Question from Subd modeler (Modo)

When Clayoo is not activated it is a normal mesh.

When Clayoo is activated, it is a Clayoo object, i.e. SubD

McNeel Rhino® ( .3dm ): Rhino is a NURBS-based 3D modeling application. It has the ability to internally convert its curve based NURBS models into a triangulated polygon model. Modo reads the triangulated polygon data from any Rhino 3DM format file (Modo cannot read NURBS data directly). Modo can both Read and Write to the .3dm file format.

Lay out one feather in 3DM format .

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An example from your Modo file.

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I like to build my subd meshes in Modo. I would like to have easy and EXACT conversion from subd polygonal meshes to NURBS which will have same functionality as native one (booleans, fillets, thickening). I don`t want to fully rebuild my designs. I would like to import it and use it in Rhino.

Unfortunately this will cause you more difficulty in the future. If you are producing files for machining, hard surface objects should be should be modeled from the start in a CAD application. Sculptural work is an exception, and requires additional consideration.

Thickening objects to a greater thickness than the minimum curvature radius will be a bigger problem with nurbs from subd. Because your rounded corners are baked in, if you run into thickening problems you won’t have any options, unless you can recreate the subd with a hard edge in those areas.
All your rounded corners should be hard edges that you can more easily change the fillet later as needed.

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@cdordoni, @inju Thanks for help.

So what is best workflow to rebuild meshes like this? I will delete all additional edges to left hard edges only and what next? Any tutorial for best manual conversion from subd to nurbs?

this is what I was trying to explain.

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An example from OBJ file.

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Was it hard to change it from subd to polysurface?

Run _toSubD, then run _toNurbs. That all there is to it.

With complex objects I’ve seen a few errors, but they were easy to spot.

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@inju @Max3 Thanks.

What about joining those polynurbs surfaces into solid and blending it with solids? Is it hard? Will edges create conflicts or it is wise as in SolidThinking Evolve (blending polynurbs and solids are seamless)?

Please look on this video below:
He mix polynurbs ear (it may be imported subd as obj) with nurbs made rest. It blending it without edge confict. Is it works same way in Rhino 7?

I`ve closed meshes (closed shells). Is it possible to merge that 3 meshes together as smoothed polynurbs and give fillet in the intersection edge? (125.1 KB)

Booleans: Ok sometimes, you just have to make sure you have no coplanar/coincident surfaces, or coincident edges, or anything that’s not a clear, non-ambiguous intersection. Also heavy/dense meshes will mail more often than not, but low-poly cage>_ToSubD>_ToNutbs will work (sometimes)

Fillets: they will fail most of them time. Rhino doesn’t really have robust fillets in their tools/solvers/kernel.
I’m questioning why would you even want fillets in beautifully modeled SubD geometry. I’d go with G2 blends everywhere. It’s more work, but it’s a more refined result.

Thickening: terrible on sharp creases and in any situations where the offset amount creates self-intersections of ‘bow-ties’, also very inaccurate since it currently offsets based on the normals of each control point, not The normal of the low-poly surfaces that those points define. You are better off converting to Nurbs first, and they doing _OffsetSrf and _Shell to the nurbs. But in either case there will be manual labor to solve tricky areas.

Sometimes we work in a similar workflow between Modo/T-Splines geometry converted to Nurbs to go from concept work to final geometry for production/tooling. In some case we fully rebuild in Nurbs, in some others we convert and prep like you describe. It depends on each case/model/detail/client/budget/timeline. It’s not a walk in the park process. It’s labor intensive, but it’s the best way to achieve topology and design details that would take about 2-3X longer if it was all nurbs. And more like 10X-20X once you consider the design evolution/changes along the way.


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I’m questioning why would you even want fillets in beautifully modeled SubD geometry. I’d go with G2 blends everywhere. It’s more work, but it’s a more refined result

If the thickening presents a problem due to minimum radius of curvature, filleting or otherwise softening the edges later might be needed.

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Certainly true. After seeing the OP posts on the Moi forum, appears he/she is looking for a way to get existing mesh models to CAD for the purpose of creating tooling, even features not needing subd. Typically, the first consideration for tooling is to build the model in a CAD application for obvious reasons.

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Yes. I produced many subd meshes and I’m very fast on it. Most of them are 3d printed but now I need some of them produce with CNC milled molds. I don’t want to change my workflow which is good (fast and effective). I am looking for some fastest way to go from my ready subd meshes to rebuilded nurbs models. I may buy and learn some new soft. Now I’m Modo/Zbrush/MoI3d user but I wanted to go into Rhino/Alias world (and maybe extend my workflow a bit). I’m a basic nurbs modeler but I’m an advanced subd modeler. When I saw that video I`ve thought that maybe Rhino 7 is an answer for my needs.

Today I`ve tried also Altair Inspire Studio which has got also mixed workflow but I think finally land with MoI3d+Rhino workflow for this.

That uploaded meshes and those filleting and shelling was only example. I may do shelling and filleting in Modo and export all subd meshes. Then I would need only booleans (addition, substraction, intersection). So in other way I may import whole complex model builded from many parts as many subd models. It may contains baked fillets and shelling as external substraction booleans model to carve it in Rhino. That post here and in MoI3d forum is my research in that area

@gustojunk I would like to say big Thank You for your answer. I`m reading this fourth time and I’m sure it’s not a last time. Cheers!!!

Yes, it’s a good rule of thumb, for sure. But once you really know what you are doing you can ignore it.

We’ve been releasing a lot of parts in the last two weeks for tooling. All SubD ToNurbs, properly smoothed and drafted, shelled, and given to our client’s engineering team to add inside features.

We do this a lot. It’s a great workflow for consumer products and things smaller than a car.


Hi, amazing model…
I expect you needed more then a day to finish this.
I it possible save your Clayoo object as is and then continue working on it later?

As soon as I close Rhino it coverts it to a Mesh object. One workaround is to change to Cage view mode before closing Rhino as is later fairly simple to continue but still, there is always need to fix converted mesh as it adds edges to deal more complex geometry.

Is there a solution for this?


Save in Box Mode (Primitive), then don’t switch to Mesh.

ClayoObject to SubD, the file is 8 times smaller in size than it was, and the quality of the part is not lost, and faster can be edited in Rhino under SubD.