Midterm Period
Activity 1
1. A flat key mounted on a motor shaft 4 in. diameter is subjected to a maximum
twisting moment of 45,000 lbs-in. Design a suitable key assuming the design stress
in bearing to be 24,000 psi and in shear at 9000 psi.
2. A flat key is used to prevent slipping of a cast-iron gear mounted on a shaft, 2 in.
in diameter. Determine the appropriate dimensions of the key if the gear delivers
125 hp at 250 rpm. Assume design stresses for shear and bearing as 19,000 psi
and 37,000 psi.
3. Design a square key for a 3 in. diameter shaft to withstand a torque of 30,000 lbs.-
in. The design stresses in shear and bearing can be safely taken as 11,000 psi
and 22,000 psi, respectively.
4. A 2-in. shaft having a yield strength of 100 ksi, has a pulley keyed to it. Compute
the length of square key and the length of flat key such that a key made of cold-
drawn, yield strength of 70 ksi, has the same yield strength as the shaft does in
pure torsion.
5. A bevel gear is keyed to a steel shaft by a steel feather key. The gear delivers a
torque of 7500 in.-lb. and the shaft has a 2 in. diameter. Compute the key length
if:
a. The key has thickness = (1/2) in. and width = (3/4) in
b. The key has thickness = (3/4) in. and width = (1/2) in
Assume permissible stress values in compression and tension of 16,500 psi and
in shear of 8500 psi, for the key material.
