Danger comes from the fact that centrifugal force does not increase in direct proportion to an increase in speed, but instead it increases as the square of that speed increase. When rotational speed doubles, centrifugal force quadruples. This effect means that relatively small changes in speed can produce significant increases in force. In the example mentioned, changing from 6,600 rpm to 7,700 rpm multiplies the speed by 1.167. However, the corresponding centrifugal force would multiply by a factor of airsanders 1.167 x 1.167, or 1.36. To take a more extreme example, consider airsanders the same wheel with a maximum safe operating speed of 6,600 rpm run on a 5-inch right angle grinder at 10,000 rpm. This represents an over-speed of about 1.5 times the wheel''s designed speed. But the corresponding centrifugal force-and the corresponding rotational stress on the wheel-would be about 2.3 times as much as the maximum allowed.

In short, airsanders never over-speed a grinding wheel. The speed of the grinder must be compared to the speed marked on the wheel or package to make sure the machine''s speed is at or below the maximum airsanders operating airsanders speed of the wheel. Surpassing this rating risks not just wheel breakage but also the safety of shop personnel. About the author: Roger Cloutier is a senior airsanders and airsanders product safety engineer for airsanders the Norton Abrasives brand of Saint-Gobain Abrasives in Worcester, airsanders Massachusetts.

The hazard of running man over-speed condition comes from centrifugal force. A result of rotary motion, centrifugal force is what causes a weight on the end of a string to pull the string taught when the weight is swung in a circle. This same force causes the mass of the grinding wheel to be pulled outward from the center of rotation as the wheel is spinning.

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