auto-balancing bench grinder arbors

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
Attachment 13073

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..
Attachment 13074

first arbor parted off
Attachment 13075

one set done - the other set was already made from a previous grinder
Attachment 13076

mounted, centered and a groove trepanned for 3/32 balls (for my mtb pedals)
Attachment 13077

both sides done, with the bearing covers also parted off from the same blank
Attachment 13078

test fit
Attachment 13079

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.
Attachment 13080

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
Attachment 13081

wire wheel side
Attachment 13082

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

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.

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 :eek: 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

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!

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, :). :popcorn:

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!

Attachment 13128

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.

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

So no oil or grease on the balls?

Quote:

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Originally Posted by C-Bag

So no oil or grease on the balls?

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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.

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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:

<div id="blocks"> <div class="block b1 pngfix"> <div class="bimg"> <div> <a href="http://www.homemadetools.net/homemade-autobalancing-grinder-arbors-2"> <img src="/uploads/155833/homemade-autobalancing-grinder-arbors.jpeg"/> </a> </div> </div> <div class="head pngfix"></div> <div class="left pngfix"></div> <div class="right pngfix"></div> <div class="blockover b1 pngfix"> <div class="title"> <a href="http://www.homemadetools.net/homemade-autobalancing-grinder-arbors-2">Autobalancing Grinder Arbors</a> <span> by <a href="http://www.homemadetools.net/builder/mattthemuppet_3">mattthemuppet</a></span> </div> <div class="tags">tags: <a href='http://www.homemadetools.net/tag/grinder'>grinder</a>, <a href='http://www.homemadetools.net/tag/arbor'>arbor</a>, <a href='http://www.homemadetools.net/tag/balancing'>balancing</a> </div> </div> </div> </div>
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Matt, I think you need some heavy oil that lets the balls move but holds them in place when they have reached the balance point. That of course would require seals to keep the oil in there while everything is spinning willy-nilly.

could be, although centripetal force (or lack of it) keeps them in place as far as I can tell once the grinder is up to speed. They only roll around on start up and just before the grinder finishes slowing down to a stop. I tried grease and it didn't let them move at all. I don't think oil would hurt but I don't think it's necessary either, plus the downsides of sealing it in as you said.

I'm getting some 3/16 balls tomorrow, just can't stop needing to itch that scratch and see if I can fully balance the wire wheel.

You go Matt. I KNOW the itch, when you are so close but not there. Some folks are with ok with 75% I'm too OCD to let it go. All of this is kinda counterintuitive for me.

It might be one of those things where less/larger bearings would work. Dunno. I'm somewhat skeptical of any kind of oil in there too.
Glad you've decided to work all the way through. :popcorn:

Thanks for the article.

you're welcome!

quick update. Finally got some time to recut the groove for 3/16 balls and I made it wide enough that the balls could stack in one spot (in a zig zag pattern). Filled the groove a 1/3 full, spun it up without and then with the wire wheel. Still some vibration and no detectable difference from the 5/32 balls, but a noticeable difference from no balls. That'll have to do, works well and what vibration there is doesn't affect the finish I get from the grinding wheel.

My guess is that it's just a crappy wire wheel - got it from Lowes and the hub is visibly out of round with respect to the center hole. I'll keep my ears and eyes open for a better one at some point.

Quote:

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Originally Posted by mattthemuppet

you're welcome!

quick update. Finally got some time to recut the groove for 3/16 balls and I made it wide enough that the balls could stack in one spot (in a zig zag pattern). Filled the groove a 1/3 full, spun it up without and then with the wire wheel. Still some vibration and no detectable difference from the 5/32 balls, but a noticeable difference from no balls. That'll have to do, works well and what vibration there is doesn't affect the finish I get from the grinding wheel.

My guess is that it's just a crappy wire wheel - got it from Lowes and the hub is visibly out of round with respect to the center hole. I'll keep my ears and eyes open for a better one at some point.

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Matthemuppet, have you seen the Oneway Wheel balancer? I ended up going that route because I had spent hours already on this silly 8" grinder of mine and it was still scaring me to death. I think it's probably and easy thing to copy and make yourself especially the balancer jig. My fine grit wheel was a real challenge and it's got it running smooth, something I never thought I'd accomplish. This is not an auto balancer, but it sure works good. I did a little write up in the tools and tricks section of HMT.

thanks for the reminder c-bag, I looked up your post and enjoyed the read. Much appreciated. It would be an interesting option for sure and one I'll keep in mind for the future. Right now though I'm itching to get on with other projects :) I need to finish up a bearing remover and some spacers for my bike bottom bracket bearings.

