Junk mill (or milling shoe) is used for milling downhole fallings by bottom or side surfacing wear resistant material, a tool for repairing top of fish. At the milling surface, the carbide particles are built up by welding, which plays a part of self-milling. It is used to mill the fallen substances, such as bolt, nut, tooth wheel, slip dog, fittings for deep-well pump, etc.