Balancing grinding wheels for surface grinders

[samthedog]

Not wanting to hijack any other threads currently going on, I just wanted to post up some ideas for balancing surface grinder wheels. I was unaware that this would make such a big difference and figured there must be some ideas floating around on how it's done.

Ray C has put up an excellent thread on making balanced hubs here:

http://www.hobby-machinist.com/showthread.php/16950-Balanced-Grinder-Hubs

When considering how to make a balancer for the least possible amount of money, I came across this idea here (scroll to bottom of page):

http://bbs.homeshopmachinist.net/threads/40475-A-Poor-Man-s-Grinding-Wheel-Balancer

I then came across another idea which I thought was quite ingenious on static balancing of wheels without the need of machining a balanced hub:

http://homemetalshopclub.org/news/sep04/sep04.html

Here is some light reading regarding surface finish and some peculiarities of rack and pinion drive table movement, the benefits of dressing fixtures and the need for a stable spindle to minimize surface irregularity when using slightly unbalanced wheels.

Feel free to add more. I have just ordered 2 books on grinding from Tony (from lathes.co.uk) so will update when I have more info.

Paul.

 

[Ray C]

Paul,

I really like the 1st link with the quick balancing on parallel bars. That would work on my mill and surface grinder which are quite level to the horizon.

I saw the "dual elliptical" method of balancing when I was trying to solve these problems a few years ago. I really wanted to make one like that but felt I could not do it properly on a manual mill. I have another idea which uses two round disks that are milled to different thicknesses. The two disks would "oppose" each other to make two legs of the weight triangle. Problem with that though was a lack of CNC machine or ability to do it on a manual machine. I like that "opposing disk" method better and am glad you showed it as an alternative. Maybe someone can show us how to make the lobes.


Ray

 

[benmychree]

The common method may well be the easiest to make; a wheel flange with a dovetail cut in the face of it, with 2 or even three weights that slide inside it and locked in place with setscrews. How big is the wheel? Generally if you buy good quality (USA) wheels for 7" diameter (normal small surface grinders, there is not any need for balancing.

 

[Ray C]

.... I just have not found that to be the case. I have several brand new wheels (Norton) costing between 30 and $120 and not a single one balances even close. They were checked before and after truing the wheel. I have only two other wheels which are around 3/8 and/or 1/2" wide and they balance OK...

As mentioned before in a different post, if someone knows of a source of decent wheels, please let me know. This is really frustrating to spend that kind of money and get junk. They were purchased from MSC over a 1-2 year time-frame. MSC will not issue a refund.

Ray

The common method may well be the easiest to make; a wheel flange with a dovetail cut in the face of it, with 2 or even three weights that slide inside it and locked in place with setscrews. How big is the wheel? Generally if you buy good quality (USA) wheels for 7" diameter (normal small surface grinders, there is not any need for balancing.

 

[samthedog]

The common method may well be the easiest to make; a wheel flange with a dovetail cut in the face of it, with 2 or even three weights that slide inside it and locked in place with setscrews. How big is the wheel? Generally if you buy good quality (USA) wheels for 7" diameter (normal small surface grinders, there is not any need for balancing.

If people are happy with the results without balancing, then I guess there is no need. If you are after the best finish possible, then why not balance them if you have a quick method of doing it? This is why the method in the last link I provided is so interesting. The aluminium weights are easy to make, can be clamped to the wheel with a normal hub and left there. This seems to be a fast and cheap way to balance.

I believe that if the machine is rigid, the bearings are in good shape and you use small wheel, you can possibly get away without balancing. For most of us resurrecting old machines though, this just is not the case. I have the sales receipt of the machine I have now and also the receipt for a new spindle and bearings that were purchased and installed. Just for the parts it came to nearly 3000 USD so I think this is outside the budget of the average home machinist. If balancing negates some of the surface irregularities caused by worn spindle bearings then this is not a bad option to squeeze extra performance from the machine.


Ray, have you experimented with balanced versus non balanced surface finish? I would be interested in any findings you have.

Paul.

 

[Ray C]

Good Evening Paul,

It's not a matter of experimenting with an out-of-balance (hereon :OOB) wheel... They simply don't work and you can't even run the machine. I have a VFD on the machine which allows a controlled start. If a wheel is slightly OOB, you can increase RPMs up to about 2000 (give/take depending on the wheel) and you can feel it start to vibrate. When you get to 2300, it starts making you nervous and at 2500 the machine could start violently shaking -Yes, a 1500lb machine will shake and start to move on the floor. It will scare the pants off you because in the back of your mind, you know darn well that wheel could blow. I had one wheel blow-up this way. Before I had a chance to hit the power there was a mighty THUD. The safety cover was in place. No harm done except for some scratches on the mag plate.

BTW: It's common practice to let a wheel spin for 1 minute before using it. Most folks claim it's to let the bearings warm up. -Maybe so but, I think for a different reason. Moisture in the air soaks into the wheel and eventually, it will gravitate toward the bottom if it's been sitting idle long enough. Spinning for 1 minute is like a rinse cycle as far as I'm concerned. Nothing more or less than that.

Anyhow, yes, if a wheel is slightly OOB to the point you can just feel it, yes, it shows up as chatter in the finished piece. It looks like the dimpled surface of a golf ball (but more shallow) but in a random pattern.

You might think I'm crazy but I can tell by standing next to the machine if the wheel is balanced -don't even have to touch the machine. A slightly OOB wheel causes a miniscule pulsing of the air around it. You can hear and feel it ever so slightly. The minute I put my hands on the machine and actually feel it, I know right then and there how good (or not good) the grind will be.

And finally, not all wheels need to be balanced to perfection. Some work is just a quick pass. I use the daylights out of that machine -and not everything needs a perfect grind... If however, you want your $600 bearings to last, you'll use well balanced wheels most of the time.


Ray

 

[samthedog]

I want the full pack - good finish, long lasting bearings and safety. To me the time it takes to balance the wheels is just part of doing the grinding I guess. I am still in the process of repairs and fixing the machine but while I am chipping away at that I will be getting a balancing rig and weights set up for when I'm done. It's a dangerous enough machine without the added risk of wheels flying apart from being un-balanced.

Out of curiosity Ray, do you have a picture of your set-up?

 

[Ray C]

I want the full pack - good finish, long lasting bearings and safety. To me the time it takes to balance the wheels is just part of doing the grinding I guess. I am still in the process of repairs and fixing the machine but while I am chipping away at that I will be getting a balancing rig and weights set up for when I'm done. It's a dangerous enough machine without the added risk of wheels flying apart from being un-balanced.

Out of curiosity Ray, do you have a picture of your set-up?

There it is... About 100 years old according to the serial number. It has a factory upgraded motor head. It runs very true.




Ray

 

[eightball]

When i ground rolls, we always stored our wheels laying flat on their side. We never stored them hanging or standing up because the moisture would settle in the wheel and cause them to be out of balance.