Split issue - things that are split seem to remain in a grouplike object

When I split the front and back edges of this ring with two pipes, the ring splits but the split away sections are still “grouped” with the inner surface of the ring. I don’t think this is really a Group.
When I explode the “group” the surfaces separate from each other and I can continue with the ring.
Why does this “grouping” happen?
Danasignet ring.3dm (667.1 KB)

Hi @Dana,

Are you able to post a model with the ring as it was before you split it? It’s difficult to work out what’s happening after the event.


Signet ring (002).3dm (511.5 KB)

Hi @Dana,

It looks like you are using the Split command with your Pipe Cutters to cut through the ring. Split cuts straight through the target from side to side and leaves the parts on each side as open polysurfaces.

If, as I suspect, you actually want to cut out scallops in your ring with the pipes, then you need to use BooleanDifference. (But I’m sorry to say you will need to rebuild your ring and/or pipes first because, at the moment, boolean difference is failing on your surfaces).


Here is a file showing the ring before and after splitting and blending.
I did not want to do scallops. Just soft edges using Blend Surface on front and back.
I have made this ring many times but occasionally I get the problem that I originally mentioned.
Perhaps someone can let me know if this is a glitch in the geometry.

Signet ring before and after splitting and blending.3dm (747.3 KB)

Hi @Dana,

Sorry, I misunderstood your intent. This isn’t a glitch in the geometry but rather a bug in the Split command. Your surfaces are not in some pseudo group, they are joined. However (I suspect in some way connected with the fact that you are isolating the middle of the inner surface from the rest), Rhino is mistakenly keeping the join to the adjacent pieces, along with all the joins it doesn’t need to disturb. The problem is still present in Rhino 7 (FYI @pascal).

If, instead of splitting, you get the intersection curves between ring and pipes then you can trim out the unwanted pieces with them and that leaves the centre section of the inside of the ring isolated correctly.


Hi Jeremy,
Thank you for the Intersect suggestion.
Most of the time the split works! Go figure.