In the attached file I have three pairs of surfaces. The one on the right is the original pair. I would like to offsetsrf by 3/8" inward and join to form a closed polysrf. But it will not join.
If I split the original gray polysrf using the end frame of the original red surface, I can join up as shown in the center or left. It appears that all joints are tangent.
I have highlighted the intersections—which are all different. If I intersect the end cross section used to create the red at the right with the gray at the right I get a line along the full length. If I intersect the resulting sweep2 or networksrf, I get the partial line shown.
It needs a figure-8 top and bottom, essentially the red capped and trimmed by the purples. The problem is that during offsets, they surface edges are no longer planar. The starting curves are all coplanar at the top and bottom.
You get the short line because the red surface passes slightly through the grey one at that point and forms an intersection within your tolerance setting, whereas the end of the red section does not unless you relax the tolerance slightly.
I’m not clear which surface or surfaces you want to offset, nor in which direction(s). Could you sketch over the image to show what you want?
In the meantime, your surfaces are quite complex - you will find intersects and offsets are better if you can start from simpler surfaces, which in turn come from simpler curves. You should be able to remake your shape something like this:
NonManifoldMerge will produce a non-manifold polysurface. However it may not be very useful and in some cases cause problems. For instance OffsetSrf a non-manifold polysurface will result in several polysurfaces. Trying to create a solid with OffsetSrf on a non-manifold polysurface will fail to create the solid.
Good point David. And, in any event, if @miano’s intention is what I now suspect it is, the OffsetSrf outcomes will need some surface extension/intersection/match work to get planar caps because the initial surfaces are not perpendicular to the caps.