Bug: Offset (layer shift) between first and second layer when printing PLA + PVA

[macio 0]

We upgraded Cura and Ultimaker firmware to latest version recently (Cura version 3.4.1, Ultimaker 3 Extended firmware release from 29.5.18)
Since then, printing a model with PLA using PVA as support material results in a layer shift between first and second layer.
See attached pictures, model is not printed with a brim, the single layer at one site is shifted but part of the model.

Edited July 16, 2018 by macio

[gr5 1,933]

90% of the time this is a loose pulley.  First figure out if it slipped in X or Y.  Then tighten all 6 pulleys (SIX - not four). on that axis.  The most likely problem pulley is the one on the stepper.  You should be able to get it with a long handled hex driver (it's okay to push the print head around to get access to the set screw).

 

Tighten the hell out of those pulleys.  If you are using an L shaped allen wrench with the short arm for torque it should hurt your fingers a lot after.  A lot.  Tighten it so much you are scared.  The steel shaft should be twisting slightly.

 

If you don't believe me you can mark the shaft and pulley with a sharpie such that after a layer shift you can see if you are right or I am right.  Sometimes the problem is high friction or overheating stepper driver (is it above 20C in the room with the printer?) but overheating stepper driver problems usually occur after an hour of printing - not just at the start.  Push the head around with your fingers to feel the friction.  If one axis seems worse then oil it.  Oil them anyway.  Just a tiny bit of oil.  Too much oil is bad.  One drop on each of the 6 steel rods in the gantry.  Any light oil is fine.  Don't use WD40.