Using an angle grinder. Dumb questions.

[N80]

I bought an angle grinder a number of years ago. It is a good quality Dewalt. I bought it to shape up my rotary cutter blades and it does a fine job. On a couple of occasions I have replaced the grinding disk with a cutting disk to cut metal with. It seems like it was a generic Dewalt multi-purpose cutting disk. Much thinner than the grinding disk. It seems to do okay but the last time I used it the disk disintigrated. I had on safety glasses and gloves and the disk parts did not hit me.

I know nothing about these tools or proper types of disks etc.

So, what do I need to know about using an angle grinder as a cut-off tool? Are some disks better than others? Certain disks for certain types of metal? What made mine fly apart? Is heat an issue? It didn't seem to be that hot. Is it common for them to come apart?

 

[HEC]

I have never had one come apart , I'm sure you wasn't doing this but you should not use a cutting disk like a grinding disk like grinding on it's face . The only thing I can think of as you were deeper in the cut it may have bound up which made it unstable and break appart . Thank goodness you had on some protection . I'm sure there are better grades of disks , like maybe not buying ones made in China for example .

 

[DarkBlack]

Grinders aren't made to tight shaft bearing fits, so a grinder's shaft will have more play to allow expansion of the bearings and shaft from heat during long grinding sessions.
That being said, running a thin cutter wheel designed for a precise intermittent duty tight bearing shaft assembly, runs the risk of side loading the cutter from what you would see as 'wobbble'. At least you wore eye protection. That's a good thing.

 

[SPYDERLK]

Could have been fractured to start or inadvertently by a side bump ... or bounced or pinched in the groove at speed. Yes, the cutoff wheels do disintegrate occasionally, whether glas reinforced or not. Be sure the mandrel is not stressing it when mounted in the grinder. Always stay out of line with the direct tangential motion of the disc and you will pretty safe. The grinder guard can be adjusted.
larry

 

[George2615]

Another thing to check is what speed (RPM) the disc is rated for. Maybe it was rated for 10,000 RPM and the grinder runs at 13,000 RPM. Disc wouldn't last too long at that RPM. Cut off wheels are pretty fragile too. If it caught or you put too much pressure on, it doesn't take to much flex for it to fail.

 

[jpm1]

I buy all my disks at harbor Freight. I have had the disks disintigrate, and also fly apart. If you look at the way they are made its suprprising that they hold together at all. I just consider it the "cost" of grinding. If you pinch or bend a cutting disk or for that matter a grinding disk, it's going to shatter and it's probably going to hurt and leave a mark. . . . John

 

[RobertBrown]

Could have been fractured to start or inadvertently by a side bump ... or bounced or pinched in the groove at speed. Yes, the cutoff wheels do disintegrate occasionally, whether glas reinforced or not. Be sure the mandrel is not stressing it when mounted in the grinder. Always stay out of line with the direct tangential motion of the disc and you will pretty safe. The grinder guard can be adjusted.
larry

x2
Expect the worst from those things. Always use the grinder guard and safety glasses or a face shield. Do not lock the grinder on when using the cut off wheels. I have been stuck with the thin disk fragments and it's not fun.

 

[N80]

Thanks guys. I think a face shield would be a good investment. The tool scares me a bit and I don't like using it but there are certain things that it does best. I think I'll look into higher quality disks too. And it was kind of strange, if I remember correctly it didn't actually disintegrate it mostly broke off in two large pieces that did not fly away with that much momentum.

Robert, good advice about the not locking it on...........which reminds me of another recent power tool mishap............

I was using a rather powerful hand drill with a wire brush on the end to clean up an old brass mailbox. The drill is too much drill for the job and I have smaller, lighter drills that I should have been using. Anyway, I had it locked on so I didn't have to hold the trigger down. At one point I was in an awkward position and leaned over and the wire wheel caught in the right sleeve of my short sleeve shirt. As you can imagine it bunched the shirt up and then dug into my arm. Then, the shirt bunched up so much it stopped the wire wheel and so the drill itself started to spin. It had the hand grip in it and it proceeded to beat the dickens out of me until I got my hands on it at which time it ripped my shirt clean in two. I was then able to throw it on the floor and unplug it.

I had a huge bruise on my little bicep with a good sized divit that the wire wheel dug out. So there I was, blood running down my arm, huge bruise already forming, half my shirt torn off, and bruising forming where it hit me in the face, ribs and belly. And all I could do was laugh. The first thought that came in my head is that I wish I could have seen it on video! The next day I felt and looked like I'd done a round with the champ.

Moral(s). Use the right tool. Don't lock power tools in the on position unless necessary.

 

[Scooby074]

Never use a chipped disk.

Cutting wheels should NEVER be used to grind. (There are a couple cutting disks made that are able to be used as a thin grinding/cutting wheel, but those are rare, like the Walter Pipefitter and HP Combo)

Watch for bends in the wheel. Bends will crack the reenforcement. This usually happens when a grinder falls to the ground or is not properly set down.

Always use the guards.

Avoid the chicom wheels. Get a good brand like Walter or Norton.

Dont bend or bind the wheel in the cut. That can cause fractures which can break later.

Lock on grinders are banned at many jobsites for good reason.

 

[SandburRanch]

Binding in the kerf ( mentioned ) and traveling the wrong direction in relation to rotation are the two major causes of wheel breakage.

 

[k0ua]

Binding in the kerf ( mentioned ) and traveling the wrong direction in relation to rotation are the two major causes of wheel breakage.

