View Full Version : What RPM's for the Small Wheels?

05-03-2010, 10:28 AM
I just bought a small wheel attachment and a .500" wheel.

Very impressive bit of kit and I'm really enjoying the versatility. To say that this one investment has opened new doors for my designs, would be an understatement.

However, I'm worried about burning the bearings up as I've heard a few folks warn about not running the grinder for more than five minutes when using the .500" wheels.

I did notice a lot of heat in the aluminum holder when I was working on a handle, yesterday. It was hot enough to make you wonder about getting burned.

Any thoughts? Nothing to worry about?

05-03-2010, 03:01 PM
Yep, it's worth worring about. The 1/2" wheels wheels spin very fast and generate a lot of heat in the bearings....which makes the center shaft get hot....and when it gets too hot, the rubber will come off.

It's hard to spec a definative speed for these wheels...the key is heat as you've noticed. For me, if it is too hot to touch, then it's too fast..for too long. I think about 2000 sfpm is about as fast as you'll want to run this little size continously.....then when you jump up to the 1" dia...you can double the belt speed to about 4000 sfpm.

Again, it's all about heat. When it gets hot...it's too fast...or too long. Use your own judgement and develope a system that works good for you.


05-03-2010, 07:14 PM
Thanks, hoss. I was wondering, but it's mighty hard to sift out the wive's tales from the real deal.

I was just in the shop and used her a good bit. Noted that the small wheel doesn't like a coarse grit, but makes cutting finger grooves so much easier, regardless. I can't believe I went so long without....

01-15-2012, 05:06 PM
I always hate to specify a single number like 2000 rpms for example. When you do that, it tends to imply that anything over will lead to certain and castastrofic failure...which is not true. For example, if the spec is 2000 rpm....who's to say that it will run fine at 2001 rpms....common sense tells you that it will be OK...but where do you actually draw the line....2002, 2020, 2100 rpms..? I always hate specs....and feel that they are mostly creative marketing or an attempt to cover your butt from liablity issues. The fact is that you can run these little wheels pretty darn fast for short periods...or slower for ever. The key is that they get hot when they run fast. The faster and longer they run...the hotter they get....and when they get too hot...the rubber flys apart. So, use this idea with some common sense....and you'll be fine. Check the wheel periodically to see how hot it gets...if it is too hot to touch, then it is probably too fast...for too long. Let it cool down, slow it down, or don't run it as long. Soon, you'll develope a sense for the speeds and tasks and you'll never have to think about it...it will just become natural.

PT Doc
05-06-2012, 07:44 PM
And if anyone wants to quantify the too hot to touch idea, an ir temp gun will work. :3:

05-06-2012, 11:43 PM
I have a variable Speed on my Hardcore Grinder and a Step pulley set up on my KMG grinder.

The last year or so I have used the KMG as a small grinder about 70% of the time.
When I am doing finger cutouts on steel or wood I never ever use top speed. It's just common sense to me.
My small wheels are up to 14 years old and I have never burned one out.
On the Variable I run no more than about a third of speed and the step pulley on my slowest which I guess to mate to be around 1100 RPM's ??

The .500 likes the super flex Hermes belts at about a 80 grit of more.
When you get up to the 3/4" or 1" you can run the heavy backed belts much easier.

Just shut it down every five minutes or so and check for heat build up like Rob has suggested.
After a time you will find the sweet spot for the speed when running Small wheels.