Vibrating grinder returns

Some months ago I had a lot of trouble with a Ryobi 8" 2-wheel bench grinder the shook the world when it ran. I flattened things and aligned things, and all seemed well. Not having a stand, the grinder saw little use. I recently bought a stand from Harbor Freight (model 3184), and put it all together on Friday. The stand is quite sturdy. But the grinder again shakes the world.

The wheels wobble from side to side, and there is lots of radial runout. OK, used a diamond dressing tool on sides and edge to true things up. Vibration sharply reduced, grinds well without bouncing the toolbit I was shaping. Turned grinder off, and put grinder back against thewall.

Next day, used grinder again. Terrible vibration, and the wheels now wobble from side to side, and radially. Huh? The wheels must be moving, sliding around even though in theory clamped. When I put the grinder back against the wall, the bumping must have caused the stones to move with respect to the shaft.

It's very hard to tighten the clamps properly, as one cannot tighten the big end nuts against one another, because one nut is left-handed and the other is right-handed. Tighten one, the other loosens.

Tried various things; ended up holding both wheels while tightening the nuts. There does not appear to be a spindle lock of any kind. I'm tempted to cut screwdriver slots in both ends of the shaft.

How do the Baldor grinders solve this problem?

Joe Gwinn

Reply to
Joseph Gwinn
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Good question. I have a Baldor 1/2 HP grinder, and it it very quiet and vibrates very little. One thing to consider is effect of resonance. Perhaps the resonant frequency of your grinder coincides with rotational frequency. However, when said Baldor slows down (it slows down for minutes after being turned off), within some speed range, it does vibrate considerably. It could have something to do with it being heavier built from cast iron (as opposed to thin sheet metal).

i
Reply to
Ignoramus26451

Do you have plastic bushings in the holes of the grinding wheels to make them properly fit the od of the shafts????? Ken.

Reply to
Ken Sterling

Yes, I do. They clearly are not very precise though, as the radial runout changes when the stones move.

Joe Gwinn

Reply to
Joseph Gwinn

I'm sure the Baldor is heavier, but does the stone slide around in the arbor? That's the issue here. When I dress the stones, the problem mostly goes away. Until the stone slips in the arbor. Then, back to square one, but with a slightly smaller stone.

Joe Gwinn

Reply to
Joseph Gwinn

I think you need to spend whatever time getting the plastic bushings tightened up. My experience is that they are quite a snug fit to the stone, the spindle, and each other.

I am not aware of any brand that locks the armature for snugg> >

Reply to
DanG

That does not seem to happen for me. It stays where it should. I am using special paper things between holding washers and the stone.

i
Reply to
Ignoramus26451

According to Joseph Gwinn :

It sounds as though you don't have the blotter-paper washers under the dished steel washers. Both should be present, with the dished steel washers oriented so they have the concave surface towards the wheel, so they press near their OD on the blotter-paper washers.

Also -- there should be a bushing in the wheel which is a pretty close fit to the ID of the wheel, and to the OD of the shaft. If you don't have one per wheel - make them on your lathe.

As for gripping while tightening, here is what *I* do:

1) Be sure to **unplug** the grinder first. 2) Put on the first dished steel washer with the concave facing out, followed by the stone -- with both sides having a blotter-paper washer, and with a proper bushing limiting the slip of the stone off center. Then follow with the other steel washer, concave side facing in (and remember that you already should have verified that the blotter-paper washers were on both sides of the stone). Then spin on the nut. 3) Now grip the stone near the OD between thumb and finger of one hand (*this* is why you want it unplugged before you start), and use this to keep it from rotating while you tighten the nut with the other hand. This should be tight enough, with the right centering bushing(s) and the paper washers. Much tighter risks cracking the stone, anyway -- something which you *certainly* don't want to do.

My 8" bench grinder (a Jet) behaves exactly like the Baldor described above -- and usually with very little vibration even during the slowdown, and the same holds true of the ancient 6" which I inherited from my father, and *he* took in trade for a spare anchor from his boating supplies.

If the stones are slipping off center from a mild bump, then they are both not fitted with *proper* bushings, and are either missing the blotter-paper washers, or somehow are not tightened enough. Note that the nuts on the left side are left-hand thread, so both wheels, if they slip during startup, will tighten the nuts somewhat while starting, so things should get better, not worse.

And your description of the wheels wobbling from *side* to

*side* as well as running off center suggests that there is something preventing the nuts from clamping the steel washers on the sides of the wheel. Is it possible that you are fitting a narrower wheel than the original, and that the threads on the shaft are not long enough to allow a proper clamping force? If so, then you need an additional washer under the nut, again likely something to make on your lathe. (Or, it *could* be that your steel washers have the concave sides facing away from the wheels instead of towards them.)

