Page 123 - Tribology in Machine Design

Friction, lubrication and wear in lower kinematic pairs \ 09

must be remembered that the use of a single lever will give rise to side
friction due to the tilting action of the screw, unless the load is supported
laterally. For a single-start square thread of pitch, p, and diameter, d,

depth of thread = |p
so

taking into account that L = Wd

alternatively

4.4. Friction in screws The analogy between a screw thread and the inclined plane applies equally
with a triangular thread to a thread with a triangular cross-section. Figure 4.15 shows the section of
a V-thread working in a fixed nut under an axial thrust load W. In the figure
a=the helix angle at mean radius, r
t// a = the semi-angle of the thread measured on a section through
the axis of the screw,
i// n = the semi-angle on a normal section perpendicular to the helix,
</> = the true angle of friction, where /= tan </>.