Exported model has holes unless first sliced

[Modeler]

I have created a transition from a round to a rectangule using a circle and a loft. The walls are 3 mm thick. When I export it to an STL it has 2 holes in it.

HolesInMesh.png (52.37 KiB) Viewed 1122 times

I sliced the original model to check the thickness in the space were it is thin, it is the same 3mm as everywhere else.

After I sliced it I exported the resulting model as an STL and it did not have the holes. All files are attached here.

If have a similar transition and it did not have this problem. Anyone have any ideas?

OS: Windows 10 Version 2009
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24276 (Git)
Build type: Release
Branch: releases/FreeCAD-0-19
Hash: a88db11e0a908f6e38f92bfc5187b13ebe470438
Python version: 3.8.6+
Qt version: 5.15.1
Coin version: 4.0.1
OCC version: 7.5.0
Locale: English/Canada (en_CA)

[M4x]

Hm, I get the same errors when exporting ReturnAir out of ReturnAirUnSplit.FCStd. I've imported this STL file (ReturnAirUnSplit-ReturnAir_Max.stl), created a shape from mesh, converted it to a solid, checked for errors -no errors found- (ReturnAirUnSplit-ReturnAir_Max_importedSTL.FCStd) and exported it again (ReturnAirUnSplit-ReturnAir_Max_importedSTL.stl).

I'm not able to look any further right now (bed time ).

Code: Select all

OS: Ubuntu 20.04.2 LTS (ubuntu:GNOME/ubuntu)
Word size of FreeCAD: 64-bit
Version: 0.20.25131 (Git) AppImage
Build type: Release
Branch: master
Hash: 7c519689f0d5ea78fb3292be36a857d283c05507
Python version: 3.9.5
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.2
Locale: English/United States (en_US)

[M4x]

Okay, I had another shot at this. It's not perfect yet but I think this is the way to do it.

Snip macro screenshot-5adb02.png (21.56 KiB) Viewed 538 times

Snip macro screenshot-57cd9c.png (15.77 KiB) Viewed 536 times

Last time I've exported the model via File -> Export. This time I've used "Method 2" as described here: Export_to_STL_or_OBJ. I didn't test this excessively but using Mefisto and set it to 1,0 mm (I think ) removed the errors which where visible from "outside". Afterwards, I've used Mesh_Evaluation to find and repair a small amount of errors. I've used Part_SimpleCopy before creating the mesh but only to get a file which only contains a single solid for testing. You can find my test file here and the resulting STL here.

To sum it up: Use the Mesh_Workbench, try different Meshers and settings. Next I'd reduce the Maximum Edge length in the Mefisto Mesher. If that wouldn't help, I'd move on to the other Meshers.

Please have a look and report back!