Good Luck, DoN.

Reply to
DoN. Nichols

Grinder wheels should not be perceptibly wobbling from side to side or radially, period.

Until you have isolated and corrected the cause of this problem per the good advice of other posters, be sure that no part of your body is in line with those wheels when you test run the grinder.

David Merrill

Reply to
David Merrill

The blotting paper discs that came on the wheels are still all there, and the big steel washers do bear on them, with just a little bit peeking out from under.

I do have them. They came with the new Norton white wheel, and the gray wheels that came with the grinder either didn't need them or had them from the start. The spacers are made of blue plastic, and to seem to fit tightly.

I don't yet have a lathe, but this would be a good idea. Actually, I'd replace the stamped-steel washers with machined washers having an integral spacer, so there could be no doubt about alignment of wheel to shaft.

Yes. The washers are on either side of the stone, with cup openings facing inward, towards the stone between. That is how things are and always were. The blotters came with the wheels, and are all still attached.

It should be noted that the terrible vibration was there from the start, before I did anything other than set the grinder on the bench and turn it on.

I was doing this same thing, but couldn't get it tight enough, and I couldn't easily cause the stone to rotate on the arbor by hand, and the degree of side-to-side wobble varied with rotation angle, as did the radial runout.

Maybe this Ryobi cannot be tamed. But I'd really like to understand why it's giving me so much trouble.

As for the Jet, which model? What is the diameter of the arbor?

That's my other suspicion, that the Ryobi's 5/8" arbor is simply too small for an 8" stone. The corresponding Baldor has a 3/4" arbor.

I'm favoring the "not tightened enough" theory, as everything else seems correct. Unless the washers are able to tilt. It doesn't seem likely, but then I'm running out of suspects.

This also allows the wheel to loosen when spinning down, although one would think that the tightening torque (while motor powers up to speed) exceeds the loosening torque (as the grinder drifts to a stop). Spindown takes many minutes.

The arbor spins more or less freely, preventing adequate tightening. That, and the shoulder the washers rest upon isn't that wide, so perhaps things are able to tilt.

The original, factory-supplied wheels have this same issue. The new Norton white wheel is exactly the same size as the gray factory wheels,

8" by 1". When tightened, the nuts fit perfectly, with perhaps 1/16" of threaded shaft sticking out.

Thanks, although I'm trying to take the luck component out of it.

Joe Gwinn

Reply to
Joseph Gwinn

I've tried running without the wheels. Quiet and smooth.

When I dress the wheels, it's quite quiet, but the quiet doesn't last, so I think that replacing the wheel isn't going to help, the problem is deeper. And one of the offending wheels is made by Norton, and yet it too has the problem. More details in my response to DoN.

Joe Gwinn

Reply to
Joseph Gwinn

Yes. I follow the old "let it run for 30 minutes alone" test for new wheels.

Joe Gwinn

Reply to
Joseph Gwinn

Joseph Gwinn wrote in news: snipped-for-privacy@comcast.dca.giganews.com:

8" wheel on a 5/16? arbor is pushing it..especially if it?s a cheap, non- hardened shaft, that thing is going to deflect.
Reply to
Anthony

The way I tighten the nuts on a grinder is to let inertia do the work for me. I tighten them as much as I can while holding the wheel. Next I spin it by hand as much of an arc as I can get out of it with the wrench still on the nut. The wrench impacts the toolrest and tightens the nut. Two or three good whacks and I'm done. Sometimes I have to put a c clamp on the wheel guard for the wrench to smack into depending on the direction of thread and whether I'm tightening or loosening.

Shawn

Reply to
Shawn

That was/is a *5/8* arbor.

Reply to
Bob Engelhardt

Truing the wobbling wheel to begin with was a mistake. If a good wheel does not run true you must find out why. If the wheel is not a good quality you are probably wasting your time. It is not unusual for the washers to be crooked. Trying various combinations of your washers on both shaft ends should identify the problem. A crooked wheel or bent shaft should be equally as easy to isolate. Once you have everything true, rotating the wheel on the shaft will not change the situation. You should never compensate for a bent shaft, crooked washers, or looseness of the wheel bushing (on the shaft or in the wheel) by (un)truing the wheel. These are the only things that will cause the trueness to change when the wheel is rotated.

Don Young

Reply to
Don Young

Do you have the proper face washers on it and the paper washers between the face washers and the stone?

