Autobalancing grinding wheel arbors

[mattthemuppet2]

winegrower's thread about arbor spacers reminded me about how I tackled this problem on my grinder and another member suggested I post up the solution as these things tend to fade out of the collective consciousness over time.

Anyway, I had read about autobalancing washing machine drums and Nascar wheels, where they have a sealed groove near the periphery partially filled with steel balls. As the drum or wheel spins up, the balls distribute themselves based on the center of mass (I think) of the wheel until the center of mass is at the center of rotation = perfectly balanced. That sounded like a neat idea, so I gave it a go (plus the stock washers/ arbor spacers were crap).

I made these on my Atlas 618 out of alu. First are the i

this is one pair - the thin one is the part that goes on the spindle first, then the wheel, then the one on the right goes on after.

 

[mattthemuppet2]

the thick outer part then gets a groove trepanned on the outer face (away from the wheel), this is where the steel balls go

and a thin cover made for each

 

[mattthemuppet2]

then for some reason that I can't remember (maybe I was struggling to balance the wire wheel) I went back and made the groove bigger for heavier balls

installed. That white wheel is a fair bit thinner now after grinding literally 100s of drills

they both work really well, the grinder is super smooth and has a lovely long coast down time. Right near the end as the wheels slow you can hear the balls rattle around, that's pretty much the only way you can tell they're there.

 

[C-Bag]

I remember you working on this but at the time it sounded like it was not quite there. Maybe I didn’t see the final mod where you put the larger ball bearings in, dunno. Glad to hear it worked.

 

[mattthemuppet2]

yeah it was a while ago for sure, you have a good memory! I think the bigger balls got most of the balance issues sorted with the wire wheel and the loss of many pieces of wire in the years in between dealt with the rest

 

[StevSmar]

That’s a great idea!!! And it will rebalance as the wheel wears!

 

[NCjeeper]

I had some of these but on a larger scale. I had some on my jeep wheel hubs to balance out the large 37" bias ply tires I had on it. I can't remember who sold them. This was back in 2001 or so.

 

[Winegrower]

I like this! It’s not clear why this works, but there are other things like this, like counterbalance weights on aircraft cranks that have some auto adjust. One issue I had was the limited shaft length on my grinder would limit the size of the balls and hence the compensation range. I was quite surprised at the weight and arm required to balance.

This is something to analyze in more depth. Good job!

 

[mattthemuppet2]

As best as I understand it, the reason why something out of balance vibrates is because the center of mass of the rotating object is not the center of rotation. Think about spinning a child around by their arms - as you try to spin around on the spot (center of rotation) the weight of the child will try to pull you away from the spot as your center of mass is somewhere between the two of you (closer to the midpoint the closer your masses are).

But any mass free to move (say a bag on a strap) will try to rotate around the center of rotation as that takes the least energy, so it will automatically end up opposite the rest of the mass so that the center of mass is the same as the center of rotation. Obviously the more the two centers are different the more mass is needed to do so. That's how I understand it at least

In my case the Norton wheel was relatively well balanced and can be dressed, which also improves the balance some. The wire wheel was a different matter and way out of balance. It has however gotten allot better with use so the balancing hubs can do a better job.

 

[DavidR8]

This is very cool. I had read about balancing beads for motorcycle tires and thought it had to be hooey but obviously not!