Here's an ambitious (and excitingly incomplete) Instructable from "Gene Hacker" explaining how to build a 3D printer from Legos.
A polar printer is a printer whose principal axes, or how it can move, are radius(in and out), angle(spin clockwise/counter clockwise), and as opposed to a Cartesian printer whose principal axes are X(left/right), Y(up/down). In other words, it moves just like a polar coordinate system.
So why did I make a polar 3D printer instead of a good ol' Cartesian 3D printer?
1. I didn't have enough Legos to build a Cartesian printer.
2. I hope to eventually add a 3D laser scanner to it so I can scan in objects and send them to another printer somewhere else in world. Making sort of a 'teleporter'.
(via Beyond the Beyond)