having a problem using ExtrudeSrfAlongCrv command. image and file are attached. the image shows three coaxial circles joined by a three cornered surface. the objective is to create a solid using any of the three circles as the “Crv”. the included command line history shows the surface has been accepted and the switch for solid set to yes. selecting any of the three circles for the “Crv” simply returns a blank command line as shown??? what am I doing wrong? “help” provided no clues…
Art stepped primary tube revA.3dm
Hello - try this:
Join the three lines (assuming you want a solid)
Select one of the circles and set a Cplane to it (
CPlane > Object)
Select the triangle and start
As the start of the revolve axis, type in 0,0,0 or just 0 and Enter (= CPlane origin)
At the prompt to set the end of the axis, press Enter to use the cplane Z
Use the FullCircle setting in Revolve to make it go all the way around.
Generally if you want the simplest most exact results for a circular shape, Revolve, if appropriate to the inputs, is the way to go rather than using path curves in sweeps etc. That said,
ExtrudeSrfAlongCrv will make a mess here even if it works - see Help on that command - the section curve or surface is not rotated along the path curve, it keeps it’s orientation.
in light of your guidance on using ExtrudeSrfAlongCrv, how do I handle the case of creating a similar solid where the external surface (existing) is defined by a two rail sweep where one of the curves is a circle and the other an ellipse (ie: an internal fillet on a curved section of tubing)?
Hi Art -
Sweep2 should do it. Is that what you mean?
used sweep2 to get the surface; now wondering about what to use to get the solid as “revolve” suggests a fixed cross section and that’s clearly not the case with an ellipse opposite a circle…
Hi Art - this works to make a solid if the section curve(s) is closed - not sure of that is what you are asking about:
your student appears to be a little thicker than usual today… collage and file attached
stepped primary tube revB.3dm
Hi Art - I was not able to get the modeern art effect here but in this case, if I follow, the simplest is probably a loft
Here, I used only half the curves because not all were complete - but it would be fine with closed curves here as well. Ideally the three curves have the same structure - but in this case it seems to work fine with this input. If you did halves like this, you could then Join, to get a closed solid. At any rate this way each ‘leg’ is made independently and finds the right height.
wasn’t able to make “loft” work but was able to create a watertight solid using three surfaces created with “sweep2” and “create solid”. that said, “Boolean2Objects” wouldn’t join it to the tubes AND provides NO actionable fault isolation information; surely McNeel can do better than a message that effectively says “sorry”! there was no problem using “Boolean2Objects” to join the fillets created with “revolve”. “Boolean2Objects” surely is one of Rhino’s most important tools AND has a finite number of criteria/steps leading to success… I used the same geometry for the creation of all the parts; does "Boolean2Objects’ " current algorithms want to see lap joints/intersecting parts versus butt joints?? or are there Rhino settings that need to be set/adjusted/updated??