Limits and Fits Mechanical Calculator

Designers often calculate and design a shaft-hole fit. This problem influences the properties of the final product and its price of manufacturing. Use the adaptable interface in Design Accelerator to design the ideal fit.

Limits and Fits are used to define tolerances for mating parts. Limits are most commonly used for cylindrical holes and shafts, but they can be used for any parts that fit together regardless of the geometry.

A limit is the upper and lower tolerance for a shaft or hole.

A fit consists of a pair of limits. There are three categories: clearance, transitional, and interference.

Clearance

• The largest shaft is smaller than the smallest hole.
• Large clearances are for relative motion.
  • A shaft in a bushing
• Small clearances are for a precise fit that can be assembled without tools.
  • A shaft in a bushing

Transitional

• Tolerance zones overlap.
  • The largest shaft is larger than the smallest hole (interference).
  • The smallest shaft is smaller than the largest hole (clearance).
• Precise location that may require tools to assemble.
  • Dowel pins in tooling to locate parts

Interference

• The smallest shaft is larger than the largest hole.
• Precise location that requires tools to assemble.
• Parts do not come apart or move during use.
• May require heating or cooling to assemble parts.
  • A gear on a shaft