Die grinder speed & RPM question

[md21722]

High quality die grinders are available in multiple power ratings and speeds. Common power is 0.3HP, 0.4HP, 0.6HP, 0.9HP, 1HP, or more. Speeds are often 12000, 15000, 18000, 20000, 25000, 30000 RPM...

A lot of the abrasives I use are rated for 25,000 RPM for both 2 and 3".

I am wondering if there are any guidelines, or if you should just use the fastest die grinder available for the abrasive in question? And where does the power come into play?

As an example, the Dotco catalog suggests using a 12000 RPM die grinder for 3" but using a 20000 RPM die grinder for 2". Power is 0.3HP.

By comparison, I have a 3M 0.5HP 20000RPM disc sander. It's bigger and bulkier than the smaller Dotco, and will power through anything but I believe it uses 2x the amount of air of the Dotco.

And then there are 1HP die grinders which use another 50+ % more air (37-43CFM).

For sure the power is nice, but if you don't need it, then you're just running the compressor longer.

The smaller tools are lighter and smaller, but not significantly. I suppose in an 8 hour day it may matter a bit, but all are industrial grade and intended for all day use.

Can anyone suggest any guidelines for speeds & power?

 

[Jim Diesel]

I have never looked that far into it. I use two die grinders, one a right angle set up and both rated to 20000rpm. I always use wire tools and abrassives rated too 25000 rpm. Because i use them daily inside a large workshop with industrial air compressors i have never had to consider air consumption rates. I manage to achieve all my die grinding task with these two units. For larger jobs i will use a 6" angle grinder, either cordless or corded.

 

[Hammer1963]

I have used die grinders on the job for 35 years and the best recommendation I can give you is this, go as slow as the cutting tool will effectively work. I have yet to see a cutting tool, abrasive or any die grinding tool that needs to be run at 20,000 RPM. As the old saying goes "speed kills" and the same goes here

 

[md21722]

I appreciate the feedback.

I was starting to wonder if the Snap On/3M 0.5HP disc sanders and die grinders are overpowered for the 2" or 3" discs they often get used for, but Dotco seems to be more likely to be used for carbide burrs. And then there are the 3" wire wheels which are often rated at no more than 15,000 RPM but typically you need to buy a 0.6-1HP die grinder to get the slower speed.

 

[sberry]

I agree. There seems to be a fascination about how much air a guy can ram thru a tool vs how to use the thing. One of airs big advantage is it can be easily regulated, run the trigger like a throttle. These are 3 real troopers. I like the 4 inch right angle for cut off wheels. Super for wire wheel too. Lots o power, very fast.
I should get a better 5 inch sander, someone gave me a cman but the trigger is all or nothing and I don't care for it as I do the 7 inch in the pic here that is super smooth and a cutting machine with 36 grit on.

 

[md21722]

Most of your tools except the die grinder with the carbide burr look to be 4"+ disc sanders or angle grinders. For these, 12,000 RPM and 1HP is the generally accepted setup? I have a half a dozen of them and wouldn't want them any less powerful. I was more curious about the 2-3" surface prep discs and carbide burrs.

 

[Fcvapor05]

There's good advice already posted, but I'll add this-

Die grinder speed ratings are free speed, i.e. the speed at which the tool will turn at the rated air supply pressure/flow, without a tool in the spindle. A 20,000 RPM die grinder will not turn a tool at 20,000 RPM. The one exception might be very very small carbide burrs- if the tool is small enough you might get close, but likely still not all the way to max rated speed.

Tool speeds are the max speed the tool can handle safely- if you're using a tiny die grinder that's rated for 25,000 RPM with a big 6" cutting wheel rated for 12,000, it's not a huge problem because the die grinder simply isn't going to spin that big tool at 25,000 RPM, especially not when you're actually cutting with it.

 

[md21722]

I notice this when using cutoff wheels in my 4.5" pneumatic angle grinders versus grinding discs. I don't run out of air with the cutoff wheel, but I do using the grinding disc. Since I only have about 18 CFM delivered, that tells me the cutoff wheel cutting into 1/8" steel slows the tool down but the grinding wheel probably runs close to/at the rated 12,000RPM of the tool. So how does one account for this? At the same time, I've run 3M large yellow discs rated at 25,000 on my Sioux 0.7HP 25,000 RPM die grinder and thought it was way too fast ... the Sioux will torque your hand when you start it. At that power level, it probably has enough HP to run at near 25,0000 RPM. My 0.3-0.4HP Dotco's don't have enough power to do that. If I'm being too academic, please tell me the practical industrial way to factor speed/power.

One of the reasons I asked was: is this marketing or practical?

I suppose if you have a more powerful air motor that can turn the abrasive at rated speed without slowing down you're getting more efficiency... but that is compared to the fact that just because the abrasives are rated at 25,000 RPM doesn't mean they should be run at 25,000 RPM....

 

[ttpete]

I have an ARO air turbine die grinder with a 1/8" collet. It is marked 85,000 RPM, and I believe it. Too fast for anything but a bur, and it really will cut at that speed.