If Positions, Normals, etc can now be Float32Arrays, VertexData.merge() fails. This is because receiving mesh's array does not have a push function. This is one of the only differences between typed arrays and Javascript arrays: typed arrays are of fixed size at the time of construction. Think a merge that will always work is one that: computes the new size of the combination,instances a new array of the final sizereferences receiving array by indexThink we should be creating a new method like, _mergeElement, that does this and returns the new array which should replace the old one. The current structure of Merge() is quite long, adding this extra stuff, would increase that. having a sub method might actually have less code. I double checked for references to push(). They are contained to the canned geometry / ribbon methods, so it looks like this is the only instance of this issue. I have so many unfinished things that I cannot address this myself right now. Wanted to bring it up, so anyone else who encountered it would know it was a known issue.