In a press fit, the shaft is compressed and the hub is expanded.
Press fits, or interference fits, are similar to pressurized cylinders in that the placement of an oversized shaft in an undersized hub results in a radial pressure at the interface.
Characteristics of Press Fits
1) The shaft is compressed and the hub is expanded.
2) There are equal and opposite pressures at the mating surfaces.
3) The relative amount of compression and expansion depends on the stiffness (elasticity and geometry) of the two pieces.
4) The sum of the compression and the expansion equals the interference introduced.
5) The critical stress location is usually the inner diameter of the hub, where max tensile hoop stress occurs.