Hi niko, here are some steps to show you how this alternate "extended surface" technique can work.

I've attached the result 3DM model as niko_protrusion.3dm .


To start with, I projected your smaller outline curve on to the surface, and used Trim to hack off the ends about where they started to curve in:



Then I went to the other side of the surface (the "inside" part of it), and drew 2 lines in at the ends of those curves so those lines are going inward towards the center of the shape:



Then I used the Move command on each of those lines, picking the line's own endpoint as the base point, and the line's own midpoint as the target point, so the lines now had some spacing off of the surface. I also trimmed back a little more off of the surface curves as well:



Then I put in curve blends and joined those pieces together to make rails that start off hugging the surface but then curve inwards towards the center of the shape:



Now a sweep can be done to make a surface that looks like this:



Or as seen from the outside, it looks like this:



So notice there that the rounded "tip" shape is a result of the sweep being submerged as it passes through the outer surface, instead of trying to build a surface directly to that outline curve.

Now with these 2 surfaces you can select each of them and use Fillet to build a surface/surface fillet to make a smooth juncture between them, you can use the G2 blend option for the fillet shape if you want a that kind of blend-like result:



That's an alternate approach to this problem which builds an extended surface that then gets trimmed back by the fillet, rather than trying to build it directly to a curve layout that does not have a regular non-pinched quad type structure.

You give up some of the "direct drawing" control over the shape of the tip with this technique, you have to manipulate that tip shape kind of indirectly by controlling how fast the surface submerges through the main one. But you're going to actually have much more regular surface structures with this way and you also gain some simplicity with a smaller number of surfaces involved, like just one fillet/blend surface to bridge between the pieces rather than fragments.

Also you can adjust the radius of the fillet which is kind of like adjusting the spacing between the 2 offset profile curves that you were using.


I hope this alternate approach may be useful. Let me know if you try it and get stuck on something.

- Michael