Insimenator.org

I'm converting an adult outfit to child size and so far I haven't had a problem. Now though, the tutorial I use says to use the Vertex Data Merge plugin in Milkshape to copy the bone assignment data from the child base mesh to my newly resized and fixed adult one. However, when I use it, the adult mesh simply disappears as if it's been deleted. I have to undo the vertex merge to get it back.

What can I do to assign the bones properly on my new mesh, and what am I doing wrong with the vertex data merge? Please help!

Pretty sure you have to mark two and two vertices (those you want to merge, such as the neck line or beween sleeves and hands, and the like). If you mark the whole mesh, the mesh thinks you want to merge all the vertices.

The Unimesh Vertex Data Merge merges the XYZ coords along with the bone assignments. Instead, use the Unimesh Bone Tool (http://modthesims.info/t/122399) to copy bone assignments from one vertex to all other selected vertices without otherwise affecting their position/normals/UV/etc. If the bone tool is not behaving for you, you can also use Extended Manual Edit and copy & paste the bone assignments one by one. You will need to do the vertices or groups that share the same bone assignment one by one, though - there's no way to just copy bone assignments wholesale from one mesh to the other.

Did you export as an OBJ file or an extracted GMDC file?

If you import a GMDC file, the bone assignments will already be there. You sometimes have to fix them a bit, but they're more or less correct. Doing a manual edit on a whole OBJ mesh is tedious work, and more often than not ends up needing a lot of adjusting.

The Extended Manual Edit is more for fixing gaps and correcting normals and such. The Joints tab is where you have to do the fixing of bone assignments.