Patent ID: 8463421

Claim:
A method of drilling a hole in a workpiece in order to control breakthrough of the workpiece comprising the steps of: a) initiating contact between a drill bit of a drill unit and the workpiece; b) operating the drill unit to rotate the drill bit to drill the workpiece; c) during drilling of the workpiece measuring the force, F, and torque, T, experienced by the drill bit; d) calculating a variable F′, based on the measured force, F, representing the rate of change of F; e) calculating a variable, T′, based on the measured torque, T, representing the rate of change of T; f) calculating a variable F″ representing the rate of change of F′; g) calculating a variable T″ representing the rate of change of T′; h) detecting the onset of breakout of the workpiece by use of the variables F′, F″, T′ and T″; i) thereby controlling the speed of rotation of the drill bit during breakthrough of the workpiece to control the degree of breakout of the drill bit from the workpiece.