Join surfaces refuses yet success after explode join then join..why?

Rhino Rhino for Windows
1

Hi,
fathoming out a silicone mould cut procedure.

black base intersects fully with cyan uppers, it should do, as it was sliced from it using a planar surface !
come to join it back on after deleting the outer area (which is the silicone I pull away) and it says select surface, I select the cyan and a quick flicker and nothing happens.

clone it, place onto blue layer, turn off original layers, explode it, select the 8 internal surfaces it abutts to, join those then select it (black) and that which I just joined up and go join and bingo, then select rest of unit and join and bingo. success.

why such hassle, why didnt it join, why the ask for select a surface when I had all surfaces selected ?

unable to join surfaces yet after explode they join.3dm (973.7 KB)

Steve

2

In my experience, sometimes (depending on the surfaces). If you mass select them and click Join due to some faulty algorithm inside Rhino the order in which they join leave naked edges (or naked points). Then if you join selecting them one by one, then the join succeeds. This should also depend on the accuracy, and distance of the surfaces from the origin point.

3

Hello - the cyan object is completely closed.

-Pascal

4

Pascal, ,

ah yes, the base has a surface around the circle, didnt spot the cross lines I guess due to ghosted black .

doh…smiley for oops embarrased …egg on face ! (there isnt one)

Steve