Excessive wall overlap settings?

[Encuana 0]

I'm using a model that is essentially only a 2D shell and is empty inside. Cura treats this fine for the most part by using walls to build the model.

However, I'm struggling with these additional walls (and infill between them) that Cura seems to invent. I want the walls of the model to be uniform and with these additional walls that becomes impossible.

 

The added images show the wall (in red) and the whatever additional walls (in yellow). It seems to have to do with the diagonal overhang of the red walls, although the second image shows that the overhang is hardly an issue. Regardless, I can't find any settings to manually play with this feature. 

In the images the wall line count is set to 1 and the top/bottom thickness to 0.0. This still generates the first and last layers though, and with the excessive overlap (5 layers before this breaks) the bottom is practically solid (see third image).

 

Is there a setting I haven't found to play with the generation of the yellow lines? I'd like to turn this off and generate these structures through the wall line count and top/bottom layers.

 

Thanks in advance.

[GregValiant 543]

If you would go to the Cura File menu and use "Save Project" and post the 3mf file here someone can take a look.  A project 3mf will contain your printer and all your settings and is very helpful.

[Encuana 0]

Of course

C7_Spleen.3mf

[Encuana 0]

By the way, according the color-scheme the yellow parts in my images should be related to the top/bottom structures. I'm pretty sure I've messed with about every setting in that menu, as well as the walls menu, still no idea.

[GregValiant 543]

You printer is there but I don't have a definition file for it so the printer wouldn't load for me.  The part came in though.  It looks like a solid.  I adjusted to 0% infill and a single wall, .4 top and bottom thickness, with .4 nozzle and .2 layer height.  The slice looks pretty much like what you show.

 

 

When Cura (or any slicer) cuts a section through a model, it is always in the XY.  When you tell the slicer that you want a wall thickness of .4 then the slicer does a calculation based on a thickness perpendicular to the exterior surface.  When the model is near vertical the .4 will be .4 in the slice.  As the angle of the surface to the build plate approaches zero then the width of the plastic laid in a horizontal slice increases as a trig function of the angle.  Those yellow lines are "skin" but think of them as outerwall.  Cura is attempting to keep your wall thickness .4 (or whatever) even though a wall might be nearly horizontal.  If you look at Layer 3 in the Cura preview I think you will see what I mean.  The center area has no plastic because the .4 bottom thickness has been met but the surrounding area requires more plastic for the wall thickness to stay at .4.

You may be able to get rid of some of that by using Adaptive Layers.  A lower layer height will decrease the amount of yellow you see, but it isn't going to go away so long as some areas are near horizontal to the build plate.

[GregValiant 543]

This might explain better.  The lines are a constant .4mm apart.

 

 

[Encuana 0]

Yes,

What you mentioned makes sense. This is effect is probably made even worse by the polygenistic (I made that word up) surfaces approximation of the original .stl file.

I've reduced the layer height from 0.4 to 0.1 and it greatly improves the issue. For documentation I made the images to show the result. 

 

Thanks for the explanation!

[GregValiant 543]

Yes, that is the little known polygenistic effect.  It's exactly like the "Snot Factor" only different.

[GregValiant 543]

If you change the Skin Wall Count to 0 and the Skin Overlap Percentage to 30% I think the top will have a better chance of finishing without the loops falling into the interior.