Surface from 2 3or4 edge curves un-joins 1 curve denying me a surface

One of the problems I face of OffsetSrf 2mm inwards,

A curved edge shrinks inwards, so overal length of item decreases, I need to keep overall length as it was before the inset.

file attached.

So my plan.

  1. explode the object. (extendSrf wont work otherwise.)
  2. extend the surface at ‘A’ then join surfaces together again
  3. offsetSrf inwards 2mm
  4. use a surface that represents the original edge to trim it so giving true length and item inset2mm.

so before steps 2 and 3 we make the surface to be used in step 4.

  1. duplicate edge ‘A’ and join, then extend ends and add three extra lines B C D to take the surface out a little.
  2. join these three extra lines B C D together, I now have two curves for the next command
  3. Surface from 2 3 or 4 edge curves, select A and it only selects part of it.
    A B C D are not planar so the only command I can use to create a non planar cutting surface fails me.

I am stuck !

Then I use patch !

why though does Surface 2 3 4 edge curves do that ?

SurfaceFrom2_3or4curves_unjoinsCurveA.3dm (197.2 KB)


If your edge is meant to be planar, just extend the surface then trim with a line from the top view.

SurfaceFrom2_3or4curves_unjoinsCurveA_PG.3dm (144.5 KB)


Hi Steve,

EdgeSrf worked in forming a surface for me. Sweep2 also worked. Now the surface is self-overlapping, but the command itself worked. I exploded the line you had BCD into three separate lines and formed them by EdgeSrf A-B-C-D.

Finding one single surface is going to be somewhat tough. Line A, in the top view, is very squiggly over short distances. Should line B also be squiggly to compensate?


SurfaceFrom2_3or4curves_unjoinsCurveA.3dm (265.6 KB)

It was doing that again to me just now, on a new version where I had extended the surface then offset it then trimmed it.

I now see whats happening, it doesnt give choice of the duplicate edge I made or the surface, if I see it selecting most of the edge, its simply selected the surface which is still exploded and not given me the option of surface edge or my dupe edge.

I raised this aspect in another thread, sometimes what options exist are not presented to you. It took me a few try’s before it showed me the dupe edge.

Then the next issue is the ‘webbing’ we see across the radiused edge, very evident for example in your third one in from the left. How do I resolve that ?

I am now in need of filling that area to create a solid , so how do I get to avoid the surface going beyond the shape across those two curved areas like some spider web ?

the wriggles , I have to accept those for what this is ! A result of a sweep, my original rails were fine. Due to a sweep from an arc into a straight profile.

Pascal…The surface is not planar for ABCD. else I would have opted for divide then PlaneThroughPt to get my cutting surface.


Hi Steve,

It does not sound like you are specifically concerned about the slope of this surface. If not, then you can add some arbitrary lines in the middle so Rhino knows where to connect general points. Try Sweep2, choose A and D as your rails, then the intermediate lines to fill in.

It’s not pretty but it works.


SurfaceFrom2_3or4curves_unjoinsCurveA_2.3dm (286.6 KB)

Briiliant minds think alike :slight_smile:
I drew those extra lines in, or similar,  before reading this, though went for EdgeSrf. Sweep2 is more sensible, now why didnt I think of that, not so brilliant a mind :slight_smile:

as you say not pretty but that doesnt matter here.