Smoothing SubDs

Looking for some advice on how to go about smoothing or fairing SubDs. Obviously, I can do control point manipulation on this and use my eye to get close to what I am looking for, but I’m hoping to find some tools to make the process easier.

My current process is: First make a crude shape and start refining the topography as I go to make it do what I want. This tends to be trial and error. I usually have some reference NURBS surfaces that I convert or use to get some edges to sweep. Generally when I get a surface that works the control points are all over the place lacking consistency and organization. What I’ve started doing is using that first SubD as a reference to make a more refined second iteration. I make this version square with all the control points aligning on a grid. Then I use cage-edit to add the curvature that I want to the part. This makes the corners all look rather consistent.

My issue is when I do a cage edit the suraces don’t have a smooth curvature when I’m done. I believe this has to do with the fact that areas that have a corner have more control points than areas that are flat.

I’ve used the smooth command a little, but haven’t had much luck. When I fix borders they have too much of an influence on the shape and when I don’t fix borders it doesn’t work.

The soft transform works a little, but I haven’t had much success with this either. Usually I want to soft edge a point in one direction (Along a U) and not in another (Along a V) In the example in the picture; I would like to be able to move the control points on the back edge (black line with curvature anylisis turned on) to resemble more closely the curvature of blue line. It would be ideal if I didn’t have to do that for every edge loop/ring. Is there a way to do this?

SubD Helm.3dm (107.6 KB)

you can use the align command on your edge loops and align them to a curve. Or grab all the points on a surface and project them to a nurbs surface (see this video) Rhino 7- Quick Tip, Project SubD - YouTube

keep in mind you may perhaps be looking for an order of precision that subd simply does not have, nor will it ever. It’s a free form organic tool and it will only ever be precise-ish.

Can you post a file with the thing smooth and then not so smooth?


I like both of those. I will look into them.

I know I am pushing the limits of SubD. For my work we produce 50+ parts like the one attached above every year. They are all slightly different, but all very similar. I like SubD because it lets me make fast modifications to the shape which wouldn’t be possible with Nurbs.

Smooth might not be the best term to use here. I am looking for a more constant curvature like the blue line, but it is producing a curve with a stronger curvature near the three control points that make up the variable radius around the saddlepoint.

I often just draw a curve and snap the points of the subd to the curve. I can then slide them around as needed to get the distribution I want.

the issue with subd is it does not work the same as nurbs… for instance in the area you are referencing you need the points close to get the corner, but can slide the points on the edges to spread them out a bit and get a smoother border.

does that make sense, or have I completely confused you?