Bench grinder accident

[Larry P.]

Removed the wire brush on my bench grinder and installed a grinding wheel.
Both grinder and wheel rated at 3600 RPM. Turned it on and checked that it was rotating without wobble. As I turned to get gloves and goggles it flew apart.
Hole in the wall, hole in my hand with 14 stitches and consider myself lucky I wasn't bent over in front of it. The wheel broke into three pieces, 1/2 and the other half is split into two pieces.
What the hell went wrong? I've never heard of this happening before.
I had the large flange on both sides of the wheel. It wasn't over tightened and it was the proper diameter.
Larry

[Ed Jennings]

Re: Bench grinder accident

Sorry to hear of your mishap, but glad to hear it wasn't any worse. It could ahve been MUCH worse. Grinding wheel incidents such as you describe are actually not uncommon. The wheel could have been damaged while it was off the machine, or could have just been defective. Another possible cause is grinding on the side of the wheel rather than the face. This is a no-no unless you have a special wheel approved for this type operation. I believe these are refered to as "vertified" (sp?) wheels. Also, grinding soft materials such as aluminum or wood on the wheel can cause failure, presumably from filling up the pores and making an imbalance. Bottom line, bench grinders can be dangerous, and not just from flying particles. Always be sure that the guards are in place and adjusted properly.

[Bill W.]

Re: Bench grinder accident

Always spend a little more for a good grinding wheel or wire brush . Those $5.00 buffalo wheels are not worth the bag they put them in.Bill

[Larry P.]

Re: Bench grinder accident

I believe it was the wheel that came with the grinder when I bought it. I had installed a wire wheel and expander sanding wheel. The grinding wheel had never been used. I had just installed it and hadn't started using it yet.
It was sitting there spinning freely all by itself when it just flew apart.
Larry

[Les Jacobs]

Re: Bench grinder accident

Larry Scarey story! You might want to alert the manufacturer to the failure. They should be keeping stats on the failure rate, and this might help determine when/if there is a product recall. And if you're lucky, they'll send you a new wheel. Regards Les

[Craig S.]

Re: Bench grinder accident

Larry - new wheels and newly mounted wheels are more subject to this failure, and they always say when you spin up a grinder you should stand along side for two minutes prior to use. Also, make sure the wheeels are dead true and in good balance. I like to use a diamond dresser to insure the face is completely true. Also, observe the wheel for side(lateral) wobble. If I observe very much, I replace the wheel. I also stay with name brand wheels, not cheap imports, good wheels are not cheap, but I trust them more. Never grind on the side of the wheel without a side face wheel for toolroom use, usually they are backed by a steel backing plate on the inside face. Make sure the wheel is vitrified for strength. Glad you came through with minimal injury, this can be much worse. I don't know what brand of grinder you have, but make sure the flanges run true and are machined accurately to hold the wheels true....Craig

[Clem Z.]

Re: Bench grinder accident

there is a "tapping method" using a piece of rod to hit the wheel and listen for the difference sound. i was taught this 50 years ago in shop but like a lot of stuff i do not remember exactly how to do it.did you have the paper disks on each side of the wheel?

[Zachary K.]

Re: Bench grinder accident

When changing wheels or wire brushes and I know that there might be a chance that I will be re-mounting either, I mark the wheel or brush so the it gets installed the same way again, directional and either the outside of the wheel or the side that faces the motor gets marked so that it goes back the same way it is was originally turning.

[Larry P.]

Re: Bench grinder accident

It is a Delta Shopmaster model GR350. I did not have anything between the flanges and wheel. I see that the warning on the wheel says to use blotters between wheel and flanges.?? I don't recall getting anything like that with the tool. I also never (40 years using grinders) heard of anything of the sort.
I can tell you that I have a whole new respect for this tool. If I had been using it, and it hits my face or neck - - .
I don't like thinking about using it again.
Larry

[Clem Z.]

Re: Bench grinder accident

yes there should have been "blotters" for the flanges and they are usually stuck to the grinding wheel. without them you get uneven pressure on the grinding wheel and causes stress points and then breakage.

[Larry P.]

Re: Bench grinder accident

The paper on each side of the wheel was present. I'm waiting for a return call from Delta. I'm curious what they will have to say.
Larry

[Chuck S.]

Re: Bench grinder accident

I'm surprised the government doesn't have some OSHA standard that applies to grinding wheels. The potential injury from a faulty grinding wheel is significant. They have gotten air blow nozzles orificed down to where you can hardly get any air out of them. A requirement for proof test to 110 percent rated operating speed would probably cost the consumer, but it's better than getting killed by chunk of faulty wheel.

[Mike S.]

Re: Bench grinder accident

Larry -

The wheel was cracked - most probably a small crack in a critical area and not visible to the naked eye. This type of damage usually occurs during shipping or handling. There are several things you can do to avoid an incident like this.

First, the method Clem referred to is called a ring test, and it should always be done prior to mounting a wheel. Insert a screwdriver through the center hole so the wheel is supported by the shaft. Lightly tap the wheel on the side at the 0, 90, 180, and 270 degree positions with a wooden dowel or wooden handle. If the wheel is undamaged, it should make a clear ringing sound (this make not work very well on very small diameter wheels).

Secondly, when starting a grinder with a new wheel, stand off to the side for the first minute of operation. If there is a problem with the wheel, it will probably manifest itself then.

Third, make sure the wheel guard is equipped with peripheral tongues adjusted to within 1/4 inch of the wheel. These tongues are small steel plates attached to the top of the guard, and they cover the guard opening above the wheel. They will help keep pieces of a broken wheel within the guard and out of your body.

Lastly, be sure you use a tool rest and keep it adjusted to within 1/8 inch of the wheel.

Sorry to hear about your injury.

Mike S
#33053

[Joe L.]

Re: Bench grinder accident

Larry------

I agree with Mike S.-----the wheel was cracked. This may have occurred after you removed it from the grinder or while it was in storage. These grinding wheels are brittle; they can easily suffer damage from being dropped, etc.

Actually, I prefer using a bench model belt sander for most things that folks use a grinder for. I use the wire wheel on the grinder but rarely use the grinding wheel (mostly for sharpening tools).

[Larry P.]

Re: Bench grinder accident

Thanks everybody for your very valuable knowledge.
I agree with a crack being the cause of failure. How it got cracked? It was either cracked when I got it or it doesn't take much to damage it. It was on my bench in a stack with other wheels. I don't remember it ever being dropped.
(I don't remember what I had for breakfast)
Hopefully this may help prevent a future problem for somebody.
I intend to compile the information learned here and create a new post with all the good advice.
Larry