"broken" mesh in STL export

TedM · Post by **TedM** » Tue Nov 10, 2020 7:44 am

OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.22665 (Git)
Build type: Release
Branch: master
Hash: b0d7850406e046f3b7a8cd5da261e7d54df6bd99
Python version: 3.8.6
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.4.0
Locale: English/United States (en_US)

I'm afraid I'm not going to be able to reduce this to a small example problem. I created a document and exported an STL file for a project to be posted to https://www.myminifactory.com/. Unlike Thingiverse, they test all posted STL files before they can be published, first by software and then by volunteers test printing. The latter can be bypassed if you include photos of the printed objects (I did). When I submitted my project, I was first told that their software detected a problem and a volunteer was reviewing the files. Later, I was informed that the problems were repaired and the project was published.

I checked the project and one STL was marked "(repaired)".
Here are the project, the original STL file and the "repaired" STL:

setup box and lid.FCStd: (505.68 KiB) Downloaded 25 times

setup box.stl: (342.56 KiB) Downloaded 27 times

repaired_setup-box.stl: (342.76 KiB) Downloaded 22 times

The STL was generated by selecting the object "setup box" and doing File->Export to an STL mesh.

I'm trying to determine why the file was rejected and how I can avoid this in the future.

The two meshes are visually identical. Loading them into FreeCAD and using the Mesh Design WB, Evaluate and Repair Mesh, I see the following: the original mesh shows self intersections and 14 folds on surface; the repaired mesh actually shows one additional fold!

The only other clue I have is from Cura 4.7.1 with its Mash Tools. It reports that the original STL mesh is not water tight. It does not report this on the repaired STL.

The original printed fine on my 3D printer, despite the Cura warning.

Any help would be appreciated. Did I do something wrong that there was a problem with the generated mesh?

Thanks