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Z-axis shifts up during print  

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hsk108
(@hsk108)
Member
Z-axis shifts up during print

I recently purchased a used MK3S, and I have sometimes had prints fail in a repeatable way. At a certain z-height, the extruder will move to the front of the bed, pause for a bit, move up several millimeters, and then resume printing in the air above the print. You can see this happen in the following video, starting at about 22 seconds IMG_6733

If I re-print the same file, it will fail at the same height.

I have tried reinstalling the firmware. I have checked the gcode, both manually and in PrusaSlicer and I do not see this Z-axis movement anywhere. The only thing that seems to help is selecting "Fix by Windows repair algorithm" in PrusaSlicer before slicing.

Does anyone have ideas on how to solve this? I suppose that the repair algorithm works, but if I forget this step, I would hate to lose a print when it is mostly finished.

 

Posted : 09/08/2025 7:52 pm
JoanTabb
(@joantabb)
Veteran Member Moderator
RE: Z-axis shifts up during print

Hi, 
Most of the time, a defective STL will show an error marking in the right hand section of the Prusa Slicer window, See image below!

if you see this, use the repair algorythm immediately... 
Please be aware, if you use the Prusa slicer CUT tool, you can often get new errors in the cut model... 
So look for the marker1

But beware, sometimes Prusa slicer does not indicate an error, but errors can still exist, so... if something looks screwey in the sliced model, try repairing it anyway

AND, If bits of model appear to b missing, & they are still missing after a repair attempt, those parts of the model may be thinner than the extrusion width, set in 'Print settings > Advanced' sub menu

above are the settings in a prusa slicer session, that I have open on my computer at the moment
these settings are for a 0.4mm nozzle, as you can see above, all of the extrusion widths (Except Support Material) are wider than the nozzle width.
also please be aware that there is a setting that affects only the first layer (in addition to the first layer extrusion width)
and that is 'Elephant foot compensation'     in the current Prusa slicer session on My PC, this setting is set to 0.2mm (I believe this is a common default value)
what it means is that Prusa slicer reduces the width of any features on the first layer, by 0.2mm on  the X and Y axis...)so you might find that the first layer doesn't get resolved as below

the error message alerts you to the fact that there is no extrusion on the first layer because the STL feature is thinner that the extrusion thickness

I Hope this makes sense. 
regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility.Location Halifax UK

Posted : 09/08/2025 10:32 pm
hsk108
(@hsk108)
Member
Topic starter answered:
RE: Z-axis shifts up during print

Joan,

Thanks so much for your detailed answer! I will definitely be extra careful to check for the warning messages. I've only been using PrusaSlicer for about a month, and I have been using Cura for the past three years, so I definitely have some new things to learn.

When importing one of the troublesome models, I did see this message:

"40 degenerate faces, 40 facets removed"

 

Posted : 11/08/2025 12:58 am
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