Hello,
I would appreciate your ideas on how to connect these profiles, they were made by sweep the same curve along the rails. I tried blending surfaces together, but the middle part is tricky, since I could not join the patched surface with the rest.
Thank you
Intersectioing Cross section.3dm (462.5 KB)
Its impossilbe to say if you don’t know what it is!
You need to know the construction point of view.
Or is it just a 3D-Printed part?
Or just for Rendering and it doesn’t matter at all?
How is the tunnel supposed to meet, with a bevel or smooth transition?
many Questions. These define what method to use!
Thanks, it would be manufactured by injection moulding. so preferably smooth transition.
In that case, as far as i know you have to model it by hand.
Define some nice Rails for the outer parts, divide your profile, you can sweeps them again.
Model the inner patch by hand, and fill it.
You can finde the rails by using blendsurface for the side walls only.
Or just use blend_srf & loft, make sure you dont twist your tunnel.
good luck 
Maybe there is someone more professional than me, maybe @Rhino_Bulgaria
ok, Thanks I will give it a try this way:)
Intersectioing Cross section.3dm (480.1 KB)
Here is one way to do it. —Mark
That is a clean way, do you mind sharing the steps you used?
Draw a straight curve across where the two surfaces touch. Then used Surface from 2,3,4 curves. Then copied the two edges on the lower end and joined them. Used 2 rail sweep next. — Mark
In reading this you can come up with any conclusions. It is just an upper surface and a lower surface.
