In prepared technical drawings for manufacturing, it may not always be possible to specify tolerance ranges for every dimension.
In such cases, specifying the tolerance class in which the manufacturing should be done on the technical drawing ensures that the tolerance is defined, including the lower and upper error limits, for dimensions that have not been specifically mentioned.
Although there are many international tolerance standards available, in this article, we will attempt to explain the usage of the most commonly used ISO 2768 or TS 1980-1 EN 22768 tolerance standards in Turkey and Europe.
For instance, if the tolerance note on the technical drawing is given as (ISO 2768 - m), it is interpreted that all dimensions for which tolerance values are not specified on the technical drawing should be checked according to the error allowances defined in ISO 2768 standard's medium quality class. If the measured sample falls within the error ranges defined for medium quality, the part can pass the quality inspection.
The ISO 2768 standard is a quality class standard that defines the error allowances for linear dimensions, angular dimensions, radii and chamfer dimensions, flatness and straightness, perpendicularity, symmetry, and axial runout dimensions.
ISO 2768 defines four quality classes for linear dimensions, angular dimensions, radii, and chamfer dimensions. These quality classes are referred to as Fine (f), Medium (m), Coarse (c), and Very Coarse (v), with error allowances specified in tables for each class. 'Fine' represents the highest quality, while 'Very Coarse' represents the lowest quality.
ISO 2768 defines three quality classes for flatness and straightness, perpendicularity, symmetry, and axial runout dimensions. These quality classes are denoted as H, K, and L.
Thanks to the ISO 2768 standard, you can determine the general quality classes of dimensions on your technical drawings using these tables and perform quality inspections on your manufactured samples according to these tables.
Wishing your production to run smoothly.
Source 1: General Tolerance ISO 2768 1 & 2
Source 2: TS 1980-1 EN 22768-1 - GENERAL TOLERANCES - PART: 1 - TOLERANCES FOR UNDIMENSIONED LENGTH AND ANGLE MEASUREMENTS
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