Your problem is in your STL export settings - the spline is perfectly smooth mathematically, and there are separate settings for the SW graphic window and STL export which both approximate the curve as a series of straight lines.
I think the words you're looking for are unfolding/unwrapping.
There are a lot of software that can do this, which is more suitable depends on your application.
Here is a good starting point :-)
So, this is actually non-trivial. Here are the key points:
In order to use the "Combine" feature, to create the volume that you want, you need to have a multibody part
In order to move the parts dynamically inside a multibody, you need to use mates with the "move/copy bodies" feature. It cannot accept a global variable for translate/...
This ended up being a small problem in Illustrator due to my usage of the Image Trace module. The end product of the module creates two separate paths that are joined as one, so although Illustrator doesn't identify it, it still results in 2 paths when exported into DWG. The workaround for this is to make sure to exclude all paths except for the ones ...
See my second comment.
Boss-Extrude3 is indeed not a merging feature. You can see in the screenshot below it creates a separate solid body.
Boss-Extrude5 is a merging feature, and causes the two solids it touches to merge into one body.
This is why your pattern works for Boss-Extrude5 only in the original part. It also explains why, at the end of your ...
This case got some history in Graphic Design SE. It got an answer which suggested making it by joining together 3D models of the blades.
The questioner, of course, was not interested in it. It's only an imagined drawing, no matter it's a 3D model. An acceptable 3D model should be based on measuring which form the paper takes after the cusps are pinned to ...