Parallel manipulators of the Stewart-Gough Platform type have been receiving increasing attention as mechanical platforms for universal machining centers. In this paper we investigate the performance of various parallel manipulator architectures for CNC machining applications. The kinematic characeristics that are most often cited as important in universal machining include qualities like manipulability, joint and link stiffness, and workspace volume. Here we quantify these various performance measures using differential geometric techniques, and investigate the performance of two six degree-of-freedom parallel manipulators which have been built as commercial products or research prototypes. The analytical methodology presented here, in combination with the graphics-based CAD software we have developed, can serve as a useful tool to designers of future high-performance parallel manipulator-based machine tools.