Figure P12-38 shows a sketch for a double-reduction spur gear train. Shaft I rotates at 1725 rpm, driven directly by an electric motor that transmits 15.0 hp to the reducer The gears in the train all have 20°, full-depth teeth and the following numbers of teeth and pitch diameters:
Note that the speed reduction for each gear pair is proportional to the ratio of the number of teeth. Therefore, shaft 2 rotates at 575 rpm, and shaft 3 rotates at 287.5 rpm. Assume that all shafts carry 15.0 hp. The distance from the middle of each bearing to the middle of the face of the nearest gear is 3.00 in. Shaft 2 has a length of 5.00 in between the two gears, making the total distance between the middle of the two bearings equal to 11.00 in. The extensions of the input and the output shafts carry torque, but no bending loads are exerted on them. Complete the design of all three shafts. Provide for profile key seats for each gear and sled runner key seats at the outboard ends of the input and output shafts. Provide for the location of each gear and bearing on the shaft.
