Mini grinder using old discs

[Luggsey]

I watched a u-tube yesterday where a body repair shop has a small air grinder that uses worn down standard 4" grinder discs in a small pistol shaped air tool.
[I know old worn discs can shatter!]
Anybody know how you do this as the only adaptor I can find is a shaft to angle grinder so you can make a drill use grinder discs.
The reason to ask is 2" grinder consumables are expensive and you can obviously use old 4" stuff on a smaller setup letting you clean up stuff in restricted areas.
I'm thinking a 2" air grinder with adaptor maybe but 'how to' is the question?

 

[winchman]

What do you know about Maximum operating speeds?
Remember the original disc is rated at its original diameter.
Personally as tight as I am I would always buy new

 

[Luggsey]

What do you know about Maximum operating speeds?
Remember the original disc is rated at its original diameter.
Personally as tight as I am I would always buy new

The grinding discs are the same material on mine to the base of the disc and would be used slower in an air tool then the fixed speed electric grinder.
I do know the risks, seen this done without problems and looking to find a suirable adaptor if you know of one or how to?

 

[merryman]

Not a bad idea, we use worn 7" discs at work on the 4.5" as the centres are the same. I guess someone with a lathe could easily make up a mandel to adapt the centres of 4" discs to fit an air grinder collet. balance would need to be fairly good, my Clarke (Dremel copy) shakes like mad with an out of balance stone in it.

 

[Kayos]

There was a hse prosecution fairly recently, a fab shop had a disc explode, killing the operator

The prosecution came about as adapters had been made on the lathe to fit the wrong disc on tools

Is it worth it for a few quid?

 

[Kayos]

Steel firm fined over foundry fatality - SHP - Health and Safety News, Legislation, PPE, CPD and Resources

A steel foundry has been fined £150,000 after a worker fatality while using a hand-held grinding machine.

www.google.com

 

[lchris21]

I made this up about 10 years ago............uses the worn out 4" 1mm discs that no longer are of any use on the mains powered grinder.
I know some of the forum HSE police won't be happy but, what goes on in my shed stays in my shed ...........I've never, and I mean never had one explode in the many hundreds that have been used on it, and like you said is great for tight spots which I find myself in regularly whilst playing with bike frames. My experience of any "exploding" disc is normally down to operator error in selection or use of the appropriate abrasive disc. Ive not had one disintegrate, or any vibration issues either. Perhaps its the make but mine tend to suffer obvious cracking or damage from man handling in the tool draw where they live so end up straight in the bin.
I made mine out of an old Ford timing pulley bolt, and when fitted to my air tools has very little momentum and can easily stall if overloading. They are normally around the 2.5" diameter by the time they get used on there. On the rare occasion I need a larger diameter for reach I will use a slightly less worn disc, with a face shield. I use safety glasses as rule normally...even in my own empire of dirt!

 

[Parm]

Steel firm fined over foundry fatality - SHP - Health and Safety News, Legislation, PPE, CPD and Resources

A steel foundry has been fined £150,000 after a worker fatality while using a hand-held grinding machine.

www.google.com

I’ve just read that. Talk about near misses with the same operator

 

[optima21]

I’ve just read that. Talk about near misses with the same operator

either that or the conspiracy theorists will say one of his colleagues was out to get him.

 

[Luggsey]

I made this up about 10 years ago............uses the worn out 4" 1mm discs that no longer are of any use on the mains powered grinder.
I know some of the forum HSE police won't be happy but, what goes on in my shed stays in my shed ...........I've never, and I mean never had one explode in the many hundreds that have been used on it, and like you said is great for tight spots which I find myself in regularly whilst playing with bike frames. My experience of any "exploding" disc is normally down to operator error in selection or use of the appropriate abrasive disc. Ive not had one disintegrate, or any vibration issues either. Perhaps its the make but mine tend to suffer obvious cracking or damage from man handling in the tool draw where they live so end up straight in the bin.
I made mine out of an old Ford timing pulley bolt, and when fitted to my air tools has very little momentum and can easily stall if overloading. They are normally around the 2.5" diameter by the time they get used on there. On the rare occasion I need a larger diameter for reach I will use a slightly less worn disc, with a face shield. I use safety glasses as rule normally...even in my own empire of dirt!
View attachment 316944

Agree 100% with your observations and actual experience. In 30 years I had one disc disengaged on me and that was not worn out but likley cracked before use and a thin cutting disc.
The discs I want to use are the thicker grinding discs that I have never seen break up even when worn down to a snub in the electric grinder.
Just to point out that when used in a speed adjustable air tool the disc is only in use on the work piece and not spinning at full speed all the time as in a electric grinder.
I feel much safer with the air tool to be honest!
I haven't bought a 2" grinder for home use yet so I will keep looking for a solution as I don't have a lathe yet.

