Posted by: dalecyr ® 01/08/2011, 14:36:48 Author Profile eMail author Edit

I need some advice. I'm building a ball mill from scratch. The motor drives the driven shaft, which is supported on a pair of pillow blocks. The drum, which is shown floating above the assembly, actually sits on and slightly between the driven shaft and the idler shaft. The idler shaft does not spin very freely. (The measured torque is .05 ft/pounds) In fact, altho the driven shaft will rotate the drum, the drum will not rotate the idler shaft. The drum just sort of slides on the non-rotating idler shaft. The only pillow blocks I could get quickly are pretty heavy duty. (CJ Bearings, UCP204-12)( https://tiny.cc/1l1mf ) Pretty heavy duty for this application anyway; I dont expect the weight of the drum (with payload) to be more than 10 pounds. Typical weight might be 3 pounds. So, I *think* I need to drive the idler shaft too, so that both shafts are driven. To do that, I'm thinking of using a chain / sprocket between the driven shaft and the idler shaft. (not shown in the drawing) Thoughts? dale   Modified by dalecyr at Sat, Jan 08, 2011, 15:32:56

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: How to drive the Idler shaft
: How to drive the Idler shaft -- dalecyr	Post Reply	Top of thread	Engineering Forum

Posted by: RWOLFEJR ® 01/08/2011, 17:07:57 Author Profile eMail author Edit

Quick thought... Pillow blocks need to be worked in some before installation. When I say worked in I mean you need to rotate the socket around before you install them. They used to put a note on that in the boxes... Don't know if they still do or not? Clamp a piece of bar that fits your bearing bore and wobble the pillow block housing around to work it in some. They can be very stiff out of the box and when paired with another block the two could be loaded against one another because they're off plane to each other. They don't always center up like you'd expect them to. This would add bearing drag. Worth a look? Good luck, Bob

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Posted by: jboggs ® 01/08/2011, 18:08:55 Author Profile eMail author Edit

Another thought - If you made the diameter of the idler roll larger, it would be more likely to turn with the drum. Here are my thoughts: the friction of the drum on the idler roll surface is a fixed amount. The torque created by that force about the idler roll centerline is inadequate to overcome the internal resistance of the bearings. Applying that same friction force on a larger roll diameter would increase the torque proportionately. Do you know how much more torque you need? If so, you know how much larger the diameter should be. This approach might be simpler than driving the idler.

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Posted by: dalecyr ® 01/08/2011, 18:57:51 Author Profile eMail author Edit

Good ideas. I'll go work the pillow blocks around a bit, and see if I can loosen them up a bit. They are supposed to be 'self-aligning', but... I understand the concept of using a large idler shaft to reduce the force needed to turn the idler. Since I already have the pillow blocks, maybe i'll rummage around and find a larger diameter rod and turn the ends down to the bearing size. But let me throw in another thought... the drum is aluminum and the driven and idler shafts are steel. Maybe I should be "treating" the idler shaft with some sort of material that increases the friction?

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Posted by: Pinkerton ® 01/08/2011, 20:09:06 Author Profile eMail author Edit

https://www.harborfreight.com/dual-drum-rotary-rock-tumbler-67632.html Dave

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Posted by: rwolfejr ® 01/10/2011, 11:06:48 Author Profile eMail author Edit

A ground urethane coating would bump up your grip to the idler without imparting any marks on your drum... if that matters? Grit blasting the idler if it doesn't? Might even be a rubber shrink tube available for the size you're using? That'd be quick but maybe not the run-out you'll need? Might still need to dust it?

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Posted by: Pinkerton ® 01/10/2011, 18:37:10 Author Profile eMail author Edit

Or -- cut some rubber bands from a truck tube and use them over the drum and some rubber bands from a bicycle tube and use them on the shafts. Or, spread the pillow blocks apart so that the drum almost falls through and reply on the jacking effect as they used to with drum brake shoes on cars in times of yore. Dave Modified by Pinkerton at Mon, Jan 10, 2011, 20:36:53

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Posted by: dalecyr ® 01/11/2011, 16:37:08 Author Profile eMail author Edit

I tried these ideas, or variations of them, to no avail. The bearings are stout enought to handle pretty large loads, and the 1/2 pound aluminum barrel just doesnt have enough mass to effectively grip the rollers, even when it and the shafts have rubber surfaces. So I went and bought 2 sprockets and some chain, and I'll drive the idler shaft and be done with it.

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Posted by: RWOLFEJR ® 01/12/2011, 08:46:12 Author Profile eMail author Edit

A loaded hold down roll or wheel on top-ish of the drum could possibly come in handy for this also. You could cock or cant the wheel a breath so it would tend to drive or screw the drum one direction. Your two shafts will still drive the drum but that third wheel pushing on the drum if kicked a bit would direct the drum one way or another. Then give the drum a cam follower or two at the end it's being pushed toward for the flat of the drum to roll on. This would keep your drum from walking around or dancing a bit and keep it from bumping into your pillow blocks. Just a thought.

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Posted by: dalecyr ® 01/13/2011, 13:54:33 Author Profile eMail author Edit

there's an interesting idea, and one that I would never have come up with. I got some gumption last night, and installed the sprockets and a longer idler shaft; I'll install the chain tonight. I think. I bought some #40 chain and a chain breaker from Big R, a farm supply house. It has been about 40 years since I've messed with chain, but I'm not sure I like how this breaker works. It doesnt appear to be able to push the pin all the way out. If I remember right, we just used to use a hammer and pin punch, while balancing the chain on a rock. In any case, once I get the thing together, I'll post a picture of it. If it is still not working right, I'll find a place to post a video of it. thanks for all the help and suggestions. I appreciate it. dale

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Posted by: Pinkerton ® 01/13/2011, 14:19:16 Author Profile eMail author Edit

A roller chain breaker is only meant to shear off the crimp of both pins holding the plate on one side. Once that is off, the plate from the other side with pins attached should just slide out. Dave

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Posted by: Bob Engineer ® 01/22/2011, 19:10:15 Author Profile eMail author Edit

wow!! really2 good idea... keep it up..

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Posted by: dalecyr ® 01/30/2011, 16:26:20 Author Profile eMail author Edit

This is the finished product. Well, the structure is finished, but I have to thread the canister to put ends (caps) on it. The chain driven idler shaft proved to be a simple, cost effective solution. This mill will handle canisters with diameters between 6" and a 5 gallon bucket. Thanks for all the suggestions. dale

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Posted by: jboggs ® 01/30/2011, 22:04:04 Author Profile eMail author Edit

Congrats! Looks great. And thanks so much for sharing the results.

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