I was wondering if anyone had a simple solution to this problem. If I do an offsetsrf inward on a slope—

—the outside edge of the plating is higher than the that of the inside on the inside. Thus I get extra plating on one side that can be trimmed off. Is there a simple way extend the plating on the other side so that the upper joint is flat?

In this particular case I have a shape that I cannot extend upwards beyond this point and trim back.

Are you wanting only a inner surface to extend up?—-Mark

yes.

Since OffsetSrf calculates the offset direction according to the surface Normals, I don’t think it is possible to have a flat-topped output. I suggest using _Ribbon on both Top and bottom surface edges then loft in between.

fastest version is to start with a closed Polysurfaces - then use
_shell

example:
_truncatedCone
_shell

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Thx,
And wouldn’t you know, the #@\$@ think won’t shell. 5/8"
Problem Shell.3dm.zip (128.0 KB)

ExtendSrf only works on surfaces, not polysurfaces.

Surfaces with zero length sides, such as the triangular surfaces, do not extend at the corners adjacent to the zero length sides. This may be cause of Shell failing.

To obtain the desired result:

Explode the polysurface.

Extend the curved surfaces higher than needed to obtain desired offset surface.

Trim the tops of the extended surfaces at the same height. (This eliminates problems in the next step due to variations in extension heights.)

Trim the overlapping corners of the extended surfaces.

Join the extended surfaces and the triangular surfaces.

Offset the polysurface as desired.

Trim the result at the desired height.

Use Loft or Sweep2 to create the top edge.

Your best friend for creating a horizontal top wall following the shape of freeform offset walls is the `! _RibbonOffset` command. It works in almost all scenarios, including surfaces with complex shape that other Rhino tools fail to solve. However, this is not a fully automatic approach with a single mouse click, so you will have to extend the offset surface past the ribbon offset surface, in order to intersect them together, and then use either “Trim” or “Split” to remove the excess portion of both surfaces. Here is a quick tutorial that shows the basic principle of the “Ribbon offset” tool:

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Ribbon is new two me. So I need to learn.

The problem with this shape is it is a structure that sits on a deck with camber (parabolic) with a rectangular support structure underneath sitting on a deck without camber. The plan of this structure has to be rectangular but camber causes the fore and aft faces end up being less than planar.

I was able to extrude a parabola and split it to form the bottom. The top is planar. Then I was able to shell.