So, we want to make a machine for 3d printing, cnc drilling, pcb routing... They have a common starting point, an X-Y gantry.
First thing we need to decide is what size we should make it.
My thoughts, for a first testbed, are to make something fairly small, bed size of about 200mm x 200mm. This can then be driven from a few stepper motors (we have some lying about from murdered printers), using either a belt drive or threaded rod (1 would be perfect).
Once we have this running, we can use a dremel for the router bit, and have a working small CNC machine, that can be used for PCBs and making small parts from foam and wood. I'm looking at 2 for guidance, which is an instructable written by oomlout, seems like it'd be a good place to start.