downwardly and the tire 42 lies within the nip between the wheels 14 and 34 see fig6 a limit switch not shown is preferably automatically activated when the safety hood is moved down into its operative position and the motor is thereby started the hood 30 therefore acts as a safety mechanism in that the machine cannot be activated without the safety hood 30 being in a closed position in this manner the user 39 s hands and fingers are not in the way and cannot be accidentally fed or pulled into the machine alternatively it is possible to provide a manually operative switch to start the motor in order to provide the same degree of safety the shredding machine can be arranged so that the manually operated switch is inactive unless the safety hood is down or in its closed operative position in either case with the tire 42 located between the driven wheel 34 and the pilot wheel 14 as seen in fig9 the driven wheel 34 begins to rotate clockwise and the tire 42 is pulled into the machine wheels 34 and 14 feed the tire 42 into the first set of grabber wheels 16a and 16b and onto the wings 22a and 22b which are located downstream of the intake rollers 14 and 34 the tire 42 is forced between the two wheels 16a and 16b and starts to flatten out wheels 16a and 16b force curved sidewall portions.