Why are there two very similar commands- Ribbon and RibbonOffset?
(https://docs.mcneel.com/rhino/8/help/en-us/index.htm#commands/ribbon.htm)
RibbonOffset is restricted to closed curves and has different options for dealing with sharp corners.
Is one command older and the other “improved”?
Why is RibbonOffset restricted to closed curves?
ribbon offset has a lot of stuff built into it…
ribbon simply creates a surface extruded normal to a surface,
ribbon offset makes a 3d curve and gives you options to create surfaces between your original curve and your projected curve.
the intent of ribbon offset it to make a parting line surface for a mold.
see video here-
Might be off topic, but is there a way to make a RibbonOffset on the naked edges of a open subd?
because ribbon offset works on a closed curve
if you dup the edges of the subd into a curve, then join them- yes-
I see, that also means that I end up with a polysurface if I join the ribbonoffset with the original open subd I guess. Thus I end up loosing my subd 
thank you for answering!
In SubD modeling normally could be enough to scale/extrude
If you use gumball you can drag the scale with cntl+shift and get the result.
Another trick could be to extrude up the SubD border, scale it and move it down back to it’s original height.
Last but not best, use the extracted CR-V and the offset to do a sweep2 SubD and join them togheter.
long way round, but make the ribbon surface, quadremesh it, then tosub the resulting mesh and then join it back up to the original part with stich and or bridge
I’m not entirely sure exactly I follow, but I’ll give it a go
Edit: Gave it a go, and sure it works and lets it still be a subd. The only negative is that I don’t get the clean 2mm Offset the entire way around. In my case I end up with less than 2mm in some areas and more in others due to the nature of the original shape. Still closest yet, thank you.
Yes I was trying to do that. But after I have QuadRemeshed the surface that I gain from RibbonOffset I can’t make the bridge or stitch since the subd and the new subd (From RibbonOffset) don’t have the same amount of edges.
I’ve tried to get the Subd That stems from ribbonoffset to have the same amount of quads as the original Subd, but the quadremesh fails.
Ive attatched my .3dm file here:
Footbed SubD.3dm (1.3 MB)
Edit: I get this far in Grasshopper (Still a brep in the end): I’ll try SubD Sweep2 from Flexibility addon for grasshopper next.
subd sweep 1 (roadlike) will get you there-
make sure your profile curve is sub friendly and work in smooth mode set your output to match your edge count (in your case 36)
@theoutside Why does RibbonOffset require a closed curve as input? It appears the same functionality would be possible if the closed curve requirement was removed.
the short answer is it was originally designed as a tool for mold making, and typically a ribbon surface is continuous.
Any reason not to remove the closed curve requirement from RibbonOffset so the functionality is available for uses other than mold making? The handling of kinks and similar could be very useful.
worth a chat with the devs to see if it can be done… @Trav may have some ideas on if that could be done or not.
If I use the dupborder as a the rail and also a simple line between the dupborder and the offset curve I get it to work.
Now I just have to figure out how I do this with a macrobutton. I’m not sure how I can generate a line between to curve wasily with a macro. But I’ll make it work somehow. Thank you for the help. Worked well after stitching.
Update, since I really would like to automate this process.
I’ve gotten this far, but since there’s no stitch or bridge in Grasshopper, to my knowledge, I have to the last stitch step manually in Rhino.
Also, if anyone reading this know how I can eliminate the manual input of vertice 6 & 27 that is to be culled, I would really appreciate it.
note: I’m using IAC addon from Food4Rhino for SubDSweep1
Isn’t joinsrf enough?
if you have two subds with coincident verts, you can simply use the join command to connect them- note the creasing option in the command line
@theoutside @skysurfer Thank you. I’m frankly embarrased I didn’t know you could simply use join. Thanks, worked great.
You shouldn’t be afarid of nothing: discourse is here also to teach options to who need it.
Enjoy !
