WOODWORKING
Drying wood:
When a board is sawn from a log, it must be properly dried
to prevent warp. You see, the freshly sawn board is saturated
with moisture, having at times a moisture content as high as 100
percent. That is to say that there is as much weight of water in
the board as there is weight of dry wood tissue; the water inside
weighs as much as the wood itself. There are two popular ways
of drying wood: Air dry and Kiln dry
Air drying: Air drying is the drying of timber by
exposing it to the air. The technique of air drying
consists of stacking sawn timber on a raised
foundation in a clean, cool, dry, and shady space.
Each column of timber is spaced equally, and each
layer is separated by small dividers called stickers.
The empty “air space” allows air to flow completely around the board and pull out the
moisture. As you might think, this is a time consuming process.
Kiln drying: Kiln drying is much quicker. It is done by stacking lumber in a wood drying kiln
and introducing heat. This introduction of heat may be done either directly with the use of
natural gas and/or electricity, or indirectly through some sort of heat exchanger, such as steam
or solar energy. At each stage of the drying process, the temperature, relative humidity, and air
circulation are controlled by the operator.
Moisture and Wood:
Moisture, such as water, liquid, or humidity, has a continual effect on wood. Simply because it has been
dried, does not mean it is immune from distortions. Because the walls around wood cells are made of a
sponge-like material (remember, sponges are made from this stuff), lumber continually absorbs moisture.
Just put a wet glass on your mother’s dining room table and see how angry she gets for “staining” her
furniture. The mark left behind is from the wood absorbing the moisture. This constant absorption of
moisture causes continual shrinkage and swelling to wood, especially in high humidity areas. Careful
attention must be paid when adjoining lumber pieces in order to prevent unsightly and damaging
deviations.
Unit II: Understanding Wood