All Inclusive Guide to Wood Classifications and Species (Part 1)

 Getting Started

Starting off, who is this series of articles for!? I’ve written articles for both consumers and those wishing to learn about woodworking alike. Luckily, this topic will be very beneficial to both groups. Whether you would like to learn more about the type of furniture you wish to buy or about the type of furniture you’re wishing to build, it all starts with the tree. This is one of the main reasons why I love creating furniture and woodworking, being able to connect with nature and using raw natural materials to make something beautiful. I will be covering quite a bit in this article so if you’re only interested in particular topics then simply follow the very well labeled headlines. I understand if you are new to many of these items that it can seem overwhelming at first but give it some time and you’ll be identifying lumber in no time.

Time for an Anatomy Lesson!

To begin I suppose I would like to give a sort of disclaimer as I am neither a botanist nor biologist. These terms, concepts and ideas are those of a woodworker and not a scientist so it would be best not to cite this page for anything other than a woodworking paper. I am aware there are plenty more terms but this will convey a very simple and rough understanding of what we’re dealing with.

I want you to picture a tall, straight tree. Now imagine the trunk and central pillar from which all the branches stem from is made from a bundle of straws. This rudimentary idea is about as complex as we’ll get so stick with me. All of these “straws”, which we call “wood grain,” are microscopic and make up the entirety of the tree. The concept of these straws will also further help illustrate wood expansion/contraction in the next section.

Now if we were to take a slice of the tree, looking at it’s end grain (from the top down), we see a more commonly known image of a tree’s growth rings. If we were to start at the outer diameter of the tree, excluding the bark and very first thin layers of the tree, we have the Sapwood. This is sometimes wanted in furniture as people like the contrast in color of some sapwood and it is also a large part of “live edge” designs. The tree uses this area to carry nutrients up and down it’s length. The principal reason why this area would not be wanted for use, is because even after death this part of the tree still holds many nutrients which some insects may find desirable if allowed access. Moving inward toward the center of the tree we have the Heartwood. This is essentially our bread and butter; it gives the tree its strength and what we’re looking for in lumber. As we continue to the center of the tree, we have the Pith. The Pith is unstable, often completely void or full of checks and cracks and should be avoided when woodworking. The Pith is also known for possibly expanding and contracting along its length, which is normally uncommon as described in the next sub sections. Pith wood isn’t normally common when purchasing hardwood lumber for furniture, however will be seen on softwood construction lumber and is almost always in construction grade 4x4’s.

Since we’re on anatomy I might as well briefly address the differences between softwood and hardwood. Simply put the only fact is deciduous trees are hardwood and coniferous trees are softwood, everything else is “usually” true but there are always outliers. Since softwood trees, such as pine, never loose their leaves they continually grow and usually at a faster rate than hardwood, making their growth rings further apart and the lumber less dense, hence softer. Examples of softwoods are: Spruce, Pine, Fir and Cedar. This faster growth makes softwoods excellent for building construction lumber. Hardwoods are “generally” harder and denser, although even super light Balsa Wood is a hardwood.

Wood Movement

After a tree is felled and milled for lumber, it is normally dried considerably to reduce the internal moisture content for more stability. The moisture exiting the tree is leaving from inside these straws, and as they lose moisture their diameters begin to shrink. This must be done very slowly or checks and cracks will begin to form as the straws start to separate from each other. As the environment around lumber changes it will continually acclimate to where ever it is placed, attempting to maintain an equilibrium of internal moisture to the humidity of its environment. With this knowledge we can assess that over time and through the seasons a piece of lumber will expand and contract along it’s width and thickness, but almost negligible along its length as the straws are only changing in diameter but not length. The larger the area, the more compounded the effects are. Due to this, the thickness and width may expand at the same rate but the width will be drastically amplified as you may be dealing with 8”-24” in width rather than 1.5” of thickness. It is along these principles of differing wood expansions and unwanted wood movement that “lasting” furniture must be designed. I enjoy practicing and prefer more traditional styled fine furniture techniques due to the allowance the wood is given to inevitably move without tearing itself and the piece apart.

Stay tuned for for the rest of the series!