I've found a shaft coupler that has a steel plate in between, but it's not clear what its function is:

enter image description here enter image description here

If it is to add strength to the coupler, isn't the coupler as strong as the weakest link, i.e. the aluminium ends? Does anyone know what the purpose of the steel plate is?

EDIT: Here's another similar design:

enter image description here

  • $\begingroup$ The purpose of the plate in between is to add flexibility. The input and output shaft can be slightly misaligned, and this arrangement will still work. If the steel plate were not there, and the aluminium ends were bolted directly to each other, this flexibility would not exist. I will follow up with a more detailed answer with a diagram et cetera if required, but can’t do that on my phone. $\endgroup$ – Jonathan R Swift Jun 21 at 19:33
  • $\begingroup$ @JonathanRSwift Right. But if you look closely at the aluminium ends, they're already cut to allow for flexibility though. Why do they bother with separate pieces of steel rather than add more cuts to the aluminium? $\endgroup$ – John M. Jun 21 at 19:43
  • $\begingroup$ @JonathanRSwift no need, the existing answer states that reasonably. $\endgroup$ – Solar Mike Jun 21 at 19:43
  • $\begingroup$ @JohnM. They are cut to allow the through bolt to provide a clamping force as the aluminium moves. $\endgroup$ – Solar Mike Jun 21 at 19:48
  • $\begingroup$ Oh right. Makes a lot of sense now. $\endgroup$ – John M. Jun 21 at 20:11

The plate allows for small amounts of angular misalignment between the input and output shafts.

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  • $\begingroup$ Is the steel plate expected to be bent? It'd need a much greater deal of force to bend the steel to mitigate misalignment than to, say, use a spider coupler, right? $\endgroup$ – John M. Jun 21 at 19:32
  • $\begingroup$ @JohnM. “Small”.. and steel is stronger than rubber. $\endgroup$ – Solar Mike Jun 21 at 19:34
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    $\begingroup$ A spider coupler also provides radial misalignment functionality, whereas this is purely angular. $\endgroup$ – Jonathan R Swift Jun 21 at 20:26

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