40 into a cylinder 41 with a heated head 42 and a discharge nozzle 61 a discharge ribbon of extruded material flows onto a moving heated platform 43 to form a prototype or mechanical element 44 the extruder system is a four post 45 46 47 48 screw press driven with a massive dynaserv u00ae servo motor 49 this motor 49 is capable of very powerful and precise movements the dynaserv motor drives 1 25 34 precision ground ball screw the end of the screw is secured on a plate 50 which slides on the four posts 45 48 this plate 50 also prevents any axial misalignment of the screw and houses a load cell the end of the screw is fitted with a cup for attaching the extrusion piston 40 the bottom plate 52 of the press has a keyhole shaped mounting insert 53 for the extrusion cylinder 41 a servomotor not shown for platform 43 is controlled by a four axis controller card in a personal computer this platform system is depicted in general in u s pat no 5 340 433 or u s pat no 5 121 329 referring next to fig2 there is depicted the piston 40 cylinder 41 and head 42 which form an integral part of the invention specifically the cylinder 41 has a smooth sided longitudinal through passage 60 of uniform diameter the top end of cylinder 41 includes a circumferential groove 62 to facilitate mounting in plate 52 see fig1 the bottom end of.