Bench Grinder Balance Plate

[Ray C]

Bill / All,

Since this is a homeshop site, it's probably best to stick to conventional methods. And I highly recommend that for most situations. BTW folks, for a brief time while earning my physics degree, I did research in rotational destruction analysis for the railroad institute affiliated with my college. THAT was some spectacular stuff. We spun the daylights out of things!

At the very least, this is a good discussion about state of quality control in grinding wheels. I'm seriously beginning to doubt that wheels are balanced at the factory -at least anymore. I've purchased several name brands and all ranged from slightly unbalanced to so far off, I didn't even try. As I said, I had a brand new 8" wheel crack on it's initial spin-up. When I tried to return the ones to MSC, there was no refund. 3 wheels and 180 bucks gone in thin air. I really wish the quality control on these things were up to snuff. On this grinder, the first replacement I got from Lowes was so bad, the entire grinder was spinning in circles. That wheel is history now -not even going to mess with it. A badly unbalanced wheel is dangerous.

I totally agree not to do anything you're uncomfortable with. I also spent many years rebuilding antique diesel engines and all had external flywheels in the 50-300lb range spinning from 650 to 1800 RPMs. Since most had single throw crankshafts, counterbalances were a necessity. The first thing we did was get rid of any old, rusty wheels -and we destroyed them for the sake of others. I've made many modern flywheels and designed/built ones with spring force mechanisms allowing the weight to move according to RPM.

FWIW, for the bench gridner, I did exit velocity calculations first but decided not to do KE (kinetic energy) calculations because I knew I was working with materials under 2 oz and well below what's considered "the speed threshold" of 200 ft/sec -the speed at which things are considered "ballistic". That said, this weight would have a hard time leaving the shaft since it's captured at both ends. If it could come off, it's exit velocity would be 45 ft/sec (because it's radius is 1.5 inches). Pieces at the edge of a wheel for example would exit at 89ft/sec. Putting into perspective, these are roughly the same exit speeds (actually less) of swarf coming off a piece turned in a lathe -albeit at higher mass. It about 2x less than a carbide insert coming off a mill face tool.

And as a final test, I mounted the weight at it's extreme extension alone on the shaft and spun it up. -And of course, this is/was done in a controlled manner! As I suspected, it was totally anti-climactic and basically no different than a slightly out of balance wheel. Used in conjunction with a slightly OOB wheel, it spins like silk. And when mounted with that wheel in the 180 wrong position well... it was just unbalanced.

Since this is a highly charged topic and specialized like rocketry and/or firearms modifications we'll leave it alone. I would like to follow-up at some point in the future about balancing mechanisms -both static and dynamic.


Ray

And for your viewing pleasure, here's pics of nice static balancer used on all my chucks and dozens of other things. It cost very little to make.

 

[Ray C]

These are the shields I use and have them located at every piece of equipment for easy access. The wire one is surprisingly good and comfortable. It distorts your vision a little bit but not as bad as you might think and you get used to it. The "chemistry goggles" are used when there's a lot of swarf flying off the lathe but I dislike how they steam-up and get scratched.

I almost made a mistake once though when doing a lot of welding (which involves a lot of grinding). I was switching back/forth between the wire shield for grinding and the welding helmet for welding. -Almost touched-off the rod with the wire screen on... -That's what you call an accidental mishap. All the other stuff is calculated and controlled.

Bill is/was right. Don't do this at home...

Ray

Ray,

Thanks for bringing up this interesting topic. We have all been down the "out-of-balance grinder" road or will be in this hobby.

Sorry I have another dumb question. I am not familiar with the term “buffer pads” which you have mentioned several time in talking about grinder wheels. What does the buffer pad look like and how is it used with a grinding wheel?

About wheel quality.......I suspect that even the "brand name" suppliers have outsourced their product to reduce labor cost and increase profits. This does not mean their product is bad. However in my opinion with the learning curve of cheaper labor it is more likely the quality control process can fail during transition and.......well you see the results.

I normally use a face shield when grinding with a hand grinder and safety glasses when using the bench grinder. A few weeks ago I was talking with my son about getting a face shield that was smaller after seeing one that fellow forum member Charley D. was using at work. My son said that was a bad idea and told me of an accident where a worker was using one of those portable cutting wheel tools and it broke severing the artery in his neck. I did not get this old by taking short cuts however I do have a few scars from making bad decisions but I am learning. Think I have decided to use the full shield more in the shop. Maybe even look for a stronger one.

Benny
The Orphanage Never Closes

 

[macrnr]

If it looks dangerous, it probably is dangerous. Some things such as grinding wheels should never be modified. Accidents of this nature happen so fast, there is no time for reaction. I am the safety officer for my company, and this would never fly in a commercial setting. It only takes one accident, and you are done. My 2 cents

 

[L98fiero]

Ray, what I've noticed as a common thread on several of the posts you've made is others saying 'run away, hide under the bed, Ray is going to kill someone' instead of making constructive critisizm. It ain't necessarily so, if you're paying attention to what you're doing and for the largest part, it seems to be the case with you.
I agree that you can't balance the wheel mounted on threaded rod _but_, you could find the rough balance on an unthreaded rod so you could get a start on placment of a balance weight. Also, as you said, you should have the proper blotters/pads under the washer but more than that, what I noticed was that you had the balance weight under the washer. The stresses in the wheel created by that are far more of a concern than anything else and that alone can cause the wheel to break.
Balancing wheels is common on larger grinders and wheel arbours are available, as on one of your posts, with the balance weights as an integral part of the arbour, and that is the proper way to balance wheels. On a surface grinder the wheels should be permanently mounted on their arbour and balanced or if there is no option for balancing, don't use the wheel. Most of the imported bench grinders have washers that are much too light and quite often not centered, it would be quite easy to make an arbour to mount the wheel and balance it. I've made new washers for mine from 1/4 steel, all that would be needed to make a balancing option would be to drill and tap equally spaced #10 holes around the rim.
As always, use the proper guarding and safety equipment, primarily, your brain!

 

[macrnr]

Perhaps the constructive "consensus" is this is a bad idea. You don't have to run away and hide to see that. Sometimes common sense needs to be your guide.

 

[Bill Gruby]

My warning to the newbies and all others stands. This is dangerous.

"Billy G"

 

[Tony Wells]

This is a bad idea. H-M cannot be responsible for recommending anything that is potentially fatal to people who may read this as perfectly safe and acceptable shop practice. If you feel you must balance your grinding wheels, buy the appropriate balancing equipment, and the balancing attachments designed and engineered, and backed by an insured supplier. This is NOT RECOMMENDED for the home shop.

Thread is closed.