This paper describes ongoing research into intelligent robot systems for application to manufacturing operations where short-term workplace or workpiece variations are unpredictable, are unavoidable or are desirable. The system used consists of a gantry robot which is controlled by a modular expert programming system implemented in Prolog. The expert system consists of three basic software modules: a design module, a sensor module and a motion module. The main advantage of this modular approach is that the modules can be easily modified to suit differing applications, in this case building timber frames for house walls and trimming operations on fish fillets. The rules-based approach has advantages when representing complex workplace and workpiece variations in the system.