Helix Tween Issue

Grasshopper
1

Could anyone give me advice how to make the following:
I need to have an extrude/loft along a helix.

image

The cross sections of the profile should be the same along the whole helix.

Helix_Tween_Issue.3dm (36.1 KB)

I have tried sweep two rails, using the two profiles as rails and sweeping the helix but the result is anything but expected:
image

I have tried standard tweening in GH:

image
image886Ă—447 54 KB

There are two issues:

  • the tween is done along a straight line
  • the section created is scaled down

Then I tried Pufferfish’s tweening components:

image
image928Ă—537 76.6 KB

image
image850Ă—437 38.7 KB

Two issues again:

  • The curve is scaled down
  • The curve is rotated in space

Helix_Tweening_Issue.gh (8.5 KB)

2

image
image1368Ă—636 124 KB

3

image
image1368Ă—636 102 KB

Helix_Tweening_Issue.gh (6.8 KB)

4

Any reason you don’t post code? I’m not going to replicate/build it from screen shots.
If no code is posted by the person who started the thread, that’s another story. No code posted, no code in the reply. But otherwise it’s easier for everyone and more accurate to reply with a GH file, eh?

5

@Joseph_Oster can you not see the files there? Or you’re answering to the answer which posted only screenshots?

btw, @rajeev_pulari , both components you show above produce wrong geometries if you zoom in.

6

My reply was to @rajeev_pulari

1 Like
7

The only solution I find rather close is if I manually copy+rotate the section to keep it tangential to the “cylinder” the helix describes.

However, the surface doesn’t quite follow the helix, I assume I’ll need more sections, thus the tween request but it sadly fails.

image
image481Ă—565 21.3 KB

image
image802Ă—459 49 KB

Helix_Tween_Issue.3dm (127.5 KB)

8

Hi Ivelin,

I just tried a standard GH sweep2 and I don’t see any significant difference from the Rhino sweep2:

image
image1026Ă—738 49.4 KB

Both use the same pair of helical rails newly created for this in Rhino at each end of the profile. I’ve tried overlaying random isocurves from the surfaces and don’t see any differences.

Helix_Tween_Issue 001.3dm (197.8 KB)
GHSweep2.gh (7.5 KB)

Where are you seeing discrepancies?

Regards
Jeremy

9

Hi @jeremy5 ,

What are your mesh properties? Your model looks much better. Could be the meshing.

10

Just the standard Smooth & Slower.

11

Ah, I got it,

image
image882Ă—561 82.3 KB

This preview is what I expected from the tween command btw

I still get some visual glitches:

image
image876Ă—593 73.8 KB

12

now it’s better

image
image1590Ă—686 113 KB

GH makes something wrong:

image
image1283Ă—507 113 KB

13

You’re right, GH sweep1 gives a different outcome to RH sweep1 (either in your case with only one profile connected or in this case where both profiles are connected). I’d say this should be considered a bug - @pascal?

image
image1026Ă—738 64.2 KB

Helix_Tween_Issue 002.3dm (167.7 KB)
GHSweep1.gh (9.1 KB)