Abstract: A control system having a touch sensing circuit for emitting a contact detection signal when contact is made between a workpiece and a touch sensitive tool received in a tool spindle of a machine tool. An auxiliary controller is also provided for controlling movement of the tool spindle relative to the workpiece along orthogonal axes by applying feed pulses and axis designation signals to a numerical controller after switching the operational mode of the numerical controller. The auxiliary controller responds to the contact detection signal to align the tool spindle with the center of a workpiece bore when receiving a centering instruction and to measure the diameter of the workpiece bore when receiving a measuring instruction. The system is further provided with a motor control circuit which controls a motor to rotate the tool spindle during the centering operation. The motor control circuit inhibits the rotation of the tool spindle during the measuring operation.