Q.1: (70 pts.)
A speed-reducer has 20° full-depth teeth, and the single-reduction spur-gear gearset has 22 and
60 teeth. The diametral pitch is 4 teeth/in and the face width is 3¼ in. The pinion shaft speed is
1145 rev/min. The life goal of 5-year 24-hour-per-day service is about 3(10?) pinion revolutions.
The absolute value of the pitch variation is such that the transmission accuracy level number is
6. The materials are 4340 through-hardened grade 1 steels, heat-treated to 250 Brinell, core and
case, both gears. The load is moderate shock and the power is smooth. For a reliability of 0.99,
rate the speed reducer for power.
Figure 14-3
Allowable bending stress
number for nitrided through-
hardened steel gears (i.e.,
AISI 4140, 4340), $S_t$. The
SI equations are $S_t =$
0.568$H_B$ + 83.8 MPa,
grade 1, and $S_t =$
0.749$H_B$ + 110 MPa,
grade 2. (Source:
ANSI/AGMA
2001-D04 and 2101-D04.)