Wont Weld or collapse and im out of ideas.

MyLittleWeirdFriend

Hello im very much just a beginner at 3d max, we have learned the basics in school and i decided to also practice at home, i am currently modelling a shark and while trying to attatch the fin to body (which i had made as two seperate objects) with the help of the "Weld" tool, it does not work on 2 of the 4 vertexes i need to atatch. i just tried to repeat the same method as for the first fin which worked perfectly. the second one however wont weld and i dont know why or how to fix it ! thanks in advance for any help !

ActionDawg

go into the object properties and enable backface culling and you will find that the normals of the fin are inverted from what they should be. this problem intentionally prevents you from creating non-manifold geometry.

all you need to do is flip the normals of affected faces and you're good to go