auto-balancing bench grinder arbors

[mattthemuppet]

still a bit of a work in progress, but I made these in the hope of balancing a wire wheel which is causing my grinder to vibrate.

Idea is to have a groove in which some ball bearings are free to rotate and come to rest at the point of lowest effective mass on the wheel, thus balancing it. Well, that's the idea anyway, not quite there yet.

blank turned and drilled


reamed to 0.501 or so, slip fit on the arbor. Face relieved so that the arbor only contacts the wheel at its periphery. Not 100% sure why this is necessary, but that's how the original ones are made so..


first arbor parted off


one set done - the other set was already made from a previous grinder


mounted, centered and a groove trepanned for 3/32 balls (for my mtb pedals)


both sides done, with the bearing covers also parted off from the same blank


test fit


balls loaded. After the 1st try, where nothing happened, I cleared out the grease. Still nothing, so I added more balls - 25 on the wire side.


stone side. This side really didn't need any balancing, ran really smoothly without any balls. Figured I'd add them anyway in case the balance changes over time with wear


wire wheel side


the arbors did help reduce vibration a bit, but not eliminate it completely. I'll be cutting the groove to 2x ball width to allow the balls to bunch up to see if that improves things. If not, I cut the groove deeper and use larger bearings for more mass. I'll report back with my findings!

here's a great article about both the physics and another machinist's trials and tribulations with balancing grinders
metalmagpie's balancing arbors

[C-Bag]

Thanks for this matthemuppet. This is a problem that has plagued me with my 8" grinder. I helped the problem a lot by truing my wheels on the mill first. I'd also seen the Norton wheels are better and more balanced assertion before. After going out and buying a set I'm also in the camp that says thats a pant-load. What I did find is they were all so off center, how could they even be in balance?

The link you provide is very interesting and I'm going to have to read through it again a couple of times. I do wish he wouldn't use washers and instead say arbor as its kind of confusing.

I look forward to your further experience with the self balancing arbor as it seems easier for me than making the balancing blades/washer set up. It's a mystery how you figure out how many and how big of ball bearings you need too.

[PJs]

Thanks Matt...interesting build for something that is always a bit of a chore. Personally, like C-Bag, I have found the Norton wheel off quite a bit, especially for the price, but they have quality grit. The trick is with the wire wheels and I have a diamond cup wheel that wobbles like a bobble head and hops like a bunny on steroids..

I've seen this ball bearing approach before but it's all dependent on knowing how out of balance they are to begin with. The guy in the link built a make shift but I built 2 pair of offset skate bearings on adjustable posts years ago and a good shaft then, stick weights on until I get the balance. Even used 4 single edged razor blades in V's back in the model airplane days for props. In your case the mass of your washer caps probably out weighs the bearings. My hit would be to go to 2x size bearings but find out how much you need first. I use/borrow our digital food scale and larger postal for big stuff. Wire wheels will continually change as they shed but your ball bearings should be great for that!! Also maybe a lighter lube than grease like 3in1 or such. Just thoughts.

Thanks for the post, look forward to seeing what you end up with. ~PJ

[mattthemuppet]

thanks you two. The Norton wheel has always been pretty well balanced, although the bore isn't completely perpendicular to the sides, which is a bit of a pain. There wasn't any difference that I could tell in vibration between the grinder with nothing on it (smooth as silk) and the stone wheel, so I think the big problem is the wire wheel.

When I get home tonight I'm going to cut the groove deeper and wider to try some bigger bearings. No idea on how full the groove should be, but intuitively 1/3 sounds about right. More than half and they wouldn't be able to distribute themselves properly, at least that's how it looks in my head. I'll report back!

[C-Bag]

To be clear and not antagonistic, I was just sharing my experience with the Norton stones. I'm glad yours is in balance.

I would love to find a way to get these 8" stones of mine dialed in. I've seen the auto balancing arbors listed but they were really expensive(way more than the grinder and stones together!) and was not sure they really worked.

Good luck and we're expecting a full report, .

[mattthemuppet]

no worries at all, I didn't take it like that. I've heard other people say Norton stones are often out of balance, I must have either gotten lucky or it's been worn down enough to smooth it out.

had a play last night, recutting the groove on the wire wheel side to fit 5/32 balls from an old bike headset bearing. After playing around with ball number, between 10 and 15 (1/4 and 1/3 full) seemed to work the best, although it didn't completely remove the vibrations. Probably about 2/3 less vibration with the balls in than not, compared with about 1/3 reduction with the 3/32 balls. 3/16in or even 1/4in balls would probably get that last 1/3 but I don't have any 3/16 balls and I don't have enough material in the arbor to safely cut the groove 1/4in deep. Good enough for me and now I can get onto the next project!



edit - for 8in stones, I'd make the arbor with a larger diameter (mine are 2 or 2 1/2in, can't remember) and start with 1/4in balls. It's a fairly simple project, the machining didn't take long at all.

[PJs]

Thanks for the follow up Matt! Great Share! Looks like you found your Balance and Groove...Grind on.
~PJ

[C-Bag]

So no oil or grease on the balls?

[mattthemuppet]

So no oil or grease on the balls?

I tried grease to begin with but it didn't let the balls move freely, which is key to it working properly. I thought about oil, but the balls move very freely in the groove and you can hear them move into position when the grinder starts up.

[DIYer]

Thanks mattthemuppet! We've added your Autobalancing Grinder arbors to our Grinding category,
as well as to your builder page: mattthemuppet's Homemade Tools. Your receipt:

Autobalancing Grinder Arbors by mattthemuppet

tags: grinder, arbor, balancing