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Bench Grinders

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jbolt

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#1
Angry with myself today. I recently bought a new Jet 8" 1hp 3600 rpm bench grinder to augment my 7" 1800 rpm Baldor. In my haste to get it up and running I made my first mistake, I did not bolt the grinder to the bench. My second mistake was not ring testing the new Norton 3x grinding wheels before installing them. Apparently the 46 grit wheel was damaged and on spool-up it broke in half as it neared full speed. The wheel guard contained the wheel halves but with the sudden stop of the wheels all the stored energy had to go somewhere resulting in the 60 lb grinder jumping off the bench onto the concrete floor. Quit amazing to see. This resulted in breaking one of the cast iron tool rests, cracking the cast iron base and bending the mounting bracket for eye safety shield. Fortunately the motor shaft and cast wheel guards are undamaged. I powered up the grinder with the wheels off and then checked for shaft run out with a TDI. After that checked out okay I put the factory wheels back on and powered it up. So far so good. Hopefully the vendor will replace the damaged wheel.

So secure your grinders and ring test the wheels before installing!

20170715_124503.png
 
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f350ca

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#2
Ouch
 

NCjeeper

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#3
Glad you didn't get hit by flying wheel parts.
 

Charles Spencer

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#4
I would contact the company that sold me the wheel or Norton's or both and explain what happened. Of course the wheel could have been damaged in shipping, but a good company would want to know that too. I'd be interested in seeing what they said and/or did.

"So secure your grinders and ring test the wheels before installing!"

Yes, absolutely.
 
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Yikes!

Glad your physically fine, sometimes our pride takes a hit but we're only humans. You posting this will surely help prevent someone else getting hurt.
+3 always inspect and ring test.
Probably could have been worse if the unit was secured. Even after a ring test, I stand to the opposite side of the replaced wheel when starting. Those HS shop safety films really made an impression on me, even after 39 years.
 

dieselshadow

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#6
Ring test?
 
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A ring test is conducted by tapping the wheel gently with a light, nonmetallic implement, such as the handle of a screwdriver for light wheels or a wooden mallet for heavier wheels. The wheels should be “tapped” about 45 degrees on each side of the vertical centerline, and about 1 or 2 inches from the outer edge of the wheel. Rotate the wheel 45-degrees and repeat the test. An undamaged wheel will give a clear metallic tone/ring. If it is cracked, there will be a hollow, “dead” sound and you will not hear a clear “ring.” In this case do not use and throw out the wheel.
 
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jbolt

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#8
Yikes!

Glad your physically fine, sometimes our pride takes a hit but we're only humans. You posting this will surely help prevent someone else getting hurt.
+3 always inspect and ring test.
Probably could have been worse if the unit was secured. Even after a ring test, I stand to the opposite side of the replaced wheel when starting. Those HS shop safety films really made an impression on me, even after 39 years.
Well I still have enough sense to stand off to the side when starting up after changing a wheel. I guess I got complacent since I've never had a bad wheel from a quality manufacturer. Lesson learned.
 

TomS

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#9
All I can say is, WOW!! Glad you didn't get hurt.

Tom S.
 

jbolt

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#10
Good news is the vendor is replacing the wheel. No argument whatsoever so good on them. I will say this experience now has me seriously considering the CBN wheels.
 

Charles Spencer

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#11
Who is the vendor?
 

682bear

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#13
I do some precision grinding at work on a cnc vertical lathe. Our grinding wheels are mounted on arbors that prevent us from ring testing them. I always inspect the wheels before installing the arbors on the grinding heads. If they have any chips or dings at all, they get scrapped. I also DO NOT crank the grinder up until the head is lowered behind the sheild doors or inside the part... I have had a few explode. You never know what the last guy did to the grinding wheel...

Also, when I scrap a wheel, I remove it from the arbor and take a big ball peen hammer to it. This prevents anyone from being tempted to take it out of the trash and try to use it...

