Machine tool control systems

A machine tool control system for controlling a plurality of machine tools, said system comprising machine control units, each comprising a numerical control device and an interface unit interposed between each machine tool and the numerical control device, and respectively provided for the machine tools, said numerical control device including a first memory area which stores a first group of programs related to the machining of a workpiece and also to the selection of cutting tools suitable for the machining, and a second memory area which stores a second group of programs for executing an interruption instruction for retracting an abnormal tool and exchanging the abnormal tool with a substitute tool or the like operation, and a machine control unit controller which monitors sequence signals arriving at said interface unit and provides access to said first and second program groups stored in said numerical control device through said interface unit in accordance with a predetermined process program.