via conduit 16 the bore means 7 is provided with an annular duct or valve means 17 which is connected via conduit means 18 to the tube means 1 in view of the pressurized source of air being connected via conduits 14 15 and 20 to the air chamber means 13 an increasing volume air pressure pocket is created in the air chamber 13 once the pressure in the air chamber means 13 exceeds the opposing force of the resiliently biased lever means 5 the piston or plunger means 6 is lifted off the second end means 28 of the inset 9 as a result of which the surface area of the piston 6 acted upon by the compressed air increases consequently the piston means 6 is strongly accelerated whereby forcibly driving the knife 4 into a cutting relationship with the stationary blade means 24 when the cutting blade 4 has been advanced into its cutting position the piston means 6 has been advanced to a position whereby opening the annular duct or valve means 17 so that the air fed from the pressurized source of air through the conduits 14 15 and 16 into the air chamber means 13 escapes into the conduit means 18 suddenly diminishing the pressure within the air chamber means 13 due to the lack of air pressure displacing the piston means 6 the force inherent with the resiliently biased lever means 5 returns the piston.