| 摘要 |
PROBLEM TO BE SOLVED: To lessen the number of tools used in thread cutting and allow elimination of any non-threaded part. SOLUTION: This thread cutting tool 60 is drawn off gradually in accordance with the lead of a screw 68 while the shank 66 of the tool is rotated round the axis 64 of threaded hole, and thereby the screw 68 is cut by a cutting edge 42b in figure (a). When the cutting edge 42b of the tool 60 reaches the starting point of the screw the tool shank 66 is offset large from the axis 64 of threaded hole so that a chamfer 69 is formed in figure (b). The tool 60 is removed, and thus the thread cutting process is completed in figure (c). According to this arrangement, a preparatory hole for threads is bored by the bottom edge of the tool, thread cutting is performed by the thread cutting edge 42b of the tool ad also chamfering can be made by either of the thread cutting edge and bottom edge, to execute thread cutting with a single tool. Because the depth of the preparatory hole and the depth of threads are identical substantially, non-threaded part can be eliminated.
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