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I'm trying to make a "slider crank" mechanism for cheap out of 1/4" x 1.5" aluminum, where all the movement is in the xy-plane (parallel to the ground). Total linear movement is ~6 inches. Not my diagram, but essentially this:

slider crank mechanism

I've seen plenty of examples all over the place, but I'm unclear how to robustly make joints (looks like they're labeled B and C in the diagram). I've tried something like this:

bolt with washers and nut

but with the continuous rotation the nut eventually loosens or tightens, depending on the orientation/direction of rotation. With the same thing oriented vertically (e.g. think scissor lift or articulated lamp), it seems much simpler as the weight bears on a connecting shaft, so as long as friction is low enough everything works fine, but I cannot change the orientation.

Accepting that I can cut/drill the aluminum to suit, are there things I can get at a regular North American hardware store to make this work (ideally for < 20$ for all connecting hardware)?

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    I'm voting to close this question as off-topic because it has nothing to do with home improvement. – Daniel Griscom May 11 '18 at 20:21
  • @DanielGriscom this is a project for installation in my home where the central concern is common fasteners. Do you feel this is more appropriate on a different StackExchange? – user2152081 May 11 '18 at 21:29
  • @DanielGriscom -- would this be a good candidate for migrating to Engineering.SE? – ThreePhaseEel May 11 '18 at 22:31
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The bolt/nut configuration you show requires high friction against the joined members to maintain tightness.

You need independent locking of the nut. The most common method is to use two nuts. They are tightened against each other, rather than the captured articulating part.

An alternative is to use a nut locking compound (a sort of nut glue), and not fully tightening the nut, but the removable type will probably also eventually loosen, and the permanent type prevents easy disassembly.

I would also add a washer between the articulating arms or rotating parts.

  • Two nuts is the way to go. Other solutions will be more prone to loosening over time – Eli Iser May 11 '18 at 13:21
  • Can you clarify where the two nuts would go? Exactly the same as the picture but with a second nut on the outside of the existing nut? – user2152081 May 11 '18 at 14:10
  • Yes. The inner nut is not quite tight against the washer, and is held with a wrench as the outer nut is tightened against it. – bib May 11 '18 at 15:01
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Is it possible to drill the hole to a larger diameter than the bolt and insert a metal sleeve that is slightly longer than the thickness of the 2 arms and tighten against the sleeve. This will act as a replaceable bushing and should reduce wear.

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Instead of a bolt and nut design, just a short length of your aluminum rod with holes drilled for cotter pins, and washers.

Or a bolt and a castle nut with a hole drilled in the bolt for a cotter pin.

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