En Iso 13920-bf Exclusive Site

This notation tells the welder: "Use Class B for most features, but tighten up this specific surface."

This class governs tolerances for straightness, flatness, and parallelism. Key Tolerance Categories ISO 13920 standard

: Controls Form and Position . It sets limits for structural straightness, flatness, and parallelism. Class F represents an intermediate workshop baseline that prevents twisting, bending, or bowing across wide plates and profiles. Core Dimensional Tolerances (Class B)

: Designers do not have to write down tolerances for every joint. They simply place "EN ISO 13920-BF" in the title block. en iso 13920-bf

Here is the breakdown:

If your "BF" actually means "B + Filter," you might add:

EN ISO 13920 is a European standard titled, "Welding — General tolerances for welded constructions — Dimensions for lengths and angles — Shape and position" . It is the European adoption of the international standard ISO 13920:2023, having been approved by CEN (European Committee for Standardization) without any modification. This standard is a critical tool in the manufacturing and engineering industries, as it specifies general tolerances for all welded structures, including weldments, welding assemblies, and other fabricated constructions. This notation tells the welder: "Use Class B

in a title block, the designer is giving the workshop a roadmap for accuracy. Here is the breakdown: The Scope:

These tolerances apply to external and internal lengths, step heights, and center distances.

Understanding EN ISO 13920-BF: General Tolerances for Welded Constructions Class F represents an intermediate workshop baseline that

This is the "Medium" class for lengths and angles. It defines the allowable deviation for measurements like the length of a beam or the degree of an angle.

Need the official document? Always refer to the latest version of ISO 13920:2023 (or EN ISO 13920) for legally binding figures. This article provides practical guidance based on the standard, but consult the original text for critical applications.

Larger parts receive broader tolerance bands because thermal distortion compounds over longer spans: Nominal Size Range ( Class B Permissible Deviation ( ±1plus or minus 1 Over 30 to 120 ±1plus or minus 1 Over 120 to 400 ±2plus or minus 2 Over 400 to 1000 ±3plus or minus 3 Over 1000 to 2000 ±4plus or minus 4 Over 2000 to 4000 ±6plus or minus 6 Over 4000 to 8000 ±8plus or minus 8 Over 8000 to 12000 ±10plus or minus 10 Over 12000 to 16000 ±12plus or minus 12 Over 16000 to 20000 ±14plus or minus 14 Over 20000 ±16plus or minus 16 2. Angular Dimensions

The most straightforward implementation is to add a note to the drawing's title block, such as . This clearly defines the baseline expectation for all dimensions not otherwise specified, removing ambiguity.

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