Abstract: A machine used in the renewal of large earthmover type tires, wherein the worn lugs are completely removed from the tire casing and replaced with convolutions of unvulcanized rubber material. The machine is provided with a heated knife blade which is utilized to cut a series of grooves in the unvulcanized rubber material of the tread in accordance with a pattern mounted on the machine. The pattern consists of a cam with a curved outer periphery which is monitored as the cam rotates on the machine. The depth to which the knife cuts into the unvulcanized rubber material as it moves transversely across the tread, is varied in accordance with the periphery of the cam being monitored.