# 249 - Reactions at the bolts of speed reducer gear box

**Problem 249**

Fig. P-249 represents the top view of a speed reducer which is geared for a four to one reduction in speed. The torque input at the horizontal shaft C is 100 lb·ft. The torque output at the horizontal shaft D, because of the speed reduction, is 400 lb·ft. Compute the torque reaction at the mounting bolts A and B holding the reducer to the floor. Hint: The torque reaction is caused by the unbalanced torque, which is a couple.

**Solution 249**

The couple resistance at the bolts is equivalent to the difference of torques on each shaft

$C = 4T - T$

$2.5R = 400 - 100$

$2.5R = 300$

$R = 120 \, \text{ lb}$

R = 120 lb up at A and down at B. *answer*