How to create smooth transition between 3 chamfer edges

Hey there, i would like to make a smooth transition as shown in the pictures. However it seems that i lack some knowledge / tricks to make this work. I am familiar with BlendCrv, NetworkSrf and the difference between Position, Tangency and Curvature. I just don’t know how to solve a 3-side polygon hole…

3part_transition.3dm (86.8 KB)

Hi Andreas - please post a file with the objects. I’d say the triangle can be a plane, in theory, but it looks like it is not.


oh right, i attached it to the first post.

In fact its not a plane plane, more like a bent triangle.
It doesn’t have to be a triangle. I just don’t know how to do this.

another attempt, but not working:

Patch works, but the transition isn’t really nice.

Well, It’s a cheap way out but Patch does OK here - you need to duplicate the curved edges as curves for the input and use the straight surface edges directly.


@andreas6 - here is my go at it with just a patch
3part_transition_Patch.3dm (139.5 KB)


yeah, thats the cheap trick, i mentioned it already. But to fulfill my needs for proper renderings there has to be no visible “edge” at the transition.

I nearly got where i want.

  1. filled the whole hole with a patch
  2. create a triangle as shown.
  3. Split patch with triangle (red)
  4. create 3x. NwetworkSrf with curvature (blue)

if there is a better / cleaner solution i would welcome it.

A different approach which needs some control point location refinement:

3part_transition_DC01.3dm (2.2 MB)

The chamfers were rebuilt so that the ends are isocurves.

IMO you are working too hard using a triangle- The singularity will fight you till the end.

I’d go for more something like this.

right about now @sgreenawalt as the master of nurbs topology should show up and tell us how we are all doing it so very wrong…

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With two surfaces something like this:

You can also make this with single span surfaces if you cleanup the surrounding curves / surface edges.

@Rhino_Bulgaria has also made a video of this approach:


You can also try this approach in case that you are aiming for a nearly Class-A surface quality with clean surfaces. But keep in mind that it’s slow. The quick “dirty” approach is already shown in the port above.

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Thank you all so much,
i will dive into this for sure, class-A surfaces are definetly something i want to aim for and the videos are indeed what i was looking for.

@theoutside yeah, i was guessing that triangles aren’t the proper solution although it seems too obvious to use them :wink: