From k8xxx-3dprinter
If your experiencing Z wobble (wavy pattern like in the left object in the picture below) you'll have to check how your flex coupler is mounted.
The Vertex manual states: "Make sure the rod is inserted fully", but this seems not to be a good idea. When the rod is fully inserted into the flexible part of the coupler it is losing its function. Just insert the rods till the flexible part (easy to see using a flashlight).
