Wood cuts and where they come from
The term “quarter-sawn oak” refers to oak lumber that has been “quartercut”. In other words, quarter-sawn oak is not a separate species, but merely oak that has been cut from the log in a particular way. The actual species of oak, such as red oak, white oak, overcup oak, etc., is a completely separate issue.
In the illustration below (left side) you’ll see where each of the three basic cuts of lumber comes from in relation to the log. Quite simply, flat-sawn lumber comes from anywhere in the log where the growth rings on the ends of each board are roughly parallel to the wide surface of the board. We are used to seeing the “U”-shaped growth ring patterns on the ends of boards and this, essentially, represents flat-sawn lumber. Similarly, rift-sawn lumber comes from an area of the log yielding growth rings roughly 45 degrees to the large surface of the board. And quarter-sawn lumber has vertical growth rings, or rings that are perpendicular to the large surface. There is nothing magical about these terms.
There are many ways to saw up a log, but the growth ring orientation on the ends of the boards determines whether the lumber is flat-sawn, rift-sawn, or quarter-sawn. One would assume then, that the only way to know what cut of lumber you have in front of you is to look at the end grain. Although this is the easiest way, especially with rough-sawn lumber (which is hard to get a clear look at), you can also tell a great deal from the grain patterns on the surface of a board. This is set out in the illustration below.
Fig. 3 shows that, in addition to growth rings, which look like concentric circles, there are also other anatomical features in a tree that radiate out from the centre like spokes on a wheel. They are called medullary rays, or just “rays”, for short.
They conduct sap horizontally in the tree and some can store carbohydrates until other growing cells need them. The tricky thing about rays is that, although all trees have them, they are not always visible to the naked eye. If you’d like to see them, one of the best and most common examples is oak. Take a look at the ends of an oak board or an oak log and you will see the rays. But look at the ends of a pine board or cherry board and you won’t see them. Rays are still present in pine and cherry, but they are so small as to be visible only under magnification. In fact, rays are so thin in all species of softwoods that they are only visible under a microscope. But in hardwoods, some rays are highly visible and some are invisible to the naked eye. Fig. 1 shows you how to identify the 3 basic cuts of lumber based solely on surface grain pattern, assuming that you don’t have access to the ends of the board in question. The first example on the left is clearly flat-sawn, based on the end grain. On the surface, though, notice the beautiful grain pattern known as “cathedrals”. The angle at which the flat growth rings intersect the surface produces a series of arches. This is one of the features for which flat-sawn lumber is desired, although it can be too “busy” looking, depending on the piece being built and your goals. It is a bold look that ought to be used carefully in already bold species like oak. The second example in fig. 1 shows you what rift-sawn lumber looks like on the surface. There are no cathedrals, but only straight lines. As each growth ring intersects the surface, it produces just a straight line along the length of the board. This can also be desirable for a more subtle, or “quiet” look, in a finished piece of furniture. For example, if you have gorgeous cathedrals on the panel of a frame-and-panel door, you might want the frame to have more subtle grain patterns so as not to distract from the panel itself. The third example in the diagram shows quarter-sawn lumber. The growth rings still produce just straight lines on the surface. However, notice the other markings on the surface. These are caused by cross-sections of the medullary rays (now parallel to the wide surface of the board) intersecting the surface at irregular intervals. It can be absolutely stunning and is known as “ray fleck figure”, or simply “ray fleck”. Remember, though, that rays are not visible in all species and, even if they are, they can be very small. In red and white oak, they are huge and add tremendous interest to the piece. In cherry and maple, they are small and add just a hint of interest. In pine, you won’t see any ray fleck at all since the rays are invisible in softwoods.
This can create a little confusion. If I give you a rift-sawn board and a quarter sawn board in a species where the rays are invisible, it will be almost impossible to know which cut you have in front of you without access to the ends. In both situations, you will see just straight lines on the surfaces. The lines will be closer together in quarter-sawn lumber than in rift-sawn lumber of the same species, but line spacing can also vary by subspecies, growing conditions, age of the tree, etc. So this is a tough thing to identify based on grain pattern alone. However, remember as well that a flatsawn board can often have a quarter-sawn surface on its edges and a quarter-sawn board will have a flat-sawn surface on its edges. This means that a flat-sawn board will often have ray fleck figure on its edges, while the edges of quarter-sawn boards will usually display cathedrals.
Remember that flat-sawn and quarter-sawn cuts are exact opposites of each other. Each is the other cut just turned 90 degrees. So if you see just straight lines on the surfaces but cathedrals on the edges, then you know the board is quarter-sawn. If you see just straight lines on all surfaces and edges, then you know it’s rift-sawn. I hope this has clarified what all of these terms mean. Realize, too, that a given board, depending on width, will often have two cuts of lumber within it. If you look at a flat-sawn board that has distinctly “U”-shaped growth rings on the end grain, it technically is rift-sawn at the outer areas and is only truly flat-sawn at its centre. Combinations of the various cuts are often involved in a single board as well.
In our next issue, Hendrik will discuss the relationship between moisture content and relative humidity and show you how each of the three basic cuts of wood react to changes in moisture content.