About this 3D model
This is a derivative of Sublime's Three jaw keyless chuck - http://www.thingiverse.com/thing:9179 , these are replacement jaws. From the discussion on that page hexitex may have some better jaws on the way, hopefully this principle can be applied to them too.I angled the base of the jaws a bit (1 or 2.5 degrees) such that when they are tightened, they will want to lean in towards whatever they are holding a tiny bit, applying more clamping force.