Yep, I have used both domestic and Harbor Freight brands, and I have never had one break, But I know they sure could. I am very careful not to put any side loading on them. I have worn a lot of the out. The face shield idea is never a bad idea.

 

[Dale_Alan]

You should be using a 4"/6" stone cup to sharpen blades. Also tuck in your shirt tail, it will take your shirt off like a magician and leave marks big time.
Dale

 

[texasjohn]

N80, I'll remember your story next time I think about locking on a grinder or drill...and avoid doing it...I can only imaging the excitement you had trying to get away from the drill!! But your description is enough to make an impression on me!

 

[DarkBlack]

N80, your story is even better than the countless people who bind up their large hole saw for the first time, while it's chucked up to a gear reduced 1/2 drill. Of course Iv'e never had it happen:donkey:

 

[k0ua]

N80, your story is even better than the countless people who bind up their large hole saw for the first time, while it's chucked up to a gear reduced 1/2 drill. Of course Iv'e never had it happen:donkey:

I was using a 5/8 bit on a thick wall pipe and a really heavy duty 5/8 hand drill. When the bit broke thu on the back side, I thought the drill was going to break my wrist as it tried to twist me into a pretzel.. Thankfully my finger finally got off of the trigger.:shocked:

Oh, I gave the 5/8 drill back to its owner to never borrow again...

 

[Sodo]

So, what do I need to know about using an angle grinder as a cut-off tool? Are some disks better than others? Certain disks for certain types of metal? What made mine fly apart? Is heat an issue? It didn't seem to be that hot. Is it common for them to come apart?

I use cut-off discs all the time on steel. I use Harbor freight (sometimes 80cents each) and name-brand ($4 each), and find that the Harbor freight work fine, and last fine too, and there's not a noticeable difference. There are thinner wheels too (.040") that are useful to have around, and some have an offset in the hub, which is nice for flush-cuts. The HF discs are about .060 thick. I use them for light grinding too, sometimes cutting welds, or grinding out tacks. I like them and consider them a valuable tool.

It has a lot to do with how you hold the grinder. Sorry I can't explain this better, but if the disc "chatters"; the disk is wearing away quickly. Actually it's chipping away. You MUST choose the direction you are cutting, and the center of the cut in relation to the spin axis, such that it does not cause the grinder to oscillate. Sorry this is hard to type, and even hard to demonstrate, because nobody wants to dempnstrate a chattering disc. Maybe someone else can explain better than I.

If it starts to chatter, stop and look at the disc, often it's frayed and un-even, not round. I've been able to heal a disc if it's less than about 1/4" out of round. If you crack/break the disk (by dropping the tool etc) then throw it away, that chunk will fly off at 10,400RPM.

These cutoff discs are not for everyone. As mentioned above, if the item you cut, pinches on the disc at the end of the cut, it can be a problem. You have to be careful.

Heres a pictorial example of using the cutoff disk. This motorcycle footpeg mount was cut off with a harbor freight disc on an angle grinder. Also the replacement part (1/2" steel) was cut entirely with one HF disc. (The photo of the 'intact' footpeg mount is the 'other side'). I did the minimum work required (that the owner couldn't do) left him to finish it out to his satisfaction. And he did, all good!

 

[newbury]

<snip?
I was using a rather powerful hand drill with a wire brush on the end to clean up an old brass mailbox. The drill is too much drill for the job and I have smaller, lighter drills that I should have been using. Anyway, I had it locked on so I didn't have to hold the trigger down. At one point I was in an awkward position and leaned over and the wire wheel caught in the right sleeve of my short sleeve shirt. As you can imagine it bunched the shirt up and then dug into my arm. Then, the shirt bunched up so much it stopped the wire wheel and so the drill itself started to spin. It had the hand grip in it and it proceeded to beat the dickens out of me until I got my hands on it at which time it ripped my shirt clean in two. I was then able to throw it on the floor and unplug it.

I had a huge bruise on my little bicep with a good sized divit that the wire wheel dug out. So there I was, blood running down my arm, huge bruise already forming, half my shirt torn off, and bruising forming where it hit me in the face, ribs and belly. And all I could do was laugh. The first thought that came in my head is that I wish I could have seen it on video! The next day I felt and looked like I'd done a round with the champ.<snip>

I was using a 5/8 bit on a thick wall pipe and a really heavy duty 5/8 hand drill. When the bit broke thu on the back side, I thought the drill was going to break my wrist as it tried to twist me into a pretzel.. Thankfully my finger finally got off of the trigger.:shocked:

Oh, I gave the 5/8 drill back to its owner to never borrow again...

You guys need to video tape your exploits!

 

[chad22]

I've had a grinding disk break and hit my finger because I didn't have the guard on. Not sure what caused that. Maybe I was using too much down pressure?

As for a cutting disk I've had a few break on me because of binding.

Chad

 

[AaronS]

I thought of this thread last night when I installed a brand new cutting disk on my Dewalt angle grinder. I don't remember the brand name but it was purchased at Rural King.

Then I thought of this thread even more when the disk broke in half and the two pieces went flying after a whopping 30 seconds of cutting. Thankfully neither piece hit me. I still haven't found one of the pieces. Back to the little pneumatic cut off tool for me. (Oh to have a plasma cutter!)

 

[Firemanbuck]

You guys need to video tape your exploits!

Now that's a visual image - someone with a drill bound up in their shirt trying to reach their cell phone thinking "I gotta get a video of this for the boys on Tractorbynet!"