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Learn About Wood

Learn About Wood Series, Part 1
Learn About Wood

Learn About Wood

General information about wood and wood terminology,
written for woodworkers by Leon Colwell.

Originally published in Wood News Issue 1, December 1977.

Learn About Wood, Part 1

Before one considers spending any considerable amount time working with wood he should familiarize himself with some of the terms used to describe and identify woods and with some of the properties of the wood itself.

Woody plants which are seed-bearing are called Spermatophytes and these trees are divided into two subdivisions: Gymnosperms and Angiosperms. Gymnosperms contain naked seeds. We are most familiar with these as conifers, or cone bearing trees such as pine, fir, spruce and cedar. These are also referred to as evergreen or assiduous (leaf retaining) leaves, although this is not always the case. Evergreens are generally referred to as softwoods but this is not always true because some so called softwoods are physically harder than these so called hardwoods. Angiosperms generally have enclosed seeds. We know these as oak, cherry, walnut, hickory, etc. These plants generally have broad leaves which they shed in the fall and from this we get the term Deciduous. Broad leaf plants are usually referred to as hardwoods.

One of the features of wood is that it is not of uniform structure. It is a tissue with very different kinds of cells even two boards from the same tree do not have exactly the same grain pattern.

A tree is commonly considered to have three parts: the crown, the stem, and the roots. In this and future issues we will deal with the stem from which comes the lumber for our workshops. If you look at a cross-section of a log (part of the stem) under magnification, you can see many parts. Here we consider only 3: the bark, the sapwood, and the heartwood. In constructing furniture we will use mainly the heartwood, although with the price of cabinet grade lumber continually increasing, more and more woodworkers are using the sapwood. Sapwood is between the bark and the hardwood and as a lighter in color than the hardwood. Part of the tissue in sapwood is at least partially alive and functions in sap conduction and storage of food for the tree. As the tree grows in size and becomes older, the tissue dies. This core of dead wood in the center is called heartwood. Depending upon age, size and kind, the ratio of heartwood to sapwood in a stem or log will vary. Growth rings of sapwood vary from a few to as many as 200 rings.

Most woodworkers by their wood after it has been cut, sawn, air or kiln-dried and planed. For furniture construction, most trees are cut into 8 and 10 inch logs. It is sometimes re-cut into shorter lengths. Most logs are tangential or plain-sawed to expose and interesting grain pattern. Some logs are quarter-sawed to result in an edge grain pattern later issues of this newsletter will discuss this in more detail.

When a green log is cut into planks the wood contains a large amount of water. The tree in the cell cavities is called "free water" and the water in the walls is called "bound water". Before wood can be used successfully to construct furniture, most of the water must be removed. Generally this is done by stacking the green planks as follows: lay planks side-by-side across pieces of dry 2 x 4's placed approximately 24" apart. The width of the first layer of the planks can vary. Lay dry 1 inch square strips across the first layer of planks and approximately 24" apart (18" apart is not too close) making sure strips are close to the edge of each end of the layer. Continue to stack and strip as many layers as is practical to handle. The strips are sometimes called "stickers" and allow air passage between layers to accelerate drying and prevent enzyme action from discoloring planks or the growth of fungi which will cause the wood to rot. Stacked lumber should be under cover in open area to allow air passage. It may be left in this stack condition long enough to completely air dry or it may be left stacked for 90 or more days, depending upon thickness and then placed in a kiln to accelerate the drying process. There is a common misconception among some individuals about air dried lumber not being suitable for furniture construction. And air dried lumber is much preferred by those who have used it. Later we will give you additional information on air dried and kiln dried lumber.

In the drying process when the "free water" in the cell cavities is removed, it does not affect the structure of the would to any appreciable extent. However as the "bound water" within the cell walls is removed the cells shrink and the wood, therefore, changes dimensions. Denser woods shrink more than lighter woods of the same species. Hardwoods shrink more than softwoods, but always remember, there are exceptions to these patterns. The longitudinal shrinkage of wood is negligible (.1% to .3%). The radial (across the plank) or tangential shrink is much greater.

When the wood is sufficiently dry it is planed to dimension and is now ready for the woodworker to begin. Remember, this information is general. Some woodworkers do their own planing with a thickness planer or a jointer planer, while some purist cut, split, dry, and hand-plane their lumber.

In the future issues we will discuss wood joinery, final finishing, staining, sealing, types of adhesives and other details of woodworking.

You must learn to work with wood the more you know about its properties, the more successful you will be in turning out professional quality items. We hope we can help you accomplish this.

Explore more of Highland Woodworking's early years in Retro Woodworking our archived collection of woodworking articles, woodworking tips and woodworking nostalgia:

Learn About Wood, Part 2 Learn About Wood Characteristics
Learn About Wood, Part 3 Black Walnut Tree
Learn About Wood, Part 4 A Tribute To American Chestnut
Learn About Wood, Part 5 Predicting Wood Shrinkage

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