Over the last several decades, gearing development has focused on improvements in materials, manufacturing technology and tooling, thermal treatment, and coatings and lubricants. In contrast, gear design methods have remained frozen in time, as the vast majority of gears are designed with standard tooth proportions. This over-standardization significantly limits the potential performance of custom gear drives, especially in demanding aerospace or automotive applications. Direct Gear Design introduces an alternate gear design approach to maximize gear drive performance in custom gear applications. Developed by the author, the Direct Gear Design® method has been successfully implemented in a wide variety of custom gear transmissions over the past 30 years. The results are maximized gear drive performance, increased transmission load capacity and efficiency, and reduced size and weight. This book explains the method clearly, making it easy to apply to actual gear design. Describes the origin and theoretical foundations of the Direct Gear Design approach as well as some of its applications—and its limits Details the optimization techniques and the specifics of Direct Gear Design Discusses how this approach can be used with asymmetric gears to further improve performance Describes tolerance selection, manufacturing technologies, and measurement methods of custom gears Compares Direct Gear Design with traditional gear design from both an analytical and an experimental perspective Illustrates the applicability and benefits of this gear design approach with implementation examples Written by an engineer for engineers, this book presents a unique alternative to traditional gear design. It inspires readers to explore ways of improving gear transmission performance in custom gear applications, from higher transmission load capacity, efficiency, and reliability to lower size, weight, and cost.