I'm quoting this extract after looking up this phenomenon...

..after roughly only an hour of use, it has developed this habit of the grinding disc spinning off...AFTER I stop grinding and place the tool down. As it is decelerating, I can just watch the nut spin loose...spinning its way right off the grinder.

It didn't do this when I first started using it. I thought that perhaps I had something on wrong. I've looked and see nothing obvious.

..as it exactly describes what has started to happen on my Fatmax. Only it occurs after maybe only 10 minutes' use.

Everything seems tight and the securing washers above and below are correctly positioned and tightened as far as possible using the tool provided.

One comment suggested that there was a small amount of play from the disc when stationary and that there might be a worn bearing....tbh I've hardly used it more than 2 hours in its whole life.

Anyone else had this issue?

Nope, this has never happened to me, the rotation normally tightens.

Hi Simon, I have had quite a lot of experience with grinders over the years and to be blunt have not really experienced anything like this. At a guess some discs wether the design thick or slim may need the securing washer to be turned over. My corded grinder , a Bosch requires this and I tend to tighten by hand with no problems at all. Without seeing the grinder I can only guess.

Funnily enough this happened to me recently (Coupe has been chopped with disc, cleaned with wheel, and the welds ground flat). With the heavier grinding wheel I've noticed that the deceleration can loosen the centre nut. Must be the centrifugal force or shock when it spins down. So I'm now extra anal about tightening the nut and checking each time it's switched on/off.

Point noted about turning the washer around for the thicker discs.

As a stone Mason for 15 years I've spent all day every day of that time with a grinder in my hand, working with granite they only last a month or 2 so I've used just about every brand in existence.
Bosch and makitas suffer this a lot. Inside the grinder head is a crown wheel and pinion, when new they have a tolerance ( slack) to allow for expansion, if they get bashed or dropped the main shaft can move by a tiny amount and eliminate that tolerance. So when it gets hot the gears mesh too tightly, you switch off and it stops too quick spinning the disc off.
Its no biggie with a disc, when doing certain shapes I use a drum waster, solid steel the size of a baked bean can covered in diamonds, weighs almost a kilo. When they spin off still doing 10k rpm they take off across the workshop at about 30mph bouncing off table legs.

Crikey that sounds scary!

I managed to catch an edge on the Coupe metalwork with the woven cleaning wheel @ xxxRPM and the whole grinder flew out of my hands and into the garage.

Managed to bend the metal work back.....

Also a warning for the DIYers out there. I wore safety glasses doing de-rusting work with the cleaning wheel and got a speck of rust embedded in my eye. Trip to opticians and a scene from A Clockwork Orange and a very sore eye later, rust removed.

Now sporting full goggles, respirator ear defenders and hard hat.

Yes, this is agreed by all references I've seen. The grinder even has an arrow on the head pointing in the direction of rotation, counter to the thread.

The loosening does seem to occur when decelerating. Oh and it was a heavier, stone-cutting disc I was using.

Sharman, that's an interesting point about the crown wheel and pinion, are you saying this might be adjustable?

Ah it's not scary once you've seen it a hundred times, usually brings out fits of laughter as everybody is jumping out the way.
Scary is when youd be leaning over a sink bowl grinding away not paying attention and you catch your shirt, it wraps up in a split second and you get a grinder buried in your chest buzzing away while you frantically try pull the plug.
Back to the point though, strip the head , clean everything and put it back together making sure the bearings are free and you've got decent slack everywhere. CV grease works well but dont go mad with it. But I've found once they start doing it their days are numbered

There’s a lot on energy in those spinning discs. The only real injury I’ve done to myself (thus far...) as a heavy duty DIYer is with an angle grinder. When doing the significant bodywork repairs on my Alfa race car when I first got it, I put the powered-off grinder down, and took my glove off to wipe my face (under visor) went to pick the glove back up and my index finger knuckle just touched the edge of the still spinning wheel. Cut a neat slot. Fortunately not deep and only nicked the tendon but I did need to go to the hand surgery clinic to have it stitched together to stop it breaking.

If you’ve ever been to one of those clinics, it’s amazing the things people do - lots of embarrassing kitchen and DIY stories.

This happened to a friend's dad when I was a kid. As I recall, he was saved from worse injury by his thick belt/buckle.

I've always thought disc cutters are the scariest tools seeing the ease with which they slice through steel or rock. A squidgy bit of human isn't going to stop it!

Reading these alarming tales above doesn't do much to alleviate the already inflated stress levels when using the darned thing!

I know that some fabricators consider it good practice to touch the grinder to the work piece to arrest the disc spinning after you've switched off the power.

Yes, I did that all the time when I was working in the oil yards, I still do it now.

I was going to say that it may be a damaged shaft but it seems Sharman has it nailed.
I've never had anything like that happen and as like some others I use one daily and have done for maybe over 40 years.

Dangerous tools and I've seen one very bad injury on site but not as dangerous a circular saw apparently.

Do a picture search on the Lancelot Chainsaw Disc, a chainsaw disc for angle grinders - popular with wood carvers until several horrific accidents requiring hours in micro surgery having bits of hands sewn back on. More dangerous than an actual chainsaw!

For me the tool I most hate using is a chainsaw.

You only have to look at the chopped up timber waste it throws out to imagine what it will do to flesh and bone.

And yet used with an understanding of what can go wrong and why, it is actually no more dangerous than most other powered tools. A standard rear handle saw has to be used with both hands making it relatively safe compared to a circular saw or an angle grinder with that Lancelot disc on. I say that as someone who practices chainsaw carving with multiple saws.

That is all quite true clanger, 2 hands needed and automatic chain brake but I still don't like using it.

Understood PeteP, many people feel the same.

Stuff of nightmares

Before everybody starts chucking out their dangerous tools, I think it’s down to common sense when using, wear the proper PPE where necessary. I worked in the oil industry for thirty years and used some interesting tools. Weighing up all the facts, the worst thing I used was a pencil grinder, the fine metal grinding went everywhere, there was more incidents with this innocent looking tool than grinders. Just my thoughts.

Its down to understanding the the tool you are using, how to use it and how not to use it. For some people it can be intuitive based on previous experience for others training is required. There is no such thing as common sense otherwise we would not see so many nasty accidents

In the oil industry we were all given training on how to use certain tools, in fact I think I still have the odd certificate with my welding certs tucked away somewhere. Common sense would involve making sure you know/ get training on said tool. You will always have accidents one way or another. Once you put a person into the equation it’s when something will go wrong, not if. Let’s face it all us car drivers have had training, but there are still accidents. Common sense can take several forms. Taking precautions and assessing the situation can all help, but accidents unfortunately do happen.

Wise cautionary words from all - if I thought too much about the sense of using an angle-grinder in my own profession I'd probably be paying someone to do it. Especially bearing in mind MRS's (who seems to attract the devil's bad luck) finger-nick experience

See, that's just macho riggers... in the office, we used a sharpener with a blade. Much safer.

(p.s. angle grinders scare me, too)

The thing about pencil grinders was the fact that the tiny grinding went everywhere, no matter what protection you had taken, eyes being the worst. My eyes still have the marks. Angle grinders were far more easy to handle.