Why sweep1 is not working here?

[Quan_Li]

sweep1 not working.gh (29.6 KB)

Hi, I am trying to understand why the sweep1 function is not working in this grasshopper file.
I analyzed the directions of the curves, seem good.

Thanks!

[HS_Kim]

Adjusting the starting point(seam) of the rail curve would solve the problem.

sweep1 not working_re.gh (31.2 KB)

[Quan_Li]

So the seam must be aligned to the first section.
Thank you very much!