What tendency do flat grain boards have?

Flat grain boards tend to cup or curl primarily due to the way the wood fibers are oriented and the structural composition of the grain. In flat grain boards, the growth rings are more horizontal relative to the surface of the board. When these boards are exposed to moisture changes, the wood responds unevenly due to variations in moisture absorption and the way the fibers expand and contract. As a result, the board may warp in a manner that causes the edges to lift or the center to dip, leading to the characteristic curling or cupping.

This behavior is significant in aviation and woodworking because it impacts the material's integrity, stability, and how it interacts with other components in assemblies. Being aware of this tendency aids in making informed decisions about material selection and application in aviation structures where precision and uniformity are crucial. Thus, understanding wood behavior, such as the tendency of flat grain boards to cup or curl, is essential for engineers and craftspeople working with timber in aviation.