What I am doing wrong?

[rs2112]

Hello everyone,

I have little experience in 3D printing, as I only recently started, as a hobby that I really enjoy.

I have recently been having some difficulty with the final finish of a part, which after being printed in white PETG bothered me. In other colors (PETG and PLA) they never caught my attention as much.

In the photos below, a crack is clearly visible at the interface of the top layer with a vertical wall. I have been reading on the forum and watching videos on YouTube and I have made some changes to the number of top layers and the thickness of the top layer.

Am I doing something wrong? Is it a design problem?

Thanks for your help.

[MM_Printing]

Try calibrating your filament. Go to the calibration tab in Bambu Studio, which will walk you through what to do.

[MM_Printing]

You should also probably dry your filament; it looks like it’s a bit stringy. That won’t fix the gaps, but you should still dry them out.

[rs2112]

Hello and thanks for yourr answer.

Already done that, and used the new fillament profile.

[MM_Printing]

Did you do both Flow and Dynamics?

[JonRaymond]

What is your K-factor (pressure advance) ?

This wiki page shows your problem and how to rectify it.

Lines not connected to the printed wall: Causes and Solutions

[rs2112]

The fillament is dry. I just printed with the same fillament and profile another design, and the resul was good.

[EnoTheThracian]

Besides drying and calibrating, you should also try to avoid crossing infills and surfaces with PETG. It loves to get stuck on the speed-bumps.

Try Honeycomb or gyroid for sparce infill and, for that first particular part, circumferential top surface may work better.

[rs2112]

Had to search where I can find this factor

Mine after calibration is 0.080

[JonRaymond]

@rs2112

Mine after calibration is 0.080

Seems a little high.

Most common results for regular filaments give a K-factor value between 0.02 and 0.04 as long as the hotend is free from any partial clog, and the extruder is clean.

[rs2112]

Hello,

I read the wiki you sent and it seems that the K factor is quite high.

But wouldn’t that lead to a deterioration of the other piece I posted?

Thanks.

[artistseth]

Not a true fix to a root problem, but running your top layer as CONCENTRIC will fill your top layer along the same geometry and probably eliminate that transition.
I’ve done this to eliminate the same problem, although my gaps were not as significant as yours appear to be.

[rs2112]

Before posting here I did run a test with concentric. It minimized the defect, but was still there.

I will perform another calibration.

[Shane_Trent]

I have resolved similar issues by opening the filament settings, and increasing the flow ratio. There are some PETG filaments that I needed to set the flow rate as high as 1.03 to prevent under-extrusion flaws on the print. Try small increases and a small test print.

[rs2112]

Thanks for all the help!!

[Shane_Trent]

Great looking print. What was the fix, or fixes?

Shane

[rs2112]

Thanks.

I did a little of everything. Honeycomb infil, concentric top layer and used the “Generic PETG” profile with a K of 0.020.

Thank you all again.

[just4memike]

@rs2112

PXL_20250326_1549038141920×2550 1.3 MB

I think your main problem was the change to the top layer (but the default K factor is big too). Before, it looks like you chose rectilinear, which is a criss-cross pattern and I don’t think that was a good pattern for the geometry. Concentric is a good choice, but honestly, I would have just stayed with the basic default pattern Monotonic (I believe). There’s a good reason its the default.

Was there a reason for the update to rectilinear? Where you looking to get a particular look?

[rs2112]

At the beginning of my struggle, I changed the top layer pattern to rectilinear in an attempt to improve, so I think concentric helps a lot, but the K factor was the determining factor.

[just4memike]

Gotcha, that leads me to believe it was simply the K factor. 0.080 is 4x the normal value. I can’t remember which way will lead to under extrusion, but being 4x off can definitely lead to something problematic.