Trying to extrude a simple profile. Unexpected results?

I’m again playing with Rhino. I’m trying to extrude a simple profile along an arc. I get unexpected results. (see pics) In Sketchup I just have the profile follow the arc and get what I want.

In RH I made the the shap in curves, made a surface from the curves, the used “ExtrudeSrfAlongCrv.” I get a very odd shape. Obviously the surface is not extruding perpendicular to the curve. I can’t find anywhere to specify this. Am I using the wrong tool?

Sketchup version
Curve and surface

Try Sweep1 instead… --Mitch

It seems that sweep only works on curves and not surfaces. I removed the surface and did get the shape I want. Thanks.
Now I’m stuck on how to Flatten/Unfold/ make the compound surface flat. I know people do what I’m trying to all the time. I just don’t know the method. Perhaps there is a video tutorial someone can point me to that explains the process?

I’ve updated the pic in the first link to explain my goal.

Here is the Rhino version.

That surface will not flatten with significant stretching and/or shrinking.

Rhino has two commands for flattening surfaces with compound curvature. Smash is the simplest while Squish provides controls over how the surface deforms. Some experimentation and knowledge of the how the material to be used and the fabrication techniques to be used are needed if a physical object is to be built using the flattened surface from Rhino.

How we would use this in my work is that the flattened shape would be sectioned into pieces that would fit on 4’x8’ (1/4" or 1/8" thickness) sheet goods to be cut on a CNC machine. This example is from project that was built. The shop skinned the form manually then cut off the excess. But to experiment, I had a friend do what I’m asking in SolidWorks, and his result was the same as the built piece. It would have saved the shop a lot of time if I could have provided them with the flattened shapes.
I did come across Smash but did not know how to use it. I’ll delve further.

It might be better to split the surface into pieces before flattening, rather than flatten the entire surface and then split the flattened shape. If the pieces are small narrow enough they should be close enough to developable for UnrollSrf to work.

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