Self-locking & overhauling of screw

$T =W\tan(\phi-\alpha).\frac{dm}{2}$ --------------(1)

Where $T= \text{torque required to lower the screw}$

$\phi$ = angle of friction

$\alpha$ = helix angle

$W = \text{load to be lifted}$

$dm = \text{mean diameter}$

The torque required to lower the screw is given in equation (1). In equation (1) …