Extruded curve results in single closed curve on one side and multiple fragments on the other

I’m very new to learning Rhino 6, so apologies if I don’t have the terminology down. My problem is that I am attempting to create a rounded rectangle, extrude it, and then close both ends to create a closed 3d object, but after extruding, one edge is in multiple pieces that I have to select individually, which seems like a waste of time.
Here is my process:

  • draw rounded rectangle
  • extrude the rounded rectangle using the Straight Extrude command
  • go to Surface -> Planar Curves and select the original rounded rectangle curve
  • a Selection Menu pops up that allows me to select “curve” as opposed to “extrusion” (the “curve” is the entire rounded rectangle). I select “curve” and complete the planar curve command to close the top end.
  • I then attempt to close the opposite end of the extrusion. Again I go to Surface -> Planar Curves. When I attempt to select the newly created edge of the extrusion, no Selection Menu pops up. Rather than select all components of the rounded rectangle at once as a closed curve, I have to select each component individually, which means I have to rotate the object and click eight different object before I can close the shape.

I’m watching a Lynda.com video where the instructor is using Rhino 5, and he is able to select the new edge of his extrusion as one curve, he doesn’t have to do it in a piecemeal fashion. This made me wonder why I am unable to do so.

I realize there are probably many ways to create a solid the way I’m describing, but because of its applicability to other scenarios, I’m specifically interested in whether I have some options turned off that prevents me from selecting the new edge of an extrusion all in one go as a single closed curve.

Thank you!

Hi Margaret - - first, if the input is a closed planar curve, then ExtrudeCrv with Solid=Yes should make all of these problems go away. Once the open extrusion exists however, again if the ends are planar, then the Cap command will close it up.

But, to answer your question, the object in V5 was probably a surface and not an extrusion - these are always split up at the tangents of the input curves in a case like this. Generally it is better if it is split up for a variety of reasons but surfaces (not extrusions, which are technically not the same) can be single surfaces all around a rounded rectangle.

Feel free to post your file…


Hi Pascal,

Thanks for your help so far, I didn’t know about the Solid=Yes command. This will certainly be helpful for future projects.

However, I still want to be able to quickly select both sides of an extruded curve without having to go through selecting each component of the line piecemeal. I think this is possible, from the Rhino 5 video I mentioned. To illustrate the problem I’m having, I’ve attached some screenshots of my process, as well as screenshots from the Lynda video (sorry, not savvy enough to make a little video clip).

The first group of screenshots show that I’ve created a closed curve, I extrude the curve, I try to use Surface from Planar Curves command and when I click the bottom edge of the extrusion, I’m able to select “curve” which highlights the entire rounded rectangle at once. I then close the surface. Then I try to repeat the process on the top edge of the extrusion, it only selects the particular line segment and there is no option to select the curve. I have to select each piece individually until I can close the top.

The second group of screenshots shows the Lynda video, in which the instructor follows the same process, first selecting the original edge of the rounded rectangle and creating a surface between that and the offset rectangle. Then, for some reason when he goes to select the newly created edge of the inner extruded rectangle, he’s able to select the whole curve at once and quickly fill in the bottom of the inner rectangle as well. This is something I want to be able to do, not just to create solid objects, but to create more complex shapes without having to select every component of the original curve individually.

(Hopefully these screenshots upload…)

Thank you in advance for any further help you can provide!

Hello - from what I can see the Linda lesson has a surface and not an extrusion. But, SelChain may help to string together edges of the extrusion. You can also turn off using extrusions altogether with the UseExtrusions command, and then if ExtrudeCrv is set to SplitAtTangents=No, then you will get, from a rounded rectangle, a single surface with a single edge at each end.


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ahhh I had wondered why in the Lynda video the command line showed SplitAtTangents and mine didn’t - your advice about ExtrudeCrv answered that question and indeed, fixed the problem I was having! I am now able to recreate what the instructor showed in the video.

Thank you so much, I would probably never figured out the connection between ExtrudeCrv and my problem by myself.

Which I personally don’t recommend, as these kinds of surfaces may cause problems downstream in other programs and often present meshing problems as well - which could be important for 3D printing.

IMO it’s much better to have SplitAtTangents=Yes and accept the result of separate edges - which you can always window select or use SelChain with Tangency. YMMV.

Good morning - thanks for this advice. It took me a minute but I figured out the SelChain command and it seems like it will be incredibly helpful.