I have the attached surface created that I want to extrude to a 2mm thick solid.
No idea how to do this.
Any hint?
seite.3dm (505.4 KB)
The problem is your object is already a closed polysurface. Explode it and remove the unnecessary extra faces, then OffsetSrf will thicken it.
Do you accidently know how offsetsurf comand is named in the german version?
I don’t but you can type “_OffsetSrf” in any language version, and in English it’s in the menus under “Surface,” towards the bottom of the list…
Found it, solved, Thank you!
Seems its not creating a solid but just a bunch of surfaces. More questions…
There is a “solid” option. I’m not sure which of the overlapping surfaces you deleted, maybe you removed the “wrong” ones. It worked fine here.
will create a new surface and start all over then
Just a wee note, you’ll also see in the command line along with the solid option, inverse which shows you which side your surface is going to offset to.
HTH
Somehow I succeeded to make it solid now and there was a second surface I deleted as well. I could unite this with the rest of the drawing as solid and export step to OrcaSlicer. There I am warned for non manifold edges. Could render anyway and send to printer. Will see what that message will get me as a printed part and if it coresponds to what I intended with that surface made solid 2mm thick. And yes, I have checked also the direction of offset right.
While I suceed to make solid freeform surfaces now I get stuck with how to join then and connect edges smoothly.
this is the whole object:
And this is where the parts interconnect, obviously with surplus edges:
How can I smooth this out efficiently without removing what needs to be kept.
Bolean operation of solid? Which one?
IMO, if you really want to use the solids you already created, I would do a side profile curve and extrude it, then boolean union all the solids and use booleansplit with the surface to bring it to the final form.
However, the best approach on this problem from my perspective would be to extract the external walls, connect then properly into a polysurface, without adding any fillets use offset srf without being solid, fix things where they need fixing (using that profile curve if/where needed), adding fillets where/if needed and close the surfaces using edge surface between surfaces with join.
That sounds very logical. Will tray that asa well.
Right now I extruded a side profileand cut it verticaly and run surface on one edge. But that does not really lead to a clean design.
Seems to have at first the whole thing as a surface with margins and then add thickness to it as you describe might work better.
Rhino is pretty consistent in everything
If you start with a bad curve, the surface will be bad too, and the solid will be even worse.
I worked about 2 years having to clean models to add thickness for 3d printing. I’ve looked so much for workarounds and everything to be able to have a good quality 3d print. In the end, my conclusion after all that time.
It is easier to redo making sure everything is good from the start, than it is to try to fix a bad srf/solid.
The “magic” tip to avoid as much problem as possible came from a Youtube series that I watched (I don’t remember the name but it was from a user in this forum)
Always use single span curves, if you need more points, you need a higher degree, if you need a degree higher than 5, you actually need more curves, never go above 5 (or even 3 if possible).
Since I adopted this mindset above, my models became much cleaner and easier to edit, add thickness, fillets and everything else.
Exactly, thank you very much.
I will take the time to rewatch it during my lunch time today 
@Walter_Born If you are struggling with understanding NURBS essentials, here is a compressed primer. Particularly the three Autodesk links at the bottom are golden.
“In any CAD software, the accuracy and quality of your primary curves (“splines” or “sections” or “sketches”) is paramount, because they determine the quality of your primary surfaces, and your primary surfaces determine how well your secondary surfaces, and tertiary surfaces (blends, fillets) will work (think of a tree: “trunk > branch > twig > leaf” relationship).”
If I found this before, it could had saved me soo much time. I learned the hard way 
Another item for my lunch break to do list
@altamiro.aj The user from those videos is @sgreenawalt