| 摘要 |
PROBLEM TO BE SOLVED: To reduce force required for machining, to smooth a screw surface, and to improve tensile strength by performing a part of screw machining by cutting machining, and performing the remainder by rolling machining. SOLUTION: A spiral groove 12 is machined in a prepared hole of a nut blank by cutting by using a cutting tool. A quantity of the cutting machining is decided as K=0.54 by using an expression D2'=D2-(D-D1)×K. Where, D2 is an effective diameter of a female screw 21, D2' is an effective diameter of the cutting machining, D is a major diameter of the female screw 21, D1 is an inner diameter of the female screw 21, and K=0.25 to 0.80 is realized. Here, the effective diameter D2' of the cutting means an effective diameter of a virtual female screw 13 in assuming that the spiral groove 12 forms a part of a trough of the virtual female screw 13. Thus, in machining the spiral groove 12, the female screw 21 having an effective diameter D2, the major diameter D and an inner diameter D1 is rolled with the spiral groove 12 as a guide by using a rolling tap.
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