Ryobi BGH827 bench grinder vibration saga continues

I think so, but have no measurements to back it up. And, only one of the two wheels has been changed so far.

Joe Gwinn

I've just gotten a DuMore series 44 toolpost grinder, and (in the downloaded manual) they warn about rigid sleeves inside the hole in the stone, or tight fits on the arbors. Apparently, changes in temperature can cause the fit to be much tighter, applying enough stress to cause the stone to shatter at speed.

Old stones had a lead centering sleeve -- soft enough so it won't induce fracturing.

I've seen newer ones with a plastic sleeve -- same principle. It is designed to hold the stone close to center when the flanges are being positioned and tightened, but not to apply forces which can cause failures.

They also state that the flanges on both sides of the stone should only apply pressure near the OD, and at the same diameter from both sides. Two different sizes of flanges create stresses which also increase the chances of the stone flying to pieces.

In particular, clamping near the center is likely to induce failures.

Obviously, the blotter paper is also important.

So -- be careful.

Enjoy, DoN.

(...)

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Thanks for the clarification and reminders, DoN.

--Winston

I assume that the stone heats up first and expands, pinching the sleeve. Dumore stones are smaller and spin much faster, but the principle should hold. I assume that given that Norton advertises that the stone can be mounted on a 1" shaft, that 1.000" diameter is OK, and this is the sleeve OD.

The tight slip fit (~0.001"?) is between 5/8" steel arbor shaft and aluminum flanged sleeve. The stone-to-sleeve fit feels looser.

Some of the new stones have epoxy-lined arbor holes, some do not. Mine came (from Norton) with a collection of telescoping molded plastic sleeves intended to accommodate various arbor diameters.

I do recall the lead-lined centers, but haven't seen one in years. I bet the advent of diamond tooling abolished the need, as they can now drill an accurate hole in a grindstone.

Yes. In a prior posting I mentioned that the flange face was relieved. It's for just this reason. The pressure is in a ring about 3/8" wide and 2.75" diameter, and not at the center.

Yes, and it is used.

One advantage of aluminum is that it doesn't rust and stick to the paper.

Joe Gwinn

That is what I would believe to be the case.

Well ... that depends on which DuMore. The illustration showing "ringing" a wheel looks like one around 10" to 12" diameter. And while I was looking for the right manual to download, I saw some really large ones which were designed to be mounted on something like a planer to convert it into a surface grinder. :-)

That sounds good.

O.K. That is where you want the fit to be good.

O.K. Lots of choices. :-)

Hmm ... I thought that the center hole was formed before they were fired. But I've never been around the manufacture of the wheels.

Good. I thought so -- but this was for others reading the thread as well. I had never even considered applying pressure at differing diameters on the two sides before reading that manual, but it certainly makes sense as something to be avoided.

O.K. They also say (for the toolpost grinder, at least) that the minimum diameter of the flanges should be one-third of the diameter of a *new* wheel.

Good -- again mentioned for others.

Yep. Though it can be smooth enough to stick anyway. :-)

Enjoy, DoN.

I don't plan to own a large enough lathe for that DuMore.

I don't think the firing process is all that precise. After all, the wheel material is a form of weak, porous pottery.

Yes. Stone is strong in compression, but weak in tension. Only same diameter yields pure compression in the stone.

Well, no bench grinder complies with this rule, not even Baldor.

But if there are desirable stones available that are 1" wide and 8" diameter, with a 3" diameter central hole, I'd be happy to make a flanged sleeve arbor for it.

I think I will oil the blotter paper next time. Vactra #2 of course.

Joe Gwinn