Simple question

I was hoping adding one additional crosssection to help shape the curve would produce
similar result as your lofting, but I guess not…
if there was some maintain height option…

Simple_Surface_extra cross section.3dm (82.4 KB)

Thanks Lagom. So you think this is a software limitation not a ‘geometric’ principle ?

This video is great Julian, quite explanatory.

Few questions:

  • I understand what you explained and makes sense. On the other hand I am just thinking that there is no reason to restrain this logic to the square - view. I could have the same two profiles, same two sweeps and still have a middle part that is equal to the start and end of my shape. I think so…not sure, definitively I am not as good as you mathematically speaking.

  • I am a bit confused since some people grant this ‘issue’ to rhino limitations and some others, like you, to mathematical reasons. So in your opinion this has nothing to do with Rhino , NX , Alias…etc. I already solved, but just wanted to explore the topic a little bit more. It seems lot of users are interested.

  • third one…How did you record the video you made?

Thanks a lot. Very much appreciate your insights.

Oh, actually you are right. I checked your isocurves, they are all the same. Great.

Thanks. I will check if i can get the shape I need with the loft. Since I am sweeping two rectangles through one rial

If you sweep a curve along a center rail like that, you have no width control in Rhino, that’s all. Only if the centre rail is a vector, the width can remain constant, also when the sweep is a “corkscrew surface”

What type of rail would be a “vector” in Rhino?

Same question as @davidcockey ?

I expect that just means a straight line… However, I think anything that is in 2D, i.e planar rail curves, anything that has no “3D twist” - should keep a constant profile width.


A vector in xyz space is straight like Single Malt Whisky ; )

I am here! I just feel there are two position regarding the issue. Honestly I think I am not have a saying about that since I have less knowledge that the people presenting their ideas.

Is this what is desired? HelicalSweepDC1.3dm (91.5 KB)

Another example: HelicalSweepDC2.3dm (66.4 KB)

Created using Pipe, CrvSeam, InterpCrvOnSrf, Sweep2

More complicated if the end of each section is not normal to the curve at the base of that section. Will show method for that situation tomorrow.

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I will upload again the file so you can see exactly what I am aiming for :wink: Thanks so much

@Bruno_Suraski Sorry for the late response,

  • My video explains the loft between two lines. I extracted the isocurve at the midpoint of the loft and marked it yellow like the others.
    Just because diagonals in relation to the outer lines of the square are smaller, exactly by the factor 1.414

  • It only works like that, this has nothing to do with Rhino or others.

  • I am using MacOS and customized Rhino preferences for a cleaner look. no sidebars etc. Using only the trackpad in my perspective view. The video was recorded just with QuickTime Player.

  • Of course you could make a loft over three equal lines. but this changes everything.

Thanks, Bruno. This is an interesting topic here.