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.
Symmetry tolerance (Class B = up to 3 mm) is not the same as coaxiality of bores. For two bores that must align for a shaft, use a separate geometric tolerance (GD&T), not ISO 13920.
This covers the "straightness" of the beam or the "flatness" of a plate. It ensures that while the part might be the right length, it isn't "banana-shaped" or twisted. en iso 13920-bf
This post breaks down the EN ISO 13920 standard, specifically focusing on the tolerance class, to help you understand when to use it and how to apply it.
| Tolerance Class | Typical Application | Cost Impact | | :--- | :--- | :--- | | | Precision machinery, jigs, fixtures | High (requires post-weld machining) | | B (Medium) | General mechanical structures, frames, supports | Optimal (achievable with standard welding) | | C (Coarse) | Heavy construction, shipbuilding, basic frames | Low (minimal inspection) | | D/E (Very coarse) | Simple structural steel, agricultural equipment | Very low | The designation specifies a standardized set of general
: This letter assigns Tolerance Class F to all geometrical aspects, controlling the acceptable limits for straightness, flatness, and parallelism.
This refers to the tolerance for straightness, flatness, and parallelism. While linear dimensions use letters A through D, shape and position tolerances use E through H. Class F is the second-most precise level in this category (often considered "Medium" for shape). Why Use EN ISO 13920-BF? This covers the "straightness" of the beam or
By defining a "medium" standard, it balances the high cost of extreme precision with the need for stability. Application in Industry
These tolerances apply to external and internal lengths, step heights, and center distances.