Note: Total flatness or straightness deviations are evaluated across the entire designated surface or section segment indicated on the technical drawing. Workshop Best Practices for Meeting BF Tolerances
This standard is a cornerstone of modern fabrication, bridging the gap between the theoretical perfection of a digital model and the practical reality of a workshop. Whether you are building a bridge, a vehicle, or a machine frame, understanding and correctly applying it is fundamental to your success.
Source: DIN EN ISO 13920 Standard.
The designation specifies a standardized set of general manufacturing tolerances for welded constructions , combining "Class B" accuracy for linear/angular dimensions with "Class F" accuracy for structural shape and position. en iso 13920-bf
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Mastering EN ISO 13920-BF: The Blueprint for Welded Construction Tolerances
Welding naturally involves extreme heat. As metal melts and cools down, it expands and shrinks, which causes the metal components to warp, twist, or shift out of line. Because some amount of variation is completely unavoidable, manufacturers rely on the ISO 13920 standard to specify exactly how much a welded structure can deviate from its original design. The standard breaks tolerances into two main areas: : This includes lengths, widths, and angles. Source: DIN EN ISO 13920 Standard
Source: DIN EN ISO 13920 Standard.
Adopting EN ISO 13920 requires a systematic approach that integrates the standard into design, fabrication, inspection, and contractual agreements.
To maintain compliance, manufacturing teams should implement several engineering best practices: This link or copies made by others cannot be deleted
This is critical for base plates and mounting surfaces.
EN ISO 13920-BF applies to various industries, including:
If you saw "EN ISO 13920-BF" on a , it is likely a typo or shorthand used by a designer. The correct standard for edge preparations is ISO 9692-1 (or EN ISO 9692-1). EN ISO 13920 only covers general tolerances (linear, angular, flatness, etc.), not weld preparation shapes.
According to the EN ISO 13920 tables , the allowed deviation changes depending on how large the section is: : Allowed variation of Sizes over 30 mm up to 120 mm : Allowed variation of Sizes over 120 mm up to 400 mm : Allowed variation of Sizes over 400 mm up to 1000 mm : Allowed variation of Shape and Position (Class F)