An assembly mountable on a machine including a gantry displaceable along an x-axis, a carriage mounted on such gantry displaceable along the y-axis, provided with means for extruding a beam of molten thermoplastic material, a tool carrier mounted on such carriage displaceable along a z-axis, a tool holder mounted on such tool carrier displaceable about a z-axis, a tool support shaft provided with an axis disposed in an x-y plane journalled in such tool holder and rotatable about the axis thereof, a dispenser conduit mounted on such shaft, perpendicular to such shaft axis, means on such dispenser conduit for ejection of a beam of molten thermoplastic material and a flexible hose with a first end supported on such carrier forming a rotary union with such material extrusion means, and a second end communicating with an inlet of such dispenser conduit.