Definition of NN on the End Face of a Gear Product
Gears are a type of mechanical tool used to transfer motion and torque from one shaft to another. Gears are widely used in many industries from the automotive to aerospace, agricultural, and even medical to name a few. The precision of these parts is paramount to insure smooth operation. To insure these parts meet high quality standards, often times a designation such as “NN” is included on the end face. But what does NN stand for?
NN stands for “Alte Nenweg”, which translates to “Old Road”. This designation is used to indicate a desired surface finish on a gear part, typically the higher the number, the more specific the surface finish. Having a specific surface finish is critical to the proper operation of a gear. It is important to note that this surface finish designation is relative to other surface finish designations. For example, if a part has a designated NN25 finish, it does not necessarily mean the surface finish is 25 microns or 25 microinches as some may presume. Rather, it means it is 25% better than the original designations (originally developed in Germany) which is NN30.
The NN surface finish is most often used with worm gears, but can also be used to describe the surface quality of othergear parts. The NN designation is a relative surface finish rating which is significantly easier to use than the traditional Rz measurements. The reason this designation is favored over other surface finish designations is because it is simpler to measure and communicate relative to other measurements.
The NN designation is a simplified way of facilitating communication between engineers, operators, and manufacturers of gear products. It is important for engineers or operators to understand what the NN designation means when described on a gear product. Since the NN surface finish is relative, making sure the original value or comparison is known is important as this will ensure desired surface finish is achieved. This relative surface finish designation is still widely used by the gear industry and is a valuable tool used to ensure quality and performance of gear products.
