I am impressed with the possibilities of the "Core XY" platform described at http://corexy.com
. In short, it is a simple, rugged, inexpensive, compact way to move a small, flat platform in cartesian space.
Once you have the above, you need a couple more pieces to do useful work:
1) A tool to mount on the XY platform. Interchangeable tools such as Dremel/drill with bits for etching, drilling, routing, etc., or a heated extrusion head for 3D printing, or a pen or marker for plotting.
2) A work surface to be processed. In the simplest case, such as a plotter, this can be just a flat work surface below the pen. Simple pen-up/pen-down control could be in the tool head. For more general work such as 3D printing, you must add z-axis motion to either the work surface or the XY platform.
You would doubtless wind up with an Arduino controlling the X/Y/Z motors and tool head.
I'm reluctant to shell out $1000 for a cheap 3D printer, but toss in PCB fabrication, fancy woodworking, drawing and cutting, and I'm in!
I'm hoping some others will be inspired to chip in designs for tool heads and a Z-motion mechanism.
To start, I propose the XY platform could be made a little simpler and cheaper by eliminating its precision shafts and bushings. Instead, constrain vertical motion of the X and Y sliders with a small lip of aluminum plate above and below, with about 0.001" shim to reduce friction. The lips could either be attached to the sliders or the slidees, with lubricant in the slots they form. What do you think, mechanical experts? Would that work OK? Would wear on the aluminum plates be a problem?