A better way to smooth a closed polysurface?

Im aware that this can probably be produced using loft or from curved network, but I have a project where I will have hundred of closed curves that I wanted to extrude and then apply some command that makes the upper part smooth while keeping the right angles on the bottom. I came close using the patch fill and adjusting tangency (as can be seen in the attached file) but Im sure theres a better, quicker way.

Please help, any advice welcome.


HelpBubble.3dm (286.1 KB)

Hello - this looks like a perfect case for SubD. Have you tried that?

HelpBubble_maybe.3dm (73.4 KB)


Thank you so much for the response Pascal.

Yes, this is exactly who I was trying to do. But when I select my closed polysurface and do command ToSubD, it just produces two flat circles. Im sure youre busy but can you fill me in on what steps Im missing? Ive been banging my head against the wall all day.

Much appreciated!


Hi Matthew - I did not convert it, I built it from scratch - I’ll see if I can make a useful example file with steps - @theoutside may have something hanging around, he’s way better at it than me.


Thank you so much. I played around rebuilding it, I think I have it pretty close. I draw a closed curve, extrude it using SubD, then use SubD fill on the opening. The only weird thing is after I extrude the curve, the extrusion is slightly differentHelpBubble.3dm (771.6 KB) than the original curve. Ill keep messing with it but if you have a quick solution it would be much appreciated.

Thank you so much for your help!


Hi Matthew - SubD cannot always match nurbs curves exactly - you can try MakeSubDFriendly on the curve then adjust it, then extrude to a SubD.


I will try that, thank you so much Pascal!


Bildschirmfoto 2021-01-14 um 23.52.15

rail revolve produces sometimes astonishing results, if you can live with a sharp edge.

1 Like

Yours looks lovely, I dont mind the sharp edge. Unfortunately it only seems to work on simple curves. Heres how mine turned out. Any suggestions? Am I using rail revolve wrong? It looks like your curve extends beyond the axis point, is that key?

well yes, that is not a magic tool for all cases, if you have several strong inflection points like your face that is not going to work. patch set to tangency is your best friend if you get the settings right which is a bit of a fiddle either.

but in your case that really would make most sense as pascal pointed out to use subd, with crease you can also set parts to hard edges if wished.

Yes, Im back to using patch for now, it almost is what Im looking for.

Thanks for your thoughts!

another idea for more complex geometry would be blend surface. but that would require some of your input curves to be cleaned up and might not be what you are after. but it could be pretty fast, so why not giving it a try. if you manage to get a good continous curve to start from you can place a little planar surface on an elevated area centroid and blend it with the perimeter. for a smoother transition you could also enlarge the inner surface and match it to your perimeter.

Ill give it a try, thank you!