Question

1. A single-threaded ACME power screw has a major diameter d=1.25 in with a pitch of 0.2 in. The threaded coefficient of friction u is 0.2, and the coefficient of collar friction He is 0.15. The mean collar diameter de is 2 in. The external load on the screw is 1200 lb. Find: a) The torque required to raise the load. b) The maximum nominal shear stress of the screw body.

Answer 1

22 Giren data → Mayor diameter (dm) = 1.25 in Pitch CP) = 0.2 in Thread coefficient of frictim (M=)=0.2 Coller " " " (Mc) = 0.15 Mean coller diameter (dc) = 2 in Load CF) = 1200 16 Screw loody dia - do = dm - p = 1.25-0.2 = 1.05 in Mean dia of screw - dont do - d = = 1.15 no in

* Troque required to raise the load - Tv - Fxdm (+ TMuda) [L- Lead = Pitch for single athreaded screws FX Mexde 2 1200 x 1.15 = 2 10.2 + LT X 0.2X 1-15) (TTX1-15)-4 (0-2 X0-2) t 1200 X 0.15 X 2 2 . Tr = 358.17 16- in

© Maximuon nominal body to shear stress — Poler moment of the body cross section - 4- ex doll = 0.12 ina Body radius to = do 20.525 in .: Stress - Ty x ro 358.17 x 0.525 Zomax = 10.12 = 1567 lb / in

angle factor of in ACME & thread torque - If we need to consider the thread then we need to factor in the B For ACME thread - 1 an (thread angle) = 14.5 0 B = cose dn = 0.768 a Torane Torgne - 1. To = F dm , LB TP Moda - + гмс тас l π daß -MAL / 2 2 values Putting all the Ir = 362.85 lb-in

And for this torque the stress is - Zman = 362.85 x 0.525 z 1587.5 0.12