Figure 1 – The screw
Formula:
M1 = F x 6r x tg (α – υ )
Where:
M 1 = turning moment
F = applied force
r = mean radius of thread
σ = angle of friction (tan σ - u, where u is the friction coelhcient)
THE JACKSCREW
The jackscrew is used to raise heavy loads by taking advantage of the theoretical mechanical advantage (TMA) of the screw (see Fig. 2).
Figure 2 – The jackscrew
Formula:
(a) Theoretical mechanical advantage
where TMA = theoretical mechanical advantage
TMA = 1 π r/ρ
r = length of the handle (m)
ρ = pitch, or distance between corresponding points or successive threads (m)
b) Force
F = FO / 2R
where
F = force applied to the circumference of the screw
Fo = resultant force
R = length of the arm of applied force
h = pitch of the screw
Obs.: Here, we assume the absence of friction
