Mendel90 is highly scalable 3d printer design. Reddit user Dekker3d started this project of large print area Mendel90. He wants to print objects like masks and fantasy armor parts sized to fit a human.
Reddit thread on this big Mendel90:
Here is the update on his project he sent me on 07.12.2013.:
When I took the pic, I had two really bad rods in the Z axis, and I was waiting for someone to bring two replacements. I just got them, and will likely continue building this project in the coming few days.
I've altered a few designs of the original, like removing a reinforcement from the original x-motor-end so the stepper could be removed without cutting all the wiring and having to re-solder later. I'll also be using my customized Z endstop again, since it works quite a lot better than the original... even though it doesn't hold a particular position quite as well, it's much easier to tweak.
I fully expect I'll have to alter proportions and designs later, but the big advantage of rapid prototyping is that you can make incremental prototypes and just see what they do. I do wish to make a printer with a volume of at least 40x40x40 cm, so that a helmet, a kitchen machine or many other types of objects will fit in partially or completely.
I currently use 12mm MDF and 8mm smooth and threaded rods for construction. I'll probably end up replacing some of those parts once I find out the weak points. I might make a bowden setup at some point, but only once I've got it printing decently with a non-bowden extruder first so I know I can fit quite a bit of extra stuff on the extruder with no worries.
If it all goes really well, I might even experiment with another idea I'd been playing with, using a sugary or salty solution for a support material. One idea that stood out to me is a sugary treat that's commonly used in the netherlands, borstplaat: http://nl.wikipedia.org/wiki/Borstplaat_%28snoepgoed%29