METHOD OF MEASURING DIMENSION OF TOOL

PURPOSE:To make possible to measure the dimensions of a rotary tool while the latter is mounted, by moving the attached tool on rotation in a measuring direction until it shields a measuring light beam, so that the dimensions of the tool is measured in accordance with the displacement of the tool at the shield point and the distance between light beams. CONSTITUTION:When the front end of a rotating tool 3 moving in the direction B crosses a measuring beam 11c, the light beam 11 irradiating a photodetector 21 is shielded, and therefore, a signal S3 from the detector 21 varies which is detected by a cutting tip detecting circuit 22 that issues its tip detection signal S4 to a control section 23. Accordingly a control section 23 retards the rotational speed of a motor 35 to feed the tool 3 in the direction B at a cutting feed speed. When the tip 3a crosses a light beam 11A during the feed in the direction B, a detector 20 stops its detection due to the shield of the light beam 11A so that a signal S1 from the detector 20 varies. Therefore, the circuit 22 issues a signal S2 to the control section, and by reading out an accumulated value TL3 from a counter 29, the displacement ZH of a head 37 is accumulated. Thus, the control section 23 calculates the distance MH between the machine original point ZP and the light beam 11A.