A method and apparatus for chopping long unwound items like fiber, fiber strands, yarn, etc. The chopper has a backup roll comprising a wheel and a working layer on the outer peripheral surface of the wheel and an engaging blade roll. The outer peripheral surface of the wheel contains spiral grooves or ridges that mate with ridges or grooves on an inner peripheral surface of the working layer such that a worn working surface can be quickly and easily unscrewed from the wheel and a new working surface can be quickly and easily screwed into place, making the job of replacing the working surface faster, easier and less costly than prior art practice.