Grinding wheel safety

Was the rest adjusted close to the wheel? I'm wondering if there was too much of a gap and the angle iron tipped into to gap and took a bite out of the wheel.

Wes S

Free speed of your grinder (1800 RPM? for a 10 incher) is a function of line frequency. Motors develop RPM proportional to frequency (1800 or 3,600 rpm) when unloaded, their "rated speed" is stated for the rated load. When a motor slows down, the difference between free speed and actual speed (called slip) makes electrical field inside develop torque. At almost zero slip (free spinning) the torque is almost zero,just enough to overcome air and bearing resistance.

I do not think that it is overspeeding, it just spins at idle speed.

I would look elsewhere.

Glad that everyone is alright.

i

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I understood Tom as saying that the wheel broke when it was free spinning, am I wrong?

i

Tom, if they are still intact...........check any bushings that were used to mount the wheel . May be one of them was allowing the wheel to wobble only after Roger tried to grind with it. Glad all is well! Lyndell

P.S. I use only a small bench grinder so I know this is apples and oranges but.............I mark all my wheels for direction as I change them around for differnet uses. That way I never risk turning one the opposite way it has run. I know this is not your problem .........just another safety point.

No. The wheel poped after the grind test that was only to see how much the wheel needed dressing. There was no human fault here that I see.

The motor is 1780 rpm with a 5" shieve and the shaft has a 3-1/2" shieve so the rpm was 2543 and the wheel was rated at 2500.

AND - I had a wheel on a Dumore toolpost grinder explode without warning (in there any other way?). Tweren't nuttin left but sand and half of that sand was stuck to my cheek (in my face). There was more sand 'welded' to the inside of the guard. Turns out I was runnning it a tad (to be truthful - a lot) over the rated speed. Got away with that for quite a while but when the shit left the fan it was way too exciting. The guard saved me from serious, nay fatal injury. Learned my lesson - cheaply! Bottom line - DON'T FUCK with this stuff! Play safe. On a historical note (courtesy of Lee Valley) knife grinders used to work lying prone over very large grinding wheels. Not a few got taken out when their wheel failed. This was at relatively low speeds but the kinetic energy contained in a spinning wheel is immense.

Another historical note: A factory in Quebec was manufacturing huge flywheels - stabilizers for freighters (or so they were told) during the second world war. Part of the operation was to spin these wheels up to certify balance. On one occasion a wheel was up to speed when one of the supporting bearings failed. This bearing failure sheared the supporting shaft! According to my information the wheel continued to spin on the remaining bearing and slowly (due to gravity) sagged downward. This sagging motion took considerable time (time being relative here). At some point the inevitable happened and the opposing bearing (and shaft) failed. The wheel dropped to the concrete floor of the plant. It sat there for a long time (again relative) and finally got a grip on the floor. When it 'left the building' the hole in the wall was EXACTLY it's size and shape. Estimated - it went sixteen miles before it stopped. History does not record what was in the way for that distance. Certaintly multiple wire fences and possibly a building or two. Most impressive demonstration of kinetic energy.

Ken.

I'm glad your guy didn't get hurt, Tom!

Now you know why they put shields on grinders .. I found out why you have to kiss the wheel on a surface grinder oh so gently once, the hard way and oh MAN it was like having a 12 gauge go off in your ear. Strange, one of the fragments from that Norton perty blue SG wheel looked like a perfect arrowhead. I kept it for a few years, dunno what happened to it.

Grant

Pretty obviously some flaw in the wheel. Didn't help that you were pushing the speed to the max. SOP is to run a new wheel for several minutes with no load, assume that it might blow in the first couple minutes of actual use. Sure is exciting if it does blow even if you were expecting it.

As for the clean underwear, when I was a young'en working in a fab shop, we were inside an 8' diameter steel tank doing final weld and cleanup. My partner was running a large air grinder (think 3hp to 5 hp), with a

5" st> From now on we will stock clean underwear in various sizes. A life changing

Have another beer, Ig!

No!, then he is posting his homosexual insights.

Nick

Maybe not. How a wheel is mounted plays a huge role in how it will perform. Even if it rang true, once mounted, if there are any anomalies (oversized bushing, for example, or the wheel isn't flat and is broken by the flanges----or there were no blotters used). Another problem could be that the bore of the wheel was not perpendicular with the sides, so the wheel was cracked when the nut was tightened. That's why a bushing shouldn't be a tight fit in the wheel. There should be room for the wheel to move about enough to be installed and properly tightened without damage.

It's my opinion that It would have little to do with this failure----wheels, at least those made by US manufacturers, are tested @ 150% of rated speed. They're perfectly safe to run slightly over speed, although it's not wise to do so. If nothing else, wheels that are run faster than their rated speed act harder than intended.

Harold

How much did the guard catch? How much got away from it? Will there be "why we adjust the guard as close to the wheel as possible" seminars on the shop floor along with stocks of clean underwear? Many people don't appear to grasp the sheer ability to do mayhem inherent in a spinning rock.

Harold wisely sez:

"...How a wheel is mounted plays a huge role in how it will perform.

As my old boss used to say, "A word to the wise is superfluous".

The often-ignored use of blotters could have been a factor. Blotters can act as shock absorbers when something grabs.

Bob Swinney

We have a couple cincinatti plunge grinders, the wheels look like they go 30" or so. I *never* stand in the rotational plain since I only have to try to fix them if there is an issue. The operator, is in front of them all day long.

Those things are scary.

Wes S

--Glad you're OK! What brand of wheel was it; i.e. an off brand or a good one? I'm thinking at the very least you might get a replacement wheel out of a reputable company. There's a reason why I've got a Baldor grinder with the thick wheels that are only ground on one side: when they blow up you're not in the line of fire! It happened to me once in the '70s but hasn't happened again since then. Back then the pieces were all captured by the cast iron housing and the iron chip pan beneath. Still plenty exciting tho..

It is indeed great when a grinder has a solid cast guard around the wheel, not something wimpy made of very thin stamping.

i

Tom,

The actual speed may be a bit higher, since you need to look at the pitch dia. of the pulleys, not the OD. In my experience, pitch dia is about 1/4" to 1/3" smaller than the O.D. Assuming 1/4", your speed would be 1780*(5-.25)/(3.5-.25)=2602 rpm. But that still doesn't sound like enough to break a wheel rated at 2500 r.p.m.

Of course, this assumes you're using a V-belt, not a flat belt.

Dave

Tom Gardner (nospam) wrote:

It was a "Jet" wheel. Don't know how name-brandy that is.