Press fit (interference fit) calculator

How the contact pressure arises

Effective interference Uw = U − roughness loss　　QA = d / DA　　QI = di / d
p = Uw ÷ ( d × [ (1/EA)·((1+QA²)/(1−QA²) + νA) + (1/EI)·((1+QI²)/(1−QI²) − νI) ] )
Press / holding force　F = μ × p × π × d × L　　Torque　T = μ × p × π × d² × L ÷ 2
Hub bore hoop stress　σt = p × (1+QA²)/(1−QA²)　　Pressure at which the hub starts to yield (DIN 7190)　pPA = (1−QA²)/√3 × ReA
Shrink-fit temperature rise　Δϑ = (Umax + Us) ÷ (αA × d)

• The interference range comes from the hole and shaft classes, using the same standard values as the fits calculator. If the combination is not a true interference fit (minimum interference ≤ 0), no holding force or torque can be guaranteed.
• Surface peaks flatten when the parts are joined, so the effective interference is smaller than the measured one. Sources differ on how much to subtract; DIN 7190 changed the factor from 0.8 to 0.4 in its 2017 edition.
• Sources judge hub yielding in three ways (maximum principal stress, DIN’s √3, or maximum shear stress with a factor of 2). Here the DIN 7190 pressure at which plastic deformation starts is compared with the pressure at maximum interference.
• Values for press fits assume about 24 hours before loading (DIN 7190). Allow a margin of several times the calculated force for presses and fixtures (bearing makers ask for 5–6 times).
• Rolling bearing rings are thin and hardened, so take interference and heating temperature from the bearing maker (heat to 120 °C at most).

Related calculators

ISO fits (limit deviations, clearance, interference) · Thermal expansion · Surface roughness