Hi albehany, so for this last one the problem is that the surfaces are not smooth to each other, they range from something around 1 to 4 degrees off of being tangent.

This kind of geometry where surfaces are close to being smooth but not fully smooth makes things difficult for filleting. That's because fillets only naturally meet up on edges that are smooth to each other. When edges are not tangent to each other it means the fillet surfaces need to be extended and intersected with each other and that process becomes difficult at shallow angles. Surfaces that are at a shallow angle to each other when extended form something more like a "zone of overlap" rather than a crisp well defined intersection.

So the main thing to get fillets on this is to tighten up the construction so the surfaces are fully smooth where they touch rather than slightly creased. It's best to do this with your original curves before you construct things off of them.

- Michael