This paper describes the design and implementation of a PC based Open Architecture machine tool controller. The PC based OAC is based on a distributed, peer to peer functional model of the entire machine controller system. Machine motion and I/O functionality is provided by a machine server module. The machine server is designed to provide a uniform interface, and layer of abstraction, for user applications to all machine services. A PC based motion and I/O solution was designed to provide an open, standard interface to the machine. The overall cost / performance ratio of the PC based OAC makes it an attractive alternative to conventional machine tool control technologies. Intelligent process monitoring and control strategies are implemented with the OAC on a 3-axis machining centre. Power, force, and vibration monitoring and control applications are discussed in this paper.