Coping with wood movement
All wood workers need to be aware of wood movement when building furniture projects. Failure to consider this important factor can cause wood panels to crack or split.
My high school biology teacher compared structure of a piece of wood with a bundle of straws. The straws represent cells and capillaries of wood. When a tree is growing water and food are transferred up through cells and are carried throughout tree.
Once a tree is fell free water in wood is lost rather quickly but bound water trapped in straw like cell is slower to dissipate. As level of bound water is reduced these straw like cells get narrower in diameter but maintain their length. This is fundamental reason that wood expands and contracts across its width but has almost no expansion length wise.
When working with wood it is very important to allow wood to expand and contract with changes in humidity. As humidity rises straw like cells expand in diameter with opposite effect occurring as relative humidity falls.
Ways to accommodate expansion
Lets use a cutting board for first example. A solid wood cutting board with a bread board edge secured with a tongue and groove joint. One edge has bread board edge secured on both ends with a dowel through tongue The other bread board edge is secured with same tongue and groove joint but this end only has a dowel in center of piece.