Tolerances and landings

Any part size may vary within certain limits. If it is a control handle, then the deviation of its dimensions, for example, length, even if it exceeds the permissible value, will not disrupt the operation of the machine. It is another matter if it is a sliding bearing. It is used for both rotational and translational motion. The sleeve bearing is a sleeve made of antifriction material, which is fixed in the housing. The shaft either rotates in the bushing or moves in it, however sometimes the bushing with the housing moves along the shaft.

In the mating parts, a distinction is made between female and male surfaces.

Details should not just fit into one another, but with the provision of the specified connection conditions.

Landings, depending on the relative position of the hole and shaft tolerance fields, can be: with a gap, with an interference fit and transitional, when both a gap and an interference fit are possible.

In the shaft system, the limiting dimensions of the shaft remain constant, and the fit is achieved by changing the limiting dimensions of the hole. However, the shaft system has somewhat limited applications. Conversely, the hole system is widely used in mechanical engineering, since ensuring a fit due to shaft deflection implies simpler and more accessible technological processes. There are industries in which a shaft system is needed - motor building and bearing manufacturing. You receive a finished rolling bearing. Its seating surfaces are usually of high hardness and final dimensions. It is clear that in order to obtain a bearing fit, for example, into a housing, it is only necessary to modify the hole, and this is the shaft system.

The characteristics of the most commonly used landings are as follows. It must be clearly understood that the nature of the fit, that is, the nature of the connection of two parts, depends on the size of the gap between the parts. If the gap is on the order of 6-12 microns or more, the parts are assembled without effort; with smaller gaps, a hammer is already required. If there is no gap, and this may be when the diameter of the shaft is greater than the diameter of the hole, then in this case, when assembling or disassembling with a hammer, it is no longer possible to do it, a press or a screw puller is needed.