I hab problems with z-axis wobble by printing with the Velleman K8200 printer.
So i hade made some modifikation.
First i had changed the solid coupler (z-axis and stepper-motor).
With the new flex coupler i had the problem thad the z-axis holter starts to wobble.
So i had made a new one to fix this.
Now the printer works correct.
For mountig you need 2x M5x10mm and 1x M5x16mm