Spherical to cylindrical surface blend

Umm… so… how?
I know it’s a triangular “patch” which isn’t preferable but I’m completely out of ideas.

Hi Stefan,

Did you already try

  • network surface
  • sweep 2

Can you post the file, it’s much easier to try and find a solution, than only based on an image.


Hi Willem!

Yes, I tried both, among others. Didn’t get it to work.

asdf.3dm (88.7 KB)

Something like this?

Hi Stefan,

I tried to find a solution in the limited time I have:

First create 2 guide surfaces to set the desired tangency

Second create a blend surface:

asdf_wd.3dm (94.3 KB)


Jordy, quite close but no cigar.
I probably should have been more clear in my original post and explain that I intend to mirror this “quarter patch” over the entire gap of cylindrical backplate. The problem with your solution is that once mirrored, the two surfaces will not be curvature continuous (see image).

You might want to use the feature “Add Slash” “Add Shapes” in blend surface in my solution to get isocurves more vertical.

Next when you mirror the surface you can use match surface to match any irregularities.


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This seems to be the right approach. Thank you!

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Smart one :slight_smile:

Hi, My approach was just to duplicate the edge, SetPt_Z to 0, ExtrudeCrv with bothsides, and trim the extruded surface using the original surface, then join all…
Attached closed solid. - Michael VSasdf_01.3dm (254.2 KB) asdf_01-V4.3dm (251.4 KB)
Not sure from you question if the intention was to have tangency at the narrowest gap or not?

Here’s one with tangential join over narrowest gap using dupborder and crvnetwork.
Both versions are in this v4 file
asdf_02.3dm (389.1 KB)

Hi Stefan - if your outline/edge on the cylindrical surface is, in theory, truly lying on a sphere than making that sphere and trimming it is the way to go, I’d say. In the file you posted it is not actually on a sphere - I don’t know if that is intentional or not…


Hi, If you are referring to a sphere/surface interaction why not use solid boolean to get the shaping you’re after:

Many thanks everyone for your help!

Pascal, my intention was in fact for it not to be a spherical surface but rather exactly like Michael shows in his other example where the tangency at the narrowest point fades off toward the ends. So simple, yet complicated…

Michael, I would appreciate if you could please explain more in detail how you went about on the 02-version as I still don’t quite get it. It’s exactly what I was going for but the steps are still a mystery…

Hi, To get the 02 shape, I first extracted the isocurve at the narrowest middle point of the shape that you supplied, which gave me pretty much a circle with gap, which I used blendcrv to fill the gap.
I then used dupborder on the cyclinder shape you made.
Using NetworkSrf and with the blended gap curve and the 2 x edges as input gave me the shape I showed.
I adjusted the edge tolerance to 0.001 sothat the created surface would join to the cylinder shape accurately. Edge tangency was set to position, as the mid gap curve is already tangential so that would control the created surface to also be tangential in that area. Hope that helps.

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