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When "The Universe" reminds you about Safety

ttrager

Cast Iron
Joined
Jul 23, 2015
Location
East Side / Detroit
We run a couple of Cincinnati Centerless grinders with those big ole stone wheels in them.

!KABOOM-CLATTER-BANGITTY-BANG!the other day. The wheel just self destructed without cause. The guy running the machine is one of our good guys, wasn't a Machinist error, he didn't drop a part into the machine wrong, nothing jammed between the wheel and part rest.

I got a look at the situation after the housing cover was removed, and the entire Centerless wheel was nothing but a pile of busted up pink "gravel" under the spindle.

Foreman went over and investigated, best answer at this point is the stone wheel had one or more fractures in it that finally let go.

No one hurt, we are pretty good here overall with insisting people wear safety glasses, the wheel disintegrating under power was pretty much contained within the housing.

But, an eye opener and reminder: Wear your eye protection if at all possible, and if the unexpected can happen it will find a way to happen, either sooner or later.
 
This brings up a point.
When you change out a wheel, you ring test the new one before mounting it.

But a wheel may stay in the machine for months or years, and you can't ring test it every day, while still mounted in the machine.
 
When I use a bench grinder I always stand to one side, same as I do with a tablesaw. Makes line of sight a bit tougher but after seeing the results of a grenaded wheel at a local repair shop decades ago I'm always cautious of them. A mechanic was grinding something when it let go. It missed him but a chunk tore a rectangular hole in the double thickness plus plaster ceiling of the shop bay.
 
When I was a lad in trade HS (mid-70's), we had an auditorium gathering so that a gentlemen could make a impactful presentation of his grinding wheel explosion accident, which left him blind.

This stuck with me over the years. Not too surprisingly, I take care when grinding or wire-wheeling...
 
I was cutting up some scrap copper pipe recently with a cut-off wheel, it flew apart and put a gash in my arm. First time a cutting or abrasive wheel of any kind flew apart in over 40 years of using them almost daily.
 
When I use a bench grinder I always stand to one side, same as I do with a tablesaw. Makes line of sight a bit tougher but after seeing the results of a grenaded wheel at a local repair shop decades ago I'm always cautious of them. A mechanic was grinding something when it let go. It missed him but a chunk tore a rectangular hole in the double thickness plus plaster ceiling of the shop bay.

I learned that the hard way, tried a little too aggressive of a cut on a manual lathe as I was doing production work
and getting tired of it. A couple pound chuck of aluminum came out of the chuck and managed to hit me in the nuts. Boxing as an amateur and doing a lot of sparring I was never knocked down, that piece of aluminum scored a quick knock down, and I did not get up by the count of 10 either.
 
if the machine sat long enough- could coolant have settled to the bottom of the wheel creating an out of balance condition that would be extreme enough for the wheel to grenade once the spindle was turned on?
 
I was in a buddy's shop recently, lending a hand, when what sounded like a grenade went KA-BOOOM! A Blanchard wheel cut loose. It was brand new too. Scared the tarts out of me. The guarding kept it all in and the operator wasn't hurt but ZOUNDS was that loud!
 
Glad no one hurt and it contained.
If the wheel on a big Cincinnati centerless blows it gets everyone's attention. Know one guy who almost lost his arm and was off work for 6 months.
Scary is the word for these machines.
When I bought mine used it had the dual stacked rough/finish wheel setup on it and everyone wanted to "fire it up".
I said no, wait for the new $900 wheel to get here. Pulled off the old wheels and the back one was cracked from center to OD.
I'm not sure you can ring test a wheel of this size.
Bob
 
Before I started at one shop they had a lumpsum tub grinder lose a wheel segment that broke the tub..The tub on those machines is about an inch and a half thick.
Easily a direct hit at that force could kill someone.

At the same shop, a worker lost an eye when a small high-speed cut-off wheel exploded. I don't know what guard that machine had, or if the guy was wearing safety glasses.

At one shop we had a couple of TC grinder wheels blow up. I checked the box and found that the stated RPM was lower than the spindle.. I had to argue with the boss to allow discarding the rest of one box of wheels.

Failure to use a grommet is often the reason for an exploding wheel. Sometimes an accidental bump transporting or installing. I have ring tested 48" vitrified wheels. On an odd/rare occasion, a wheel seems to explode for no reason at all.
Being in the blow direction is dangerous with any wheel, standing to the side is the rule.
Even just a bar in the blow direction makes better, but a proper gaurs is the rule.
 
if the machine sat long enough- could coolant have settled to the bottom of the wheel creating an out of balance condition that would be extreme enough for the wheel to grenade once the spindle was turned on?

I didn't ask this question, but my feeling is no. The machine is used every day, use/maintenance the same as it has always been for decades. Our Foreman did the investigation into the issue, so I'm trusting his judgement given his almost 40 years of experience with these very machines.

Good question though. I learned something from it, at least something to perhaps ask about in the future if the need arises. Thanks.
 
I was in a centerless grinding shop recently where one machine had a chunk the size of my fist missing from the regulating wheel and they were still using it. I did not ask why, but the chunk creation must have been exciting and likely involved the main wheel. The regulating wheel on these machines turns very slow RPM except during dressing. The main wheel on the other hand goes at the surface speed of any normal grinder and is a couple feet in diameter and several inches wide.
 
We have 4 Cincinnati centerless grinders at our shop running all day long, great machines but the smallest mistake usually has a massive consequence. Ive seen and heard a wheel blow up from operator error and it is the machine shop equivalent to a black hole forming lol
 
I have never done it but have watched guys hand-feeding a CG all day long with never a miss hap..

But I have done some pretty dumb things on SGs and ODs.

Grinding push rod flags I always had to find out how deep a pass I could take before the magnetic chuck would not be able to hold it. Every once in a while I could get one to stick in a cork board on the wall. Good times, that was a boring task, had to have some fun. That was a small tool room that was empty on my shift. The night plant manager stayed out of my end of the building for the most part. Pretty sure I would have lost tool room privileges if caught playing darts. Only about one guy a department was allowed in there.

I am a little on the reckless side when it comes to working fast but I won't risk more than getting a couple stitches. Even then I haven't even needed as much as stitch from a shop oops. I probably could have used a few here and there but I am a pretty good cut man.
 
Some of these stories make me happy that I make small parts.

I have never done it but have watched guys hand-feeding a CG all day long with never a miss hap..

But I have done some pretty dumb things on SGs and ODs.

I was talking with a sales engineer that used to run a small centerless grinder making hypodermic needles. He said he hand fed them, I asked how many times a day doo you get stuck ?
 
I scrapped a Cincinnatti centreless last year,and had a dozen or so mounted wheels .....I gave each wheel a belt with a sledge ,and three of them broke with rusty cracks radiating from the mount.They wernt out in the weather ,either.....wheels likely cracked from wet blotters causing rust between wheel and mount.
 








 
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