ISO 2768 standard is a creation of the International Organization for Standardization (ISO). Like for any other standard of this nature, the technical committee was the team behind this work. Other participants in this process were international organizations, governmental organizations, NGOs and other interested parties.
This standard, generally titled “General Tolerances”, consists of two parts:
- First Part: Tolerances for linear and angular dimensions without individual tolerance indications
- Second Part: Geometrical tolerances for features without individual tolerance indications
Below is a breakdown of the contents of each of these sections of the standard.
Part 1: ISO 2768-1
This part of the standard has the crucial role of simplifying drawing indications. As mentioned in the introduction, this section deals with general tolerances for angular and linear dimensions. Note that dimensions should not have individual tolerance indication.
The seven topics covered in this document are:
- Scope
- General
- Normative references
- General tolerances
- Indications on drawings
- Rejection
Part 1 applies to three dimensions as listed below:
- Angular and linear dimensions for machined assembled parts
- Angular dimensions for uniform polygons (unless there is reference to IS0 2768-2)
- Linear dimensions
Dimensions not covered in this part of the standard are:
- auxiliary dimensions
- angular and linear dimensions referred by other standards
- theoretically exact dimensions
Under the general section, this part of the standard reiterates the importance of workshop accuracy in determining tolerance class. The section also explains when reference should be made to the standard and when to revert to International Standards.
Normative references are formal parts of the standard. By the time of publishing this standard, the two International Standards recognized by ISO and IEC were IS0 8015 and ISO 2768-2.
For general tolerances for angular and linear dimensions, the document provides some guidelines. You can find these degree/ millimeter values in Tables 1, 2 and 3 of the standard.
You will find Annex A of the document very useful. All sections of the annex (A1-14) mostly expound on general tolerances, with A3 listing the following advantages of general tolerances:
- more effective communication through drawings
- time savings because lengthy tolerance calculations are unnecessary
- inspection levels
- more effective order negotiation by supply engineers
Part 2: ISO 2768-2
Similar to Part 1, this separate document of the standard has several topics as listed below:
- Scope
- General
- Normative References
- Definitions
- General geometrical tolerances
- Indications on drawings
- Rejection
Part 2 of the standard is concerned with drawing features that are devoid of individual indication. It mainly covers features that arise when material is removed from a component. Tables are also included to describe geometrical tolerances for several single features such as flatness & straightness, cylindricity and circularity. Related features covered in this part of the standard are parallelism, perpendicularity, coaxiality and circular run-out.
The document also comes with Annex A and Annex B to provide further information. Annex B provides important further information on General Geometrical Tolerances, Circularity, Cylindrity and Parallelism. Others are Symmetry and Example of Drawing.
As you plan to get hold of this part of the standard, you may want to look at equivalents and identical standards. One of near identical standards is the PN EN 22768-2 of 1999. The Polish Committee for Standardization published this document that focuses on limits and fits. An equivalent of the document is the BS EN 22768-2:1993 that was published by the British Standards Institution.
Examples of other equivalent standards are:
- DIN ISO 2768-2- German Institute for Standardization (Deutsches Institut für Normung)
- JIS B 0419:1991- Japanese Standards Association
- UNI ISO 2768-2:1991-Italian Standards
- NS ISO 2768-2 Ed. 1 (1993)- Norwegian Standards (Norges Standardiseringsforbund)
- GB/T 1184-1996- Standardization Administration of China
ISO 2768 Certification
When two parts of a mechanical system need to merge to fulfil a certain role, correct tolerancing is of utmost importance to ensure a good mechanical design. Remember that each component bears features with a geometrical shape and size. Deviations related to geometrical characteristics and size need to have a limit to maintain proper function of the component. Therefore, complete tolerancing is necessary on the drawing. In other words, judgment or any form of guesswork should not be part of inspection or workshop processes. Applying general tolerances is the best way of ensuring this condition is met.
Apart from enhancing technology standardization, ISO registration builds customer trust and grows your business. Order rejection should be outdated with this kind of flaw-preventing standard. You have probably seen some products with ISO quality marks. You can attain this through ISO 2768 certification. Find out from your local regulatory agency how you can get started.
