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As my first serious mechanical engineering project, I've built a wall-mounted folding table using of a pair of 4-bar mechanisms (WIP, ignore the wall mounts): folding table with 4-bar mechanism

I'm using fisheye bar ends with spherical bearings, like this: fisheye spherical bearing bar-end

The mechanism behaves more or less the way I'd intended, but the spherical bearings have introduced a lot of lateral motion into the mechanism, which I'd like to minimize.

What is a good way to minimize or eliminate this lateral motion? Should I replace the fisheyes with clevis bar ends?

damian
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2 Answers2

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Can you cross brace between the left and right side of the mechanism. If I understand correctly there are two parallel four bar mechanism that in tandem.

I am afraid that if you place more constraints in the joints, if they are not aligned correctly the mechanism will not work correctly as it will try to bend some of the linkages.

Proposal:

Weld the red bars below to the linkages

pic

John Alexiou
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  • Thanks for the suggestion! Unfortunately the lower set of bars has to pass through the plane of the table, so a cross-bar wouldn’t work there. My plan is to have items (music machines) fixed inside the table, so a cross beam in the top pair would interfere with that as well! – damian Aug 07 '17 at 07:59
  • Try with pins, but have some way of alinging them all in parallel. – John Alexiou Aug 07 '17 at 12:06
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For reference, I'm answering my own question with the solution I used.

I replaced half of the fish-eye bearings with clevis bearings (on the wall end of each of the bars), which has eliminated most of the lateral motion while still allowing enough flexibility to actually mount the thing.

There is still some lateral motion but, because the table has one side flush with the wall in both the fully-open and fully-closed configurations, it doesn't matter in practise.

damian
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