Basic Wood

  • Basic Wood  

    Introduction

    Before we can begin any work in the shop, we have to understand a little bit about trees and how trees are processed into a usable resource. So let's begin with the tree itself.

    The Tree

    The tree is composed of three basic parts: the crown, trunk and roots. The crown is the part of the tree that supports the growth of leaves. The tree depends on the leaves to convert the energy from the sun along with nutrients from the soil into a usable food source for the tree. This process is known as photosynthesis. 

    The trunk of the tree is its super structure, or skeleton. It provides the strength to support the weight of the crown along with providing a method of transportation for the food sources between the roots and the leaves. Think as the trunk as big bundle of straws or tubes. The trunk is the part of the tree that the woodworker is most interested in.  How the trunk has grown over the years and how it is handled at the saw mill greatly affects the ability to work with the wood in the shop.

    The last part of the tree is the root system. The roots perform two main functions: The first is to supply water and nutrients, from the soil to the tree, to produce food. The second function is that of an anchor. It holds the tree in place. It is said that the root system of a tree is equal to the size of its crown. The root system must have a strong hold in the earth to withstand the many storms that it will face over the course of its lifetime.



     

    Two Basic Types of Trees

    As a woodworker, you should be concerned with the types of wood you will work with. To explain it as simply as possible, you have two types: softwoods and hardwoods. 

    Softwoods come from a group of trees known as conifers. These are better known as pine trees. These trees do not have leaves but they do have needles. Plus, they do not lose their needles in the winter. 

    Hardwoods come from a group of trees that are deciduous. Deciduous means that they lose their leaves in the winter time. 

    We need to clarify something right up front: Do not get this classification of hardwoods and softwoods confused. Yes, there are types of conifers that are harder then some deciduous trees.  The distinction is just a simple method of classification that has been used for centuries.

    Forest to Saw Mill

    A tree a long time to grow to its full size. It is our responsibility to make sure that we use the wood from these great giants carefully and efficiently. Do not waste it! It is okay to harvest trees but it is important to make sure that conservation efforts are taken to ensure a constant wood supply for the future.

    There are two methods of logging used today. One is clear cutting and the other is selective cutting. Clear cutting occurs when an entire stand or part of the forest is cut completely down. Selective cutting is when a logging company goes into a forest and selects only certain trees for harvesting. Obviously, selective cutting has less impact on the environment as compared to clear cutting. The drawback is that selective cutting is more expensive in terms of dollars and cents.

    The act of cutting a tree down is called felling. Once the tree has been felled the limbs are removed and the log is skidded to a staging area. At the staging area, the log is cut into specific lengths. The cutting of the long to a certain length is called bucking. The preferred bucking length is 16 feet. If this is not possible, the bucker may cut the log into 8,10 or 12 foot lengths. From here, the log is loaded onto a truck and taken to the saw mill. In some smaller operations the saw mill is portable, so it is taken directly to the staging location.

    If we look at the end of the log that has just been bucked we can tell many things about what has happened over the lifespan of the tree. By counting the concentric rings we can determine the age of the tree. By looking at the gaps between the rings we can tell how fast or how slow the tree grew. We can also see any scarring that might have occurred to the tree in a certain year because of a flood, fire or insect infestation, just to name a few. See the diagram below to see the sections of the tree. Make sure you know each one.

     


    The bark is like your skin. It protects the tree from such variables as weather, bugs, birds, etc. The phloem is similar to your veins and arteries. This is where nutrients flow to feed the tree. The cambium is the new growth of the tree relative to the girth of the trunk, making the tree larger in diameter. The sapwood is the pipeline of the tree. Carrying water and minerals to the leaves so that photosynthesis can occur, the sapwood creates food for the tree that is then distributed through the phloem. Sapwood is what most furniture like products are constructed of. The heartwood is the center of the tree. It is usually distinguishable by its darker color. Basically, it is sapwood that has been clogged up over time. The heartwood is a nonliving part of the tree, but it does give the tree added strength. Now let's look at how the log is cut up at the saw mill.

    Saw Mill

    There are two types of saw mills, a circular saw mill and a band saw mill. A circular saw mill can be looked at as a giant table saw used to cut the logs down to size. How big is a circular saw mill well the blade that is used can be four feet in diameter or wider.  The other type of mill is a band saw mill. This type of mill uses a blade that is one continuous band, very similar to the smaller band saws that we have in the shop. Band saw mills are more popular at the present time because they create less waste, due to the smaller thickness of the blade.

    There are three accepted methods to sawing a log into lumber.  Plain sawn, quartersawn and through and through sawn. The main reason for sawing a log a certain way is to produce lumber that is stable with as little waste as possible. In this scenario, stable means keeping the board from cracking or warping. So, to keep the wood stable certain sawing techniques are better then others because these techniques allow the lumber to shrink or swell in a uniform manner. We will get into more detail later about what makes a board crack or warp but for now, you must realize that moisture causes a board to swell, and uneven drying causes a board to warp or crack.  See the diagram below for the three types of sawing techniques.

      



    Plain Sawn 

    With plain sawn lumber the heartwood is usually separated from the sapwood. Most types of furniture or construction lumber come from the sapwood. The heartwood is used for secondary types of items. As you can see, the right side of the log is sliced off and then the log is rolled. The top is then sliced off. The log is rolled a total of four times to remove the sapwood. The big disadvantage to plain sawing is that as the log is rolled, the boards get more and more narrow. This method does produce stable lumber for creating projects.

    Quartersawn 

    With quartersawn lumber, the log is divided into four equal parts, as the name suggests. These four pieces are then cut individually at roughly a 45-degree angle. The heartwood and sapwood are generally not separated. This method of lumbering produces the most stable and desirable grain patterns for lumber. The only disadvantage of this method is that it is more expensive to produce.

    Through and Through

    By far this is the simplest method of lumbering, but it produces lumber that is relatively unstable. When using this method, the saw mill operator just keeps slicing off boards from the log until it is all gone. These boards have a tendency to shrink or swell across the board that must be compensated for when using this type of sawn lumber.

    Drying Techniques

    Once the board has been processed through the lumber mill, it is still not ready to be used. It must go through a drying process. All of its life the tree has been moving water and nutrients throughout the sapwood and phloem. This water or moisture must be removed at a certain rate to avoid cracking or warping of the wood. The two methods of moisture removal are kiln drying and air drying. Both methods are acceptable.

    Kiln drying removes moisture to facilitate production. When the boards leave the saw mill they are stacked in a certain manner. This stack is then moved into a giant oven where the temperature and moisture are controlled. The object of the kiln or oven is to remove the moisture from the wood at a specific pace. By removing the moisture at a specific rate, one can control how the board is dried thus controlling the amount of warping and cracking that occurs. This method of drying is more expensive than air drying but it is much quicker. Once the moisture level has reached a designated level it is removed from the kiln and it is ready to be used by the woodworker. The moisture level is determined by the geographical location in the country or world.

    Air drying is also a proven method for controlling moisture in wood. The boards are removed from the saw mill and stacked in a specific manner that allows air to flow around each board. The stack of lumber is then placed in a protected area away from the elements. You will notice that in the drying practice, the ends of the boards are painted to help control the rate at which the moisture can leave or enter the ends of the boards. The stack is then left to dry for roughly one year. The time frame is an estimate due to the fact that the drying process is controlled by the weather. If one lives in a hot, dry climate, the wood will dry much faster than if one lives in a cold, damp area.

    Conclusion

    As you can see it is a long process from the forest to the shop. Respect the trees and the wood we will be using. Try to waste as little as possible.