Reducing in mesh stretch at bone junction I'm new to Blender. I apologize in advance if the question is not clear, I will try to explain the problem as best as I can.

I have a mesh that represents a knocked-down box (think rigid, hard material) ans I'm trying to animate it into a folded box container. To do that I rigged my mesh as follow:



From a high-level overview, everything works fine. However, I notice that the stretch at the junction of the bone when folding 90 degree is too large.



This behavior causes undesirable hole in corner of the folded box because the stretching of the joint was too large.



How do I reduce this stretching.

File for reference: 

https://drive.google.com/file/d/0B5PLUki5PE9sWHRuQUJQT1F4M2s/view?usp=sharing
Bones heads here need to be placed on the exact place of the folding.

Here the bones and the box are not on the same plane. So when the bone rotates it stretches the box:



This is the main problem.

Make so all bones are well aligned with the wanted folds, in all directions.

When the bone is aligned: