Extruding Surface using two closed curves?


Im trying to make a extruding surface connecting two closed curves which I’d like to use as the edges of the result surface, so just extending surface is not an option. (attached image most right)

I tried using loft, but that caused a twisting of the surface. I changed the starting points but that also didn’t work…(attached image center) <I added fillets to the curves- is this why the twist happens?>

Other was network surface, but that created the edge surface of the result surface to have a slight bulge in the corners. (in the flat area) (attached image left)

Often BlendSrf with the Continuity set to G0 is a good choice for this, since you can add guide sections to control the twisting.

Just tried Blend surf but I’m not able to highlight the two curves.
Does blend surf work on closed curves?

Oh, forgot the step where you have to extrude the two curves a short distance to get actual ‘edges’ to blend. It would be handy if BlendSrf worked on curves.

I’ll try that out! Thanks!

I’m not sure why the loft didn’t work.
Is your file anything like the attached?
Loft.3dm (315.8 KB)

Loft should work but you’ll need to set the curve seams accurately using Osnaps. It might pay to SimplifyCrv on the inputs as well.


Hi Pascal,

SimplifyCrv worked!!!
The points seems to be the same number and same position though…
I wonder how the troubled curve was made…
I just copy pasted the bottom curve and used gum-ball to make it about half in y-axis…

I saved before closing the file and now I can’t get the failed curve. It’s ok, but leaves a mystery…

Thanks anyway! got it to work.


Thank you for the attached file.
Yes the loft was as you attached.
Though, I copied the bottom curve and used gum-ball to shrink in y-direction.

I wanted to post the troubled curve/surface, but I used simplycrv and saved the file which made the loft ok now.

I’ll avoid copy paste for now…

Thank you again!


THANK YOU all for the reply!

Next time I’ll make sure to upload the data as well.

And, I’ll try recreating the curves before trying out different ways to create the surface, though it was a good study.

Is there anyway to Close this post?

Hi Toshi - scaling a ‘polycurve’ non-uniformly is likely what ‘did it’. That is, tuned, I am guessing, the polycurve into a single NURBS curve which SimplifyCrv reversed. Can you post the original curve? Just curious…since scaling a polycurve that I made did not do this.


sorry Pascal,
I lost my original curve…
I did the simplifycrv and it saved it…

tried to reproduce it a couple of times, but now it seems fine.
All I have is the screenshot pasted on this thread.


Now I’m at it, I have one additional question if it’s alright.
Not related to the topic but I get this but I get this error often.
The shell command…

From the surface created from loft, I capped it then
fillet one side(2mm) then shell(1mm) from the other.

I get the error, the output is not a solid.
But it seems like a solid… shell.3dm (1.9 MB)