John

Reply to
John

According to Joseph Gwinn :

O.K. And if you try to hold the wheel with your fingers and tighten the nut, does the other wheel turn? If so, you can't get the nut far enough on for some reason or other.

Tightly on both the ID of the wheel and the OD of the shaft? If so, it should not be possible to get it off center even if the washers are not tight enough to keep it from slipping. (Though it might be possible to get the wheel to tilt, depending on how soft the bushing is.

Yes -- plus you can make the washers plus bushing long enough so the washer can't tilt. (That can be a problem with the stamped steel washers.

[ ... ]

O.K.

Which suggests that the nut can't screw onto the shaft far enough to clamp the wheel properly.

Try removing the wheel and the washers, and screw the nut on as far as it will go. Measure the gap between the shoulder on the shaft and the inner face of the nut. Compare that to a measurement of the sum of the wheel, the two blotter paper washers, and the two cup washers. Subtract a little for the compressibility of the blotter paper washers. If the nut won't go at least 1/8" closer to the shoulder than that sum, you can't clamp the wheel tight enough. Is there still some thread left but the nut won't run up onto it? If so, then either there is a burr preventing the nut from going on far enough, or (perhaps) you have a mix of a metric thread on one and a near (but not exact) inch match on the other.

Hmm ... the cup washers may be distorted. Here is where having your own lathe to make known good cup washers would be beneficial.

The model is JBG-8A. I bought it from the window display of a hardware store which sells to the construction industry, and it has been there long enough so the box was well faded.

As for the diameter -- without actually unscrewing it from the shaft, I get something pretty close to 5/8" (perhaps 16mm if it is a metric thread, which would be likely with a JET brand grinder).

Well ... the 5/8" threaded part of the shaft which I have is the same as yours (more or less). Without removing the wheel, I can't be sure that there is not a larger diameter unthreaded section, but the physical location of the grinder makes that difficult at the moment.

Note that this was an *and* -- the "not fitted with *proper* bushings" was one precondition, and the choice of either "missing the blotter-paper washers" or "not tightened enough"

Most of the stamped steel washers *can* tilt, especially if the center part may have been dented by a severe bump during shipping. If you had a lathe, I would suggest that you machine a proper set of washers with a longer hole to reduce the chances of either tilting or of distortion if bumped.

But first check out how far the nut will go onto the shaft.

Compare the spin-up time (less than a second) to the spin-down time (minutes). The wheel will not get enough torque during spin-down to loosen the nut -- unless the bearings freeze. :-)

Exactly!

Probably. One reason to make new washers if you have problems. (Lack of a lathe makes this more difficult, of course.)

Hmm ... my Jet has the threaded shaft end about 1/2 thread

*inside* the end of the nut. Add a washer or two and see whether that m makes a difference. Ideally two -- one between the shoulder on the shaft and the inner cup washer and the other between the nut and its cup washer.

A pity you aren't close by. I keep thinking that a short time examining it would show me what is wrong. (You aren't anywhere near Northern Virginia, are you?)

Good Luck, DoN.

Reply to
DoN. Nichols

According to Joseph Gwinn :

One other possibility which has not been mentioned before (but which should not have produced the wobble of the wheel) would be that it had gotten wet. If more water was soaked into one side than the other side, it would be unbalanced and would vibrate. If it was trued to eliminate that, and then shut off for some time, the water (or other liquid) would migrate to the side which was down, likely changing the balance with nothing else shifting.

I don't *think* that this is the problem, based on the visible wobble from side to side. Washers, bushing, and nut not moving far enough to properly clamp things are the most likely -- though someone else mentioned a bent shaft as well. With no wheels, are the sides of the shaft blurred somewhat? This would be likely, even if there was not much vibration with only the weight of the shaft a little off center. (Since you don't have a lathe, you probably also don't have a runout indicator to measure the shaft.) Hmm ... if the wheels have been running loose on the shafts, it is likely that they have ground down the threads as well if the size needed no bushing. If it needed (and had) a bushing, then you are protected from that, at least.

Good Luck, DoN.

Reply to
DoN. Nichols

Have you verified that the shafts aren't bent? It'll run reasonably quiet and smooth without the wheels even without the wheels on, even if the shaft/s are bent, there isn't an enormous amount of mass in the shaft ends compared with the rest of the grinder. It might be worth spinning the shaft with the covers and wheels off and looking to see if there is any perceptible movement in the centres that are, hopefully, in the ends of the shafts.

Sorry If you have already done this, just brainstorming...

Regards Mark Rand RTFM

Reply to
Mark Rand

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