the cutting operation of the web which is thus not tensioned upon cutting the counter shaft 13 is rotatably supported at its ends 30 a 30 b by the vertical bearing walls 10 and carries near to these ends 30 a 30 b a pair of cylindrical gears 31 whose diameter is same as the diameter of the gears 18 of the shaft 11 and meshing therewith referring in more detail to fig2 a driving unit generally designated as 32 is operatively associated to the rotary cutting assembly 7 which includes an electrical motor 33 conveniently of the brushless type driving in rotation through a first gear pair 34 and a second gear pair 35 the end 23 a of the shaft 12 of the counter blade 28 and the end 91 a of the shaft 11 of the blade 16 respectively via a cardanic shaft 36 the electrical motor 33 is operated by means of an electronic control unit not shown in a programmable way and in synchronism with the driving motor of the drawing assembly 6 and rotates the shaft 11 and the shaft 12 not continuously but instead in an intermittent timed way as a function of the desired cutting length of the web n which accordingly is not subjected to any limitation the arrangement is such that the shaft 11 and the shaft 12 are driven in rotation by the motor 33 whenever cutting is to be performed with same peripheral speed whereby following each complete revolution the blade 16 and the counter blade 28 are placed in a mutually facing angular.