Sweep Marble run / rollercoaster track

I want to design elements for a marble run. That means: two rails that have the same distance, but follow a (more or less) free spline.

I tried to draw my spline (Since the spline is not on a single plane, I created the line by projecting line A to Surface B. Afterwards I used sweep.
This worked fine, except that the end of the track does not have the correct “rotation”. Look at the images, then my problem becomes pretty obvious.

Is there a way to tell the Sweep tool the “Target surface”? What would be the “best practise” way to create my rails?

Instead of sweep, you can try Loft, and use the spline as a guideline between the start and end surfaces.

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Loft might work, but I would have to draw MANY guiding lines or my shape would morph.

I don’t think so. I think you are referring to profiles, not guide curves. Check out how to use guide curves in loft: https://support.shapr3d.com/hc/en-us/articles/115001414954-What-does-the-Loft-tool-do-

Your example shows exactly what should NOT happen: The “Crossection” changes/morphes. In my example, this would mean, that the wall thickness changes, or the diameter of my pipe.

Here is what happens if I draw 2 curves: (1 and 2 ).

Only these 2 lines follow the curves, all others stay straight. Suggestions?

What I need is Sweep, but with the option to use multiple guiding lines.

In my opinion using Sweep with multiple guide lines is really no different than using Loft with multiple guide lines. The problem is…creating the guide lines. I fully understand your situation using Sweep with one compound curved line and that it does not work as expected.

The simplest method is to use a partial revolve provided your curve is an arc (first video). The problem with this is the lack of a nice tangential transition at the start and end of the new body.

Another approach is to use Sweep using some work-arounds- second video. I know this isn’t the solution you’re looking for but it can come close.



Thanks for the workaround. That looks good.

However: I see a big difference between “Sweep with multiple guide lines” and “loft”.


  • Uses a single face
  • The face (Crossection/cut) does not change (and is always in the same angle to the guide lines)


  • Uses two (or more) faces
  • The Crossection/cut may be totally different to the original faces

Anyway. Sweep with 2 or more guide lines would be complicated since all lines would have to be exactly parallel. Maybe a “intelligent” Loft-mode “Try to adjust shape to guide line” would be a better Idea.

Could I get any “official” feedback to this topic?
It seems that it is not possible to sweep a shape around 2-dimensional curves without getting “twisted”. Is this a bug?

TigerMikes workaround is nice, but does not really help because rotating the face changes the shape/crossection itself.

Is this something that you cannot do with shapr3D? This would be a serious limitation.