Calculate the nominal values of torsional, axial, thread bearing, and thread shear stresses under starting conditions for the power screws in Problems (a) 10.3, (b) 10.8, (c) 10.9, (d) 10.10, and

(e) 10.11. Assume in each case that the length of thread engagement is 1.5 times the outside diameter

of the screw.

10.3 A square-threaded power screw with single thread is used to raise a load of 25,000 lb. The screw

has a mean diameter of 1 in. and four threads per inch. The collar mean diameter is 1.5 in. The

coefficient of friction is estimated as 0.1 for both the thread and the collar.

(a) What is the major diameter of the screw?

(b) Estimate the screw torque required to raise the load.

(c) If collar friction is eliminated, what minimum value of thread coefficient of friction is needed

to prevent the screw from overhauling?

[Ans.: (a) 1.125 in., (b) 4138 lb • in., (c) 0.08]

10.10 An ordinary C-clamp uses a 1

2

-in. Acme thread and

a collar of 5/8 -in. mean diameter. Estimate the force

required at the end of a 5-in. handle to develop a

200-lb clamping force. (See Figure P10.10.)