Abstract: A controller for optimization of metal-working on CNC-operated machine tools, includes a first unit for monitoring the torque of the main drive of the machine tool to establish the actual, instantaneous cutting torque, a second unit for setting the rated cutting torque in the teaching mode in dependence on the main-drive torque as monitored, a third unit for calculating the feed rate required to maintain the cutting torque at a constant level and controlling the feed drive, and a fourth unit responsive to the monitored main-drive torque and providing feed rate limiting signals to the third unit for protecting the tool against breakage.