 

[Luggsey]

There was a hse prosecution fairly recently, a fab shop had a disc explode, killing the operator

The prosecution came about as adapters had been made on the lathe to fit the wrong disc on tools

Is it worth it for a few quid?

A 9" modified grinder used in an industrial setting is a million miles away from a 2" air grinder used carefully at home for a very short time.....
9" angle grinders are monsters in comparison to an air driven 2" grinder that would get used very occasionaly to clean a hard to get to weld.
I appreciate the sentiment but there's no realistic comparison here in my honest opinion.

 

[anto44]

Steel firm fined over foundry fatality - SHP - Health and Safety News, Legislation, PPE, CPD and Resources

A steel foundry has been fined £150,000 after a worker fatality while using a hand-held grinding machine.

www.google.com

I've only had one disc suffer a catastrophic failure in over 20 years, it was a 4.5" thin cutting disc. The safety gaurd did its job and stopped any big pieces coming back at me and the visor stopped the bits of debris that did come back at me.
If grinding disc failures are a major problem in a work place, you have to question the use of them in that situation because my experience with grinders and cutting/sanding discs is that they're extremely reliable and rarely fail under normal use.

 

[Kayos]

I've only had one disc suffer a catastrophic failure in over 20 years, it was a 4.5" thin cutting disc. The safety gaurd did its job and stopped any big pieces coming back at me and the visor stopped the bits of debris that did come back at me.
If grinding disc failures are a major problem in a work place, you have to question the use of them in that situation because my experience with grinders and cutting/sanding discs is that they're extremely reliable and rarely fail under normal use.

Completely agree, however the OP has asked about using discs on a machine they were never intended to be used on

 

[Kayos]

A 9" modified grinder used in an industrial setting is a million miles away from a 2" air grinder used carefully at home for a very short time.....
9" angle grinders are monsters in comparison to an air driven 2" grinder that would get used very occasionaly to clean a hard to get to weld.
I appreciate the sentiment but there's no realistic comparison here in my honest opinion.

Im sure your family would take great comfort in the fact you were only using it carefully when it failed and maimed or killed you

 

[Maker]

for a very short time

Doesn't matter how long you use it for, it'll explode in a few milliseconds if it's going to explode.

Personally, I've made an adapter like Chris shows to put worn out wheels on a die grinder, as long as you don't exceed 80m/s at the edge, the hoop stress in the disc will never exceed what it would see at it's original size at it's rated RPM, so it *should* be fine.

Having said that, I might be wrong, there might be another factor that makes discs explode which I'm overlooking. Ultimately it's your decision, I won't be responsible (Legally speaking) if you get cut in half because I said it's fine but I'd feel pretty awful! On that basis, I wouldn't suggest anyone do it.

I think if you have to ask, the answer is no. Perhaps the fact that I can't seem to find the adapter you're looking for on eBay suggests Chinese manufacturers think it's too dangerous, and they make kits to put a chainsaw bar on an angle grinder...

 

[Luggsey]

Look at about 30:20 to see the tool I'm talking about.
This looks totally solid and the guys been doing this 30 years so I'm not seeing any exaggerated risk over any other grinder.

 

[Kram]

The difference is a thin 2" dia disc has so little mass it is not going to kill or even scratch you, provided you have adequate eye protection.. where as even a small chunk from a 9" can do a lot of damage and will kill.

Beyondthepress did a u tube of oversped 9" discs vs face shields and melons. You need more than a bit of plastic when a big one lets go.

 

[Morrisman]

The difference is a thin 2" dia disc has so little mass it is not going to kill or even scratch you, provided you have adequate eye protection.. where as even a small chunk from a 9" can do a lot of damage and will kill.

Beyondthepress did a u tube of oversped 9" discs vs face shields and melons. You need more than a bit of plastic when a big one lets go.

I remember when music CD’s first came and the media was awash with fears that spinning at a massive 300rpm they were probably going to explode and wipe out whole families.......

 

[Pete.]

The difference is a thin 2" dia disc has so little mass it is not going to kill or even scratch you, provided you have adequate eye protection.. where as even a small chunk from a 9" can do a lot of damage and will kill.

Beyondthepress did a u tube of oversped 9" discs vs face shields and melons. You need more than a bit of plastic when a big one lets go.

Die grinder stones can kill you. A guy on a long-lost forum I used to inhabit had one explode and took out his eye socket.

 

[brightspark]

nothing wrong with using worn disks they dont run as fast as when they are new . been doing it for over 50 years and not had one go yet