4.5" Angle Grinder disk blew up!

[SuperDave456]

Another safety notice by yours truly:

So I was cruising around Home Depot earlier today checking out their Angle Grinders and related gear. I have 2 angle grinders, a cheapo chinese one, that I use to sand stuff with, and a cheapo Black and Decker, that I use as a chop saw.

Well I came upon these 1/8" thick metal cutting wheels and thought it would be good to cut up this L6 steel that I have in 1'x2' sheets into smaller bars for making knives.

I was almost finished cutting out what I wanted when I got away from my clamps and the 1/8" thick steel started to vibrate. No clamps were nearby and the steel began to chatter against the cutting edge of the grinder. Almost instantly the wheel grabbed and the steel torqued the disc just right to snap it.
I imagine that the 3600 RPM that my grinder was going, perhaps faster, the forces are pretty tremendous, because by the time I stopped it the 4.5" cutting wheel was nowhere to be found, just a few jagged pieces attached to the grinder and a sliver stuck though the steel I was cutting.

I had the steel guard on my grinder, had the grinder set up so it threw sparks AWAY from me, and wore glasses and long pants.
That being said, I think I need a face shield. If a 1" piece of that disc smacked my face or head I'm not sure I'd be out of the hospital yet. (I'm ugly enough, I don't need any cool facial scars.)

So, add a Face Shield to my short list of things I need.

Also, the fragments of that disc are stuck between the 2 nuts that hold them to my angle grinder.
The tool that I have to get the nut loose is bending before the nut loosens. So I hosed it down with Kroil and am letting it set up.

Anyone know of a better way to get that nut off without destroying the grinder?

Learn from me, be careful.

Stay safe!

 

[KD0AXS]

I've had the exact same thing happen a few times. I'm not a real stickler about wearing safety glasses when using power tools, but the angle grinder is the one thing I ALWAYS wear them when using.

Angle grinders typically spin about 10,000-12,000 RPM.

 

[doitmyself]

What brand of grinding disk were you using and did that factor into the accident?

Glad that you are o.k.. Thank you for sharing.

 

[SuperDave456]

Not sure of the brand of grinding disc.
I will have to find my receipt.

The factor that made it blow up is it getting wedged in a vibrating piece of steel that I should of clamped down better.

I'm not sure a "better" grinding disc would of survived. Although a thicker one probably would have.

I should of done a better job of clamping down the sheet of metal I was cutting.

 

[KD0AXS]

Yeah, I've only had the thin cutting discs disintegrate like that. Never had it happen with a grinding disc, which is much thicker than a cutting disc.

 

[RS250]

So,how do you know that the vibrating metal caused the cutting wheel to break. Did you take a slow motion film of the operation, or is this just speculation on your part? I would have to ask you if you looked at the RPM limits on the cutting wheel. I am thinking that maybe you where useing a cutting wheel outside of it's design paramaters. If the removal tool is bending upon removal then you have not installed the cutting wheel properly. Sounds like you have used an additional nut as a locking jamnut.If you did I would ask why. Did you use the proper washer under the nut to distribute the fastening torgue across the cutting wheel? Did you have burrs under/on the nut that contacted the cutting wheel and maybe introduced stress risers into the cutting wheel? I would finish by saying to ALWAYS evaluate the need to use protection gear first, before starting to use power tools. I have a friend who is a brilliant mechanic who is minus one eye because he did not think about his protective gear first.

 

[sciphi]

I'd rather rock a cheap tool with a quality consumable (bit, blade, wheel) than the other way around.

Thanks for the reminder, my face shield is POR-15'ed to uselessness. Time to get another from HF...

 

[Driz]

You really ought to have a face shield when using these thin disks. I personally don't like them and try to use the thicker ones when I can and the chop saw most of all. Still, you can't beat them for what you need them for. FWIW I almost buy nothing from my local welding shops as they are a rip off. Still, safety goggles and shields seem to be dirt cheap there. Take a look, glasses, nice simple not the ultra protection you won't wear but simple workable wearable ones, $3. Shields (yea they are all about the same are around $14 with replacement shield pieces being around $7. Get a couple of them so you can always find one and not get tempted to attack that one time without it and get hurt. I don't use any guards on mine as it gets in the way too much, just a shield and pair of safety glasses. I do make sure to have thick clothes and use the lower part of the shield to protect my neck.

 

[Errtt]

I've had a number of cutting disk's destroyed in a nano-second. Easy to do when the metal vibrated and jammed the disk. Or me side torque the disk in the cutting slot causing a jam.
Seems to happen less often with my pneumatic high speed cutter, maybe because its smaller and easier in the hand, I dunno.

Now those little thin cutting disk for my Dremel, I buy several packs/stacks because I destroy them as fast as I eat M&M's. Dremel does have a fiber looking disk that's thicker and takes more a beating, but that's not as fun.

 

[stephen9666]

Yup, time for a full face shield. I use one whenever I'm using the bench grinder or dremel tool or anything similar.

Mine was cheap. I think I paid under $10.

 

[durallymax]

Face shield is always needed with abrasives. Don't forget you still need glasses on behind it though. Same applies for welding mask. Once a cherry comes around in and hits your eye lid you'll realize why so many recommend the use of glasses as well. I have no scientific data of why this happens, it just does. That should be all that matters right?

3500rpm sounds slow. Most machines that size are doing 10,000rpm or so.

With cheaper cutoff blades, I have had a lot explode. I recently switched to Metabo grinders which have been great. They are a little more than the big name brands, but are built well and made in Germany. A 4.5" quick change one will run you around $140. When I switched I also decided to just buy a bunch of Metabo abrasives as they were very reasonably priced.

