Size factor

The size factor K_S reflects non-uniformity of material properties. It depends primarily on:

• Tooth size
• Diameter of parts
• Ratio of tooth size to diameter of part
• Face width
• Area of stress pattern
• Ratio of case depth to tooth size
• Hardenability and heat treatment of materials

The size factor may be taken as unity for most gears, provided a proper choice of steel is made for the size of the part and its heat treatment and hardening process.