Hi Lewis, and then for your Fillet problem - there are messy areas in the swirly shape in these spots here:



If you zoom in to those areas you can see that there are little curve spans in those areas which wiggle around a bit right where they come to a juncture area:



That type of little wiggle with an inflection point is going to make things much more difficult for the fillet engine to construct good fillet surfaces off of, when the fillet surfaces are created they work by tracking along those edges and moving off some distance from them and any wiggly shapes like that will have the wiggles sort of magnified in the fillet result. So that's not good for filleting.

In the attached 3DM file I have edited the curve to just delete many of those points to eliminate the wiggles, you should be able to extrude and fillet this version much more easily.

This is another good example of something that the 2D vector program is not sensitive to but which becomes a problem when you try to do CAD type geometry construction off of that type of geometry.

- Michael