Invalid surface when using surface extrude curve straight

I need to create a surface to act as a cutting tool and I am using the left edge of the shape in the attached file, however I get invalid surface error when extruding it both ways.
If I select the lower part only so no horizontal lines I still get this error.
invalid surface.3dm (47.2 KB)

not sure why ?

I had by the way originally wished to create a surface heading outwards from the outlines you see, less the two lines added in heading north and south ! Couldnt see how to do that leaving that shape as a hole in the middle.
since realised to make the cut I didnt need that, just a ‘cutting sheet’.

invalid surface_re.3dm (98.9 KB)

What I would do is project the lines to a plane, clean up the duplicate and overlapping lines so I get one poly-curve. Then use that curve to extrude.

Hello - the line segments in the curve that are parallel to the extrusion direction will make degenerate, zero-width surfaces.


good idea, avoids the lines Pascal refers to running parallel to extrusion.
Even the base of the curve causes failure as it eventually ends up parallel to extrusion distance.

I see by the way you are v6, it wouldnt open in v5.

My original quest was to generate a surface outwards from my closed shape, how would I have done that ?
(closed shape being less the two lines heading north ad south. )

invalid surface_reR5.3dm (213.0 KB)

BTW I noticed something weird, somehow the proper solid is not created when extruding 2 closed curves and I believe this is a bug. I hope someone from McNeel sees this.

Hello - for Solid to apply to extruding a curve, the curve must be both closed and planar.


Hi Ivelin,
I was after achieving something like the attached, direction outwards along 'green ’ axis.

MANY THANKS for the video, I am so grateful when a visual reply appears, means so easy to see what to do.

I achieved this now by projecting the shape to a planar surface, selecting one instance of each bit of the shape joining them then extruding curve to form surface then trimming with the red shape.

However still interested to know if another command could have generated such surface outwards from a closed curve.

surface outward from closed curve.3dm (118.1 KB)


Hmm I missed that point :slight_smile:, thanks Pascal.


As far as I know there isn’t such command, but I don’t work with Rhino on a daily basis since Rhino4, so what do I know. What I can suggest is to offset your curve outwards (this will most likely change your poly-curve. You could as well try to scale it 2d and project it on the (extruded) surface and trim accordingly.