Log grading primarily assesses a log's potential yield and quality of lumber based on visible defects and clear areas.
Grading logs is a process used to determine their quality and potential value, primarily for lumber production. This system relies heavily on the presence of "cuttings," which are clear areas on the log's surface that are free from defects. The initial step in this grading process involves a systematic division of the log.
The Basis of Log Grading: Cuttings and Faces
Log grading is fundamentally based on identifying and measuring clear areas on the log's surface that can yield high-quality lumber. These clear areas are often referred to as "cuttings." Defects like knots, decay, or excessive sweep reduce the size and quality of these potential cuttings.
According to the system, to begin the grading assessment:
- The log is divided into four equal sections or faces.
- Each face is one quarter of the circumference, extending the full length of the log.
This division creates four distinct surfaces along the log that graders can inspect individually to locate and evaluate the size and quality of the potential cuttings within each face.
The Grading Process Explained
While specific grading rules can vary depending on the species, region, and intended use (e.g., saw logs vs. veneer logs), the general process often follows these steps:
- Measure the Log: Determine the log's diameter (usually inside the bark at the small end) and length. This provides the basic dimensions for volume estimation and grade consideration.
- Divide into Faces: As the reference states, the log is conceptually or visually divided into four equal faces along its length.
- Inspect Each Face: Examine each of the four faces for defects. These defects include:
- Knots (size, type, frequency)
- Splits and checks
- Decay
- Sweep, crook, or bow (deviation from straightness)
- Seams
- Insect damage
- Scars or wounds
- Identify and Measure Cuttings: On each face, identify clear areas free from significant defects. These are the potential cuttings. Measure the size (width and length) of these clear areas. The grade often depends on the number, size, and quality of these cuttings that can be obtained from the log.
- Determine Grade: Based on the size and location of defects, the proportion of clear cuttings achievable from the four faces, and other factors like minimum diameter requirements, the log is assigned a specific grade. Higher grades typically require a greater proportion of clear wood and fewer defects.
Factors Influencing Log Grade
Several factors are assessed during the grading process:
- Size: Larger diameter and longer logs often have the potential for higher grades, assuming quality is present.
- Sweep and Crook: Excessive curvature can significantly reduce the amount of usable lumber.
- Knots: The size, type (live vs. dead), and distribution of knots are major grading factors.
- Surface Defects: Seams, scars, and splits affect surface cuttings.
- End Defects: Checks and decay at the ends can indicate internal issues.
- Species: Different species have different grading standards and values.
Example Grading Considerations (Simplified)
Let's consider a simplified view using the four faces:
Face | Observable Defects | Potential Cuttings (Clear Area) |
---|---|---|
1 | Small scattered knots, minor seam | Large clear area achievable |
2 | Large knot cluster, some decay | Limited clear area |
3 | Mostly clear | Very large clear area |
4 | Moderate sweep, several pin knots | Moderate clear area |
A log with faces showing large, high-quality clear areas (like Faces 1, 3, and 4 in this example) would likely achieve a higher grade than a log dominated by defect-filled faces (like Face 2). The grading rules provide specific requirements for the size and number of cuttings needed on each face to qualify for a particular grade.
By systematically dividing the log into four faces and assessing the quality and size of potential clear cuttings within each, graders can objectively determine the log's value and best use.