<p>All slicers have their own peculiarities, and one of Cura's peccadilloes seems to be that It likes to generate an even number of shells for narrow structures, even if an odd number of shells would work nicely. Slic3r and Simplify3D have no problem with this, and will automatically generate an odd number of shells if they will fit the model.</p>

<p>Cura, on the other hand, will reduce the number of shells and generate infill. If you have set the infill percentage to less than 100%, it will try its best to fulfil that requirement, and in your case, generate zigzag infill. However, if you set the infill to 100%, it will, in effect, create an additional shell, although it is really infill that follows the direction of the walls as far as Cura is concerned, since there is no space to generate the specified infill pattern pattern.</p>

CC BY-SA 4.0
2019-03-06T14:35:23.087Z
Setting infill to 100% did not change anything.
Joel Coehoorn
CC BY-SA 4.0
2019-03-06T16:11:01.877Z
@JoelCoehoorn That's a pity. It did on the test model that I created (a square pipe with 1.2mm walls). Even reducing the infill to 99% caused it to switch to zigzag infill. Are your sure that your walls are exactly 1.2mm wide?
Mick
CC BY-SA 4.0
2019-03-06T17:25:04.640Z
@JoelCoehoorn Can you proved a link to the STL file so that I can play around with it? This is an interesting little problem.
Mick
CC BY-SA 4.0
2019-03-06T17:39:17.413Z
You can get the stl files here: https://www.thingiverse.com/thing:3424550 
I used both the 2x2 brick and the 2x2 plate, with the raw stl files included there (no need to use the thingiverse customizer app yet). Remember, I'm looking to match the second image, not the first.
Joel Coehoorn
CC BY-SA 4.0
2019-03-06T18:53:00.367Z
What if you set the infil to a square pattern, essentially limiting it to one pass along each side of the brick?
Carl Witthoft
CC BY-SA 4.0
2019-03-06T19:03:23.153Z
I think there's a misunderstanding here. The diagonal striping is _not infill_, because it completely fills up the space even with infill set to something low.
Joel Coehoorn
CC BY-SA 4.0
2019-03-06T19:38:35.930Z
@JoelCoehoorn You're partly right. Cura shows them as Top/Bottom layers (colour-coded yellow), and the direction can be controlled in the value for Top/Bottom Line Directions. However, if you set the infill to 0%, they disappear. If you set the infill to anything other than 0%, they are included, but they are generated as if they are part of top/bottom layers, not infill. Now I remember why I switched to S3D.
Mick
CC BY-SA 4.0
2019-03-06T20:12:57.757Z
I see what you're saying. I hadn't tried 0% infill, and when I do not only does the striping disappear, but there is nothing inside there at all!
Joel Coehoorn
CC BY-SA 4.0
2019-03-06T13:17:13.917Z
2019-03-06T13:52:37.260Z
2019-03-06T13:52:37.260Z
Mick
<p>I'm playing with printing some Lego-like bricks. I'm using brick models where the wall thicknesses are aligned to match an exact multiple of my printer nozzle (.4&nbsp;mm nozzle = 1.2&nbsp;mm brick walls, vs the standard 1.4&nbsp;mm), with other adjustments to the interior ridges of the brick so they should still fit with real Legos. </p>

<p>I'm seeing an odd effect when slicing in Ultimaker Cura 3.6. My settings for Wall Thickness/Wall Line Count are 1.2&nbsp;mm/3 lines. And yet, in the layer view, I see <em>one</em> wall line, with diagonal striping between those walls:</p>

<p><a href="https://i.sstatic.net/1rHEK.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/1rHEK.png" alt="Legos Layer View"></a></p>

<p>Part of it could be the interior ridges creating some thicker walls in places, but if you look at the piece on the left, there are no ridges (it will be a plate, rather than a brick, and Lego plates don't use ridges). Yet it still has the striping. I re-measured the STL in 3 different modelling programs (Meshmixer, 3D Builder, Tinkercad) and all show the walls as exactly 1.2&nbsp;mm thick.</p>

<p>I then noticed I can remove this by putting something small (even .001&nbsp;mm is enough) in the "Horizontal Expansion" setting:</p>

<p><a href="https://i.sstatic.net/cbGVi.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/cbGVi.png" alt="Lego Layers view without striping"></a></p>

<p>This is more what I wanted, and it cuts the print time almost in half. I can also fix this by setting enough bottom or top layers to handle the whole piece with a wall thickness of 1 line...</p>

<p>... but why was it necessary? What is going on here?</p>

CC BY-SA 4.0
2019-03-06T01:27:40.657Z
Have you tried increasing the number of shells? Why do you want a wall thickness of one line?
Mick
CC BY-SA 4.0
2019-03-06T01:44:41.907Z
a good note: print quality improves a little if you use a little wider extrusion width than the nozzle.
Trish
CC BY-SA 4.0
2019-03-06T04:45:14.317Z
@Mick I want a wall thickness of three lines, like the second image.
Joel Coehoorn
CC BY-SA 4.0
2019-03-06T12:28:24.440Z
Hmm! It's not a problem with Simplify3D, which is what I mainly use. With Cura, the only way that I could do it is by changing the wall line width to 0.3mm. Could you not create a solid brick, and then print with no infill and no bottom layers? Personally, I would would adjust the wall line width to get the required number.
Mick
CC BY-SA 4.0
2019-03-06T12:31:56.050Z
Slic3r seems to do what you want, although I am not familiar with it.
Mick
CC BY-SA 4.0
2019-03-06T12:54:45.537Z
OK. Try setting the infill percentage to 100%. That should do the trick.
Mick
CC BY-SA 4.0
2019-03-06T18:43:53.233Z
The fact that shifting by 0.001 mm changed things suggests a rounding error or sharp threshold between "wall layers" and "infil" selection.  And that it's dependent on the extrusion width setting.   But in the end, will you have trouble if you, say, set the infil to 5%?
Carl Witthoft
CC BY-SA 4.0
2019-03-06T18:52:05.060Z
If I use the default 0.8mm, 2lines, and do the horiz expansion, I get the desired result.   I also get the desired result with horiz expansion =0 but the source model scaled to 100.1% . But scaling to 100.01% reverts to infil.  So I'm still voting for roundoff error.
Carl Witthoft
<ultimaker-cura><slicing>
Ultimaker Cura 3.6 choosing to fill in narrow walls with diagonal striping
Joel Coehoorn
# Ultimaker Cura 3.6 choosing to fill in narrow walls with diagonal striping

