Thread: belt grinder wheel

the 2x72 grinder suddenly developed some vibration and the left side of the wheel is noticably bumpy from about 500 rpm. so looking at the wheel im seeing 16 consecutive radial cracks, the other 8 ribs dont have them. no idea if they are new, i got the wheel used.

can these radial crack somehow make the wheel expand at speed and cause the two effects? i cant really see that happeing, but what else could be the problem? also its kind of improbable 16 identical cracks developing all of a sudden in a consecutive manner. the wheel is seeing around 2000 rpm max.

any thoughts before i take the whole contraption appart?

I don't think the radial cracks are a problem. I see where you may have some separation where the rubber is bonded to the AL. Centrifugal force may be causing the wheel to bulge at this or another separation. I had a 2 x 72 that had a big gouge taken out (long story) and it did not vibrate.

Radial cracks are probably from the friction on the belt tugging across the empty space between them if someone was pushing hard and holding a fairly small contact area against that side of the wheel. They are just on the "upspin" side of the bottom of the grooves which makes sense as to where the maximum stress concentration is.

Like crossthread said I don't think that's your biggest problem, it does look like the rubber is separating from the wheel with a tangential crack near where your poker stick is.

As for the 16 consecutive cracks, you mentioned that it is "bumpy" and you are considering that those "bumps" come from unbalanced rotation? That would cause different contact force along different positions the wheel. Makes sense if you accept my hypothesis above, those 16 are on the high force side, and the 8 uncracked ones are at the lowest force where the tear resistance was not overcome.

"Suddenly" means the rubber is starting to delaminate from the hub. With continued use, at some point it will let go, and probably be pretty gol-dang exciting, especially if you're grinding a knife blade at the time.

Sorry, she's junk. Toss it and replace it- sooner, rather than later. No one I've read about has been able to successfully repair a wheel once it starts breaking up.

And yes, they can and do 'explode' like a rock grinding wheel. Just 'cause it's rubber doesn't mean it won't hurt.

Doc.

I’ve had wheels crack, sent them for recoat at a local printing machinery roller maker, they said they had used the wrong urathane or rubber for a contact wheel running a hot belt, they seemed knowledgeable so I left them redo and grind as they saw fit, no trouble after, I think the cheaper rubber doesn’t do so well hot, they were smooth wheels btw, not notched, the rep from Norton agreed with the diagnosis and suggested putting a small air jet onto the belt to cool, never tried it but it did make sense at the time, after fitting the belts were lasting a lot longer
Mark