Overview
ISO 13912:2017 - Structural timber - Machine strength grading - Basic principles defines the fundamental principles, rules and quality procedures for machine sorting (strength grading) of sawn timber for structural use. Applicable to conventional bending-type strength-grading machines and to modern systems that grade by other measured properties, the standard sets minimum, flexible requirements so different machine types and processes can be defined, controlled and documented for reliable structural performance.
Key topics and technical requirements
- Scope and applicability: Applies to machine strength-grading operations used to classify sawn timber into structural grades.
- Machine concepts: Describes the grading machine and scanner roles, scanned length vs unscanned end portions, and processing of recorded data into grading criteria (e.g., low-point parameter, predicted strength).
- Input control: Specifies identification and periodic checks of resource parameters (species, silviculture, log source/size, cutting pattern) and sawn timber parameters (condition, moisture content).
- Quality procedures: Requires qualification and ongoing quality control across four components - resource & inputs, machine operation, visual requirements (when specified), and graded output.
- Machine-controlled system: Quality maintained via controlled inputs and machine settings.
- Output-controlled system: Emphasizes initial statistical evaluation (larger sample sizes) to confirm 5th-percentile strength requirements.
- Machine verification: Mandates scanner calibration, repeatability, consistency checks and manufacturer-specified tests.
- Acceptance testing: New grading processes must be backed by testing of reference grades to establish mean modulus of elasticity and the 5th-percentile of a strength property to support structural grade models.
- Evaluation and monitoring: Includes initial and daily evaluation procedures (Annex B explains CUSUM use for daily evaluation).
- Documentation & product ID: Requires product identification, records and documentation of grading procedures, settings and evaluations.
- Informative annexes: Examples and guidance - Annex A (example conformance standard), B (CUSUM for daily checks), C (machine acceptance considerations), D (training, supervision, oversight).
Applications and who uses it
ISO 13912:2017 is used by:
- Sawmills and timber processors operating strength-grading machines
- Machine manufacturers and integrators (scanners, sensors, software)
- Quality managers, testing labs and certification bodies
- Structural engineers and specifiers requiring machine-graded timber data
- Standards bodies and auditors developing or assessing grading schemes
Practical benefits include consistent structural-grade production, traceable grading criteria, improved quality control and assurance that machine-graded timber meets required characteristic strength performance.
Related standards
Keywords: ISO 13912:2017, structural timber, machine strength grading, strength-grading machine, scanners, modulus of elasticity, 5th‑percentile, quality control.
