Problem with fillet and shell failed

Why the fillet smaller edge (ie the cross) to 1.5 (and above) is performed, while, with values less than 1.5 fails?
In addition, the shelling of the rear face (the face with red border) always fails.
you can better control this kind of situations, both with fillet edge that with the shelling?

Thank you
problem fillet and shell failed.3dm (226.1 KB)

The fillet edge fails even with a value of 2.0 (the point , enlarged image, we can see better).

Probably because your absolute tolerance of 0.1 is too large. For a object with a maximum dimension of 25 I’d use a tolerance of 0.001.

I tried with different tolerance values (0.05, 0.001); Sometimes the fillet edge only works for a certain value, increasing or decreasing the size of the fillet sometimes it works, sometimes not.

I think it should be revised.
You can test yourself on my file and you will not always work, indeed, hardly ever!

This example is part of the special cases, in which Rhino still struggling a little.
At times with radius 1 works, the works setting it to 2 times, and other times operates below of 1 …
It 's too frustrating!

Not to mention the schelling: in these cases almost never works!

Did you start with an absolute tolerance of 0.1? If so you may need to rebuild all the curved parts and their intersections with a tighter tolerance.

Why the tolerance of 0.1?

Yes, you’re right, maybe tolerance is a little low. I tried with 0:01, but even in this case the fillet edge over 1 does not work. If imposed a radius of 0.8, for example, the fillet works, but the shell of the rear face does not work over 1.
Try it please.
problem fillet and shelling.3dm (140.2 KB)

Excusme, I wanted to write “tolerance 0.001”.
how do you know what is the limit where the fillet edge (and shell) works?
If I set a radius of 1 works, if required 1.1 no longer works.
This also applies to certain values of thickness (in the shell)

Have you tried rebuilding the curved parts with the tighter tolerance? Changing the tolerance does not affect existing geometry.