Variable height fixture V4.1 for smartphone photo studio

UPDATE: This design has been superceded by http://www.thingiverse.com/thing:1347425
YES THAT'S RIGHT IT GETS EVEN BETTER! CHECK IT OUT: http://www.thingiverse.com/thing:1347425

I sat down to make a 5 minute demonstration of TinkerCAD and ended up burning a weekend getting this object just right. Version 4.1 and I think I nailed it! I made a few versions using the threads/nut from the 'MakerBolt' model (http://www.thingiverse.com/thing:9095) but ultimately the sharpness of the knurling and th