Sweep1 - help for new rhino user

i’m having trouble understanding how to complete the shape I want.
I want to extrude a profile around a closed curve – a ceiling cove around the top of a room.

I think sweep1 is the right tool?
however I’m getting two resulting objects and they cross each other in a way that makes no sense

rail object 1 is closed curve

cross section object 2 is a closed curve (a polyline imported from autocad)

the resulting two sweeps (from one rail)

what’s odd to me is that where it fails is exactly the same geometry as another part of the curve that sweeps just fine
also, there isn’t a begin/end condition at the location of the odd sweep crossing

any tips appreciated


how did you produce that upper curve? the only answer i would have that the upper curve is broken or has some glitch at that point. i dont think that something would be with the imported polyline since it works all the way around.

if you take those 2 curves and place them into a new file you can upload it and i have a look.

upper curve was traced along the top of the walls with the line tool, using close to finish

i have a hard time zooming in to tight spots so I can’t tell you if it’s got a Z discrepancy, but i THINK it’s all in the same plane

here’s a file with the isolated objects
sweep-test.3dm (41.8 KB)


Hi Adam - I see that, thanks - my guess of the moment is that the success of the mitering depends upon the curve direction - if the path is flipped the error shows up on the other side. How it hits that sequence of short and long path sections… For now trimming up the result with some miter planes will do it - I’ll see if I can figure out a better way and thanks for the example, I’ll put it on the bug heap.
sweep-test_PG.3dm (643.6 KB)


not the answer i was expecting! goodnews/badnews, i guess! :smirk:

now, to figure out how to trim with planes…


your width of the profile exceeds the width of the narrow sections so it fails
below i copied it to that corner to show how much bigger it is.

profiles which are smaller than those corners will work again.
your curves are ok otherwise just not very straight a bit off but should not matter.

you can also draw a polyline along where it is too much from top view for example. select it and trimm the parts off. then rejoin the rest. to get it done you have to be precise so its a bit tricky but it should work. you can also use planes as pascal suggested and place them along the corners select it use the trimm command and click on the parts standing over.

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I wondered about the size differences, but one corner was successful & the other was not (two sides of that same bump into the room), so I was confused about that. thank you for taking the time to look at this!

I was able to trim using your reload of my isolated geometry, so thanks for that file


yes it suggests it could work, but maybe when sweep gets reworked, i personally never had much luck with profiles which where too big.

if you ever encounter that again here is how you can use a simple line from top view to trim the rest away

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I will try that, thx