After seeing multiple trying to use some z couplings, that was not meant to do what they want them to do, I decided to write a bit about them.
These are both meant to do only rotating. But still the one to the left has been tried by multiple on a RepRap Prusa, and some have even complained about it being a bad coupling. The coupling them self are very good, and are doing an excellent job, because they are both doing what they were meant to do, rotate the axle. None of them are meant to do any lifting, or pulling, so there are nothing wrong with them at all, besides the user not checking their specs properly before trying to using them.
But how are they meant to be used then?
To use this kind of couplings, you normally take a thrust bearing, which is using the same principle as a ball bearing, with a steel ball rolling between the stationary and rotating part.
This bearing is then lifting the thing you are rotating, and the coupling allowing the motor and axle to not be perfectly aligned.
What can be used instead then?
When I first tried the original Prusa z couplings, I already from first sight didn’t like them, and while I have being in the RepRap community, I have also seen a few who had them breaking.
But instead of the original, I made these in stainless steel.
The good thing about these, is that they will last for ever. But there are also downsides. There are absolutely no room for the threaded rod to move around if it isn’t perfectly straight, and you need a clamp to hold the them while tightening the nut holding the rod in.
So what is the best?
That totally depends on how much effort you are going to put into it.
But if you want to do it right, go with the flexible couplings, and use a thrust bearing to hold the load up.