Changes in the standard of unified system of tolerances and fits

The unified system of tolerances and fits is a very important system that provides internationally the interchangeability of products, and is widely used in machine-building and instrument-making industries, in repair and maintenance of machinery and in other fields. The new standard 286-1:2010 of International Organization for Standardization provides an improved international system of tolerances on linear dimensions containing series of tolerances and deviations. It contains the clear indication that the system refers to the two types of dimensional features, namely a cylinder and two parallel planes. In the older version of the standard 286-1:88, to interpret the part feature dimension the rule of outer limits was applied a priori, however, in the international standard 14405-1:2010, the interpretation of dimension on the double-point measurement was established. It means that the accuracy of form deviation no longer depends on the dimension accuracy and the requirements to the form should be established separately. Now, in many cases, normalization only of the diameter tolerance is not enough to control the design and performance characteristics of the joint. Theoretically, as provided by geometrical product specifications, it is necessary to establish the requirements and determine the outer limit; as well as in some cases, it is necessary to normalize the requirements for tolerances of form, waviness and surface roughness. The article describes the changes in the terminology from the perspective of the theory of precision and interchangeability. It is concluded that all minor changes in the terms, concepts and regulations do not affect the overall construction of the unified system of tolerances and fits, but clarification of a number of old terms and introduction of new concepts take place. Most significant is the arising of new link between the standards on geometric characteristics of products based on the principle of the general construction of models of precision and common terminology. Of particular note is a bad translation of English version into Russian language. The scientists working in the theory of precision and interchangeability were not involved in the translation. Most of the newly introduced terms could be interpreted more technically-oriented and more understandable.

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