Hi Arian, another kind of problem area in general is having sort of "stressed" surfaces that are bunched or compressed in awkward ways.

There's one such surface here:




Note that the surface looks somewhat irregular in it's shaded appearance? It means the surface has a kind of lumpy quality to it rather than being a nice smooth simple surface.

Usually to get high quality surfaces you need to make the surface to a more regular simple 4 sided outline. If you try to directly build a surface to an irregular outline with pieces pinching down or one side a lot longer than the other, etc... it will make for a stressed surface and later on when you try to fillet it, the filleter will be going crazy trying to track along teeny tiny little bumps in the surface.

So generally instead of trying to build surfaces directly to fill in an irregular boundary, you instead need to build larger more extended surfaces to start with, something say that extends more out into this area here:



Then use cutting operations (either Edit > Trim if you're working at an individual surface level, or booleans if you're working with solids which can save time if you're able to keep things as solids more throughout the process) to slice off some parts to form the final shape, rather than trying to build individual surfaces to the final boundary in every single spot.

So for example something like this type of big broad cutting surface to slice off the ends of the extended shape:


That's not quite exactly right, just a very quick example to hopefully give you the idea.

If you can form more pieces by cutting operations especially with many pieces cut by a common surface or also constructed from a common edge it will make for a much better quality model both with better alignment between pieces and also smoother and higher quality surfaces that are not stressed by trying to be initially constructed in a stressed way.

Hope this makes sense on some things you might try for a better overall approach!

- Michael