Frictionfit

Frictionfit, also known as an interference or press fit, refers to a joint design in which two parts are held together primarily by friction between their mating surfaces. The connection transmits torque or axial loads without the need for fasteners such as bolts or pins. Frictionfit joints are common in mechanical assemblies where a permanent or semi-permanent connection is desirable.

The mechanism relies on a deliberate interference between components. Typically, a slightly oversized shaft or a slightly undersized hole is pressed or hammered into place so that clamping forces exceed the static friction and any potential movement is resisted by the contact pressure. Assembly may involve cold fitting, heating one member or cooling the other, and the surface finishes and tolerances are chosen to develop an appropriate frictional force. Lubrication is usually minimized at the contact to maximize friction, though care must be taken to avoid galling in some materials.

Design considerations for frictionfit include selecting appropriate interference levels, material pairings, and surface finishes. Tolerances are tailored so that the interference is reliable across manufacturing variations. Surface finish quality, hardness, and the presence of a oxide or coating can influence friction. Temperature sensitivity is important, as thermal expansion can alter the interference and load transfer. The joints are typically not designed for frequent disassembly.

Common applications include hubs on shafts, gears, pulleys, bushings, and cylindrical sleeves in power transmission or machine assemblies. Advantages are high torque transmission without fasteners and compact assembly; disadvantages include difficulty of disassembly, potential for material yield or creep under load, and sensitivity to temperature changes.