Maximum Speed Ratings for Grinder Discs

Hi All,

As I mentioned in another post, I'm about to start a repair job on some rusty steel-frame windows.

After a bit of research and forum discussion I decided that the best way to remove the rust was with a grinder and some of the special "stripping" discs that are now available. I was hoping to get the 3M Scotch-Brite™ Clean and Strip Discs but couldn't find any so I opted for the Josco Strip-It discs and some "Work Force Nylon Scouring Discs".

I ended up getting a Makita GA5030 125mm grinder which seems pretty standard and has a No load speed of 11,000 rpm.

I'm new to grinders so I thought it would be a good idea to watch a few safety videos before using it. Something that's recommended is to not exceed the maximum speed of the disc, so I checked the discs I bought. The 125mm Joscos have a maximum speed of 10,500 rpm while the other ones have a max speed of 9000 rpm. So I assume that means that these discs can't be used with this grinder. But here's the thing - most of the 125mm grinders I looked at have a speed of 11,000 rpm (some 12,000) and most of the 125mm discs are rated lower than this. So does this mean that most of these discs can't be used with the same size grinder?

After a bit more online research I noticed that the smaller Josco discs (100mm) have a rated speed of 12,000 rpm so I imagine these would be ok?

Anyway, it seems a bit strange that most of the maximum sized discs for 125mm grinders can't be used with them.

Or am I missing something here?

Cheers,

Chris

You can get variable speed grinders. Often more $$

Not sure I would worry about 10500 vs 11000 rpm

Quote:

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Originally Posted by cpsmusic

Hi All,

As I mentioned in another post, I'm about to start a repair job on some rusty steel-frame windows.

After a bit of research and forum discussion I decided that the best way to remove the rust was with a grinder and some of the special "stripping" discs that are now available. I was hoping to get the 3M Scotch-Brite[emoji769] Clean and Strip Discs but couldn't find any so I opted for the Josco Strip-It discs and some "Work Force Nylon Scouring Discs".

I ended up getting a Makita GA5030 125mm grinder which seems pretty standard and has a No load speed of 11,000 rpm.

I'm new to grinders so I thought it would be a good idea to watch a few safety videos before using it. Something that's recommended is to not exceed the maximum speed of the disc, so I checked the discs I bought. The 125mm Joscos have a maximum speed of 10,500 rpm while the other ones have a max speed of 9000 rpm. So I assume that means that these discs can't be used with this grinder. But here's the thing - most of the 125mm grinders I looked at have a speed of 11,000 rpm (some 12,000) and most of the 125mm discs are rated lower than this. So does this mean that most of these discs can't be used with the same size grinder?

After a bit more online research I noticed that the smaller Josco discs (100mm) have a rated speed of 12,000 rpm so I imagine these would be ok?

Anyway, it seems a bit strange that most of the maximum sized discs for 125mm grinders can't be used with them.

Or am I missing something here?

Cheers,

Chris

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I’ve used grinders quite a bit Criss, safety glasses ear muffs Gloves if you must tho I think there more dangerous than good.
DO NOT USE A GRINDER WITHOUT ITS GUART IN PLACE
With regards the speed ranges, I’ve never ever had an issue,
Let the disks do the work, don’t push hard down on them.
Make sure you know we’re the cord is facing.

Hope that short reply helps.

Cheers Matt.

Make sure the guard is always in the optimal position between you and the closest edge of the wheel and wear a full face shield… the wires can come out due to centrifugal force and they are like tiny arrows. I once had a wire embed itself in my forehead above a pair of double shield goggles; now I wear a full shield over a pair of safety specs.

Quote:

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Originally Posted by Chief Tiff

Make sure the guard is always in the optimal position between you and the closest edge of the wheel and wear a full face shield… the wires can come out due to centrifugal force and they are like tiny arrows. ....

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Hear! Hear!

have a fried who neglected to have the guard on he almost died [heard the paramedics say to let him go]from disk breaking up and severing his juggler vein he has gone through lots of medical treatment since.

These 1mm thick would chop a jugular no probs.:o
H

Quote:

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Originally Posted by clear out

These 1mm thick would chop a jugular no probs.:o
H

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My experience is that broken 1mm discs simply don't fly far probably because their surface area to weight ratio is high, so their air resistance to weight ratio is also high and this rapidly slows then down. I've broken at least a couple of dozen 1mm discs on angle grinders and On my thin kerf abrasive disc table saw. Usually they break round the collar and flop onto the bench and stop spinning almost immediately. Of they ones that have generated broken pieces (eg 5c piece sizes) off I have been hit in the arm and hand several times and only once have these broken any skin and it was very minor cut . Except for eyes, small pieces simply don't have enough momentum to do a lot of damage.

2mm+ discs are a different matter because of their lower surface are to weight ratio enables them to retain a much higher momentum.

Nevertheless I always wear a full face shield when cutting with them. I have set several things on fire with thin kerf discs including a buffing wheel and the armpit of A flannel shirt.
Attachment 527509

I was cutting steel in the bench vise so about a foot from my face. The first one hit me on the cheek and my beard wouldn’t slowed it considerably.
I then put on my full face shield and the second one exploded all over.
H.