Wood Movement Part 1

In this world of plywood, particle board and veneers, woodworkers are losing an understanding of solid wood movement with sometimes disastrous results.  Generally wood moves along growth rings.  Rapid movement in wood is about one quarter of the movement along growth rings and almost nothing in length.  When wood is being air or kiln dried the majority of the movement or shrinkage doesn't start until the wood reaches 18%, when the free moisture between the cells is removed by the drying process and moisture within the cell structure starts to be removed.  If a solid wood panel is glued or fixed with screws or bolts to a solid wood frame or particle board, not allowing the panel to shrink and expand in width, the panel will crack, warp or break the frame.  In most hardwoods a general rule should be 1/16" space per 12" width for kiln dried wood with about 10% moisture.  I will provide more detail in Parts 2 and 3.