Yup, know the feeling, that's why I opted for the Oneway. Just didn't have time and had to get 'er done.

Good luckmwithmthe nearing remover and bottom bracket spacer.

thanks, nearly finished it, just have to part off the bearing pusher. Also made a couple of spacers by trepanning into the face of the slug at the desired ID, turning down the OD and then parting off. After that all I had to do was turn the nub down to the ID of the bearing. I was rather pleased with myself about that :)

I do not have any personal experience with this but have heard of using lead shot in car tires as an auto balance. In this case I would wonder if they would hold up, nothing like filling the air with lead dust. Just a comment. Good idea though, I have an old arbor shaft I'm looking to get hooked up when time allows.

Good idea but I just balanced the wire wheels. I made a simple jig and use short self tappers to counter balance a bit like the way they used to do car wheels.
Stopped nearly all the vibration which used to drive me crazy. Nice work you have done there. Cheers Stuart, Australia.

I have not read all the follow up posts here so I hope that I am not being repetitious.
Decades back I had access to mercury and I made similar devices using mercury instead of balls. Years later after some house moves , new grinders and the loss of the mercury source I tried the same with water. That only worked when I made them with impractically large diameters.
This theme has prompted me to revisit this. A month or two ago I wanted some hard and heavy balls and I bought a box of 1/4" tungsten carbide balls. They were not expensive and should be better for this application. In fact when I finish writing this I'll be in the workshop making one from a Delrin case for low friction and carbide balls for their mass. Also their greater mass to size ratio should reduce any sticking problems. Lead balls might work but I doubt that they would retain their shape over time and start sticking. Delrin might suffer a similar fate over time from brinelling by the carbide balls. If so then I will change to metal cases.

PS. I'll do this with a square groove about 1 mm wider than the ball diameter. The balls will only contact the holder on the outer part of the groove when in use so plenty of clearance on the inner wall will do no harm unless it is so big that the balls jam under one another.
I'll report back.

PPS. I have already changed my mind. I will go for steel cases and forget the Delrin.

Suggestion: Use a larger quantity of smaller diameter balls. Lead shot comes to mind as well as ceramic balancing beads used for tire balancing. The ceramic beads can be had in as small as 1oz. bags online or at a lot of automotive parts stores. They are heavy for their diameter and "flow" easily. I have been using them for years in my motorcycle and car tires with great results. The farther away from the shaft the more effective they are. Don't use lubrication as it will cause the beads to clump together.

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Thanks for the write-up gents!

Tony: Where did you find "affordable" carbide balls? I've been looking and they'd cost more than the grinder I have... (which does a natty rumba across the bench).
Also, the case looks pretty easy to 3D print, I may have a go at that!

Dave H. (the other one)

Quote:

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Originally Posted by Hopefuldave

Thanks for the write-up gents!

Tony: Where did you find "affordable" carbide balls? I've been looking and they'd cost more than the grinder I have... (which does a natty rumba across the bench).
Also, the case looks pretty easy to 3D print, I may have a go at that!

Dave H. (the other one)

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Try https://www.acerracing.com they also have a presence on Amazon and eBay. Good luck. IIRC I bought a pack of 10 1/4" balls, I think that they were around US$15.
I actually bought the balls to use in a Leeb style hardness tester that I built. However, I found that steel balls worked better in that application.

Attachment 34071 Attachment 34072 Click pix for full size

Quote:

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Originally Posted by 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.

.......reamed to 0.501 or so, slip fit on the arbor. Face relieved...it only contacts the wheel at its periphery. Not 100% sure why this is necessary, but that's how the original ones are made so..
Attachment 13074

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Relieved drive washers, aren't exactly a requirement to run a wheel, it's a function of manufacturing process in conventional lathe work.
CNC programming compensates for the differing by Feed Rate Per Revolution from the lesser at larger diameter, to increase at center; though facing typically moves outboard.
Conventional lathe cross slides driven by feed screw have a continual rate regardless face diameter.
The .00X per revolution rate nearer center causes a slightly raised profile. Trepanning a depression keeps that interference from outer portion of washer and blotter. Likewise, cast washers streamline facing process by incorporating that feature in the mold pattern. Many machine pads have that, most floors aren't so flat.
Broad contact doesn't assure stability.

I used to make these things for race car engines. Used 1/2 in ballbearings but they had to run in STP to avoid wear. Ran two circles of them.
Helped avoid crank nose breakage in the cars.