En — Iso 13920-bf [best]
| Nominal Size (mm) | Permitted Flatness Deviation (Class B) | | :--- | :--- | | Up to 120 | 1 mm | | 120 to 400 | 1.5 mm | | 400 to 1,000 | 2 mm | | 1,000 to 2,000 | 2.5 mm | | 2,000 to 4,000 | 3 mm | | 4,000 to 8,000 | 4 mm | | > 8,000 | 5 mm |
Understanding these codes ensures that fabricators aren't over-engineering parts and that clients receive products that fit their structural requirements without unnecessary expense.
For linear measurements, Class B dictates the following permissible deviations: ±1 mm Over 30 mm to 120 mm: ±1 mm Over 120 mm to 400 mm: ±2 mm Over 400 mm to 1000 mm: ±3 mm Over 1000 mm to 2000 mm: ±4 mm Over 2000 mm to 4000 mm: ±6 mm Over 4000 mm to 8000 mm: ±8 mm Over 8000 mm to 12000 mm: ±10 mm Over 12000 mm to 16000 mm: ±12 mm Over 16000 mm to 20000 mm: ±14 mm Over 20000 mm: ±16 mm Angular Dimensions
If you need me to:
A good default recommendation for many industrial fabrications is the balanced combination, which aligns with the BF in this article.
). The letters move sequentially from the tightest, most precise limits to the loosest. Linear and Angular Dimensions (Class B)
: The international standard for general tolerances of welded structures, covering lengths, angles, shape, and position. en iso 13920-bf
Angular deviations are calculated using the length of the of the angle as the baseline: Length of Shorter Leg ( Class B Permissible Deviation (Degrees & Minutes) Permissible Deviation ( Up to 400 ±20′plus or minus 20 prime ±6plus or minus 6 Over 400 to 1000 ±15′plus or minus 15 prime ±4.5plus or minus 4.5 Over 1000 ±10′plus or minus 10 prime ±3plus or minus 3 Class F: Shape and Position Tolerances
The code is split into two distinct parts that cover different geometric features: B (Linear and Angular Dimensions):
"USE STANDARD WELDING TOLERANCES"
Angles are notoriously difficult to maintain in welding due to distortion.
The feature is a combined designation for general tolerances in welded constructions. It specifies an accuracy level for both dimensional and geometric variations on technical drawings. The designation breaks down as follows: