How to fasten rotating articulated arm without self-tightening?

by user2152081   Last Updated May 11, 2018 03:21 AM - source

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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