Hi Giovanni, can you please post the .3dm model file as well as your screenshots?

It is very difficult for me to debug a screenshot, but a .3dm model file does give me something I can test and debug with.

What you are seeing there though is an area of extra subdivisions to make the divided mesh meet the angle tolerance. It is possible that there are very small differences in the fillet surface from one side to the other which could cause that kind of a thing.

Like PaQ mentions, probably the best way to absolutely ensure symmetry is to model half and then mirror, that ensures 100% complete identical surface forms (and also edge topology) between 2 halves.

It's not really very feasible to do only a completely uniform mesh generation in all circumstances, because in many situations it would cause an immensely dense mesh to be created.

Here is an exaggerated example to illustrate, notice how this surface is flat in many areas and only has curvature in a localized area:



If that was meshed with only a completely uniform and regular mesh with no subdivided areas, it would require putting a very heavy and dense mesh even in the flat areas that didn't need it, just to try and adapt to the curvature of that localized area.

So the mesher does not try to do that for every single type of surface. It does try to do it for regularly shaped surfaces like a sphere or a cylinder, but on more general surfaces (which your fillet there falls under) it would in general blow up polygon count by a very large amount.

So in situations like this the mesher does an "adaptive subdivision" which subdivides the mesh only in areas of higher curvature, like this:



That greatly helps to keep the polygon count lower.


Your fillet there is also a pretty high radius in relation to the outer cylinder piece, this probably makes it more likely to have some slight deviations in form since it is spanning an area of higher curvature changes, you will probably tend to see less of this on fillets that are somewhat smaller in size in relation to their surrounding outer forms.

Anyway, if you can post your .3dm file I can take a look at it, but it's probably related to the adaptive subdivision mechanism I described above, which is not really a bug it is a way to try and keep polygon counts lower.

- Michael