PURPOSE: To improve the detecting accuracy of the breakage of a tool by detecting the process resistance operating to the tools held by a multishaft head by a detector respectively, and deciding that a tool is broken when the detecting value exceeds a set value.
CONSTITUTION: In a multishaft head 8, a rotary shaft 12 rotated by an NC motor is held rotatable by a pair of the front side and the rear side angular bearings 13, in plural holding tubes 11 formed integral in front of the multishaft head 8, and a reaction in the thrust direction as a process resistance operating to the rotary shaft 12 is transmitted to an inner lace 15 through a flange 12a on the rotary shaft 12. In this case, a step 11b is formed at the rear position of the bearing 13 inside the holding tube 11, and a thrust reaction detecting unit 20 is provided between the bearing 13 and an outer lace 14. And it is discriminated whether the detecting value of the detecting unit 20 exceeds a set value or not at a specific position after the process is started, and the breakage of the tool 9 is detected.
KAWAI MASAE
YAMAZAKI KATSUMI
