Making a tapered polysurface from varying curvature surfaces; subD issues

[Ariel_Tan]

Hi everyone,

I’d like to make a closed polysurface with a tapered/chamfered/bevelled edge on one side, from two identical varying-curvature surfaces. Instead of using the usual offset surface to create a solid polysurface out of a varying-curvature surface, how can I do it?

I have thought of doing it by duplicating/offseting the surface, then taking the two parallel surfaces and tilting them so they intersect at the top in profile (see diagram), then trim off the extras and then do EdgeSrf on the rest to create a closed polysurface.

Is there a way to preserve the original curvature of the surface as much as possible? If not let me know, that’s fine too. Just wanna know how to have a class-A type surface, and how much it’s possible to have the surface geometry change as little as possible.

This is what I want to do:

Screenshots:

Here is the Original Surface:

This is the goal, in subD form:

Diagram:

3dm file:

question for Rhino Forum.3dm (10.6 MB)

ways I can think of are:

1. grasshopper — extract point grid from surface and offset these points to the normal of the surface frame at varying distances (however seems quite tedious)
2. loft/sweep2 from isocurves — extract isovcurves across set intervals in U, V directions, and then loft/sweep2
3. Shear surface/Shear curves from Contour command

For now I have offset the surface, then done a QuadRemesh to SubD at 50 faces, and then deleted the top faces to give the object a triangular instead of rectangular profile.

Things I don’t think will work:

1. SoftEditSurface: For a sharp and non-bulgy surface, edge that aligns well with the original surface, it doesn’t seem to be the best option.
2. SoftMove Control Points: doesn’t seem precise enough to match the curvature in 3D?
3. Manually moving control points: too tedious and risk of introducing kinks
4. MatchSrf: Surfaces need to be untrimmed but I cannot shrinkTrimmedSrf to the surface shape for this.

Any thoughts? Really appreciate it

P.S.

When I have tried to do it in SubD, I run into these Boundary Edge problems I don’t know how to solve too (details written in photos attached):

I wish to have the rear profile of the subD be only a triangular subD like the rest of the subD but I’m unable to do that:

I’m not sure how to resolve this. The file for just this subD shape is here:

question for Rhino Forum subD only.3dm (5.5 MB)

Thanks again for all the help!