Screw measuring method, screw measuring probe, and screw measuring apparatus using the screw measuring probe

摘要

A screw measuring apparatus comprising: an internal-dimension measuring unit for obtaining internal-dimension information D w 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 D e of the female screw from the internal-dimension information D w obtained by the internal-dimension measuring unit, diameter information 2r of the stylus-tip sphere, and thread angle information ± and pitch information P of the female screw, by using an effective-diameter calculation expression D e = D w + 2r x cosec(±/2) - (P/2) x cot(±/2).