Where ADD fails during Extrude

steve_shubin

A post by @omri_r got me to looking at why ADD doesn’t work at times while Extruding.

So we have a single part made up of a cuboid and a cylinder. And right through the middle of the cylinder we have a sketch of an inverted V.

There’s actually 3 different sketches that I used in the below GIF’s where the sketches have different end points on the inverted V.

NeilCooke

Hi @steve_shubin - thanks for posting this. These examples will create non-manifold geometry (easiest way to think of this is that an edge of a solid can and must only be shared by 2 faces - in these examples the edge would have 4 faces). These conditions arise when an edge or vertex touches a face from the same solid body creating an infinitely small region or singularity. I'm sure there's a more mathematical reason, but always think 1 edge, 2 faces.

steve_shubin

@NeilCooke

That’s a very good explanation you gave Neil. Even I could understand that. LOL