the grains do not travel along the same path on the surface, which produces a super fine finish. This is superfinishing.

The term Superfinishing is applied to a number of different processes; most conventionally, an abrasive cutting stone oscillates while applying pressure on the work piece, which may be round or flat. Usually, though, superfinishing is done on round work pieces (such as automobile engine bores and gun barrels) to improve roundness and reduce friction. Processes utilising moving tapes and abrasive paste, and even 'tumbling' with abrasive stones are also frequently marketed as Superfinishing; the suitability of the finish and of the process must be established before use!

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.^[2]