What is a normal module?
There are two types of tooth profiles for helical gears, normal and transverse types, depending on the reference cross section of the tooth profile.
When meshing a pair of helical gears, even if they have the same helix angle and module, they cannot be meshed if the types of tooth profiles mentioned above are different.
As shown in the figure below, the module in the normal plane, where the reference cross section of the tooth profile is perpendicular to the tooth trace, is called the normal module.
The advantage of selecting the normal module in helical gearing is that the gear cutters and grinding wheels used to manufacture spur gears can be used even if the helix angles are different. On the other hand, the disadvantage is that the center distance is different from that of a spur gear with the same module and number of teeth, and the center distance is usually a fractional value.
Due to the manufacturing reasons mentioned above, most helical gears currently manufactured in the normal plane.
In addition to helical gears, worm gears also have normal and transverse types, and tooth profiles with different reference cross sections cannot be used together.
相关链接 - 法向模数