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The tightness of fit is controlled by amount of interference; the allowance (planned difference from nominal size). Formulas exist [2] to compute allowance that will result in various strengths of fit such as loose fit, light interference fit, and interference fit. The value of the allowance depends on which material is being used, how big the ...
Engineering fits are generally used as part of geometric dimensioning and tolerancing when a part or assembly is designed. In engineering terms, the "fit" is the clearance between two mating parts, and the size of this clearance determines whether the parts can, at one end of the spectrum, move or rotate independently from each other or, at the other end, are temporarily or permanently joined.
Outer dimensions (such as the diameter of a railroad car's axle) may be cut intentionally oversize, or inner dimensions (such as the diameter of the railroad car's wheel hub) may be cut intentionally undersize, to allow for an interference fit (press fit). A part may be cast intentionally too big when it is desired to later machine the surface.
In mechanical engineering, limits and fits are a set of rules regarding the dimensions and tolerances of mating machined parts if they are to achieve the desired ease of assembly, and security after assembly - sliding fit, interference fit, rotating fit, non-sliding fit, loose fit, etc.
Shrink-fitting is a technique in which an interference fit is achieved by a relative size change after assembly. This is usually achieved by heating or cooling one component before assembly and allowing it to return to the ambient temperature after assembly, employing the phenomenon of thermal expansion to make a joint.
An interference fit ensures the device moves in perfect step with the crankshaft. It is essential on engines with long crankshafts (such as straight-six or straight-eight engines) and V8 engines with cross plane cranks, or V6 and straight-three engines with uneven firing order.
Interference of measurement distributions to determine fit of parts. Mechanical parts are usually designed to fit precisely together. For example, if a shaft is designed to have a "sliding fit" in a hole, the shaft must be a little smaller than the hole. (Traditional tolerances may suggest that all dimensions fall within those intended tolerances.
In general, a tight fit is desired, to the extent of crimping the bullet into the case. In straight-walled rimless cases, such as the .45 ACP, an aggressive crimp is not possible, since the case is held in the chamber by the mouth of the case, but sizing the case to allow a tight interference fit with the bullet, can give the desired result.