Object with a creased surface. Use DivideAlongCreases

[CalypsoArt]

I was working filleting an object. At some point with FilletEdge I got this error:
“Ignored 1 edge in object with a creased surface. Use DivideAlongCreases to fix the object.”
What is this and what causes it?

[John_Brock]

This thread describes it:

Cannot explode a single surface?

I downloaded a gear from Grabcad. I exploded it and got this. I really just wanted the outer ring and thought it would explode further with the fillets being separate parts. It would not, and I get the error, “Cannot explode a single surface.” I was unaware a object like this could be a single surface. I’ve actually gotten what I needed, but have two questions for my own edification. Can such a surface be broken up? How does one build a surface like this? [gear] ring.3dm (1.9 MB)

[CalypsoArt]

I started that thread. Two responses suggested “Use DivideAlongCreases” to break apart a surface. I don’t understand how my current problem object that started out as as simple cube with other shapes Boolean Unioned to it, would need that command to make filleting possible. Though the command fixed the problem, I don’t know what it actually does, or what in my modeling process mad the object need it.

[pascal (Pascal Golay)]

Hello - it is possible to have single surfaces that have hard corners, or creases - FilletEdge does not like these, so the command mentioned splits up an object into a polysurface with faces joined where the input had creases.

-Pascal