Thanks guys for your explanations and help.
solutions are sometimes more simple as my approaches.
have a nice weekend!

thanks for your suggestions.

@chrisb: i will try that workbench

@ kisolre: changing the profile of the sweep results in the same error. the overlap at the corner is still there.

File is attached

Hello Users, I am a beginner with FreeCAD and want to model a fuel tank. My version is 0.18 the inner part of the tank is no problem, just an extrusion of a b-spline. With the side walls I am stuggeling. the schape should be like this: http://liebels.net/fc1.png this was modeled by a sweep of these ...