'Sine wave' deviation in X-Axis on moving bed printer. I've built a a PrintrBot inspired printer with a moving printbed for the X-Axis movement. It's controlled by a RAMPS board running Marlin firmware. And there is a problem with the X-Axis positioning.


As can be seen in the image the X-Axis is not really stable. The blocks should be 10x10x10 mm, and the top and bottom are perfect. The waving does not appear in the Y-direction, it's only in the direction of the bed movement.
Each block was printed at different speed, from medium to dead-slow. I limited the acceleration and in the last block I also limited the non-printing speed so the bed would never experience a higher acceleration than with the printing itself. But the wave effect remains. And it's also remarkably repeatable so it looks more like a synchronisation error somewhere. Does anyone has a clue, or experienced a similar effect ?
This is the issue of your z-axis rather than x- or y-axis because printing speed doesn't have any influence on the results.

I bet:


your threded rods are bent or
nuts on these rods have too high clearance or
nuts on these rods have eccentricity or
couplings (between motor and threded rods) are bent or
these couplings are badly fitted


All above suggestions concern z-axis.

[edit] because it's PrintBot its z-axis has the following disadvantage