This paper discusses a Group Technology (GT) and Computer Aided Process Planning (CAPP) installation at JLG Industries, Inc., an international manufacturer and marketer of specialized hydraulic machinery. An efficient architecture for the design, development and implementation of the system is presented along with system design requirements and characteristics. A GT software shell is described, and for the architecture that is defined, a formal model of the process planning system is developed. The model is used as the basis for the creation of a generic semi-generative CAPP system. Implementation of the model along with experience with the system is included. Run time examples of the system are provided to illustrate the features of the system.