Reprap is an open source project to create a 3D printer that can make its own parts, essentially printing itself. While looking through the RepRapWiki one day, I found the FTIStrap which is a Repstrap made out of fischer technik parts. I didn't have any access to fischer technik parts, so I decided to recreate the Mendel frame out of k'nex.
The overall goal of this project was to create as much of the mendel frame and chassis as possible, so you would only have to add motors, belts, and electronics. Additionally, while k'nex would not be suitable for long-term use, they should be good enough for enough prints to create a set of parts for a reprap machine. I tried to make as much of the project out of k'nex as I could--the only exceptions are the nuts, aluminum tape, threaded rods, and hot-glued lego gears (I had to grind out the central hole to have them fit on the threaded rods) on the z-axis.
An issue that I had with the final design was that since the top joint of the frame was not at a 45 or 90 degree angle, it didn't fit perfect, causing the z-axis rails to flex a bit. Another thing to note is that since the build platform is a plastic, blue k'nex plate, it would have to be covered with a heat resistant material before actually printing.
(I apologize for the lack of notes on the photos. I tried firefox 4, chrome 10, and safari, and none of them were able to properly create and save notes on the images.)