One potential source of serious injury in grinding comes from airsandersandpaper an oversight that is easy to make: operating the wheel in an over-speed condition. While a wheel that is run airsandersandpaper far enough in excess of its rated maximum speed may shatter within minutes airsandersandpaper of operation, danger may also result from a wheel run just slightly faster than its rated speed. This less severe over-speed condition can cause the wheel to be damaged, airsandersandpaper and the damage may result in breakage after further use. For example, operating a reinforced, 9-inch diameter, Type 27 wheel rated for a maximum speed of 6,600 rpm on a 7-inch angle grinder with a speed airsandersandpaper of 7,700 rpm can cause the wheel to crack. This cracking can lead to breakage later. Any of these actions sets up airsandersandpaper a disastrous scenario that could lead to an accident involving serious injury or death.

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 airsandersandpaper rpm to 7,700 rpm multiplies the speed by 1.167. However, the corresponding centrifugal force would multiply by a factor of 1.167 x 1.167, or 1.36. To take a more extreme example, consider the same airsandersandpaper 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. airsandersandpaper But the corresponding centrifugal force-and the corresponding rotational stress on the wheel-would be about 2.3 airsandersandpaper times as much as the maximum allowed.

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