A double-threaded Acme stub screw of known major diameter is used in ajack having a plain thrust collar of known mean diameter. Coefficients of running friction are estimated as 0.10 for the collar and 0.11 for the screw. Assume (1) the starting friction is about 1/3 higher than running friction and (2) the screw is not exposed to vibration. Required:
a. Determine the pitch, lead, thread depth, mean pitch diameter, and helix angle of the screw.
b. Estimate the starting torque for raising and for lowering a 5000 lb load.
c. If the screw is lifting a 5000 lb load at the rate of 4 ft/min, what is the screw rpm? What is the efficiency of the jack under this steady-state condition?
d. Would the screw overhaul if a ball thrust bearing (of negligible friction) were used in place of the plain thrust collar.