(Asked by: username_0 on 2019-03-05)

I'm playing with printing some Lego-like bricks. I'm using brick models where the wall thicknesses are aligned to match an exact multiple of my printer nozzle (.4 mm nozzle = 1.2 mm brick walls, vs the standard 1.4 mm), with other adjustments to the interior ridges of the brick so they should still fit with real Legos.

I'm seeing an odd effect when slicing in Ultimaker Cura 3.6. My settings for Wall Thickness/Wall Line Count are 1.2 mm/3 lines. And yet, in the layer view, I see *one* wall line, with diagonal striping between those walls:

[![Legos Layer View](https://i.sstatic.net/1rHEK.png)](https://i.sstatic.net/1rHEK.png)

Part of it could be the interior ridges creating some thicker walls in places, but if you look at the piece on the left, there are no ridges (it will be a plate, rather than a brick, and Lego plates don't use ridges). Yet it still has the striping. I re-measured the STL in 3 different modelling programs (Meshmixer, 3D Builder, Tinkercad) and all show the walls as exactly 1.2 mm thick.

I then noticed I can remove this by putting something small (even .001 mm is enough) in the "Horizontal Expansion" setting:

[![Lego Layers view without striping](https://i.sstatic.net/cbGVi.png)](https://i.sstatic.net/cbGVi.png)

This is more what I wanted, and it cuts the print time almost in half. I can also fix this by setting enough bottom or top layers to handle the whole piece with a wall thickness of 1 line...

... but why was it necessary? What is going on here?

**Tags:** ultimaker-cura, slicing
> **Comments:**
> **username_1**: Have you tried increasing the number of shells? Why do you want a wall thickness of one line?  
> **username_2**: a good note: print quality improves a little if you use a little wider extrusion width than the nozzle.  
> **username_0**: @Mick I want a wall thickness of three lines, like the second image.  
> **username_1**: Hmm! It's not a problem with Simplify3D, which is what I mainly use. With Cura, the only way that I could do it is by changing the wall line width to 0.3mm. Could you not create a solid brick, and then print with no infill and no bottom layers? Personally, I would would adjust the wall line width to get the required number.  
> **username_1**: Slic3r seems to do what you want, although I am not familiar with it.  
> **username_1**: OK. Try setting the infill percentage to 100%. That should do the trick.  
> **username_3**: The fact that shifting by 0.001 mm changed things suggests a rounding error or sharp threshold between "wall layers" and "infil" selection.  And that it's dependent on the extrusion width setting.   But in the end, will you have trouble if you, say, set the infil to 5%?  
> **username_3**: If I use the default 0.8mm, 2lines, and do the horiz expansion, I get the desired result.   I also get the desired result with horiz expansion =0 but the source model scaled to 100.1% . But scaling to 100.01% reverts to infil.  So I'm still voting for roundoff error.  

---

## 1 answers

### Answer by username_1 on 2019-03-06. Score: 3

All slicers have their own peculiarities, and one of Cura's peccadilloes seems to be that It likes to generate an even number of shells for narrow structures, even if an odd number of shells would work nicely. Slic3r and Simplify3D have no problem with this, and will automatically generate an odd number of shells if they will fit the model.

Cura, on the other hand, will reduce the number of shells and generate infill. If you have set the infill percentage to less than 100%, it will try its best to fulfil that requirement, and in your case, generate zigzag infill. However, if you set the infill to 100%, it will, in effect, create an additional shell, although it is really infill that follows the direction of the walls as far as Cura is concerned, since there is no space to generate the specified infill pattern pattern.

> **Comments:**
> **username_0**: Setting infill to 100% did not change anything.  
> **username_1**: @JoelCoehoorn That's a pity. It did on the test model that I created (a square pipe with 1.2mm walls). Even reducing the infill to 99% caused it to switch to zigzag infill. Are your sure that your walls are exactly 1.2mm wide?  
> **username_1**: @JoelCoehoorn Can you proved a link to the STL file so that I can play around with it? This is an interesting little problem.  
> **username_0**: You can get the stl files here: https://www.thingiverse.com/thing:3424550  I used both the 2x2 brick and the 2x2 plate, with the raw stl files included there (no need to use the thingiverse customizer app yet). Remember, I'm looking to match the second image, not the first.  
> **username_3**: What if you set the infil to a square pattern, essentially limiting it to one pass along each side of the brick?  
> **username_0**: I think there's a misunderstanding here. The diagonal striping is _not infill_, because it completely fills up the space even with infill set to something low.  
> **username_1**: @JoelCoehoorn You're partly right. Cura shows them as Top/Bottom layers (colour-coded yellow), and the direction can be controlled in the value for Top/Bottom Line Directions. However, if you set the infill to 0%, they disappear. If you set the infill to anything other than 0%, they are included, but they are generated as if they are part of top/bottom layers, not infill. Now I remember why I switched to S3D.  
> **username_0**: I see what you're saying. I hadn't tried 0% infill, and when I do not only does the striping disappear, but there is nothing inside there at all!  

---

