Extrude using set path option

 From:  Michael Gibson
5122.2 In reply to 5122.1 
Hi Rich, that's just the way that "Set path" for Extrude is intended to work.

It builds what is called a "Sum surface", where the generated surface is a direct combination of the 2 input curves, there is no rotation of the path involved unlike Sweep.

If you want to generate a result where the profile rotates to stay perpendicular to the path, then use the Sweep command to get that type of result rather than Extrude.

So what you show there is actually the intended behavior for extrude - you usually should not use it on a path that has pieces of it that go in the same plane as the profile curve because that will make for squished-flat zones like you see there, it would be more normally used for something like this:

You can see there that Extrude with "Set Path" generates a kind of sheared final result where the profile is not rotated.

- Michael