Make 3D fabricators from old floppy drives, CDROM drives DVD drives.
Use radial coordinates to convert the points of your 3D print to locations on the platter.
All the circuitry, software, and hardware is there for moving the print head and turning on the print nozzle. Only need to add mechanism for vertical motion. Raising and lowering the platter on the spindle would be easiest.
Markus Kayser has built a 3D printer that uses sun light to turn sand into 3D glass objects. Free energy making things from the free materials.
He calls the device a Solar Sinter. The process works by spreading thin layers of sand then focusing a beam of light with a magnifying lens on a point to melt the sand turning it into glass. The object is built up a layer at a time. The movement and focusing of the beam is powered with photovoltaic but the high energy melting is done with a magnifying lens. This allows the device to be very low cost and potentially long lasting
A rover equipped with a solar sinter could be placed in deserts on earth or another planet and let run making useful objects. Even though this device makes crude items similar 3D printing technology has been used to make high precision objects of many materials.
In addition to a 3D printer, which is an additive technique, he has made a solar cutter which is a subtractive technique.
Ideas to make high precision low cost head positioning systems for 3D printer / fabricators / CNC machines. Precision stepper motors are expensive. What if you could use cheap analog motor? They could be very fast and cheap.
Run a length of wire along each axis of the printer / fabricator / CNC and measure the resistance at the head position. Using a table of actual resistance measurements on the device could increase accuracy and even heat differences could be taken into account. This could be extremely accurate and low cost.
Optical is another approach, this is how mechanical mice and mane printers function. Using a digital camera with distance measurements on a scale printed from a long format printer could make the device very fast and accurate. Using optics the accuracy could increased fine precision even with cheap webcam sensors.
Mounting an RF transmitter on the head and antennas at the corners of the tracks could allow triangulation of the head to extremely high precision even over very large distances. This is the same technique used by GPS and cell phone towers. The precisions scales with size and frequency transmitted.
Using opposing electrical currents to create a balance for any location along the rail. With the correct calibration this can be very accurate plus provide very fast movement.