Curve Tangent direction always changing depending on extrude

Question

my problem is that the curve tangent changing all the time the direction depending when I extrude one of the edges of a pre existing face:

How do I prevent it from changing all the time?

Answer 1

A tangent of the curve, is the direction of the curve. If you aligned lines with the tangent, they would overlap with the curve. So you want to align them with the normal of the curve, which goes perpendicularly to the tangent.

Also, you're supposed to connect the Vector you're aligning to, into the "Vector" socket, not "Rotation" socket. The latter is used if you want to pretend whatever you're rotating has some rotation applied, typically useful when you chain two "Align Euler..." nodes like here.

So in your case try this:

This still may leave one problem unresolved - the spawned lines can still swipe around the spawning curve - on the GIF at all times the lines remain perpendicular to the curve:

So maybe you want to use the normal of the nearest face instead?