Is OpenSCAD generating corrupt STL files?

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Is OpenSCAD generating corrupt STL files?

AKADAP
I published this design on Thingiverse: https://www.thingiverse.com/thing:4582540/comments

The design includes both source code and an STL.

At least two users reported that the STL did not slice properly in Prusa Slicer.

It sliced fine in Cura.


Is this a problem with Prusa Slicer? Or is OpenSCAD screwing something up in the STL?

I don't have Prusa Slicer to test with, and I would not be able to recognize an error in the STL file.


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Re: Is OpenSCAD generating corrupt STL files?

OpenSCAD mailing list-2
I can confirm that it errors out with Prusa Slicer but Simplify3D has no problem with it. Meshmixer doesn't find any errors either.

">


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Prusa Slicer makes a good section of the model disappear!

I don't have the OpenSCAD skills to make suggestions how to adjust your code to remove the Prusa failure.


On Friday, September 25, 2020, 12:57:27 PM EDT, Douglas Peale <[hidden email]> wrote:


I published this design on Thingiverse: https://www.thingiverse.com/thing:4582540/comments

The design includes both source code and an STL.

At least two users reported that the STL did not slice properly in Prusa Slicer.

It sliced fine in Cura.


Is this a problem with Prusa Slicer? Or is OpenSCAD screwing something up in the STL?

I don't have Prusa Slicer to test with, and I would not be able to recognize an error in the STL file.


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Re: Is OpenSCAD generating corrupt STL files?

nophead
The STL has degenerate triangles and self intersections according to NetFabb studio. 

image.png

Something in the design must generate vertices too close together for OpenSCAD.

On Fri, 25 Sep 2020 at 18:13, fred via Discuss <[hidden email]> wrote:
I can confirm that it errors out with Prusa Slicer but Simplify3D has no problem with it. Meshmixer doesn't find any errors either.

Inline image


Inline image

Prusa Slicer makes a good section of the model disappear!

I don't have the OpenSCAD skills to make suggestions how to adjust your code to remove the Prusa failure.


On Friday, September 25, 2020, 12:57:27 PM EDT, Douglas Peale <[hidden email]> wrote:


I published this design on Thingiverse: https://www.thingiverse.com/thing:4582540/comments

The design includes both source code and an STL.

At least two users reported that the STL did not slice properly in Prusa Slicer.

It sliced fine in Cura.


Is this a problem with Prusa Slicer? Or is OpenSCAD screwing something up in the STL?

I don't have Prusa Slicer to test with, and I would not be able to recognize an error in the STL file.


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dpa
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Re: Is OpenSCAD generating corrupt STL files?

dpa
In reply to this post by AKADAP
I don't know the reason (it's really broken without reason) but after Rendering in OpenSCAD I exported it as AMF, this can be imported in PrusaSlicer and it works.

Am Fr., 25. Sept. 2020 um 18:57 Uhr schrieb Douglas Peale <[hidden email]>:
I published this design on Thingiverse: https://www.thingiverse.com/thing:4582540/comments

The design includes both source code and an STL.

At least two users reported that the STL did not slice properly in Prusa Slicer.

It sliced fine in Cura.


Is this a problem with Prusa Slicer? Or is OpenSCAD screwing something up in the STL?

I don't have Prusa Slicer to test with, and I would not be able to recognize an error in the STL file.


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Re: Is OpenSCAD generating corrupt STL files?

cacb
In reply to this post by AKADAP
On 2020-09-25 18:56, Douglas Peale wrote:

> I published this design on Thingiverse:
> https://www.thingiverse.com/thing:4582540/comments
>
> The design includes both source code and an STL.
>
> At least two users reported that the STL did not slice properly in
> Prusa Slicer.
>
> It sliced fine in Cura.
>
>
> Is this a problem with Prusa Slicer? Or is OpenSCAD screwing something
> up in the STL?
>
> I don't have Prusa Slicer to test with, and I would not be able to
> recognize an error in the STL file.

I ran the STL through AngelCADs polyfix application, it reports several
zero area faces, one duplicated face and one  nonmanifold face (=face
with at least one free edge). After a couple of iterations it seems to
be fixed though.


$ polyfix Spade_Bit_Rack.stl

Parameters:
   input_file = Spade_Bit_Rack.stl


polyhedron 0 ================= volume=75230.9, dtol=0.01, atol=1e-06,
maxiter=10
iteration 0: vertices=43296 faces=14432
              warning: 31 zero area faces.
              warning: nonmanifold edges: uc(1)=43296
              merged 36208 vertices
              removed 256 collapsed or zero area faces
              removed 1 duplicate face
              removed 1 nonmanifold face
              total changes=36466
              no warnings

iteration 1: vertices=7088 faces=14174
              removed 1 unused vertex
              merged 14 vertices
              removed 28 collapsed or zero area faces
              total changes=43
              no warnings

iteration 2: vertices=7073 faces=14146
              total changes=0
              no warnings

Summary:
              polyhedron 0: vertices=7073 faces=14146 : no warnings

Writing: Spade_Bit_Rack_1.stl

... polyfix finished, time used: 0d 00h 00m 01s




Another thing I tried was using OpenSCAD to convert your .scad file to
.csg and then read that into my experimental .csg interpreter. It
reports that at least one of your polygons has wrong winding order:

...Warning: 1st polygon2d contour staring at (0.000000,-1.000000) has
wrong winding order

I'm not sure what the polygon point winding order policy is in OpenSCAD
(whether it automatically reverses wrong-winded polygons or not), but
wrong winding order can get one into trouble. The documentation at
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#polygon
does not explain proper winding order clearly, but the examples show CCW
winding order for the outer contour.

Regards
Carsten Arnholm


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