Abstract: A control system (41) comprises a control program (42) which accesses a stored database (43) holding a predefined set of rules for performing predetermined machine tool operations, from which rules computer instructions can be derived for controlling an NC machine tool. A solid model (44) of a component to be manufactured is input to the control program (42). The solid model (44) is in the form of a computer model programmed using the International Geometry Export Standard (IGES). In operation, the control program (42) performs a feature recognition operation on the IGES data to identify geometric features present in the solid model (44). Having identified the geometric features present, the control program (42) uses the set of rules in the database (43) to generate control data in the form of a composite set of computer instructions for working the features of the component represented in the solid model (44).