Verified - Iso 13920 Bf

A welded bracket with a 500 mm width under BF tolerance would allow ±2.0 mm deviation. 2. Angular Dimensions (Class B) Angular tolerances apply to angles between welded parts, bevel angles, or non-right-angle joints.

| Shorter leg length (mm) | Permitted deviation (± minutes or mm/m) | |------------------------|------------------------------------------| | up to 400 | ±15' (0.25°) or 4 mm/m | | >400 to 1000 | ±10' (0.17°) or 3 mm/m | | >1000 to 2000 | ±7.5' (0.125°) or 2 mm/m | | >2000 to 4000 | ±5' (0.083°) or 1.5 mm/m | | >4000 | ±5' (0.083°) or 1 mm/m |

| Symbol | Meaning | Applies to | |--------|---------|-------------| | | Fine class | Angular dimensions, straightness, flatness | | F | Fine class | Linear dimensions | iso 13920 bf

| Nominal size range (mm) | Permitted deviation (± mm) | |------------------------|----------------------------| | up to 30 | 0.5 | | >30 to 120 | 1.0 | | >120 to 400 | 1.5 | | >400 to 1000 | 2.0 | | >1000 to 2000 | 2.5 | | >2000 to 4000 | 3.5 | | >4000 to 8000 | 5.0 | | >8000 to 12000 | 6.5 |

A 1500 mm long beam must not bow or warp more than 1.5 mm over its total length. How to Specify ISO 13920 BF on a Drawing The correct drawing notation per ISO 13920 is: ISO 13920 – BF Or fully detailed: General tolerances: ISO 13920 – Linear class F, Angular class B Avoid ambiguous notations like "Tolerance BF" without referencing ISO 13920. BF vs Other Common Tolerance Classes | Class | Linear (mm over 1m) | Angular (over 1m) | Typical application | |-------|--------------------|-------------------|----------------------| | A (Very fine) | ±1.0 | ±2 mm/m | Precision machinery, tooling | | BF (Fine) | ±2.0 | ±3 mm/m | General machine parts, moderate fit | | C (Medium) | ±3.5 | ±4.5 mm/m | Structural steel, platforms | | D (Coarse) | ±5.5 | ±6 mm/m | Heavy frames, agricultural equipment | A welded bracket with a 500 mm width

A 300 mm tall vertical post welded to a base plate must be perpendicular within ±15 arc-minutes (approx. ±1.3 mm measured at the top). 3. Straightness & Flatness (Class B) These apply to individual plates, beams, or fabricated faces.

Introduction In welding fabrication, achieving perfect dimensions is often impractical and cost-prohibitive. ISO 13920 is the international standard that specifies general tolerances for linear and angular dimensions, as well as for straightness and flatness, of welded structures. | Shorter leg length (mm) | Permitted deviation

| Nominal length/width (mm) | Permitted deviation (mm) | |--------------------------|--------------------------| | up to 400 | 0.5 | | >400 to 1000 | 1.0 | | >1000 to 2000 | 1.5 | | >2000 to 4000 | 2.0 | | >4000 to 8000 | 3.0 | | >8000 to 12000 | 4.0 |