Use the design procedure outlined in this section.
Step 1. Consider the given data.
Step 2. Specify N_P = 18 and P_d = 16 (Design decisions)
Step 3. D_P = N_P/P_d = 18/16 = 1.125 in. This seems reasonable for mounting on the 0.625 in motor shaft.
Step 4. Compute the transmitted load,
W_t = (126 000)(P)/(n_PD_P) = (126 000)(0.25)/[(1160)(1.125)] = 24.1 lb

Step 5. Specify 20° full-depth teeth. Then Y = 0.521 for 18 teeth from Table 9–15.
Step 6. Specify a safety factor, SF. The shredder will likely experience light shock; the preference is to operate the gears without lubrication. Specify SF = 1.50 from Table 9–1.
Step 7. Specify unfilled nylon. From Table 9–14, s_{at} = 6000 psi.
Step 8. Compute the required face width using Equation (9–42).

F=\frac{W_tP_d(SF)}{S_{at}Y}=\frac{(24.1)(16)(1.50)}{(6000)(0.521)}=0.185 in

Step 9. The dimensions seem reasonable.
Step 10.Appendix 2 lists a preferred size for the face width of 0.200 in.

Comment:

In summary, the proposed pinion has the following features:
P_d = 16, N_P = 18 teeth, D_P = 1.125 in, F = 0.200 in, Bore = 0.625 in,
Keyway for a 3/16 × 3/16 in key. Unfilled nylon material.

Step 11. Gear design: Specify F = 0.200 in, P_d = 16. Compute the number of teeth in the gear.
N_G = N_P(n_P/n_G) = 18(1160/300) = 69.6 teeth
Specify N_G = 70 teeth
Pitch diameter of gear = D_G = N_G/P_d = 70/16 = 4.375 in
From Table 9–15, Y_G = 0.728 by interpolation.
Stress in gear teeth using Equation (9–41):

σ_t=\frac{W_tP_d(SF)}{FY}=\frac{(24.1)(16)(1.50)}{(0.200)(0.728)}=3973 psi

Comment:

This stress level is safe for nylon. The gear could also be made from acetal to achieve better wear performance.