19 November 2012: Gunter Effenberger

This article presents the basic standard ISO 8015 and illustrates its “umbrella function” for the entire series of GPS standards. We do not intend to discuss every single aspect of this standard but try to focus on the contents the author considers relevant for the purpose of defining specifications, especially of creating drawings, and interpreting them.

The status of ISO 8015 in the GPS concept

The introduction to ISO 8015 considers its function to be “fundamental” since it affects all other standards in the GPS matrix system including global, general and supplementary standards.

The title of this standard already implies that it contains concepts, principles and rules describing and defining fundamental and comprehensive aspects and, due their specification in an official standard, issues relevant to liability; applying this standard is an acknowledged rule of technology.

However, please note that the text of this standard only describes a single concept, no principles at all but 13 fundamental principles and 3 rules.

Fundamental assumptions for the reading of specifications on drawings

The heading of the 4^th chapter literally reflects the authors’ efforts to implement their intentions neither as a principle nor as a rule. This fact is highly regrettable since the “assumptions for the reading of drawings” are of such vital importance that we rather hoped for clear “rules for the creation of drawings”.

Assumption 1 - functional limits

• Functional limits are based on a comprehensive analysis.
• It is either an experimental or theoretical analysis.
• The known functional limits do not include any uncertainty.

Assumption 2 - tolerance limits

• The tolerance limits comply with the functional limits.

Assumption 3 - workpiece functional limit

• The workpiece whose characteristics are within the tolerance limits functions.
• The workpiece whose characteristics are not within the tolerance limits does not function.

The 2^nd assumption deserves an additional comment. The reader of the drawing has to assume that the product developer or design engineer is not addicted to safety thinking. He thus specified tolerance limits that are narrower than the functional limits. There are numerous real-life examples where the engineering department had narrowed the tolerances and in the end, this restriction led to major difficulties and incurred high process costs as soon as these characteristics were linked to process capability requirements...