Years ago I put a brand new wheel on my grinder, turned it on and when I moved to the side to get the piece that needed grinding, the wheel exploded. There is a good chance that I could have avoided that by doing this simple ring test but I didn't know about it then,. Now I do and so will you!
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Ring Testing Grinding Wheels

A simple way to identify cracked wheels

Text, photos and video by Tom Hintz

Posted – 2-24-2012

This ring test for checking grinding wheels has been around about as long as grinding wheels. The ring we are listening for comes from the hardness of the material and its ability to transmit sound (vibrations) around the wheel which produces the sound the ringing sound we hear. The vitrification process used to make many grinding wheels loosely means that the materials were heated until they fused. That continuous glass-like structure allows the sound waves/vibration to radiate around the wheel which produces the ringing sound. If the wheel is cracked, the vibration waves stop at the crack so the sound we hear is dead with no ringing to it.
It is important to know that the Ring Test does not take the place of other more sophisticated testing or a good visual inspection. The ring test won’t reveal all defects in a grinding wheel either. If there is any doubt about the integrity of a grinding wheel DON’T USE IT! The cost of a grinding wheel just isn’t worth the risk.

The ring test can be used most effectively on vitrified bonded grinding wheels that are over 4”-diameter. The wheels can’t be mounted as that inhibits the ring. The grinding wheels should be free from dust buildup and they should be dry as water within the wheels porous structure also deadens the sound very effectively.

The cuts in this table saw blade (left) help control wobble caused by expansion. However, they work much like a crack in a grinding wheel by not allowing the sound vibration from circulating around the blade. Use a hard plastic or hard wooden handle to tap on the wheel. Listen closely for the ringing sound that tells us thee are no cracks in the wheel.
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Setup

To do the test we need to either suspend the wheel on a pin or shaft that fits within the hole without being in contact with the sides of the hole which can also deaden the sound. If the wheel is too large to suspend safely it can stand on a clean hard surface or the floor.

I put a piece of dowel or a practice turning that I saved in my bench vise so that I can hang the grinding wheel on that. That keeps both hands free which can be handy as the wheel wants to rock side-to-side when tapped and the last thing I want is to hear a nice clear ring as the now proven to be good wheel falls to the floor and shatters.

Ring Testing

The tones we are listening for can be fairly subtle so this is not a good time for your (OK my) usual concert-level Bon Jovi shop music. We need to tap the wheel with something solid but not metal. The hard plastic or hard wood handle of a screwdriver or similar tool is perfect. Tapping with a metal tool causes the metal tool itself to ring and we don’t need to be confusing the situation with another ring.

Imagine a vertical plumb line up the center of the wheel and then tap it about 45-degerees to either side of that line on the top half of the wheel. Turn the wheel 180-degrees to bring what had been the bottom to the top and tap it about 45-degrees to either side of the imaginary plumb line again.

Video Tutor

If the wheel “rings” when tapped at all of the positions, it passes the ring test. If it sounds dead at any of the positions it fails and should be inspected very closely or discarded. Grinding wheels aren’t free but they are way cheaper than an explosion so error on the side of safety.

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