When running 2 railes , surface has problems

I am making a bendy tube. I need this tube to be made in two halves. The tube need a 1/4" thickness. I analized my curves, made sure they were running in a uniform direction. I try to sweep the two rails with half round cross sections and the resulting surface creates problem areas where the normals go in different directions than the rest and I see no way of changing just those areas. This also creates some funky artifacts that blow out in those areas. This is intensified when I try to offset the surfaces. Anyone have a fix?

reworked stem linework.3dm (3.0 MB)

The two red curves used as rails have some messy control points near the middle. That’s the reason for the problem.

Hi Jim,

I am trying to understand your model and have some questions.

  1. Are the rings all circular and do they have the same radius?
  2. Are they perpendicular to the centreline of the tube in the xz plane?
  3. Are they deliberately not perpendicular to the centreline in the yz plane?
  4. Are the cutting lines deliberately not in line with the centreline in the back viewport?