The suffix tells the manufacturer exactly which tolerance "bracket" to use for different types of measurements:
±15 minutes (approx. ±4.5 mm per meter) Over 1000 mm: ±10 minutes (approx. ±3 mm per meter) Class F: Straightness, Flatness, and Parallelism Tolerances
(titled “Welding — General tolerances for welded constructions — Dimensions for lengths and angles; shape and position”) specifies general tolerances, permissible deviations and requirements for weldments' dimensions, shapes and positions when no specific tolerances are given in contract documents.
Q: Can EN ISO 13920-BF be used for non-welded constructions? A: No, the standard is specifically designed for welded constructions and parts. Other standards may apply to non-welded constructions.
The designation EN ISO 13920-BF refers to a specific combination of tolerance classes for welded constructions. It is a standard shorthand used in engineering drawings to define acceptable variations in dimensions without needing to label every single part. Breaking Down "BF"
between functional accuracy and manufacturing cost. It requires skilled welders and decent fixturing but does not mandate expensive post-weld heat treatment or machining.
| Wrong usage | Correction | |-------------|-------------| | "EN ISO 13920-BF" as tolerance class | Use C/D/E/F only. BF is weld prep code. | | Assuming BF means both tolerance and prep | Split into two references: ISO 13920 for tolerances + ISO 9692-1 for BF | | Using Class B | Not defined – switch to Class C if fine needed |
Its primary purpose is to answer the ever-present question on the workshop floor: "The drawing doesn't specify a tolerance; how should we measure this?". The standard provides a universal, agreed-upon answer, ensuring that a part designed in one country can be consistently fabricated in another.
Understanding EN ISO 13920-BF: A Guide to Welding Tolerances
In the context of EN ISO 13920, is not a tolerance class from the standard itself. Instead, it appears in welding symbols or technical notes to denote a specific weld preparation shape – typically Backing run with Flat face or Backing + Flat .