# Sweep Marble run / rollercoaster track

**URL:** <https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902>\
**Category:** Modeling Questions\
**Created:** [February 2, 2023, 8:52am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902 "2023-02-02T08:52:46Z")\
**Posts on this page:** 11\
**Page:** 1

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**Author:** ![ThomasR](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@ThomasR](https://discourse.shapr3d.com/u/ThomasR)\
**Post date:** [February 2, 2023, 8:52am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/1 "2023-02-02T08:52:46Z")

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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.

 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/3/2/327cec7bc9a1ac3ae0ce07b415f6fbda18b77765.jpeg)  
 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/f/a/fa51663a44f474e8ed70b6f872714663c664cd72.jpeg)

 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/e/1/e1a02f9a3a8541e45a76f9bb1bbdbff94ce5083b.jpeg)

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

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**Author:** ![Laci\_K](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/laci_k/32/8196_2.png) [@Laci\_K](https://discourse.shapr3d.com/u/Laci_K)\
**Post date:** [February 2, 2023, 8:55am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/2 "2023-02-02T08:55:06Z")

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

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**Author:** ![ThomasR](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@ThomasR](https://discourse.shapr3d.com/u/ThomasR)\
**Post date:** [February 2, 2023, 9:53am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/3 "2023-02-02T09:53:01Z")

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

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**Author:** ![Istvan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/istvan/32/23668_2.png) [@Istvan](https://discourse.shapr3d.com/u/Istvan)\
**Post date:** [February 2, 2023, 9:55am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/4 "2023-02-02T09:55:39Z")

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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-](https://support.shapr3d.com/hc/en-us/articles/115001414954-What-does-the-Loft-tool-do-)

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**Author:** ![ThomasR](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@ThomasR](https://discourse.shapr3d.com/u/ThomasR)\
**Post date:** [February 2, 2023, 10:03am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/5 "2023-02-02T10:03:09Z")

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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.

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**Author:** ![ThomasR](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@ThomasR](https://discourse.shapr3d.com/u/ThomasR)\
**Post date:** [February 2, 2023, 10:38am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/6 "2023-02-02T10:38:22Z")

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

 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/c/1/c155ffc197d99a928c3e98801efa715e85997bbb.jpeg)

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

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<div class="post-metadata">

**Author:** ![ThomasR](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@ThomasR](https://discourse.shapr3d.com/u/ThomasR)\
**Post date:** [February 2, 2023, 10:48am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/7 "2023-02-02T10:48:05Z")

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

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**Author:** ![TigerMike](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/tigermike/32/32650_2.png) [@TigerMike](https://discourse.shapr3d.com/u/TigerMike)\
**Post date:** [February 4, 2023, 12:04am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/8 "2023-02-04T00:04:40Z")

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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.

[https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/4/7/47a1e6f4b7607907831a8519dcba2e94cf12be5e.mov](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/4/7/47a1e6f4b7607907831a8519dcba2e94cf12be5e.mov)

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<div class="post-metadata">

**Author:** ![TigerMike](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/tigermike/32/32650_2.png) [@TigerMike](https://discourse.shapr3d.com/u/TigerMike)\
**Post date:** [February 4, 2023, 12:05am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/9 "2023-02-04T00:05:31Z")

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<div class="post-metadata">

**Author:** ![ThomasR](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@ThomasR](https://discourse.shapr3d.com/u/ThomasR)\
**Post date:** [February 4, 2023, 9:31am UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/10 "2023-02-04T09:31:33Z")

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Thanks for the workaround. That looks good.

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

Sweep:

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

Loft:

- 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.

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<div class="post-metadata">

**Author:** ![ThomasR](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@ThomasR](https://discourse.shapr3d.com/u/ThomasR)\
**Post date:** [February 25, 2023, 3:45pm UTC](https://discourse.shapr3d.com/t/sweep-marble-run-rollercoaster-track/23902/13 "2023-02-25T15:45:08Z")

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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.