Grinding wheels are designed to operate at high speeds, and can throw fragments at over 300 MPH if they shatter during use. For safety, the wheel should be regularly inspected for cracks; however, visual inspection cannot be relied upon to reveal hairline fractures. A wheel can be tested by lightly striking it with a metal object. A ringing sound may mean the wheel is sound, however the "ring" test is not definitive, and will not work for all types of wheels. The "vibration" test, which uses a specially-designed vibration tester, is more conclusive and will usually detect even minute cracks on all types of wheels.
Things You'll Need
Vibration test fixture
Lay the wheel on its side on the test fixture.
Spread a coat of sand evenly over the wheel.
Turn on the test fixture and observe the sand. If the vibration causes the sand to move away from a specific area, it indicates a crack. Having the sand remain evenly spread across the surface of the wheel is an indication the wheel is probably okay.
Even the vibration test is not 100 percent conclusive. As most damaged wheels shatter at start-up, it is important to stand clear until the wheel reaches its full operating speed.