Boolean Difference makes the polysurface all twisty

??.3dm (3.2 MB)

I am trying to boolean difference these two close extrusions, essentially making a hole in the bigger object with the smaller object. However, when I input the command, the bigger extrusion gets all “twisty”. I was wondering what is the reason of this? and how can I fix this problem? Thanks in advance!

Hello - please run the command DivideAlongCreases > SplitAtTangents =Yes on the larger object.
The problem is in the mesher - it does not like single surfaces that are only tangent internally. You can also adjust the meshing settings sometimes to fix this - DocumentProperties > Mesh page.

Incidentally, the objects can be greatly simplified - that would not hurt if there is more to do with them:


Hi Pascal,

Thanks for your reply! However, when i run the command DivideAlongCreases on the extrusion, it says “one object cannot be divided”, and nothing happens. What is the reason for this? Also, the image that you posted showing the isocurves being simplified - what command did you use to do that? Again thanks for your help!

Make sure SplitAtTangents=Yes. You are working in V6, so start the command with no selection in order to see the command line options.

I exploded the object after splitting at tangents and replaced the messy surface with a new clean one.


for some info on how to model more cleanly.


I used the command, made sure SplitAtTangents=Yes, yet it still says “one object cannot be divided”.

Hm - checking V6…
I see that in V6 - looks like a bug to me. Hold on, and I’ll post a split version.

@user1186 see
SplitAtTangents.3dm (440.0 KB)