I use Metabo "Slicer" Cutoff 4.5" cutoff wheels. They are only 0.040" thick which is much smaller than you 1/8" blade. Don't let it scare you. We have multiple guys working in the shop and none of us have broken one of these yet. They slice through like butter. I don't see the need for a thick cutoff wheel. You just want to cut why spend all the extra time making such a big kerf. I buy them in boxes of 100. They are just under $1 each IIRC. Below is a picture.

If you cannot get it off with the wrench then you put it on too tight to begin with. NEVER use the wrench to put a disc on. Spin the nut down hand tight and then grasp the blade for a little extra snug. That is plenty. You want to have it loose enough that it will come off by hand when you need to change the blade. This method came to me from a large production shop. it does not cause issues. We had an issue with one guy still swearing by the wrench. This put a dimple in our daily work as we would then always have to hunt for one to remove the nut. Now that I switched us to Metabo grinders, I opted for the quick nut on them. It has a snap ring in it that keeps tension on it. There is no provision for a wrench. This provides an added level of security, but mostly for us its nice that he cant put a wrench on it.

Check the local welding shops. one of them should carry Metabo's line.

Heres a link to their site.

http://www.metabo.us/

Heres a pic of one of our 4.5s and the 9". The 4.5 also has an anti kick feature which stalls the motor when it senses a harse kick back. It actually does work too, you really don't notice it happening when it does it.

 

[JimPghPA]

Originally Posted By: Errtt
I've had a number of cutting disk's destroyed in a nano-second. Easy to do when the metal vibrated and jammed the disk. Or me side torque the disk in the cutting slot causing a jam.
Seems to happen less often with my pneumatic high speed cutter, maybe because its smaller and easier in the hand, I dunno.

Now those little thin cutting disk for my Dremel, I buy several packs/stacks because I destroy them as fast as I eat M&M's. Dremel does have a fiber looking disk that's thicker and takes more a beating, but that's not as fun.


The new Dremel EZ-Lock arbor work with disk made for metal and disk for plastic. And while the arbor is an initial expense, and the disk(s) are more expensive, they are much more robust, and can take a lot more abuse without breaking into little pieces. They do wear down, but you get much more use from them compared to the thin brown (neco-wafer) type that shatter with the slightest side torque or any other abuse such as getting to aggressive in how hard you apply the disk to what you are cutting.

For cutting the 1/8 thick steel, a band saw might be a better option. There are some low cost band saws that can be used upright or as a horizontal saw that falls down against the piece it is cutting. Harbor freight sells them, but for about the same money you can get a better quality one from ENCO. The harbor freight ones use a low cost (cheap) china motor that is rated for 110 VAC and will over-heat and burn up if you run it on 125 AC. Your have to have a bucking transformer to reduce the line voltage. And also these china motors do not have enough air cooling, and you have to have an external fan blowing on it when it runs or it will burn up.

The same type and size of saw is available from ENCO but the over all quality is better and the motor is better.

Also Morse makes metal cutting circular saw blades of different diameters. You have to pay close attention to the maximum RPM the blade of the diameter you are going to use has, and the RPM of the chop-saw you are going to put it in. Don't even think of using one of these blades free hand. The metal MUST be clamped down very well, and you can only use them in a chop-saw.

McMaster-Carr sells the Morse metal cutting blades, and you can call Morse and they will tell you who the local reps near you are. Morse also sells some large cut-off saws with the proper RPMs for the blade of the size those saws use.

A 10 inch diameter metal cutting Morse circular saw blade with 52 teeth rated for 5200 RPMs maximum cost about $100. McMaster-Carr has it as their part no. 2431A4 Check the RPMs of your saw before ordering, and if the RPMs are greater than the maximum for the saw of the size you want to get, don't get it.

 

[JetStar]

free-hand cutting with these thin disks often results in a disk explosion like you experienced. They are not designed to take much sideforce. If much of the disk is in the kerf of the cut, the problem is agrivated. You may have been better served by taking the stock somewhere to be cut properly on a bandsaw or a shear.

 

[durallymax]

Originally Posted By: JetStar
free-hand cutting with these thin disks often results in a disk explosion like you experienced. They are not designed to take much sideforce. If much of the disk is in the kerf of the cut, the problem is agrivated. You may have been better served by taking the stock somewhere to be cut properly on a bandsaw or a shear.



Ive burntbthrough tons of the metabo alicers cutting off bucket cutting edges where a lot of the blade is in the kerf. Never broke one yet. Broke plenty other brands thougv.

 

[JimPghPA]

Craigslist has plenty of large bandsaws for good prices.

 

[STREETRACE69]

I am new here and just saw this post and it hit a nerve..well almost literally!

I used to do a lot of metal fabrication for street rods and used cutting discs on a angle grinder all day. I always used a full face mask but had the gaurd removed as most due for clearance issues.

Of course one day I did not use a mask and grabbed the grinder to cut a stupid strap off a crate. I didn't make contact for a second and I heard and felt this incredible thumb right above my right eye in my eyebrow area. I shut the grinder off and felt part of the disc was stuck in my head. I yanked it out and yes it hurt like [censored].

I stood in front of the mirror petrified and 1/2" lower I would have lost my eye. The worst part is I had just read in Street Rodder about a month before about how someone had a grinding disc get lodged in the roof of a metal building.

These things are no joke!!! Also before this happened I noticed you better inspect your discs carefully especially from the box stores as they get thrown around and sometime you can see cracks and other damages.

Please if one person learns from my mistake, it is not worth the risk!!