Bearing Frustration

May 26, 2007 25 Replies

Originally I was looking at using a pot just like you say -- but the least expensive ones I was finding in Digi-Key were well over $5.00, with some over $10. The one I'm looking at now is $1.50 in quantities of 1, and I can mount it on the PCB which will eliminate some hand wiring (which is always expensive).

I like your idea of an adjustable friction source -- I want to keep the friction as low as possible initially, because one should know how to wring the most performance from a well-behaved plant, but being able to increase it would be good, too.

I'm thinking four or five inches high, and somewhere between five to seven inches wide between the uprights. "Accuracy" is intimately tied to "$$$" in my brain, so I'd rather find some bearings that can tolerate some slop than try to make this into an aerospace-quality part.

I'll look into channel, though, and see what I can find about having it fabricated from that instead of bent up from sheet.

Sintered Bronze bearings are more commonly known as "oilite", (a brand name) in North America.

Steve R.

All joking aside, take a look at Radio Shack. They have a 10K linear pot for $2.89 qty = 1. I worked at a place that needed stereo volume control pots and the best price they could find was Radio Shack. They got a lot better price than the retail price in the few hundred per month volumes they needed.

Regards, Bob

I will keep that in mind -- I know that you can buy in quantity from those guys.

At this point, if I can mount a PC board with enough accuracy (there's that expensive word again!) the $1.50 pots that I've found will work with no adjustment -- so the whole system will just slap together without fiddling. I find this a very appealing alternative to just about anything that needs special skills to assemble.

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One thing which the extruded channel will free you from is the problem of alignment of the holes in the bearings. Bent aluminum is likely to relax a bit over time after bending, so what started out with holes properly aligned would be likely to change (and bind) over time.

If I were building it, and bending, I would look into bearings which were sintered bronze (like Oilite) with a spherical outer dimension, mounted in a hole with a spring plate holding it in position, so the sphere could turn to correct the aligment of the holes.

Enjoy, DoN.

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