Abstract: The cutter assembly contains an axle having a number of parallel, equally spaced troughs along the axial direction, and a number of circular blade discs, each having a center hole threaded through by the axle. Each blade disc has a number of teeth along the circumference of the center hole corresponding and matching to the troughs of the axle. The blade disc has fewer blades than the teeth and the blade discs therefore can be mounted on the axle in different orientations so that their blades are spirally arranged. The axle of the cutter assembly has a fixed end and the blade discs can be sequentially installed to or removed from the other free end. The bearing at the free end has a smaller diameter so that the blade discs can be removed or installed directly passing through the bearing without removing it first.