Hi Heiner,

> i created the curves of a combination of curves which i then joined.
> So that seems to be a no no ...

It's ok to have a combination of curves that are joined together to use as rails, but the "no no" part is that the individual pieces were not smooth to one another. When you draw a control point curve you want to pay special attention to what direction the first and second (and last and second-to-last) points are going in, that controls the tangent direction of the curve and if you have 2 pieces that do not have the same tangent direction where they are joined that makes for a sharp corner crease in the shape of the joined curve, that will translate into some kind of sharpness or juncture area in your sweep result.

- Michael