Build a low-cost CNC machine in your kitchen, for under $120, using tools obtainable at your local art and hardware stores.
This project seeks to lower the ground floor of CNC machine construction. It utilizes foamcore - an easy to work with and cheap material - for its structural components. The most important advantage of this approach is how quickly new ideas can be implemented. Modifications can be built nearly as fast as they can be thought of because the material is so readily cut and glued. It's also very easy to repair - I shipped my first machine out to Maker Faire in San Mateo (from Boston) a few years ago and it (naturally) arrived completely crushed. Half an hour later, with the help of a hot glue gun and a few scrap pieces of foamcore, it was working as well as ever.
On the flip side, the constraints of foamcore as a material have led to mechanisms which are different than on most CNC machines. The drive system uses shafts which are directly driven by stepper motors and are stabilized using tensioned wire rope. Because the foamcore cannot be cut with high accuracy, the accuracy of the bearing system is independent of the accuracy of the foamcore.
A much more complete writeup of the project from a technical perspective can be found here:
Watch it in action!
This video shows an earlier version of the Foamcore CNC, to which some modifications have been made.