Vertical dunes problem

[radoxpi]

Hi all, I noticed my 3d printing results have "vertical dunes". And I can't comprehend how this can be. This happens in the surface that is close to a curve. It sometimes also happens on the curves. Some curves do not have it as we can see on the right side of the printed model in the picture.


Also, the top surface seems so "stringy". Is it perhaps a flow problem?


Did anyone encounter this problem before? Or know how to fix this?


As a note: I printed this in relatively fast speed with Anycubic Kobra Neo. Normal speed seems to have this problem as well, though less influence. This did not happen before. The filament is in the state of almost over.

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[radoxpi]

Vertical dunes on 3D prints are often caused by loose belts, frame vibrations, or Z-wobble. Tighten belts, stabilize the frame, and check the Z-axis for alignment. Stringy top layers may result from under-extrusion or filament nearing the spool's end. Ensure smooth filament feed, clean the nozzle, and dry the filament if needed. Reduce print speed, adjust slicer settings like layer height and top thickness, and calibrate flow rate to improve results.

Got it. I will try stabilizing the frame, etc. Do you know how filament nearing the spool's cause the stringy top? Isn't the amount of filament entering the nozzle is just the same as when the spool's still full? Funnily it is actually the case of mine - spool's almost done. But, I haven't made sense of this.