A common disadvantage of helical gears is the presence of which axial force?

• A. Side thrust
• B. Pitting
• C. Wear
• D. Noise

Answer: (A)

When teeth are cut on a helix, the contact force between gears isn’t directed purely perpendicular to the gear faces. Instead, it has a component along the gear axis. That axial component is a thrust, or axial thrust, on the shaft. Because of the helix angle, this thrust increases with both the angle and the transmitted load, so larger helices push harder along the shaft. This is a disadvantage because it adds a longitudinal load that bearings and housings must support, often requiring thrust bearings or other restraints to keep everything aligned. Pitting, wear, and noise are concerns in gear operation too, but they aren’t the axial force produced by the angled teeth.