Hi Brian, Extrude with Set Path will make what is called a "Sum surface". It's a surface made from 2 curves where all the U direction isoparms will be from the first curve and all the V direction isoparms will be exactly the shape of the second curve.

An extrusion is one example of this type of surface with a line being one of the curves.

I think that I didn't understand properly what you were looking for, I kind of thought you were looking for something like the convex hull around a set of curves or surfaces.

Does the Offset command applied to your path curve give you the side pieces that you need?

Trying to generate a sum surface using Extrude with Set path as in your example will not be good because the result is a self intersecting surface that folds back over on top of itself.

- Michael

Hi Michael,
Thank you for the explanations.
I've been experimenting/messing around, trying to manage an "envelope" of a family of one 2D profile, offset in the same 2D plane, along a path.
My profile will be composed of 4 circular arcs, but the tests were with a circle, for simplicity.
This is sort of like a convex hull...
So Extrude does not create (in this case) a useable desired result for the circle.
Planar sweep of a planar circle does not create (in this case) a useable desired result.
The 3D tube created by sweep, is promising for a circle, but using part of a circle gives variable results, due to the auto placement I guess.

( As in other posts, a few hundred boolean differences is not practical...:-) )

I'll post my 2D object, after it gets created, in a few days...

In theory, the parametric equations can be solved with Matlab and calculus, likely beyond my ability.

- Brian