OK, I'm not sure if I would consider this a teardown but they thoroughly examined the MOD-t 3D printer - see http://hackaday.com/2014/06/09/a-clo...-t-3d-printer/
I'm really impressed by how simple of a design this printer is and the minimalization of parts used.
Check out how simple the extruder is:
http://hackadaycom.files.wordpress.c....jpg?w=1000&h=
And of course the 3d printer
http://hackadaycom.files.wordpress.c....jpg?w=1000&h=
