ballscrew to stepper shaft alignment

[JAZZCNC]

This is not all due to poor alignment.?
Because your rear plate and front plate are so long and so thin you are always going to struggle with screw alignment because has your front plate extends and becomes a very long lever the 10mm plate will flex and because the ball nut mounting is attached the screw alignment will also shift. Combine this with a tall and thin rear plate, even though you say it's supported, you will get some flex. On top of this, you have other weak links like the stepper mounting being thin and weedy so together they play a part in the total misalignment you are getting.

Yes changing to a better coupling will buy you extra time but eventually the same will happen unless you remove the cause of the problem which to me is mostly down to the weak nature of the Z-axis causing misalignment while in use which you will never be able to adjust out as it's random with the flex.

To me, you either live with it and replace it with another cheap coupler, buy a spare, and realize you'll need to replace them often.!.... Or . . Upgrade the Z-axis with a stiffer setup.

Changing to a pulley and belt setup will remove the alignment issue but it could introduce other issues because now you will be putting lateral forces on the ball screw and Bk bearings and like was mentioned lower down if your BK bearings are the cheap Non AC kind they won't handle those forces for very long and you'll introduce other problems like binding and stalled motors etc.

If it was me I'd beef up the Z-axis before wasting any money on expensive couplers.