Aizatulin
Yes in your second example you are accumulating over the dir.
To avoid confusion, imho it is better to use “tangent” for the tangents of the curve and N for the normals. Sometimes the polyframe gives strange results for straight lines, but you will find some examples with ptf (parallel transport frames), which gives you stable frames for curves.
According to my first file, here is another modification, where you can perform a bend just using the first ramp (or second aswell for torsion). After this you can apply the node again to use just the second ramp to rotate the normals.
That's exactly what I want to do!!!
Tanks for help!!
cheers!