<p>STL does not know quads: STL only knows trigons, defined by three vertices and the normal that belongs to this trigon, though there are extra properties that each trigon can have (such as color). When saving a quad as STL, it has to be converted into two trigons next to one another. The problems appear when some quads have a single point that is not contained in the plane created by the three others: What works as a bend quad, can be solved as two different Trigons: ABC+CDA is jsut as valid as ABD+BCD - but one has a high ridge, the other has a low valley.</p>
<p>To fix such topology issues, you need to convert to trigons <em>first</em> then export as STL. To correct such errors after exporting, a 3D modeling software that can alter Vertex Edge and Surface level details is needed. Blender is such a solution and free, though with a somewhat steep learning curve.</p>
<p>You might be able to fix your surface by carefully merging vertices until your surface does not have the ridges you encounter - because they are already in your model.</p>

CC BY-SA 4.0
2022-01-16T14:55:30.157Z
2022-01-16T14:55:30.157Z
Trish
<p>My model is purely quads, (I know about tris/quads for .stl files and other formats, etc.) but when I import it in slicer software (Ultimaker Cura), it changes the topology (and that repeating triangular shape is very visible on the print). Is this just how 3D printers work, or can I change the settings somewhere to make it go away?</p>
<p><a href="https://i.sstatic.net/EP44q.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/EP44q.jpg" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2022-01-15T05:19:01.590Z
Not having read about this before, I went looking for info and stumbled across this on Blender.SE: [Triangles to quad for 3D printing](https://blender.stackexchange.com/questions/76413/triangles-to-quad-for-3d-printing). The answer says that .stl files don't support quads.
agarza
CC BY-SA 4.0
2022-01-15T16:37:15.890Z
I don't get it, if you look at the image on the right, your edges aren't cubical, they form triangles.
0scar
CC BY-SA 4.0
2022-01-16T08:40:27.073Z
stl files don't have quads. Every face is a tri
AzulShiva
<print-quality>
Topology problems
sblx1
# Topology problems

(Asked by: username_0 on 2022-01-15)

My model is purely quads, (I know about tris/quads for .stl files and other formats, etc.) but when I import it in slicer software (Ultimaker Cura), it changes the topology (and that repeating triangular shape is very visible on the print). Is this just how 3D printers work, or can I change the settings somewhere to make it go away?

[![enter image description here](https://i.sstatic.net/EP44q.jpg)](https://i.sstatic.net/EP44q.jpg)

**Tags:** print-quality
> **Comments:**
> **username_1**: Not having read about this before, I went looking for info and stumbled across this on Blender.SE: [Triangles to quad for 3D printing](https://blender.stackexchange.com/questions/76413/triangles-to-quad-for-3d-printing). The answer says that .stl files don't support quads.  
> **username_2**: I don't get it, if you look at the image on the right, your edges aren't cubical, they form triangles.  
> **username_3**: stl files don't have quads. Every face is a tri  

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## 1 answers

### Answer by username_4 on 2022-01-16. Score: 1

STL does not know quads: STL only knows trigons, defined by three vertices and the normal that belongs to this trigon, though there are extra properties that each trigon can have (such as color). When saving a quad as STL, it has to be converted into two trigons next to one another. The problems appear when some quads have a single point that is not contained in the plane created by the three others: What works as a bend quad, can be solved as two different Trigons: ABC+CDA is jsut as valid as ABD+BCD - but one has a high ridge, the other has a low valley.

To fix such topology issues, you need to convert to trigons *first* then export as STL. To correct such errors after exporting, a 3D modeling software that can alter Vertex Edge and Surface level details is needed. Blender is such a solution and free, though with a somewhat steep learning curve.

You might be able to fix your surface by carefully merging vertices until your surface does not have the ridges you encounter - because they are already in your model.


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