FIELD: mechanical engineering. SUBSTANCE: knife that is set in reciprocation has the first and second cutting sides inclined to each other and forming the lengthened cutting edge along the intersection line. The cutting edge is shifted from the base plane passing at the same distance from the generatrices of the knife sides. The first side is in the base plane of symmetry away from the respective side of the knife in the direction to the cutting edge. At least the first cutting side has thin covering made of a hard material, the hardness of the material being higher than the hardness of the knife base. In cutting the second cutting side is re-sharpened so as the cutting edge is formed from the hard material of the coating on the first side. The multiple re- sharpening results in gradual shifting the cutting edge to the base plane. EFFECT: increased longevity. 3 cl, 9 dwg
