Slope of grain
Slope of grain is the angle between the wood fibers and the long axis of a board, stated as a ratio such as 1 in 4 (the grain drifts 1 in across for every 4 in along). The Uniform Standard allows a maximum slope of grain of 1 in 4 in pallet parts, for both reusable and single-use pallets.
Also called cross grain, grain deviation
Reviewed
How slope of grain is measured
Follow the grain lines along the face or edge of a board. If the grain crosses 1 in of width while running 4 in along the length, the slope is 1 in 4. A steeper slope, such as 1 in 3, means the fibers run out of the board sooner.
The limit
| Use class | Maximum slope of grain (Uniform Standard 2012, Table 1) |
|---|---|
| Reusable | 1 in 4 |
| Single-use | 1 in 4 |
Unlike knots and wane, the slope-of-grain limit is the same for both use classes.
Why it matters
Wood is much stronger along the grain than across it. When fibers run off the board's axis, bending loads pull partly across the grain, so steep cross grain can let a deckboard or stringer break at a low load. Short, steeply sloped grain is also where splits start. See lumber grades.
Questions
- What does 1 in 4 slope of grain mean?
- The grain drifts 1 in across the board for every 4 in of length. That is the steepest slope the Uniform Standard allows in pallet parts.
Related
- Pallet lumber gradesPallet lumber grades set limits on knots, wane, splits, decay and slope of grain. Reusable pallets need roughly PDS Standard grade; single-use roughly Economy.
- KnotA knot is the base of a branch embedded in a board. The Uniform Standard limits sound knots to half the cross-section on reusable pallets and 7/8 on single-use.
- SplitA split is a lengthwise separation of wood fibers through a board. The Uniform Standard limits deckboard splits to one third of length on reusable pallets.
- Pallet lumber: species, grades and moisturePallet lumber is cut-to-size hardwood or softwood stock specified by species class, grade and moisture. Mixed hardwood, oak, SYP, SPF and Douglas fir lead.
- Specific gravitySpecific gravity (G) is wood density relative to water. It drives nail strength: withdrawal resistance rises with G to the 2.5 power in the Uniform Standard.
- StaplePallet staples are two-legged wire fasteners, often adhesive-coated. The Uniform Standard requires a crown of at least 3/8 in, set across the grain.
Sources
- Uniform Standard for Wood Pallets (NWPCA, now Woodpack Global), 2012 edition