3D Printer Frame

I have more or less an idea what I want to do with for a frame. How to realize my vision that's another store.

What I have in mind is to construct a cube from square tubing and have the bed travel up and down by using four M12 threaded rods. I will connect the four rods via chain and sprocket to have them move in sinc using one NEMA 23 1NM stepper motor.

To move the print head I will use a gantry system like the cutting head on a CNC plasma cutter.

or something like the Reprap Darwin I am quite fond of the frame design and "personally" think is more robust than the Mendel.
                                     

I will be replacing the threaded rod with square tubing.
for my first printer I will make use of mild steel parts turned on the lathe or milled on the milling machine
there after I plan to make version 2 that uses printed parts as to the machined steel parts.