Why are worm gears less efficient than spur gears? Unlike spur gears which have primarily rolling contact, worm gears operate on sliding contact. The worm thread slides against the worm wheel teeth as it drives.
Friction Loss: This sliding action generates significant frictional heat, which is essentially wasted energy.
Lead Angle (γ): Efficiency (η) is mathematically linked to the lead angle and friction coefficient: η= tan(γ+ϕ)/tanγ
Smaller lead angles (common in high-ratio worm gears) result in drastically lower efficiency.
Typical Range: Single-start worms might be 40-50% efficient, while multi-start worms can reach 85-90%.