For moderate speed of mating gears, what is the ideal ratio of contact?

For moderate speed applications involving mating gears, the ideal ratio of contact is indeed between 1.25 and 4. This range is broadly recommended because it helps ensure that the gears maintain adequate contact under moderate loads, which in turn aids in reducing wear and ensuring the longevity of the gear teeth.

When gears operate within this contact ratio, they can effectively distribute the load across multiple teeth, which minimizes stress concentration on any single tooth. This is particularly important in moderate-speed applications where fluctuating loads are common. A contact ratio in this range also helps to ensure smoother engagement and disengagement of gear teeth, which helps in reducing noise and vibration during operation.

Gears generally benefit from a higher contact ratio as it leads to a more efficient power transmission and lower risk of failure, particularly in instances where alignment may not be perfect or where there is slight deformation due to wear or thermal expansion. The specified range is a practical guideline that balances performance, durability, and manufacturing considerations for most moderate-speed gear applications.