Well, spent some time trawling ebay, settled on 10mm rod for the X axis, and 8mm for Y and Z. Just using sleeve bearings for now. the rods are 50cm and 30cm respectively, which should cover most PCBs. I should be able to make a stick-vise-like board clamp for the bed, so that through-hole components could be removed. A heated bed would probably be a good idea as well, so that the hot air pencil doesn't have as much work to do...