Why Cura does this line

[kerekes 0]

Hi everyone!

Can anyone help me with a setting to avoid this line? I am afraid that this layer would fall in when printing. 

Layer height: 0.12

Infill: 100%

Top/Bottom Line Directions: [ 90,0]

Any other is default

 

cura1.png: previous layer

cura2.png: next layer

cura3.png: line I want to avoid

 

Thank you.

[Slashee_the_Cow 271]

Can you please provide the .3mf file (in Cura, go to File > Save Project) so we can have a look at it? A few screenshots aren't really that much to go on most of the time.

[kerekes 0]

Of coure.

Interestingly, it does well at 0.1 mm layer height. But as I know, this is not supported by Ender 3.

CE3E3V2_spittoon_disc.3mf

Edited October 20, 2023 by kerekes

[Slashee_the_Cow 271]

It's drawing a first layer of skin to cover the gap that ends in the previous layer - it's considered a new area so it's drawing the first skin wall (because you have Extra Skin Wall Count set to 1, which is a good idea, anyway...

 

Edit: Accidentally hit post button. Will continue below.

Edited October 20, 2023 by Slashee_the_Cow

[Slashee_the_Cow 271]

Because your line width is roughly the size of the gap, it thinks it'll get enough adhesion from the overhang of the layers below it to put it there - you can test this by lowering your line width to 0.33mm (or lower).

 

But first, I'd like to point a serious "WTF" in your print settings: You have bottom layers set to 999999. This will make the whole object skin with no infill. 100% infill will be as strong but print a bit quicker and use a little less material doing it. That, and the slicer really isn't designed for doing it that way, so it might actually be a bit weaker to do it with skin.

 

Setting it so you have a reasonable number of top and bottom layers (usually based on thickness so it adapts to different layer heights, I usually go for 0.6-0.8mm depending on how strong I want something to be (or how frugal I'm being with my filament) so that the inside of it actually uses infill is standard practice. That being said, it won't actually change this behaviour by itself, but it does give you more options to.

 

Probably partial list of things that will affect its behaviour:

• Quality > Layer Height, as you pointed out earlier: On a thinner layer it counts less on adhesion and can also more accurately start covering the point where it ends in the model file. FWIW, according to the specs, the Ender-3 can go down to 0.1mm layers - but that's not necessarily a good idea.
• Quality > Line Width: With narrower lines, it doesn't rely on adhesion as much to cover gaps. It's also probably that it calculates a thinner line isn't wide enough to cover the gap - I found by setting it to 0.33mm or lower it'll just bridge it with the rest of the skin.
• Top/Bottom > Top/Bottom Pattern: If you set it to Concentric, it'll just start in the centre of the layer and keep drawing laps around it, not worrying about doing skin walls first each lap around the layer is basically its own wall. But this can affect the strength and look of your print.
• Requires infill: Top/Bottom > Minimum Skin Width for Expansion: Changes how wide a skin layer would have to be in order for it to bother, just leaving out parts narrow enough. With this set to 1mm, it basically figures "eh, that's not big enough to bother with" and just covers it in infill.
• Walls > Print Thin Walls: It makes it fine on layer 115, because it will just print thin outer walls to keep the gap accurate to the model. But it will cause a bit (not quite as much, but some) extra skin wall to be printed on 116.
• Quality > Line Width > Top/Bottom Line Width: See above explanation for line width, but this is more targeted (or at least it would be if you weren't printing ALL skin).
• Experimental > Slicing Tolerance: Inclusive will make sure at least all of the original model gets printed. This makes layer 115 solid. Exclusive will remove any printed lines that would go outside the bounds of the original model. This makes the curved gap continue into layer 115 and makes layer 116 solid above it.
• Top/Bottom > Extra Skin Wall Count: It doesn't hurt to have this on, but skin is usually printed at the same settings as walls, so it's not 100% necessary. Requires infill: Infill > Extra Infill Wall Count: Much more effective at adding strength than skin walls.

Conclusion: For the love all things beefy, use a reasonable thickness of skin layers but then use infill. You can probably get away without fixing it, since you're not going to be able to see it through a tiny gap and it's covered by at least a couple more layers of skin above it which should hide it.