Gap in wall around support

[MiSTerConsoles]

Application Version

4.11.0

Platform

Windows 10

Printer

Creality CR10S Pro

Reproduction steps

I'm printing parts (boxes) that have openings in the side walls where supports must be placed in order to ensure the tops of those openings don't sag. The wall of the box is 1.8mm at the top and bottom of the openings. The diameter of my nozzle is 0.6mm and I'm using a 0.9mm line width. The preview after slicing shows two shell lines at the top and bottom of the openings. The support is being printed with a 0.4mm line width in a zig zag pattern with a Support Wall Line Count of 1. There is a Support Z Distance of 0.3mm at the top of the support and 0.2mm at the bottom. I've included some photos of a partial box I printed that has the issue along with the project file for it. .

Actual results

The wall of the box is solid at the bottom of the opening as well as on the sides. However, a gap is observed in the wall at the top of the opening.

Expected results

The wall of the box should be solid all the way around the opening.

Checklist of files to include

• [ ] Log file
• [X] Project file

Additional information & file uploads

Project File.zip

[fvrmr]

Hi @Gamepimp thank you for your report. If you are using a 0.6mm nozzle it is better to set the line width to 0.6mm instead of 0.9mm. Let me know if that works for you!

An other option is use our Arachne build. Which uses variable line width to fill the available gaps better. See here more about Arachne: https://github.com/Ultimaker/Cura/releases/tag/Arachne_engine_beta

[Ghostkeeper]

Arachne could indeed help by printing 3 lines instead of 2, which the stable Cura version can't currently do.

The problem is really that the lines at the top are printed above a gap. The Support Top Distance is 0.3mm, which at 0.2mm layer height ends up as a 2 layer gap (0.4mm). This causes the material to flow down instead of towards the sides. So the lines become less wide than intended.

I'd suggest reducing the Support Z Distance, but that could also make the support attach too well to the print. Another alternative is to reduce the wall line width to make it fit 4 lines there instead of 2, but that would have a big impact on the whole print.

[MiSTerConsoles]

Hi all. Thanks for looking into this issue. I attempted to use the Arachne build, but when I sliced the STL file of the partial box it did not place a support in the opening like it does in the normal builds of Cura even though I do have supports enabled. Is this a bug? I've included the project file for review if desired.

Console Box Front (Arachne).zip

I attempted to do a 0.6mm wall line width in 4.11.0 and the preview showed a gap between the outer and inner walls directly above the support. [CCR

The gap didn't fill in the preview until I changed the line width to 0.56mm. I tried printing with that and it appears that a gap still remained between the walls around the support. Normally the gap is just above the support itself. Incidentally it is always the same line width and doesn't appear to be a full line "sagging" due to gravity.

I messed around with a different slicer program called SuperSlicer which is based off Slic3r/PrusaSlicer to see how it would handle these openings. I noticed that directly above the support it actually had two thin wall lines with a gap that it refers to as "Overhang Perimeters". Is it possible that Cura is doing something similar?

[fvrmr]

Is this a bug? I've included the project file for review if desired.

It looks like this is related to your profile. If I slice your project file, I indeed see no support. When changing the profile to Standard Quality 0.2mm it shows support. If you change your line width to 0.6mm it is showing support.

[Ghostkeeper]

In the current state of Arachne, I'm not getting any support at all in this model. There seems to be something up with the Support X/Y Distance there. Lowering the X/Y distance to 0.97mm or lower makes support appear for those two bumps, but makes the support come way too close to the model (less than the 0.97mm indicated, maybe halved?). And the long ridge doesn't get support at all. This is an issue, though it's unrelated to what you're reporting.

4.11 and 4.12 indeed show a gap there. That is expected since the width of the model is more than 2 line widths but less than 3 line widths wide.

[Ghostkeeper]

Developers, see issue CURA-8700.

[MiSTerConsoles]

Thank you @fvrmr and @Ghostkeeper for the continued follow-up on this issue. The wall of my box is 1.8mm thick on the non-raised surfaces which is where the gap appears. I designed it at that thickness to ensure that a 0.9mm line width would be an even multiple. I've seen some information from Slic3r that the lines overlap for proper adhesion and therefore you can't just divide the wall width by the line width. Is the same true for Cura? If so, what wall thickness would I need in order to accommodate two full line widths?

[Ghostkeeper]

For the walls there is the Outer Wall Inset which, like Slic3r, is there to improve adhesion between the outer wall and inner walls. In your project file this is set to 0.0mm though.

According to Cura's preview, the walls are properly fit next to each other, each at 0.9mm width and filling a space of 1.8mm. So Cura designed the g-code as you'd expect here: The extrusion is made for a line width of 0.9mm and layer height of 0.2mm, and would fill the space exactly. You could double-check it from the g-code (by calculating it from the E value, or by loading the g-code in a visualiser).

However this assumes that the line gets squashed in a 0.2mm vertical space. And that's just not the case here, above that support. Above that support there is the Support Z Distance (0.2mm) and any additional sag too. So there's really 0.4mm+ space in which the volume of plastic can spread. As a result, the lines will become a bit less squished, and more round. This effectively reduces the line width in printing, which prevents the lines from attaching well.

So this is not a problem with the g-code generation, but a print quality problem. We can't really solve it for you. It's a matter of adjusting the print settings (particularly Z distance and support infill density).

There is the remaining issue in Arachne still about support X/Y distance though.