TOOL TROUBLE FORESEER

PURPOSE:To prevent a cutting failure and a reject from occurring, by detecting a fact that the exhaust passage installed in a cylinder varies because the cylinder of a tool holder and a tool holding shaft are slipped if unusual large resistance occurs during operation, with a pressure sensor. CONSTITUTION:When resistance of more than specified value due to wear in a drill, a selection failure, or the like is added to a tool holding shaft 8, a fixed positional relationship among a flange 13, a ball 12 and an actuating member being solidly rotated together with a cylinder 6 becomes broken down, whereby an exhaust port 9 and an interconnecting port 20 both are slipped. If so, this exhaust port is cut off, therefore air pressure in an air feed passage 22 suddenly goes up. At that time, a pressure sensor 36 detects this and a signal is emitted, and this signal is inputted in a control part of a machining center, stopping a spindle 1. Simultaneously with this stoppage, an alarm is operated, and since proper handling takes place before breakage of the tool, a cutting failure and a reject are preventable from occurring.