1. A method of machining a workpiece by means of a multi-tool machine provided with a numerical control system for individually controlling different tools of the machine, comprising the steps of: providing machining instructions for controlling individual ones of said tools, said instructions being divided into groups, the instructions in one group being further divided into sets, the instructions in a first set relating to the control of different tools being executable simultaneously; simultaneously executing the instructions in said first set; and subsequently simultaneously executing a second set of instructions within said group after a condition imposed by a first instruction in said first set has been satisfied.