Extruding joined curves problem

See attached.

Hi Asterisk,

change the SplitAtTangents option in the commandline from Yes to No


^ Nope. That option doesn’t affect it in this case.

Exploding this extrusion and MergeSrf with Roundness=0 seems to do the trick.

You´ll end up with a polysurface instead of an extrusion. Is your line tangent to the arc ? Can you post an example ?


MergeSrf is what “blends” two separate surfaces into one. And exploding the extrusion converts extrusion into a surface.

As I said. It worked just fine like I described and yes, the line is tangent.

Untitled.3dm (34.3 KB) <a class=“attachment”

You really do not want to be doing this.

Rhino CAN create single surfaces from joined tangent curves by a number of methods, but these objects with internal G1 (tangent) areas will often cause you problems either with meshing or downstream exporting to other programs.

There is a logical “joint” between the arc section and the linear section, my suggestion is to leave it that way, as a polysurface.


well, yes but i thought you´re trying to achieve an extrusion object. This workauround should not be done to achieve it. On my system (PC) if i create a simple arc and join with a tangent line then use the command option described, i end up with a single extrusion object. This has been the case for years and since this option was added to the command.

If you´re satisfied with a polysurface instead, you can run the command _UseExtrusions and set it to Polysurface, then extrude using SplitAtTangents=No and you will get a single surface without merging anything.


The problem with leaving a “joint” there is that when I script unfold that surface, it thinks there’s a “bend” there and turns it into rout. Can’t have it there. Thanks for your input though, Mitch.

Oh no, it doesn’t matter to us if it’s a surface or an extrusion. but UseExtrusions with PolySrf is what I actually needed. Thanks a bunch!

OK, if you’re unrolling the surfaces afterwards, that is fine…


Weird, just ran UnrollSrf on that open surface and it unrolls it into polysurface creating that break there???.. Why?

I guess Rhino is telling you it doesn’t like that internal G1 joint so much after all…

I guess you could run MergeAllFaces on the unrolled object to fix it.


Thank you!! Works like a charm!