Tangential, radial, longitudinal — why shrinkage differs by direction

Wood is anisotropic, and the three directions shrink very differently (green to oven dry, typical values):

• Longitudinal (along the grain): about 0.1%–0.3%, effectively negligible;
• Radial (across the rings): about 4%–6%;
• Tangential (along the rings): about 8%–12%, roughly twice radial.

What it explains

Cupping: in a flat-sawn board the two faces sit at different distances from the pith, tangential shrinkage is uneven, and the board cups away from the ring curvature. This is why ring orientation is alternated when gluing panels — adjacent strips cancel each other out.

Quarter-sawn is more stable: across its width a quarter-sawn board shrinks mainly radially, less and more evenly. Flooring faces and table tops are worth the premium for it. White oak ray fleck only appears on quarter-sawn faces, so stability and appearance arrive together.

Length barely changes: longitudinal shrinkage is negligible, so glue lines open across the width, not along the length.

Using this when you order

• Wide panels and tops — quarter or rift sawn, or narrow strips;
• When gluing up — alternate ring direction, keep strips to 60–80 mm;
• For critical flatness — state a quarter-sawn percentage in the contract and we sort for it.