Hi Jurgen,

> How could I create surfaces with this curve (like the
> two surfaces of the original solid)?

Right now it looks like you're trying to think of following the 3D curve that is swooping around in 3D space.

Instead try to focus on the 2D profile aspects of the shape and try to figure out how you would create some 2D curves to construct it.

So for example note that these side surfaces are straight in one direction:



That kind of straightness usually implies an extruded surface, so to build something like that, get a flat profile curve drawn in one of the 2D Top/Front/Right views that looks like this:



Then you can Extrude this to build the base underlying shape, like this:



Now you want to remove some of that material, create some side profiles something like this:





Now you can use a boolean command to slice the extrusion with that side profile, in this case use the Boolean Intersection command - that will only keep the area from the extrusion that is also inside of that 2D profile curve, like this:



It's also possible to run boolean intersection just directly on the 2 planar profile curves, it will automatically do the extrusions for you, see the help file topic for an example:
http://moi3d.com/2.0/docs/moi_command_reference7.htm#booleanintersection


But basically you can get stuck pretty easily if you're trying to think about how to create something following contours that are swooping around in 3D - instead of thinking like that, try to imagine some larger uninterrupted forms of the object, and build those as some larger initially more simple extended piece (like the extrusion above), and then get your final shape by cutting that object with other profiles to remove material from it.

Basically try to ignore things that look like cut out areas for the first stage of figuring out how to build the basic shape - build a bigger piece first and then make the cut out areas happen by slicing that shape, rather than trying to do something like try to sweep directly along complex 3D swooping boundaries or things like that.

- Michael