4 1/2" angle grinder RPM

[lardy1]

Yesterday I purchased a 4" coarse wire brush (twisted strands) and began the cleanup of the underside of my 52" lawn tractor deck. The brush has a stated RPM maximum of 8500. There is nothing on or with the grinder that gave that spec so, the trusting (and sometimes gullible) type that I am worked awhile with it.

This morning I decided over coffee that I really don't like dodging high velocity darts so I researched a little and I see that my machine is operating around 10,000 RPM freewheeling.

My thoughts are that by keeping it under load and often inspecting the brush should be relatively safe combined with proper PPE.

Any thoughts?

 

[Stooge]

I wouldn't worry about the 1500 rpm difference, but I would definitely wear atleast safety glasses and gloves when using a wire brush wheel. The twisted ones seem to stay together longer than the crimped ones, but there's still always an opportunity for a stray wire to go flying off now and then.

 

[Dr.JohnnyFever]

Quality 4" wire brushes should be rated for around 20,000 RPM.

8,500 seems really low. What brand is it?

Cups are rated lower, but still usually north of 10,000 RPM.

My small Dewalt and Makita grinders spin at 11,000 no load.


Edit to add: Safety glasses are a must even with quality wire brushes. Gloves and a thick long sleeved shirt are optional depending on how much you enjoy pulling wires out of your skin.

 

[mike93lx]

Screw safety. Send it!

Realistically, if it is ansi certified, it is tested at well past the rating. That said, if you have a problem, you're taking the risk on yourself.

 

[lardy1]

I appreciate the input. I'm experienced with a lot of power tools but not so much the angle grinder. I failed to mention in the initial post that it is a cup type wheel.

The entire premise here is safety first. 30 plus years as a carpenter then twelve years at sea as a Merchant Marine and so far I'm still in possession of my major appendages. I can't stress PPE's, situational awareness and following your gut enough.

Thanks guys.

 

[Dr.JohnnyFever]

What diameter cup is it?

 

[mike93lx]

I appreciate the input. I'm experienced with a lot of power tools but not so much the angle grinder. I failed to mention in the initial post that it is a cup type wheel.

The entire premise here is safety first. 30 plus years as a carpenter then twelve years at sea as a Merchant Marine and so far I'm still in possession of my major appendages. I can't stress PPE's, situational awareness and following your gut enough.

Thanks guys.

Angle grinders are one of the most dangerous shop tools. I personally don't screw around with them, regardless of PPE. If the consumable doesn't match the tool, it doesn't go on. I would buy a properly rated wheel or a slower speed grinder, but we all have our own thresholds.

 

[MoonRise]

The attachment MUST have a higher RPM rating than whatever highest RPM the tool spins.

Attachment RPM rating is lower than the max RPM of the tool? Then that attachment does NOT go on that tool. At all.

PPE for an angle grinder includes safety glasses AND a full face shield (both at all times, not one or the other).

Trying to skip around the RPM rating mismatch by claiming that you will never let the tool run at no-load speed and will always bog the tool down below the attachment RPM rating is foolish and unrealistic. No sugar coating here.

Just go and get attachment(s) with the correct RPM rating for the tool(s) you will run them on.

 

[bcradio]

Brand?

 

[superduty1]

Quality 4" wire brushes should be rated for around 20,000 RPM.

8,500 seems really low. What brand is it?

Cups are rated lower, but still usually north of 10,000 RPM.

My small Dewalt and Makita grinders spin at 11,000 no load.


Edit to add: Safety glasses are a must even with quality wire brushes. Gloves and a thick long sleeved shirt are optional depending on how much you enjoy pulling wires out of your skin.

What quality brands do you recommend?

Sent from my SM-G973U using Tapatalk

 

[cherrybomb]

I bought a Makita variable speed grinder.I don't worry about the issues of safety,concerning speed,some of you should be careful of the attacments and the speed they run.A grinder is and can be unsafe.

 

[lardy1]

The brush is a 4" Forney.

I've nearly completed the project I bought it for. After reading a few of the initial responses I went ahead and suited up and cautiously approached the task. So far, no problems.

My thinking is that, as someone stated, those types of ratings are highly discounted for idiots like me. With the tool under load and the expected freewheeling RPM of around 10,000, I think I'm within my own window of comfortability with it now.

I did pose this question because I have been taught all my life to be safety first.

Would I suggest this to an inexperienced user? Probably not. I do agree with all who have stated the dangers of this type of tool. Or any tool, for that matter.

 

[MFolks]

Look for wire wheels embedded in rubber; https://www.mcmaster.com/rubber-bonded-abrasive-wheels

 

[johninct]

Wear a face shield over your safety glasses. You will get wire stuck into you.

 

[engineer2]

Agree on the face shield. Got a wire in the cheek in my younger days. No harm, but it was annoying.

 

[bargainhuntingking]

Rookie question: Are gloves unsafe while using an angle grinder? Seems to be a balance between protection from flying chunks vs a glove catching and twisting in the grinder.


Sent from my iPhone using Garage Journal

 

[lardy1]

Definetly a face shield. Project complete. I wore a heavy leather biker jacket, welding gloves, safety glasses, full face shield and a heavy canvas cap. She cleaned right up. I sprayed it down with Fluid Film and it's ready for reassembly.

Thanks all for the input.

