| 摘要 |
A screw measuring apparatus comprising: an internal-dimension measuring unit for obtaining internal-dimension information Dw of a female screw placed on a coordinate measuring machine when the stylus-tip sphere having the diameter selected according to the pitch of the female screw is butted against the screw groove of the female screw; and an effective-diameter calculating unit for obtaining effective-diameter information De of the female screw from the internal-dimension information Dw obtained by the internal-dimension measuring unit, diameter information 2r of the stylus-tip sphere, and thread angle information alpha and pitch information P of the female screw, by using an effective-diameter calculation expression De=Dw+2rxcosec(alpha/2)-(P/2)xcot(alpha/2).
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