Press Fit Calculator: Elastic Pressure & Assembly Force

Published September 22, 2026 · MfgWorkbench editorial reference

Explore a simplified elastic interference fit: a solid cylindrical shaft inside a uniform thick-walled hub, with full circumferential contact. This is not a fit-selection or structural-approval tool.

Assumptions that must hold

The model assumes small elastic deformation, isotropic materials, uniform diameter, free axial strain (plane stress), and no surface roughness loss or temperature change. It excludes hollow shafts, short-edge effects, keys, split hubs, plastic deformation and nonuniform contact. Moduli are entered in GPa; interference is diametral, in micrometers.

The defaults are hypothetical isotropic material properties, not certified data for a named alloy. Use properties at the service temperature. Positive interference alone does not prove the hub or shaft stays below yield. The 0.5% interference input guard is a numerical scope limit, not a safe-design threshold.

Equations and example

With interface diameter d, hub outside diameter D, diametral interference δ, moduli Es and Eh, and Poisson ratios νs and νh, define K = (D²+d²)/(D²−d²). The elastic compatibility equation is p = δ / {d[(K+νh)/Eh + (1−νs)/Es]}. Use consistent mm and MPa units in this equation.

For d = 20 mm, D = 40 mm, δ = 0.020 mm, Es = Eh = 200,000 MPa and both Poisson ratios 0.30, contact pressure is 75 MPa. Hub bore hoop stress is Kp = 125 MPa. These stresses still need a separate material, geometry and fatigue assessment.

Force is especially sensitive to friction

Ideal sliding force F = μpπdL, and ideal friction torque T = Fd/2. With the preceding geometry, contact length 20 mm and μ = 0.10, F = 9,424.78 N and T = 94.2478 N·m. The same coefficient is used for both displayed estimates only as a simplifying input. Static and sliding friction can differ.

Assembly chamfers, lubricant, scoring, coatings, interference tolerance and thermal expansion can change the result substantially. Check minimum and maximum interference, material stresses, assembly tooling and service conditions with a qualified engineer. Do not use a calculated force as a press setup or lifting-load rating.