| 摘要 |
To present a method of manufacturing a multipitch screw easily by using flat dies suited to mass production. A flat die 4 includes linear ordinary screw threads 40 a, and multipitch screw threads 40 b consecutive to the ordinary screw threads 40 a, slightly shorter in height than the ordinary screw threads 40 a, with both side walls formed alternately and consecutively, alternating between a section departing from the central line 40 c of screw threads and an approaching section along a central line 40 c, and symmetrically to the central line 40 c of screw threads. After forming the tacks of a constant lead angle screw on the outer circumference of a shaft-like blank piece by the ordinary screw threads 40 a, tracks of a multipitch screw are formed by the multipitch screw threads 40 b, and therefore the tracks of a multipitch screw varying in the force applied at the time of rolling can be formed easily.
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