Explain this mystery to me

I don’t understand what caused these diagonal lines on an otherwise good print. Any ideas? I did notice I accidentally turned on ‘Detect Thin Walls’ which I usually don’t, but I don’t know if this was the reason. The seams were not in this location on the slicer preview.

Grey PLA, 0.2 Standard nozzle. Didn’t tweak very many settings from the basic set.

Thanks for the help!

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Thoughts or any advice from anyone?

Hey @Seratti,

Yeah, that does sound odd. I’d say, power off the printer and manually move the printhead over those sketchy areas to see if there’s any resistance. Also, try displaying all commands in the preview to check if a travel move might be messing things up over those sections.

If that doesn’t help, best bet is to open a support ticket. Attach your printer logs and the Bambu Studio file with your print settings. That should give them a clear picture of what’s going on.

That’s a weird one, for sure. Never seen the like. I have to think it’s mechanical. It almost looks like the defects would be fully symmetric if the one on the right started on the same layer as the one on the left. Not a rod issue, since that would only be happening on one side. I’m thinking belts. But the CoreXY system gives me a headache when I think about it, so I’m not coming up with a specific idea about how it might be busted… but the first place I’d look is the belts. Check for missing cogs or a spot where there’s some debris stuck to the cogs…


Huh…I wasn’t expecting those answers. Now I’m more perplexed. I’ll try re-printing and checking the mechanics as best I can. Thanks for the replies.

I looked more carefully at the slicer preview and followed the nozzle travel. It turns out that while the nozzle is traveling to form that wall, it pauses then starts again, even though it is just a straight line to be printed. Further up the print, it does two separate pauses along that straight line. That accounts for the weird ascending diagonal lines.

It’s very strange that the slicer rendered it in that fashion. The print came from Printables and it doesn’t seem that others have had that weirdness. I created a wall of similar thickness and height on the exact same place on the plate and it prints perfectly fine, so there is no mechanical problem.

Just a weird decision by the slicer to render that way. Anyway, just wanted to update the thread in case anyone else has similar issues.

I’m curious which Wall Generator you are using “Classic” or “Arachne”? This is under the Quality tab in Bambu Studio.

While I prefer Arachne, this result can occur when using this wall generator type.

Interesting thought but when I checked it was classic walls.

Maybe its at the inside? What filling do you use? How is the infill at this positions? Maybe you can share some pictures from the slicer?

It looks like a seam IMO

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That’s what I thought at first but you can see from the preview I posted that it isn’t.

Do you perhaps have a Time-lapse setting on that could be overriding what the gcode preview is showing and creating a seam?


Down towards the bottom of the model it makes one continuous movement from left corder to right corner to make the outer and inner walls, and these look great.

However, further up on the model, it makes a small travel movement along the wall, pauses, then moves again. Even further up, it pauses twice along the wall to complete the movement from left corner to right corner.

The travel:

The pause:

More travel:

Then another pause then completing the line at the corner:

Maybe the model has errors in it causing the pause in the middle of a straight? Did you try and repair the modle inside BBL Studio?

Wrong vector normals, manifold edges and stuff like that might cause the issue perhaps. Worth a try I guess.

Perhaps because it’s printing classic it’s a result of the wall thickeness being not quite what the slicer can handle to do the run in one run, hence the pause. Just a guess. I would do what others have said and try repairing the model. I would also try simplifying which will show up if there are any weird triangles on the side. I’ve noticed that sometimes chamfers created after a basic shape is created can cause the straight sides to do weird things once imported as an stl. I know you said you’ve checked and it’s not a seam but try turning on random seam and see if there’s any difference. If it’s on aligned and there’s no corner for it to align to, then it may also be getting confused about where to put the seam start and end. Thinking about it, I had the exact same looking seam the other day. I’ll find these model and take a pic.