ISO/FDIS 2768: Why the undated reference is critical for existing drawings
The new ISO 2768 does not primarily change the tolerance values but the scope of application. For existing drawings with an undated reference, that creates a risk of interpretation.
I had the opportunity to contribute to the SNV appeal on ISO/FDIS 2768. My thanks to everyone involved and to the SNV for the constructive collaboration and strong commitment to this topic.
Through my work in Swissmem NK 1 I am close to the ISO GPS topics. At the same time, I see in practice every day what effects such changes can have on industrial companies.
The critical point is that the new edition is to be introduced as the successor of the existing ISO 2768. With undated drawing references, that is exactly the problem.
The starting point
Countless drawings exist in industry that state nothing more than "ISO 2768-m". Often without an edition date, without a clear restriction and without additional specification.
In practice to date, such references were understood very broadly. General tolerances per ISO 2768 were applied to many dimensions that were not individually toleranced on the drawing.
That was not always perfect in the sense of today's ISO GPS system, but it was established in industrial practice, understood, and applied for decades.
Practice to date
With the planned new ISO 2768, it is not primarily the numerical tolerance values that change. That is important to understand. What changes is the scope of application.
The new ISO 2768 applies only to linear and angular sizes in the sense of the ISO GPS system. Many indications that were previously covered in practice via ISO 2768 would no longer be automatically covered. That affects, for example:
- hole spacings
- step dimensions
- radii and chamfers
- broken edges
- certain geometrically relevant indications that were often handled pragmatically via ISO 2768
For new drawings this can be solved cleanly. ISO GPS can be applied correctly, specifications set unambiguously and the appropriate standards referenced deliberately. For existing drawings, however, the situation is entirely different.
Possible impact
If an existing drawing references ISO 2768 without a date, a new edition creates a considerable risk of interpretation. What was understood as toleranced in the supply chain yesterday can suddenly count as no longer specified tomorrow.
That does not lead to better products, but very probably to more queries, more internal clarifications, more discussions between design, purchasing, supplier, production and quality assurance. And in the end to costs that create no direct customer value.
In Swiss industry in particular, considerable uncertainty in applying ISO GPS is already noticeable today. Many companies are in the middle of the transformation from old drawing conventions to a clean ISO GPS application. An ISO 2768:2026 as the direct successor of the existing ISO 2768 would, in my view, increase this uncertainty considerably.
My position
This edition should not be introduced under the same standard number as the direct successor of the existing ISO 2768.
A new number, a clear transition rule or another mechanism for safely handling existing drawings would, in my view, be far better for industrial practice.
Now it remains to be seen how things proceed. As the Swiss committee, we have probably done the last thing that was still possible on this path.
