Step 1: Make a chocolate extruder.
Step 3: Drill and reem the bore hole for the worm screw.
Step 4: Cartridge heaters.
i got mine from watlow:
Step 5: Interchangeable nozzle and set screw
Step 6: Cartridge heater positions around extrusion chamber.
Step 7: Fully assembled extrusion chamber.
Step 8: Testing the extrusion chamber
Step 9: Build a lego gantry
there are lots of ways to do this. You really want z axis too. i hacked the Z axis by using a layer by layer increment ratchet that was mechanical. given the memory limits of the PCX bricks, one layer was about all you could program before having to upload a new layer code anyway.