Totally understand the problem, I just can't remember to have had this problem in a CAD software I once used at work. But thanks for the link and the correct term of that issue. I will definitively stay with FreeCAD.

Thanks for the clarification (and fix). The airchannel was meshed with (or from) FreeCAD itself while the other part was, as I already wrote, imported. I ended up reworking that part as well and doing the substraction with the two FreeCAD parts. Worked for a first prototype but I came across a bunch...

Did you mean that serious? How else do you say when you do a boolean difference operation: remove mesh B from mesh A, so of course two meshes. After that binary boolean operation I assume a single mesh C to be the result (C = A && !B).

Sorry, I didn't find time in the last weeks to have a look on this problem. I checked another way as well: creating solids from the meshes and take the difference from them but it also fails (the one solid seems to have errors, removed them again as the file was to big). Find the example attached. I...

Ok, I can report back that a) Changing my install from freecad-python2 (which was chosen by default when installing freecad package on 18.04) to freecad-python3 (and of course removing freecad-python2 and all otherwise unused dependencies) works with the old OpenSCAD 2015.03-2+dfsg-2~18.04 from thei...

Thanks for the hints and sorry for not providing more details on the version. I just installed from the respective PPAs and did not realize that there is a freecad-python{2,3}. Seems that it installed freecad-python2 on my machine. I really wonder that I did not saw the OpenSCAD news. I will check a...

I just ran across the same issue with FreeCAD 18.1 in combination with 2015.03 on a Ubuntu 18.04. Boolean operation even on simple regular geometry meshes do not work neither in Mesh Design nor in OpenSCAD mode. I could not make OpenSCAD to finally render the Boolean operation on the imported meshes...