Interference for a Target Press-Fit Holding Force

Scopei = holding x 2 Do^2 / (E x (Do^2 - D^2) x pi x L x mu) -- the holding force is linear in the interference, and the interface diameter cancels between the pressure (E i / D) and the contact area (pi D L). A 25,447 lb target on a 2 in shaft, 4 in steel hub, mu 0.12, 3 in engagement wants 0.0020 in, developing 11,250 psi contact pressure and 18,750 psi hub bore stress. Enter the hub yield to flag a burst. Same-material solid-shaft model; the materials and assembly method govern.

Formula or tableinterference = holding_force x 2 Do^2 / (E x (Do^2 - D^2) x pi x length x friction); p = (E x interference / D) x (Do^2 - D^2) / (2 Do^2); hub_bore_stress = p x (Do^2 + D^2) / (Do^2 - D^2).

Source and editionLame interference-fit model (Machinery's Handbook 'Forces and Fits'; the Lame thick-cylinder equations, same-material solid shaft) solved for the interference, by name; the actual materials, surface finish, and assembly method govern.

Free accessThe Lame thick-cylinder press-fit relations are published in standard machine-design references; the target force, interface diameters, and modulus come from the fit and the material.

What governsEstimate. AHJ and licensed professional govern.

API field namestarget_holding_lb, shaft_dia_in, hub_od_in, modulus_psi, friction_coeff, engagement_in, interference_in, p_psi, hub_stress_psi

• Linear in interference the holding force is linear in the diametral interference; the interface diameter D cancelsLame thick-cylinder
• Hub stress the interference raises a hoop stress at the hub bore that must stay below yieldLame thick-cylinder
• Same material solid shaft assumes elastic same-material parts and a solid shaft; hollow or dissimilar changes the coefficientsscope of this tile