Hi Michael,

Image A: OBJ from Moi3D to 3dCoat:
In this case i used the 'smooth' option in 3dCoat

With more complicated objects from Moi3d (especially
when i use boolean)with sharp edges,it seems that
3dCoat sees them as single surfaces.

IMAGE B: OBJ from Moi3D to SILO:
Here you can see two narrow surfaces(using Blend in Moi)
welded to three big surfaces
You can see that the vertices of the big surfaces don't end
in the same vertices of the narrow surfaces

IMAGE C: Export OBJ in Moi
I used join and welding vertices set to on

Thanks Brian,DannyT and Anis