For a cuboid to have a cubic net, it must be divided into simple parts. The transfinite gmsh setup can always be defined on solid parts with 5 or 6 faces. Therefore, the division of the cuboid must be different 
I invite you to add to the guide, make corrections, and share your own experiences
Part 1:
So basically just:
Then, of course, export to step and create a compound in PrePoMax.
I would still prefer datum planes, but this approach is good too. And you can explode and use multiple extrudes if the sketches have to be made on different planes.
Why is plane cutting better than extrusion? The section plane must be larger than the body. When using sketches, this can be easily forgotten and result in errors in the file.
I mean datum (construction) planes. They are treated as infinitely wide and thus can be easily used for cutting:
Also, since FreeCAD 1.1, they can be created independently of Part Design Bodies.
I understood your suggestion. I asked myself why you were doing this and I answered my own question. (translator).
I created another fiddly model for training and I can’t mesh it properly. What’s your solution?
MODEL_3.pmx (2.9 MB)
i like the extrude with recombine option -one segment does not behave quite as the others do, I may have done something wrong here but i think the solution looks ok otherwise
MODEL_3Extrude.pmx (139.7 KB)
The transfinite algorithm is meant for volumes having 4 or 6 faces (with 3 or 4 edges each). If you create a compound, it can’t be meshed this way:
So it’s better to only partition the surface and use extrusion or (better) sweep meshing.
The right piece is where the seam edge lies, breaking the curved edge into 2 segments:
You could just delete the parts with seam edges and rotate (with copy) the ones without them:
MODEL_3Extrude_mod.pmx (142.4 KB)
Thank you for your time and analysis
I didn’t notice that line. It seems to be the primitive’s direction vector.
To avoid any problems, I made a copy of the part and deleted the surfaces adjacent to the redundant line on both solids.
Now each solid has fewer than 6 surfaces, and you can use “Transfinite Mesh.”
My files:
MESH 2.zip (2.4 MB)
Now I know why I couldn’t use “Transfinite Mesh” for the cuboid. Two lines ruined the model.
Thanks again
Seam edges are always generated on the cylindrical surfaces by the OCC geometric kernel. There’s no way to get rid of them other than splitting the surface/volume, deleting the side with a seam edge and mirroring or copying the other side.
Sometimes seam edges may cause some trouble with further modeling, but they might be useful as well (if you need an edge in that direction for measurement or something).
Btw. PrePoMax has an option to automatically split the cylindrical face opposite to the seam edge so that it can be sweep meshed:
But this feature may cause some trouble too.
The usual setting is 2 just to fulfill the requirements of sweep meshing (all side faces must be 4-sided so a cylindrical surface with a seam edge must be split at least one more time:
That’s why I made this post. The problem is solved and you can extrude a nice mesh.
