Interference fit

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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.

A press fit is also required to mount wheels on an axle to make a wheel set.

How Much?

The following appeared in Live Steam Magazine, September 1985:

The subject of interference fits was covered more completely in my series on "Strength of Materials" which ran in Live Steam between February 1984 and January 1985. The pertinent issue was Part XI, December 1984. This demonstrated that an interference fit greater than 1/2 thousandths of an inch per inch is not needed. It also showed that an axle 3/4 inch thick with an interference of 1/2 thousandths of an inch requires an assembly and disassembly force of 3,000 pounds. Surely this is more than adequate.
If there is any problem due to skill or equipment of machining the axle and hub to an interference of approximately 1/2 thousandths, an easy solution is to produce a close fit and assemble the wheel and axle with Loctite. This produces a strong and durable assembly and the alignment of the wheel on the axle is no problem.
Richard E. Evans, PhD
18955 W.W. 288th St.
Biscayne Drive
Homestead, Florida 33030

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