Sweep 2 rail

I am trying to sweep this profile around 2 rails.
I get close to what i want but where the rail curves get tighter rhino makes my profile curve tighter too and starts loosing the shape.

any advice how to sweep the profile somewhat even all around ?


see file

palette2.3dm (5.6 MB)

Not sure if it helps but just as a remark: Using the Tweener package (shameless plug) from the Package manager you avoid the undercut, the isolines then look like this in top view.


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If you are asking Rhino to follow 2 rails and the distance between the rails varies, then the shape of the profile has to change to fit.

The AddSlash button in Sweep2 might help a little.

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Thanks, i will try with add slash.
I don’t mind the profile getting smaller or larger but i would like it to maintain the same shape or curvature

The maintain height option might also help. Check rhino help for what the various options do.

Thank you Mathias, I am not familiar with the tween package. I noticed there is a tween command, is that the same as what you are mentioning here? Excuse my ignorance!

Hello Gonzolopez,
no, it’s a different one. Rhino’s built-in command TweenCurves was the inspiration to write my own, so I called mine TweenCurves2 and published it in the “Tweener” package. Its purpose is the same - to tween curves - but it takes a very different approach at doing that. Feel free to try it out. To do that, type _PackageManager in the Rhino command line, search for “Tweener”, click install, restart Rhino, select two closed curves like yours - but they have to be in the XY plane, one contained in the other - and call the command “TweenCurves2”. It gives you lines that would be the level curves of a different way to look at your geometric problem. You would have to go up in the third direction, but you would have a potential workaround for the sweeping procedure.
Don’t hesitate to drop me a line, whether it worked or not!
The output should look like this, indicating how the undercut is avoided (which might or might not be what you wanted?)

Hey Mathias,thanks for the thorough response and sorry for the delay, I’m back at this trying to figure it out. I type _PackageManager on the command line, but nothing comes up. Any idea what i might be doing wrong? Thanks.

Hello @gonzolopez ,
maybe it’s Rhino 6? If on Rhino 7, it should be there, at least in Tools → Package Manager.
Cheers, M