How to sweep a joined Rail

Hello, I have been looking for how to fix this problem, but if there is a video out there that touches on the subject, I have not found it. I am trying to sweep a rail in rhino that was originally two unjoined segments. When I sweep, Rhino 6 keeps thinking they are still separate and gets confused. Is there any way to still sweep a line that has been joined to another? Please let me know. I tried rebuild but that does not seem to fix anything.

Hi @abbyemalcolm,

Could you upload your model? If you cannot share the whole thing then export just the rail curves and the object you are sweeping to a new file.


Hello - does the ChainEdges option do anything for you? It’s there to allow multiple segments to make one rail.


Here is an example for what happens. please let me know and thank you
learning file 2.3dm (34.0 KB)

Just rebuild the joined curve, then Rhino will make a new curve of it. Using 16 points will give you a “good” result. (I say “good” because your circle has a larger radius than that of your rail curve so the result will intersect it self, which never is a good thing, so either resize the circle or widen your bends in the rail curve so at no point it has a lower radius than your circle)

Good luck!

@abbyemalcolm The root cause of the problem are the kinks in the polycurve used for the rail. Explode the polycurve and modify the individual curves so the individual curves are at least tangent to each other. Match can be used. Sometimes Sweep1 works using a rail with kinks but not always.

As Holo said if the radius of the rail curve is too small the sweep surface will fold back on it’s self.

Alright thank you both I will give it a go.

Use Untrimmed miters and it works though with folding due to the small radius.

Another method is to divide the curve with the minimum number of divisions that will replicate the original curve, delete the original curve and build a new curve through the points left by the division. I do this with some regularity to create “simpler” surfaces from the new curve that will meet the original intent of the model.