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I could use a hand choosing the mechanism for joining the ends of 2 flat metal bars (each around 3/4" wide and 1/8" thick) so that they pivot freely but without play.

What I'm currently planning is to drill a 1/8" hole in one and a 1/4" hole in the other, put a 1/8" diameter rivet through the bar with the 1/8" hole, then a thin plastic (Teflon maybe) washer, put a Teflon plain sleeve bearing (looks like a tiny 1/8" long pipe with a .126" I.D. and a 1/4" O.D.) into the 1/4" hole, pass the rivet through that, then through another thin plastic washer, a thin metal washer, and then close the rivet.

I think it's important to avoid metal-on-metal contact, but I'm not certain about that. Is there a simpler design that I could use?

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  • $\begingroup$ What are the dimensional tolerances on your metal, your machining tolerance capabilities, and how much radial motion qualifies as "no play"? You could just use a shoulder screw with a shoulder length slightly longer than the combined width of your parts installed in a plain through hole. $\endgroup$
    – Chuck
    Commented Jan 1, 2016 at 3:18
  • $\begingroup$ I was thinking it would be best to avoid metal-to-metal rubbing, which I would have if the shoulder screw simply passes into holes in the bars. I suppose I could use a shoulder screw with a Teflon bushing, to separate the shaft of the screw from the inside of the hole in the bars. This is a joint that's going to do a lot of motion. $\endgroup$
    – uncaged
    Commented Jan 1, 2016 at 3:35
  • $\begingroup$ Metal-to-metal rubbing is how most bearings work, like roller chain in a bicycle, or crankshaft bearings in a car. Like those bearings, you just need to remember to lubricate them as often as your load and use cycles require; typically just often enough as is required to maintain a lubricating film. If you never want to lubricate the joint then PTFE bushings will work, and you can also get oil impregnated bronze bushings. Just a matter of cost now vs. cost in the future (maintenance). $\endgroup$
    – Chuck
    Commented Jan 1, 2016 at 14:58
  • $\begingroup$ Its not metal-to-metal rubbing you want to avoid, its to not have the same type of metal in contact with itself that is critical. Hence bronze/steel, steel/cast-iron, aluminum/steel all will work. Assuming that this is a robot arm that will see less then 10,000 cycles of movement, the teflon is probably overkill. $\endgroup$
    – Mhz4.77
    Commented Jan 1, 2016 at 15:35
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    $\begingroup$ See also this related question: engineering.stackexchange.com/questions/22/… $\endgroup$
    – hazzey ♦
    Commented Jan 5, 2016 at 2:12

2 Answers 2

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Thrust bearings and thrust washers are made for this exact purpose. Your design intent is pretty close to that of a thrust bearing but more complex.

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  • $\begingroup$ I assumed that, in the way I'm planning to use the Teflon washer between the 2 bars, that washer would serve as a thrust washer. I was actually looking at thrust bearings first, but a Teflon washer looks like it'll accomplish the same result, at a lower cost. $\endgroup$
    – uncaged
    Commented Jan 2, 2016 at 3:08
  • $\begingroup$ Makes sense. You can find flanged bearings, too, that might let you eliminate the rivets. $\endgroup$
    – SteveO
    Commented Jan 2, 2016 at 3:10
  • $\begingroup$ How would a flanged bearing let me eliminate the rivets? $\endgroup$
    – uncaged
    Commented Jan 2, 2016 at 15:34
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Use a 1/4" dia x 3/16" long shoulder screw with 1/16" thick washer. Also use nut and washer on the thread. You can get the screw at: http://www.mcmaster.com/#90298a530/=10jcicb A steel shoulder screw will be much stronger than a rivet and teflon (plastic) bearings. Steel on steel is commonly used in pivots from door hinges to motorcycle chains.

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