Why is the pinion wider than the big gear 5-10mm?
Is to ensure that the two gears in the overall width of the teeth meshing work. If the two gears are equally wide, the gears will be dislocated in the axial direction (which is unavoidable)
The main purpose is to prevent gears from slipping and increase the hardness and strength of gears
Reduce the actual working width of the gear pair. The small gear larger than the large gear 5-10mm, is the most material savings, but also to meet the aforementioned requirements of the best choice
