Hi bisenberger - that's usually caused by differences in length between the rails.

For a shape that should have a kind of tube like uniformity you may want to use one-rail sweep with just one rail running down the center instead of using 2-rail sweep.

To control it with 2-rail sweep you would need to add more profiles like Pilou says - and you'll need to position the profiles directly touching the rails instead of using "auto place" mode.

So for example in your case here you would want to put in another profile curve right at this location here to force the profile positioning at that point:



- Michael