Rhino 6 - problem in joining curves

Can’t create a shape with curves only, I get UNABLE TO JOIN CURVES ALL THE TIME.
Sort of a simple task. Not happening.
The green line is not joining with the red one, where it is now visually.
Can somebody help me?

pz_375_curves.3dm (624.8 KB)

This is normal. Rhino does not allow non-manifold joins, that is where more than 2 curves meet at a single point. Once two curves are joined by their endpoints, nothing else can be joined at the same spot.

What are you trying to accomplish?

Hi Helvetosaur, thanks for your help.
Yes, it makes sense: one curve made of two single ones, and a third can’t join.
BUT: exploding them and trying to join all 3, then 2 of them get together the third one no.
Two by two they work fine. Llike: the magenta line can join either with red or green
and red and green or red/magenta can join.
This doesn’t make sense to me, although there is something in the tolerances I am not aware of.

I am trying to make that solid you can see in pic2 so I can do a boolean difference on another one.
I alread tried sweep1 and 2, no chance. Next it will be lofting but if lines don’t join, will the resulting surfaces join allright and create a watertight solid? I doubt it.

Yes, well, that was what I tried to explain above, but apparently not clearly enough. In Rhino you cannot have any “T” or “Y” structures where more than two endpoints come together - you cannot make any valid NURBS structure with things like that in Rhino. In meshes it is of course allowed at vertices, but we’re not talking about meshes here.

Yes, no problem. You actually don’t need to join any of the curves in this particular case.

I exploded all your curves then:

  1. Used EdgeSrf with curves A,B,C, and D
  2. Lofted lines E and F together to make a surface
  3. Used PlanarSrf to make the vertical ends using the appropriate curves and surface edges
  4. Joined the 4 surfaces together
  5. Used Cap planar holes from the solid menu to make the top and bottom and join all.

Solid.3dm (662.1 KB)

1 Like

adding to the excelent explanation of @Helvetosaur I would suggest to start with the training manuals level 1 and 2, to fully understand the principles of NURBS modeling and how Rhino works.
In the meantime, here is another strategy:


You explained it well, it’s me that I am very basic in my knowledge of geometry + Rhino.
Although I create quite complex objects in Rhino, I am limited to use straight tools, extrude lines, revolve and other straight creation tools, so any time something slips out of that, I get lost.
I expected such a “simple” thing as creating the skeleton of a solid with lines to be possible, now I see it needs a little work. Good to know.
Thanks a lot! You really saved me!

Hey Diego, thanks a lot for your tutorial. I would need a lot of those. But I am not exactly new to Rhino, I just have “knowledge holes” due to the fact that I am self taught, I always need to do stuff fast-faster-now! without exactly knowing what I am doing, and I am used to work with solids and very little with surfaces, etc.
I end up doing pretty neat things sometimes, as I am showing in this picture, and pretty soon I will have to animate all this stuff. Thrilling but … oh my!


specially for that is why I’m suggesting you to start with the basic. to fill those holes

You are totally right, but Rhino is just one of my field of work, not even the more important. And there is another problem: my memory is worse and worse by the day (age problems) and I would like to quit and dedicate myself to … whatever, but I got a couple interesting projects that came up, so I could not resist.
Work is a drug sometimes, especially if you like what you are doing.