Standard work for technical mechanics
DIN 2768 was the standard for general tolerances and tolerances for linear and angular dimensions until mid-2021. This standard, which has been in force since 1991, ensures that the same tolerances are used for certain conditions. This considerably simplifies the production of series parts. In addition, this standardization enables the production of suitable measuring and testing equipment. However, the standard, which is now over 30 years old, is becoming less and less applicable to modern technical challenges. It has therefore been replaced by DIN EN ISO 22081.
Resistance from users
The outstanding feature of DIN 2786 was the universally valid tolerance tables. They provided a reliable framework that designers and workers throughout Europe could use as a guide. These tables are missing in the new standard. Instead, determining the tolerance is now the sole responsibility of the designer. There is resistance to this and many companies are still working with DIN ISO 2768.
Application of ISO 2768
The particular convenience of DIN ISO 2768 was that, when using its general tolerances, the entire tolerance information could be omitted from a drawing. A reference in the title block “Iso 2768 mK” or “ISO 2768 M” is sufficient. In this case, any user familiar with the standard knows what the components should look like and no longer needs to specify them separately – for example “fit H7”. The new standard does away with this advantage. This makes the drawings more dense and increases the effort involved.
ISO 2768 tolerance tables
At the heart of the standard are its tolerance tables. It specifies tolerances for three types of dimension:
- Length dimensions
- Diameter
- Angular dimensions
The tolerance is specified in four classes:
- fine (f)
- medium (m)
- coarse (g)
- very coarse (g)
In the fine gradation, the tolerance range is +- 0.05 mm or 5/100. In the coarse gradation, it is only +- 5/10.
For the angles, the fine gradation is +- 1°. For a very coarse grading, a tolerance of +-3° is sufficient, depending on the leg length.
Which tolerance for which application?
The tolerance to be applied must be determined from the following parameters:
- Technical manufacturability
- Technical necessity
- Economic efficiency
- additional factors.
A tolerance must be technically feasible. It is possible to grind steel to micrometer accuracy, but this is not possible with wood. The technical necessity is reflected in the application. A car engine or a clockwork require much lower tolerances than a switch cabinet housing. Additional factors such as thermal expansion, lubricity or abrasion resistance also influence the tolerance determination. Finally, the production of the tolerance in accordance with DIN ISO 2768 must also be economically viable. Basically, the tighter the tolerance is selected, the more expensive it is to achieve it.
ISO 2768 MK – Farewell or return?
The last word has not yet been spoken on the abolition of DIN ISO 2768. The use of its tolerance tables is still common practice. It is therefore not unlikely that it will come back into force.
