Hi there. I’m rather new to rhino. I have a project I’m currently working on and I’m trying to figure out what the best method of creating these curves into a polysurface would be (see below image).
I have tried to create them into a polysurface like this but no matter what I try I always end up with the large curved surface creating an undercut (see below image). What am I missing?
Here is the Rhino file:
Create Surfaces.3dm (36.0 KB)
Thanks in advance
Maybe you need to add some control lines。
Hi @Neil_Smith
If I understand you correctly, you can use Sweep2 to make the 3 curved surfaces - the trick being that you extrude the top curve and use the edge of that surface as one of the sweep rails, forcing the resulting surface to be completely vertical by setting the edge continuity to curvature; and then use PlanarSrf for the 2 other sides - see video.
Thanks so much Jakob. I appreciate the help. This worked perfectly and is a useful technique for future use.
Using ‘Edge Curves’ from the surface menu will get you a result too, its a handy tool, hope it helps some point in the future if not this time 
Hi @milezee
EdgeSrf will indeed get you a result, but the front surface will have a noticeable undercut, which was what @Neil_Smith was trying to avoid - hence the use of Sweep2 and the surface edges to “force” the edges to be tangent to the XY plane 
that all depends on which sequence you use the ‘edgecurve’ command, its probably one of those situations where a mix of both gives the best result 
No, sorry to be an annoying old man, but just in case someone comes across this post looking for help. I’m fairly convinced that no matter the pick order, there’s no way to create the larger surface using EdgeSrf without creating an undercut/negative draft. Unless there’s something I’ve overlooked/misunderstood, of course 
-Jakob
yeh a slight undercut just on that front face, you’re right, use sweep2 for that part, the rest I’d use edge curves 
. Many ways to skin a cat
Indeed the essence of modeling in Rhino 
