cutting devices 34 above the box shaped casing thus formed is a pneumatic cylinder 76 whose piston 77 is equipped with two shafts 78 the shafts 78 are connected to the slide 73 pneumatic cylinder 76 is axially perforated to permit the passage of the wires 32a also for this purpose the slide 73 and the pin 65 have suitably positioned holes such that the wires 32a reach between the cutting parts 69 of the jaws 63 64 jaws 63 64 are arranged to close by means of angular rotation effected by lowering the slide 73 under the control of the pneumatic device 76 thus cutting the wires 32a through the reciprocal elongation of the pins 71 that engage the slots 72 the panels 2 are caused to move or advance in a jogging motion on the conveyor platform 1 by the advancing device 7 so that each overlapping pair of transversal warp wires 5 of the netting 4 is positioned under the set of cutting devices 34 for the time necessary to carry out the following operations a length of parallel wires 32a is unrolled from each of the pulling and inserting devices 33 and inserted through the layer of expanded plastic 3 on.