Rims appearing every 5 layers on fine prints?

[DrWoo 2]

I don't own an Ultimaker, but several CEL Roboxes. The printer is really excellent, easy-to-use, very versatile with interchangeable tool heads (dual material just released, drag knife under development, laser engraver and paste extruder on the horizon) and quite affordable.

The custom-built AutoMaker software relies on Cura for slicing, which is why I'm posting my question in this forum:

I've spotted not only on mine, also on other people’s Roboxes on very fine prints (20 micron layers) the phenomenon of tiny rims, vertically reoccuring approx. every 5 layers. The precision with which the rims reoccur makes me believe that it is not a mechanically-indicated issue, but an issue caused in software, perhaps something like a numerical rounding error.

Has anyone of you folks ever seen these rims on any fine Ultramaker prints? If so, could you post images?

Edited April 23, 2016 by Guest

[Dim3nsioneer 558]

No, we don't as long as the machine is working as it should. Must be a Robox specific issue.

[gr5 2,230]

It looks like a Z axis issue. The Z axis moves a smaller distance than it should every 5 layers. I'm wondering if you are close the resolution of the Z and you lose a step every 5 layers. Stepper drivers are very complicated and with microstepping it is very common for some microsteps to do nothing (not advance the motor) for complicated reasons that I don't fully understand such that it is not quite linear movement (but close enough for most things).

Alternatively is that Z distance where the pattern repeats an identical distance to one full rotation of Z screw? It seems unlikely but worth checking.