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Originally Posted by M. Krass
or "How I Need to Make A Turntable That Will Not Bind."
So, I am in the midst of designing a mechanism that rotates about a vertical axis and I'm worried that the enormous attached moment arm will cause binding in this vertical pivot joint.
McMaster-Carr shows needle roller bearings that are rated for 1900+ lbs. of thrust, but I assume that is assuming even thrust on the washers at each end of the bearing. How does an uneven load affect the performance of such bearings? Are they a viable solution for this problem, or is there some other method that's commonly used for supporting vertical axles under torque load?
Attached is a graphic and, by circumstance, a vague look at the arm design. I hope it makes my concerns clearer.
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I think what you are saying is you are trying to prevent the shaft that has the arm on the end from twisting in its bearing.
We also have a long arm on a turret, we pulled it off using a long (4 feet or so) pipe. It has an oil-impregnated bronze plain bearing at both the top and bottom of it, so there will be no radial loads, only side loads, which plain bearings stand very, very well. The drawback is you have to design around it because it gets in the way, and its a little late to be working one in, but it is the best way we could think to do it.
I'm so nice, I cropped a pic of ours to make you a special teaser. Maybe I'll talk to my team about posting full images tommorow or something. For now, be content with this sliver of a picture. Both the top plat that has a bearing and the bottom plate are secured and very stable . . the pole will be driven and our arm will be mounted to the top of it. Thus, no radial loads on the bearings, only a side load.
The pole and bearings weigh maybe 3 pounds. There 'may' have been other stuff used that has mass and whatnot, but the entire turntable system (not including motors and arm) is probably aroun 5 pounds or so.