The standard covers the following aspects:
Specifying tolerances that are too tight (Class A or C) when they aren't structurally necessary drives up fabrication costs significantly. ISO 13920-B (specifically Class BD) offers the best balance between quality and cost-efficiency.
is a specific technical designation used in manufacturing to define the general tolerances of a welded structure. When a technical drawing features this code, it means the weldment must meet two distinct criteria from the ISO 13920 standard:
For Class , the tolerances for common geometric features are defined. The value shown is the permitted deviation based on the length of the measured feature.
For linear dimensions (length, width, spacing), the deviations are roughly for small dimensions, scaling up based on the nominal size. en iso 13920-bf
This article will serve as a definitive guide to everything you need to know about the EN ISO 13920-BF standard, from its fundamental structure to its practical application.
callouts. It ensures that different fabrication shops produce parts to a consistent quality level, reducing the risk of components not fitting together during final assembly. comparison table
Specifying is a clear signal to the fabrication floor: "Build this with standard professional care." It eliminates the need for individual tolerance notes on every single weld, streamlining the design process and ensuring that everyone from the engineer to the quality inspector is on the same page regarding what "good enough" looks like.
In the ISO 13920 coding system, the second letter regarding geometrical tolerances is either C (Fine) or D (Medium). There is no "F" class for geometry. When a technical drawing features this code, it
In the world of metal fabrication, precision is relative. Achieving surgical accuracy on a massive steel girder is neither practical nor cost-effective. This is where comes into play. It provides a standardized framework for general tolerances in welded structures, ensuring that parts fit together without requiring the impossible level of precision typically reserved for machined components.
The main criterion for selecting a particular tolerance class is based on the functional requirements that must be met for the structure to perform as intended.
: Eliminates the need to add individual tolerance limits to every single dimension, keeping technical prints clean and legible.
Therefore, a callout of indicates that a workshop must meet medium precision constraints across all dimensional, angular, and geometric orientations. Linear Dimension Tolerances (Class B) This article will serve as a definitive guide
EN ISO 13920-BF is frequently cited in technical drawings and specifications for: Structural steel frames. Bridge construction components. Machinery baseplates. Pressure vessel supports.
This article explores what EN ISO 13920-BF entails, its classifications, and why it is critical for quality control in manufacturing. What is EN ISO 13920-BF?
To make this standard useful, we must look at the specific numerical allowances it grants. All tolerance tables in the standard are based on the "nominal dimension," which in the case of a length is the measured size, and for parallelism, it's the length of the shorter surface being measured.
Note: If the drawing explicitly writes "BF", you must clarify with the client. However, standard-compliant codes are: .
The chosen class for shape and position . It governs characteristics like straightness, flatness, and parallelism across the welded framework. The positional classes range from E (Fine) through H (Very Coarse), leaving Class F as the standard "medium" benchmark. Class B: Dimensional Tolerances (Linear & Angular)