Strange horizontal lines on MK4 prints  

Strange horizontal lines on MK4 prints

Hi everyone,

I am having some problems that are difficult to diagnose.

In some prints (not all) some layers seem to suffer from under-extrusion, while in others from over-extrusion. The rest of the print is perfect. Initially I thought it might be a mechanical problem, but sending the same print again, the problem recurs identically in the same spot, while making some variation to the slicing, it either does not occur or occurs in a different spot. This suggests more of a software problem (gcode or firmware).

The printer is a pre-assembled MK4. The firmware was updated to version 5.0.0 as soon as it came out, but some of the prints are earlier. The same goes for the version of PrusaSlicer. I checked every model for defects and the slicing looking for difference in volumetric flow rate, printing speed and so on, but I found nothing strange.

I now include some photos with explanation.

This first PLA print consists of a base and 3 thin columns that rise vertically. The print was submitted prior to the release of firmware 5.0.0 and consisted of 3 copies of the piece just described. An entire layer about halfway through the model has an under-extrusion (so all 9 columns were affected) and the photos show one object with broken columns and one where we attempted to repair the damage with epoxy.

Thinking it was a printing problem (or a filament problem, a Prusament Pineapple Yellow) I sent the same gcode back to print, only to find that the problem recurred the same in the same spot.

The second print consisted of 3 objects that were printed in Prusa PLA with firmware 5.0.0 and profile 0.2 Structural with Input Shaping.Each plate consisted of 3 objects and only one of them had an under-extruded layer.

I sent the same gcode again and got the same result with the same under-extruded layer.I tried rotating the model that had the defect, so the gcode could be regenerated, and the problem did not recur.

This third case was printed in Prusament PETG and is a large 100 mm storytelling die.The first print, yellow in color, was made with 0.2 Structural profile and Input Shaping enabled. The second print, blue in color, was stapled with 0.2 Quality profile without Input Shaping, following the poor result of the first print. I wanted to remove Input Shaping to see if it could be the cause of the problem.

As can be seen from the photos, the defect is a layer that appears to be consistently over-extruded around the perimeter of the die, but in the two prints it occurred at two different heights.

This last print (made long before all the others) may actually be a case of "benchy hull line," since the problem occurs in the same layer as a large top layer. However, since it is visually similar, I include it.

Here you can also see a bad layer stacking, problem that seems reduced with latest firmware.

Now my shift at work is over, but tomorrow I will contact Prusa support, hoping they can help me figure it out. In the meantime I wanted to see if anyone had experienced a similar problem. For example, it sounds like the same problem that is reported in this post.

Thank you for your attention.

Regards,
Andrea