: The letter "F" represents the tolerance class for geometric characteristics such as straightness, flatness, parallelism, and perpendicularity. The standard defines four such classes for geometric tolerances, denoted E , F , G , and H , with "E" being the finest and "H" the coarsest.
A recurring question in engineering forums is whether a note like "ISO 13920-BF" is sufficient on its own. While the standard provides the tolerance values, some engineers argue for more explicit controls using datum references, especially for critical features. For complex structures, special provisions for individual dimensions may be necessary. The standard itself acknowledges that general tolerances are for dimensions without individual tolerance specifications. If a drawing includes linear and angular dimensions without individually indicated tolerances, it is considered incomplete if there is no reference to general tolerances. Therefore, including "EN ISO 13920-BF" in the title block is the correct method to complete the drawing and provide the manufacturer with the required tolerance information.
The permissible deviation (in millimeters) for linear dimensions such as lengths, widths, and heights. As the nominal dimension of the part increases, the allowable tolerance increases correspondingly. en iso 13920-bf
This refers to tolerances for straightness, flatness, and parallelism. Class F is the "intermediate" tier for these geometric features. It ensures that a welded frame is sufficiently "square" and flat for its intended use without requiring expensive post-weld machining. Why use "BF" instead of other classes? The ISO 13920 standard offers four classes for dimensions ( ) and four for shape ( are the finest (tightest) and are the coarsest. Intermediate Very Coarse Dimensions (Length/Angle) B Shape & Position F
EN ISO 13920-BF is a combined tolerance designation used in the fabrication of welded structures to specify acceptable deviations in dimensions and shape without detailing every single measurement on a technical drawing. Standard Breakdown EN ISO 13920 : The letter "F" represents the tolerance class
Class F defines limits for flatness, straightness, and parallelism. Similar to linear dimensions, these limits scale with the size of the component, ranging from mm for smaller sizes (30-120 mm) up to mm for structures larger than 20,000 mm. Benefits and Compliance
Q: How do I determine the tolerance class for my welded construction? A: The tolerance class depends on the specific application, industry, and required level of precision. Refer to the standard or consult with a qualified engineer or inspector. While the standard provides the tolerance values, some
The second letter defines tolerances for straightness, flatness, and parallelism.
While EN ISO 13920 has existed since 1996 in various forms (ISO 13920:1996), the 2023 revision introduces key updates. Compared to DIN EN ISO 13920:1996, the 2023 version has been editorially revised to align with new ISO drafting rules, and all normative references have been updated to their latest editions. The technical content, however, remains fundamentally consistent, ensuring compatibility with existing design and manufacturing practices while modernizing the document's structure.
Dimensional values under Class B change according to the nominal size of the structure. As components scale up, the standard allows for larger deviations to account for increased thermal shrinking over long weld paths. 1. Linear Dimensions