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I have two parallel shafts, 3 millimetres in diameter and offset by 8 millimetres, both anchored in surrounding housing by ball bearings. When one shaft is rotated (via gear), I want the other shaft to rotate with it. I have less than a cubic centimetre of space between the shafts in which to place the coupling mechanism.

So far I have been using a stiff orthodontic elastic looped around high-friction rollers fixed onto the shafts. However, this introduces backlash, resistance, and unpredictability.

A timing belt would work well but the pitch length would have to be no greater than 1.07", which is smaller than any timing belt I can find on the market.

Any suggestions for coupling these shafts precisely in a space- and preferably cost-efficient way?

Edit: I believe the offset is too large for Oldham coupling. Here's an image of the shafts without surrounding housing:

Shafts 8.79 mm apart

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  • $\begingroup$ What about the belts used in printers - they have a small pitch : less that the 1.07” and so do the belts used for car timing.... a pitch of around 6mm... $\endgroup$
    – Solar Mike
    Jul 4, 2018 at 20:21
  • $\begingroup$ I suggest here two conventional options, maybe you have considered them already, the first one is Oldham coupling, and the second one is Schmidt coupling. The Oldham requires much les volume than Schmidt coupling. $\endgroup$
    – user14407
    Jul 4, 2018 at 21:15
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    $\begingroup$ @Sam Farjamirad, your answer would collect recommendations, in my opinion. I researched the suggestions and agree that the Oldham would be suited for this purpose. If you moved/converted your suggestion to an answer, I would upvote it. $\endgroup$
    – fred_dot_u
    Jul 4, 2018 at 21:48
  • $\begingroup$ @Solar Mike: My problem isn't the pitch, it's the pitch length--the circumference of the belt. The circumference needs to be around 1.07". $\endgroup$
    – FisherPeak
    Jul 5, 2018 at 15:27
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    $\begingroup$ Do they need to spin the same direction? Can you use gears? You could add a middle gear to keep direction the same. $\endgroup$
    – GisMofx
    Jul 6, 2018 at 15:32

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The first option is Oldham coupling, you say ' I have less than a cubic centimetre of space between the shafts in which to place the coupling mechanism.', so i recommend Oldham coupling. They require less space in compare to the other options. Another name for Oldham is cross disc coupling (German). Friction is unavoidable, so you should consider a way to lubricate it now and then. This type of coupling is way old and they are not popular anymore in industry.

The second option is Schmidt coupling, i don't recommend it here, because they demand much more room than Oldham coupling, and they are designed to compensate extreme radial deviations think about rolling machines.There are also some issues(start up of machines), that make the application of this type of coupling less interesting.

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