Errors in horizontal lines that occur regularly

Hi all, I’m new to 3D printing, so I’m not very familiar with it. My Bambu Lab P1S is still quite new, a few weeks old, and I’ve printed less than 10 objects so far. But now I’ve noticed some unsightly and irregular lines on vertical surfaces. I printed with Bambu Lab matte PLA with the standard settings.
I have already searched for solutions here in the forum and have mostly come across suggestions about optimising the hardware, i.e. maintaining, cleaning, calibrating the printer or something similar.
However, I have now realised that the irregularities in the lines are not random at all, but when I print out the same object again, it has exactly the same errors and irregularities. In other words, it can’t actually have anything to do with an inaccuracy in the hardware, but the printer always reproduces the same errors very precisely.
What could be the reason for this? If I reason logically, the problem should actually be in the slicer, shouldn’t it? The model in the stl file is completely straight and the printer always reproduces exactly the same errors, so they should actually occur in the slicer…
Whereby the lower half of the model actually still looks good, and the upper half then looks unattractive and has the misttakes. I am attaching two photos where you can see the reproduction of the same errors in two different colours.
It would be great if someone could help me. How should I set up the slicer so that these problems don’t occur? Or could the problem lie elsewhere?

Make sure your belts are tensioned correctly and that your filament is calibrated is where I would start.


If you’ve the same defects at the same height, and the slicer doesn’t report anything unusual, I suggest to start to check your Z axis first.

Clean them very well and lube them.

The height of the defects on your parts will helps to identify where on Z axis you could potentially find something.

Also ensure nothing it blocking the bed, like cables on the back, and check the bearing, if they are correctly in place.

You can simply print a small cube high enough to just test without loosing to much time and filament.


Ok, thanks for the tips. that’s a good idea, I’ll try it out.

Thanks again for your feedback. I have tried it out now as you suggested and printed out a very simple cube to test it. This was printed out completely smoothly and without any irregularities. (in the same hight as my previous object) This means it must definitely be a software problem and not a hardware problem. It looks as if the BambuStudio Slicer has built up the lines of my previous object differently from a certain height than below that point. The lower half of the object is OK. Are there any settings to fix this and to create vertical surfaces more evenly?

To be on the safe side, check the screws for the belt tensioners at the rear. Sometimes they are not tightened.

Publish your print settings, and show us the Speed and Layer time (Under Preview) to see if there is a relationship between slicing and print result.

Thank you, that was a very good tip. I have taken screenshots. Now I see clearly where the problem is. But I don’t know why this is happening and how I can change it. If I select the “travel” option, you can clearly see that everything is built up regularly up to line 210. (Image 1) The print head always follows the same path. Accordingly, the result is also very regular. From line 211 onwards, this changes and the print head seems to move back and forth in a relatively chaotic manner and the lines are always built up differently. (Images 2 and 3) What is the reason for this and how can I change it so that it builds up the remaining lines in the same way as the lines up to 210?

And here are the screenshots of the settings…

Ok, nothing too weird on your settings but Inner wall acceleration set to 0, Outer wall rather slow, and a lot of wall loops.

Regarding the travel, even if far from optimal, should not produce such a catastrophic result IMHO.

You can try to force the seam position to Back, or set it manually.

You can also try Wall generator : Arachne.