Abstract: A chipper knife blade assembly for a rotary disk chipper has first and second flat knife blades of substantially identical construction, with one of the blades serving as a chipper blade and the other serving as a counterknife supporting the chipper blade. The counterknife is seated on a sloping support surface in a recess in the disk and has its proximal edge reposed against a support or a thrust bar. A bolt-down clamping member has a shouldered surface with a flat portion clamped down against a top surface of the chipper knife blade, and with a shoulder supporting the proximal edge of the chipper blade. In a preferred embodiment, the chipper blade projects about one-half inch to three-quarters inch beyond the cutting edge of the counterknife blade. With this arrangement, a warn cutting blade can serve a second useful life as a counterknife, absorbing the wear that results from the chips moving at high speed into the chip slot.