Ryan (other ryan). Having owned 9 different 3d printers now I can tell you that you DONT want to enclose (trap) the top of your Z axis lead screws. ANY variation in their straightness (its hard to get perfectly straight ones) will be translated in to your prints if it isnt allowed to release itself with a slight deviation at the top.
More easily stated, Trapping a nut on the Z axis doesnt allow that slight movement it needs.
SO there is really 2 options. Leave them open at the top (which a lot of these printers do, like the makerfarm, but he uses lower quality lead screws) and that gives them room to move.
My taz 5 captures them at the top, and ANY slight deviation in the straightness of the lead screw presents itself in Z axis banding on your prints (repeatable bands, every time that Lead screw hits the curvature point).
Thats my take on it.
I am VERY interested in making this printer . I have many others, but I am working on a job that may require a fleet of printers to be running for a while. This would be a nice cost effective way to build some.
Any option to make it bigger?