What is ʼJoinʼ vs. ʼGroupʼ in Rhino?
Short Answer
In Rhino, Join creates one joined polysurface, polycurve, or polyline from touching geometry, while Group only keeps separate objects selected together as a set. The most common professional method is to use Join when you need connected editable geometry. Group does not make geometry continuous.
What You Need to Know Before
Warning: Grouping objects does not fix gaps, bad edge alignment, or open curves. A very common failure is assuming a Group will behave like one closed object for trimming, hatching, extrusion, or export, which it will not.
How to…
Command: Join
Shortcut:
JoinQuick Steps:
- Select the curves, surfaces, or polysurfaces you want to combine, then type
Joinin the command line or use the standard command search. - Press Enter to run the command and let Rhino join touching valid edges or curve ends.
- Check the result in the Properties panel to confirm it became a polycurve, polysurface, or closed object if expected.
- Select the curves, surfaces, or polysurfaces you want to combine, then type
Variables & Settings
Key Setting: Join only works when curve ends or surface edges meet within file tolerance.
Expert Setting: Check Document Properties > Units > Absolute tolerance. If tolerance is too tight, edges that appear to touch may fail to join; if too loose, Rhino may join geometry that should stay separate.
Why it Fails
- Cause 1 (Geometry): Curve endpoints or surface edges do not actually meet, or the gap is larger than model tolerance.
- Cause 2 (layers/Locks): One or more objects are on a locked layer, so the selection set is incomplete and the join result fails.
- Cause 3 (Command/Logic): Group was used instead of Join, so the objects remain separate geometry and cannot behave as one continuous object.
Quick Fix & Best Practice
- Quick Fix: Use
SelOpenCrvorShowEdgesto find open geometry, then fix gaps and runJoinagain. - Manager’s Verdict: Use Join for real model continuity, fabrication prep, booleans, and clean export. Use Group only for selection management when objects should stay independent.
FAQ
Is Group the same as Join in Rhino?
No, Group only links selection behavior, while Join changes object structure.
Can grouped curves be extruded as one closed shape?
No, not unless they are actually joined into a closed curve.
How do I ungroup objects in Rhino?
Use the Ungroup command.
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