Thanks for your fast reply.
The solution from Chris does not work for me as the angles are not even.
And when I do a shell command after the fillets my model goes crazy :) So I ended up without fillet, but still got some problems with the shell command. I need a tube with 1 mm thickness. Or is there anothe way to get the thickness except the shell command?
Can I ignore these problems when I 3D print this model or is there any solution to fix it?