Abstract: The constructing principle of tooth profiles with micro-segments is introduced. The profile curve equations of micro - segment racks and gears are derived. It is proved that the micro-segment profiles meet the basic theory of gear mesh and there are many zero comprehensive curvature points when they are in mesh, so it can be said that the tooth profiles have better meshing characteristics. A gear is designed with use of the profile curve equation, and the part data and the gear graph are given.

Key words: Gear Tooth profile curve, Meshing theory, Micro- segment