Sweep Marble run / rollercoaster track

Need help? We are here.
1

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
image1453×1121 127 KB

image
image1165×922 135 KB

image
image1920×1186 155 KB

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

2

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

1 Like
3

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

4

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-

5

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.

6

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

image
image614×821 101 KB

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

7

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

8

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.

2 Likes
9

4 Likes
10

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.

13

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.