January 21, 2015
Grinding wheels must be inspected and "ring-tested" before they are mounted to ensure that they are free from cracks or other defects. Wheels should be tapped gently with a light, nonmetallic instrument. A stable and undamaged wheel will give a clear metallic tone or "ring."
That distinctive ring comes from the hardness of the material in the wheel and its ability to transmit sound vibrations. If the wheel is cracked, the vibrations stop at the crack and there is no ring. However, a ring test may not detect all defects in a wheel, so a careful visual inspection is also necessary.
Before mounting the wheel, check the machine's spindle speed to ensure that it does not exceed the maximum operating speed marked on the wheel.
After mounting the wheel, stand to the side of the machine when powering it on in case a crack or defect was not detected.
Make sure the wheel is dry and free of sawdust or other material that could deaden the sound of the ring.
You will need a hard plastic or hard wood object, such as the handle of a screwdriver or other tool, to conduct the test. Use a wood mallet for heavier tools. Do not use metal objects.
The wheel passes the test if it gives a clear metallic tone when tapped at all four points. If the wheel sounds dead at any of the four points, it is cracked. Do not use it.
See 1926.303(c)(7), Abrasive wheels and tools
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