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WOODWORKING

Chapter 9

Ever-moving wood

Ever-moving wood:
As we have seen, the fibers in wood resemble straws. These straw-like
fibers carry water and minerals up the tree in what we call free water. This
free water moves into the branches and into the leaves. There, photosynthesis
takes place and produces food for the tree and oxygen for us. To say nothing
of water that is simply absorbed from outside the cell walls, which we call
bound water, you can imagine how moist the inside of a tree is. In fact, this
“free” and “bound” water weight can be heavier than the wood itself.

Moisture and wood:
Because the moisture content in a tree is so high, it should be dried before it is used for construction. If
it is not, as the wood loses moisture, it will warp. A warp is when the shape of a piece of lumber deviates in
any way from its true or plane surface. Although warp, regardless of how severe, has no effect on the
strength of a board it does limit its usability. Types of warp include: bow, crook, kink, cup, and twist.
 Bow - Flatwise warp: A deviation from the true
shape of a board from end-to-end when it is laid
flat on its face. In other words, if the board is laid
flat, the board ends touch the surface while the
middle does not. Or, conversely, the board rocks
back and forth from the middle on its face.
 Crook or Crown – Edgewise warp: A deviation
from the true shape of a board end-to-end when it
is laid on the edge. In other words, if the board is
set on its edge, the corners of the board ends
touch the surface while the middle does not. Or,
conversely, the board rocks back and forth from
the middle on its edge.
 Kink or Dog leg – Edgewise end warp: Think of it as one-half the crook or crown warp. This
edgewise deviation is only on one end of the work piece. The edge is no longer perfectly straight.
 Cups – End warp: A deviation from a flat plane, edge to edge. In other words, if you looked
the board from the end, the warp would resemble a cup or bowl.
 Twist – Corner warp: A deviation from the true shape of a board from corner to corner in a
twisting or spiraling fashion.
 Split: A separation of the wood completely through a piece of lumber.

Wood warps because it shrinks as it loses moisture. If it shrinks evenly on both faces and both edges of
the board, it remains flat, but if it does not the board warps. It is not selective as to how. Wood can cup,
split, and twist all in the same board. To control this, the removal of moisture from the cut lumber must be
controlled, or at least monitored, so that it shrinks evenly. This is done in two ways: Air drying and kiln
drying.

Air drying Kiln drying

Unit II: Understanding Wood