Iso 13920-bf | En
If you saw "EN ISO 13920-BF" on a drawing or welding symbol, 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.
If you encounter EN ISO 13920-BF:
Understanding these codes ensures that fabricators aren't over-engineering parts and that clients receive products that fit their structural requirements without unnecessary expense.
Have you encountered confusing tolerance codes on drawings? Share your experiences in the comments below!
#Engineering #Welding #ISOStandards #Fabrication #QualityControl
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 international standard for "General tolerances for welded constructions". : Refers to the tolerance class for linear and angular dimensions en iso 13920-bf
(lengths and angles). Class B is generally considered "medium" or standard workshop accuracy. : Refers to the tolerance class for shape and position
(straightness, flatness, and parallelism). Class F is often used for structural assemblies where moderate precision is required. Summary of Tolerances
The exact deviation allowed depends on the nominal size of the component. Larger components are permitted greater absolute deviations than smaller ones. Linear Dimensions (Class B)
Class B specifies the following typical tolerances based on the length ( ) of the part: plus or minus 1.0 plus or minus 1.0 plus or minus 3.0 plus or minus 6.0 (Tolerances continue to scale for larger structures) Shape and Position (Class F)
Class F governs how much a part can warp or sit out of alignment (straightness, flatness, and parallelism): : Max deviation of : Max deviation of : Max deviation of Why This is Used Using a general tolerance like EN ISO 13920-BF
simplifies technical drawings by removing the need for hundreds of individual plus or minus If you saw "EN ISO 13920-BF" on a
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
of the different tolerance classes (A, B, C, and D) to see which fits your project best? EN ISO 13920
This review is designed for engineering, quality assurance, and drafting departments to determine if this standard is suitable for a given project.
If you are a design engineer, using this standard correctly will save your workshop hours of confusion.
Incorrect usage:
"USE STANDARD WELDING TOLERANCES"
Correct usage (per ISO guidelines):
"GENERAL TOLERANCES: EN ISO 13920 – B (MEDIUM). ALL OTHER DIMENSIONS ± 0.5 mm"
Advanced usage (with modifiers): If your "BF" actually means "B + Filter," you might add:
"EN ISO 13920-B, BUT FLATNESS OF MOUNTING FACE F1 (reference surface) TO BE HELD TO CLASS A (±0.5 mm)"
This notation tells the welder: "Use Class B for most features, but tighten up this specific surface."