| 摘要 |
PROBLEM TO BE SOLVED: To provide a work machining method, a tool breakage detection method, and a machining device easy in maintenance and inspection and excellent in hole depth accuracy. SOLUTION: A bush 41 formed of a conductive material is disposed at the tip of an earthed pressure foot 20 through a bush holder 40 formed of an insulating material. The bush 41 is connected to a comparator 44 through a filter 43. When a drill 14 abuts on a copper foil 31c on a printed circuit board 31, a rotor shaft 6 and the bush 41 are set to the same potential. A voltage with a predetermined frequency is taken from a shaft voltage generated in the rotor shaft 6 through the filter 43 and compared by the comparator 44. Then, when the voltage with the predetermined frequency exceeds a predetermined value, a drill 14 is determined, to abut on the surface of the copper foil 31c, i.e. on the surface of the printed circuit board 31.
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