I am very anal about 'preaching' this to anyone I happen to be training... a couple of years ago, I gave this lecture to a trainee as we were setting up a grinding job. 2 minutes later, we cranked the grinder up (inside the part) and the wheel exploded. He now 'preaches' about this as emphatically as I do...
 

bfd

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#14
did it scare the brown stuff out of you? when I blew up a grinding wheel it sounded like a shotgun going off right next to me bill
 

682bear

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#15
It absolutely will scare you... I guarantee that you won't be able to find the off switch quick enough...

Several years ago, I was running my machine when the machinist at the next machine cranked up his grinder. He had just mounted a NEW diamond wheel (its an aluminum alloy of some sort with a diamond coating bonded to the face)... the aluminum wheel shattered and slung apart inside the machine cabinet... it sounded like someone was hitting the inside of the cabinet with an aluminum bat...

After he finally managed to remember where the emergency off button was, he had to sit down for a few. He was white and shaking all over... thats the only time I've ever seen an aluminum wheel shatter...
 

Mikebr5

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#16
Even after a ring test, I stand to the opposite side of the replaced wheel when starting. Those HS shop safety films really made an impression on me, even after 39 years.
+1 on old HS shop lessons. I remember my shop teacher's warnings all these years later even though as young punk kids we all probably figured we knew enough... "Sure, sure, let's GO!"
To this day I -always- start grinders by standing to the side. Ring test only works when the wheel hangs free.

Same with the chuck key lesson. If I see a chuck key in a chuck without a hand on it I get a jolt of "DANGER WILL ROBINSON!" adrenaline pumping.
I make up for my caution around moving machinery by doing the most foolish things like lifting too much with my back. I think I finally learned my lesson this year.
 

TRX

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#17
a couple of years ago, I gave this lecture to a trainee as we were setting up a grinding job. 2 minutes later, we cranked the grinder up (inside the part) and the wheel exploded.
The guy who taught me how to use a crankshaft grinder told me how he set a wheel up one day, turned the grinder on, and the wheel exploded. You run a crank grinder standing in front of the wheel, and there's not much in the way of guards on the older machines. Half of a three foot diameter wheel caught him in the chest and knocked him across the room. He still got the shakes telling me about it, a couple of years later.


btw, a 36x12x1-1/8 wheel costs about a thousand bucks.
 

kvt

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#18
I remember those crankshaft grinders. Lucky enough have not had a grinding wheel come apart yet, But have a nice scar on my belly from one of the angle grinder disk that came apart, and that was bad enough.
 

KBeitz

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#19
Back when I was a teenager I made my own grinder...
I had no idea what i was doing. Young and dumb.
I bought what looked to be a new white grind stone
that I know today is for low speed grinders at a yard sale.
I knew nothing at the time about ring testing. My grinder
was home made with a 3600rpm 1 hp motor that i belted
to a 1" arbor at 2 to 1 ratio. So I was spinning the rock
around 8400rpm. No guards. All done I sat it on the tailgate
of my pickup and plugged in. It ran great. No vibration.
I reached for the plug and it exploded into 3 pieces. One
bounced off my overhead crane and down to the wall where
my set of wenches was hanging. That piece snapped a 9/16
wench in half and left an imprint of the wench in the wall. The
second piece went up through 30 press sheets of alum a 2/8
floor board and then bounced off the roof rafters to land back
on the second floor. The third piece disappeared out the
garage door in to the big blue sky. As I was was walking around
looking at the damage I heard a glass braking crash outside.
All I could think of was my cars windshield. I ran to check my cars.
No damage. I said to myself what could it be. Oh no.... My home...
I have big picture windows. I could find none broken. Then I seen
a big chunk of my siding missing. The third piece came down from
the big blue sky and enter my home through the siding through
the 2x10 sill plate through the basement window and laid on the
basement floor.I survived... Lesson learned...
 
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