This book introduces 3d CAD modeling for design and manufacturing of gears. Volume 1 covers basic principals of Direct Digital Simulation method with 3d gear models and software samples for design and manufacturing of spiral bevel, hypoid, helical, spur, worm, worm face, globoid and other gears and variable ratio racks. Direct Digital Simulation modeling has been widely advertised since 1999 originally by ZAKGEAR. Since 1999 a number of spiral bevel gears and other gears and racks have been cut on universal CNC milling machines by ZAKGEAR customers to demonstrate advantages of the new method. Because the new CNC technology is common today, the demand for educational literature increases. This publication contains inspirational ideas of a scientist and an engineer in the very beginning of the revolutionary transition from commonly used Gleason and Klingelnberg gear cutting technology into simplified 3,4,5-axis CNC technology. With this book the authors address numerous inquiries about the original basics of today’s popular technology. We do not know any Universities yet to educate engineering students in this area of gear manufacturing. So this publication could be the only textbook available.