Cannot Join Adjacent Surfaces

In the attached file I have 7 curves. I have two long curved “rails” going left/right (red) and have four frames also in red.

I am trying to create two surfaces here. On the outer side, I can do a sweep2 or networksrf. On the inner, I can do planarsrf.

Whatever I do, these two surfaces will not join. I am curious why.

Problem Sweep.3dm (3.0 MB)

Hi Jim - the surface edges are slightly out of tolerance (CrvDeviation is a good tester) MatchSrf for Position, with Refine set to Yes & ‘Match by closest points’ should bring it in close enough to join.



Is there something I am doing wrong here or should be doing differently to get these to match up? I have a problem with Matchsrf because the planarsrf come out trimmed.

If the first surface (U-shaped) is realized with a 2-track sweep and then the flat surface with “Planar Curve Surface” using the curve the joint will fail.
But if you use the U-shaped edges plus the purple curve the joint will be possible.


I would not try to make this as one long sweep2. That’s like pounding a square peg into a round hole. You are asking Rhino to make a G2 surface that follows G1 curves and that doesn’t work well

Explode the red rail curves and then do this as 3 separate sweep2 operations and the result will be far more accurate to the rail curves and you won’t have problems joining.

There is a simple option in Sweep2 that should produce a polysurface made of 3 surfaces, if that option was working.

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I would do it as above too. 3 separate sweeps

if you use network surface it can quickly happen that surfaces dont join depending on how tight you set the tolerance. try if lowering the tolerance helps in creating a joinable edge. if you duplicate the inner boarder of the outer surface and make PlanarSrf it joins.

Problem Sweep.3dm (76.7 KB)