TweenCurves not possible

_TweenCurves gives no useful result on the 2 curves:

The curves are duplicated borders of a planar srf.

See also attached 3dm.

What can I do to get a result?

CP_Between.3dm (24.7 KB)


Hi Charles

I think the two curves might be “heading in opposite directions”. Try using the Dir command to flip one of the curves and see if that helps? I haven’t got Rhino with me here, so it’s just a guess!

HTH, Jakob

Click the handle point on the end of the right curve when in the preview. This will align the start points for the tween and make it linear. You could also rebuild the curves to 4x3.

I think you may have selected the first curve at the bottom and the second at the top. Try selecting both at the same general side (bottom or top), that should work.



I didn’t know I can adjust the start points.
The command line doesn’t tell me, and the help doesn’t as well.

Ok, solved, thank you.


Maybe we can make it more clear with an additional image in the Help but seam adjustment is mentioned now. I’ll file something for @margaret to make this more clear.

“Adjust the curve seams or direction if necessary.”

My conclusion was to use _Dir (in case of an open curve).
Maybe I’m the only one who is so dense.
If not, then a slightly changed sentence would help for sure.


Would you mind making a bug report out of this? If you can conjure up a
simple model that I can use to demonstrate, that would also be helpful.

~M Becker

Sure, I made this one this morning and just added the file.

Example added. Thanks.