Cylinder Pin Bolt Press Fit Equations and Calculator

An interference fit, also known as a press fit or friction fit, is a fastening between two parts which is achieved by friction after the parts are pushed together, rather than by any other means of fastening.

An interference fit is generally achieved by shaping the two mating parts so that one or the other, or both, slightly deviate in size from the nominal dimension. The word interference refers to the fact that one part slightly interferes with the space that the other is taking up.

For example, a shaft may be ground slightly oversize and the hole in the bearing (through which it is going to pass with an interference fit) may be ground slightly undersized. When the shaft is pressed into the bearing, the two parts interfere with each other's occupation of space. The result is that both parts elastically deform slightly to fit together creating an extremely high force which results in extremely high friction between the parts — so high that even large amounts of torque cannot turn one of them relative to the other; they are locked together and turn in unison.

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(1) Inner Body Poisson Radial Displacement

(3) Outer Body Radial Displacement Caused by Rotation

(4) Inner Body Radial Displacement Caused by Rotation

(5) Interface Pressure as a result of Diametrical Interference

For the Outer Body Subjected to Internal Pressure, Axial Force, Torque, and Rotation.

(6) Radial Displacement of the inner Surface Caused by Internal Pressure.

(7) Radial Stress Caused by internal Pressure

(8) Circumferential Stress Caused by Axial Force

(9) Axial Stress Caused by Torque

(10) Shear Stress Caused by Torque

(11) Circumferential Centrifugal Stress at the Inner Surface

(12) Von Mises Stress at the Inner Surface

For the Inner Body Subjected to External Pressure , Axial Force, torque and Rotation

(13) The Radial Displacement Caused by External Pressure

(14) Radial Stress Caused by External Pressure

(15) Circumferential Stress Caused by External Pressure

(16) Axial Stress Caused by Axial Force

(17) Shear Stress Caused by Axial Force

(18) Circumferential Centrifugal Stress at the outer Surface

(19) Von Mises Stress at the outer Surface

Ideal Case

Worst Case for Loose Fit:

Joint may not be able to transmit desired force or torque

Worst Case for Tight Fit:

Yield stress may be exceeded and outer body may rupture

Open Press Fit Design Calculator
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Webpage Contribution: Santhosh Mallala, Hyderabad, TG India

References: Slocum, A.H.Precision Machine Design, 1995, Society of Manufacturing Engineers, Dearborn Published by Prentice Hall, 1992.inee

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