Turns out Helical Beam Couplers aren't meant to handle that much stress . . .

[Monochron]

Originally Posted by AdamHeard

You are using these incorrectly.

You are relying on them to provide bearing support to the leadscrew (via the CIMs bearings) and they are not designed to do that. The end of the leadscrew should be in bearings properly in some structure, the CIM bolting to that, and then coupled with the beam coupler. The helical portion of the coupler then just handling shaft misalignment.

As Gregor mentioned, yes we are aware that lead screws operate less than optimally when they are not supported on both ends. It performed exactly as intended with our original coupler in competition though and the only issue we ever had when when the lead screw got a little bent. It still worked well, the vibration just drastically increased.
Unfortunately, our team does not have a Mechanical Engineer of any sort. Us computer guys learn as much as we can about mechanical operation and actuators, but the finer points are sometimes missed. While it never actually failed, it could certainly be improved, so thanks for the input.

They're also not really good at dampening vibration as they are intended to be stiff.

Maybe they are intended to be stiff, but they are bendable by hand. If it was as stiff as I expected maybe it would not have deformed as much and taken the vibration a little better?