This is the internal assembly of a large unit gearbox that will be used for hydraulic fracturing and heavy pumping conditions. This gearbox was designed with helical overlap ratio to accommodate for floating of the pinion and output gears. This allows us to have full contact in the gear meshing during operation, and helps to distribute the load. Other reasons for doing this type of design are for strength and endurance rating, as well as making sure the gears won’t be overloaded. This stacked gear train has an input gear, double idler gears, and output gear with helical overlap. It also has multiple shafts and bearings, and generally operates in the 1800-2500 rpm range.