Detecting cracked grinding wheels

[woodsmoke]

I have my first grinding wheel set-up. It is a cobbled together very old motor and arbor head with two stones.

I'm refurbishing it for my use.

I saw a couple of utube clips that warn about using cracked wheels and test them by suspending loosely on a screw driver shaft and tapping with the handle end of a second screw driver.

A good wheel should ring. A bad, or cracked on, will sound like a thud.

Well, I tested my two which went thud, and a new one in the hardware store which went thud too.

Is this a valid test, or is the ringing/not ringing due to many other conditions? What do you guys do?

I would like to avoid a disintegrating wheel at speed. LOL

[wtnhighlander]

You DEFINITELY want to avoid fracturing a wheel on a home made machine, which likely has no guards. Flying pieces of broken stone are very dangerous, even deadly.

I've heard the tale of the ringing stone, but don't know how valid it is. Tapping the stone seems likely to introduce a defect, IMO. You might try using a pice of hard wood (hammer handle, maybe), rather than a plastic screwdriver handle. I can't imagine the relatively soft plastic making anything other than a thud.

[TerryMcK]

When I started as an apprentice engineer years back one of the instructors in the training school warned specifically against side grinding. A look at his face confirmed what could happen when confronted with an exploding wheel. His face was pock marked with the remnants of a wheel that had exploded. Fortunately he was wearing goggles as the time. But he had a lifetime of scarring.

Be wary of unknown stones if you don't know its provenance even if used on the edge. If possible only use a new stone. I'm not too certain of the ringing test either - might be an old wives tale.

[..Kev]

I never trust an unknown wheel..

[woodsmoke]

Not planning on any side grinding.

I would just go with a new wheel, but a new one in the store produced a thud too.

Could it have been dropped while stocking the shelf?

My grinder is not home made and has guards.

I did more googling and the 'ring test' seems wide spread and accepted.

Having tested 3 stones and found all to have failed is disturbing.

[wdwerker]

Tap with a piece of hardwood like maple. Listen for a tink instead of thunk.

Tap around the perimeter ,sound should stay the same.

You could turn off the breaker then plug it in and turn it on. Go hide by the panel & flip the breaker on and see what happens. Maybe leave it running for a few hours? Wearing full face protection & plenty of clothes too.