SCREW JOINT STRUCTURE OF EXCAVATING TOOL

PROBLEM TO BE SOLVED: To prolong the life of a tool by preventing a sharp edge from being formed at an incomplete thread part even if the wear of a screw is advanced to some degree as well as before the wear, while suppressing the premature promotion of the wear of the screw. SOLUTION: In this screw joint structure of an excavating tool in which a male screw part is formed on a screw shaft and a female screw part 1 is formed in a screw hole, the male screw part and the female screw part 1 have respective cross sections of isosceles trapezoidal shapes in which the threads 3 at the complete thread part has a pair of slopes 3A, 3B and a flat part 3C at the crest part. The threads 3 at the incomplete thread part of at least one screw part 1 are configured so that the slope 3A thereof in contact with the other screw part is arranged continuously with the slope 3A thereof at the same inclination angle and twist angle as the slope 3A of the thread 3 at the complete thread part which faces the same side. The crest part crosses the bottom surface 4 of the thread with the height of the thread 3 lowered while the flat part 3C arranged continuously with the flat part 3C at the incomplete thread part is formed. COPYRIGHT: (C)2011,JPO&INPIT