CNC 3D printer

[sciencenerd]

Hey all,

I've been involved for a few months now with an effort to create an open-source 3D printer for around $400 in parts. It's a really cool system that's worth checking out; more details can be found at their website.

However, that's not the most immediate reason for my post. I'm working on adapting a 3-axis CNC platform (originally designed to be used with gearmotors) for use with stepper motors, as this will make it more compatible with the RepRap project. Currently the design relies on X and Y stages made of 3/4" Medium-Density Fiberboard driven along aluminum tracks by a threaded rod (pic). My question is: does anyone have an idea of what kind of torque requirements a stepper motor would have to have to drive those stages (particularly the bottom one)? If it's too high, I suppose I'll have to modify the design to use linear bearings, but those can get pricey. Does anyone know of a cheaper alternative?