Example alpha 14.5 degrees
Alpha is the angle you enter into sec(alpha). It is not defined here as half of 29 degrees.
Worked example
Lifting torque 1.2432 N·m
Lowering torque 0.5808 N·m
Efficiency 26.0138 %
T_R uses sec(alpha) plus collar torque
T_L uses the lowering fraction plus collar torque
(F × Lead) / (2 × pi × T_R) × 100
Efficiency uses the raising torque in the printed equation. A separate lowering efficiency is not calculated.
For these inputs, f x sec(alpha) is greater than tan(lambda). That is only the textbook comparison used here. It does not prove the screw will hold a real load.
Mean diameter and lead angle
Mean diameter 11.43 mm
d_m = major - pitch / 2
Lead angle 4.0461 deg
tan(lambda) = Lead / (pi × d_m)
Diameters are converted to meters so newtons give newton-meters. Alpha is the angle you enter. It is not defined as half of 29 or 30 degrees.