Fits and Tolerances

摘要

'Fits and Tolerances', a very important topic of mechanical and production engineering helps in a long way towards mass manufacture of components within dimensional limits. Mass production obviously leads to economy of scale and low prices of components. Such components assemble into properly working and durable machines and household appliances within the reach of masses resulting in todays high and comfortable living standards. One can get a replacement part with the assurance that it would fit into the appliance in place of the failed part, function well and offer high durability even years after purchase. The science of fits and tolerances is not only useful for mass manufacture, but in maintenance situations too. An antifriction bearing mounted on a shaft of proper dimensional tolerance would serve for years and years. On the other hand mounting it on a shaft of even a few microns larger in diameter requires excessive force or over heating to expand the inner ring. Antifriction Bearing (AFB) so fitted lo oses part of its working clearance and fail prematurely, bringing an important machine and in turn a production process to a grinding halt. Hopefully, the treatment of the subject in this article with illustrative examples, ready reference tables and case studies would impress the need for dimensioning mating parts with appropriate tolerances. This way parts would fit to render the intended service with no time-consuming field adaptation each time, reducing maintenance downtimes significantly and promote long lives and reliability of repaired machines.