Posted by dxli on Mar 27, 2024; 7:39am
URL: https://forum.librecad.org/Fillet-command-tp5724526p5724549.html

This is actually a long-overlooked bug in fillet. I can see the fillet arc is created properly, but trimming fails.

One workaround would be cutting the circle into an arc of 360 degrees (Tools > Modify > Divide and cut the whole circle by any point on it). Fillet works with arcs but not circles/ellipses. This also shows it's actually a bug.

I also found the fillet size GUI input is quite buggy. Need to be fixed.

This is not an issue of trimming, since trimming is not meant to handle tangential cases. For fillet, the trimming is by the closest point to the fillet arc center.

Dobro wrote

Thanks for the explanation, it sounds quite scientific, but I guess I could catch the core of it.

I've tried the other way as well, first trimming and then fillet, and the result is excellent.
Example_fillet.dxf

On the left there is the first attempt, where fillet is bad. On the right the second, where the line is uninterruptedly continuous.

So there's a solution for this problem, but one have to figure it out.