What are the fundamental reasons for additional dynamic loads and impact vibrations caused by gear transmission?

Generally, it is caused by the precision of gear machining, for example, the common expression of gear precision level is 888FJ.
The first 8 represents the long cycle error, which is used to evaluate the accuracy of the transmission. This error can lead to inaccurate transmission ratios, which is related to the tooling equipment.
The second 8 represents short cycle error, used to evaluate the smoothness of the transmission. A large error can lead to significant meshing impact. Related to tool equipment.
The third 8 affects the uniformity of load distribution, and shaping can effectively improve it.