 

[bargainhuntingking]

4 1/2" angle grinder RPM

(duplicate)

 

[mike93lx]

Gloves are generqlly unsafe with spinning tools.

Grinder spin so fast, they will likely burn/cut through before binding, but the risk is there.

Follow the manufacturer's guidelines to be safest.

I wear gloves when grinding, you may not want to

 

[Spacey_G]

My thinking is that, as someone stated, those types of ratings are highly discounted for idiots like me.

I appreciate that the project is done and no one got hurt.
However, I wanted to point out for future reference and for anyone else reading the thread that the kind of thinking in the quoted text is not a good way to approach safety.

Manufacturers often do build extra margin into ratings for max load, RPM, etc. But they do it specifically to create a more robust product that's less likely to fail if it's unintentionally abused or if any number of other possible things go wrong, including variability in manufacturing. The goal is a combination effect where multiple things need to go wrong for a failure to occur.

If you push the tool beyond its rated limit assuming there's extra margin, even if there is extra margin, you've intentionally defeated one of the checks against failure. Sure, sometimes you might need to do it. We've all probably done it in one way or another. But it's venturing into the territory of unknown risk.

If you have a choice, don't push a tool like a grinder attachment beyond its rated limit assuming that's not the real limit. It is the real limit.

 

[ClappedOutBport]

It's a wire wheel, not a grinding wheel, it's not going to explode. That said, a lower speed grinder with more power might cut a lot better. I often run 4" cups on 4000RPM 7" grinders so I can put some weight into for thick stuff. Not always the best but sometimes ok. You will lose your wires a lot faster overspeeding it though.

 

[Dr.JohnnyFever]

What quality brands do you recommend?

Sent from my SM-G973U using Tapatalk

Norton, Dewalt, etc. However, when I said that regarding speed rating, I was referring to wire wheels, not wire cups.

 

[Dr.JohnnyFever]

The brush is a 4" Forney.

Sounds like it all worked out fine in the end.

In the future, you might consider using a 3" cup on small grinders. Dewalt and Norton 3" cups are rated for 14,000. The 4" cups only for 9,000.

Save the 4" cup for 7" or larger grinders. My Makita 7" grinder only spins at 6,600.

 

[gearhead1]

One time I was using a crimped wire brush on angle grinder and felt something hit my chin. I had my safety glasses on. About a week later my chin was sore and I felt something in it. I pulled out a 5/8” long wire from that brush.

I don’t always use gloves or face shield but I always use safety glasses without exception when using grinding discs and wire brushes.

 

[mike93lx]

One time I was using a crimped wire brush on angle grinder and felt something hit my chin. I had my safety glasses on. About a week later my chin was sore and I felt something in it. I pulled out a 5/8” long wire from that brush.

I don’t always use gloves or face shield but I always use safety glasses without exception when using grinding discs and wire brushes.

Not only do you get hit with wires from these things, but they are guaranteed to be covered with dirt, rust, paint, etc. Great chance for infection.

Long sleeves, pants, face shield

 

[Monte]

A 4" cup brush on your small grinder will kill the bearings on the long run.

 

[CJM8515]

I used a 3" )4" maybe?) cup awhile back, nice dewalt one too. That stupid thing spat wires at me quite a bit. I took precautions and wore a thick shirt, gloves, face shield too. Be VERY careful!

 

[lardy1]

Now that I have done it, I don't think I'm going to do it again. It worked very well. But I never really was comfortable and the risk factor is higher than I want. Now that it's stripped clean and coated, I think I can maintain it without using an angle grinder.

The experience shared, the good advice and the sound safety warnings are all appreciated.

 

[neophyte]

The standard speed for 4-1/2” or 115mm angle grinders is 10,000 rpm or 11,000 rpm on some models like Bosch.
Most manufacturers of angle grinders usually only recommend using smaller steel brushes than 4-1/2” on this size of angle grinder. I think 2-1/2” or 3” is usually the size typically recommended for a 4-1/2” angle grinder.

For safety reasons, and under OSHA safety specs, you’re not supposed to use an accessory on a power tool if the power tool has a maximum rpm above the maximum rpm listed for that accessory, even if the power tool is a variable speed version that can have the rpm reduced below the accessories maximum rpm.
The reason for this is that the variable speed modules most power tool motors use can fail, and if the speed control module fails, the motor might immediately speed up to maximum rpm, which can cause accessories with a lower rated rpm to fracture or shatter leading to serious injuries.

While 4-1/2” angle grinders may have a speed of 10,00 or 11,000 rpm, 5” and larger angle may have a lower rpm rating.
The typical speed for a 5” angle grinder is 10,000 rpm, whith some angle grinders essentially being the same as the 4-1/2” angle grinder from the same manufacturer, nust with the 4-1/2” and 5” angle grinders supplied with different sized guards.
5” angle grinders are also much more likely to be available with a variable speed dial installed.
Some 5” angle grinders are abailable in a slightly lower rpm version made for working with stainless steel. The rpm on these models varies, but 8,000-8,500 rpm is usually about average for a 5” angle grinder meant for use on stainless. Angle grinders for stainless also almost always have a variable speed module, so the speed can be lowered to 2,500-3,000 rpm give or take.
8000 rpm is typically the speed 6” angle grinders have
As far as manufacturers go, Fein, Flex, and Metabo have all manufactured grinders for stainless. Fein tends to put “Inox” in the model number. Metabo and Flex may do something similar.