A rendering of a log sawn into board products. http://www.vincentkohler.ch/billon.html
One of the more interesting phenomena of today's world is the insulation we have from the source of our sustenance, or raw materials. Many modern folk would have a hard time explaining where the natural gas, electricity, or water in their home comes from, or how bread is made, or even what the very walls around them are made of. So when I saw the above picture of what I call a "lumber log", I thought it a good opportunity to share just a little bit of the story of lumber.
This artistic work is a nice way to demonstrate in a visual way just where the lumber comes from. One sees many different sizes of boards, and a cant in the center of the log; it begins to give one a sense of how many different products can be produces from a log depending on how the log is sawn up. And the placement of all cuts, and therefore the size and value of each board produced, depends most importantly on the very first cut into the log.
In the early 1970's, the US Forest Service developed a computer program that mathematically calculated the highest volume of lumber that could be sawn from a log of specified dimensions based on what it called the "best opening face". Soon, computerized sawing equipment incorporated this computer algorithm into their equipment along with the scanning technology that allowed the log to be spun and scanned prior to sawing, thereby allowing the computer to determine just exactly where that first critical cut should be made. The resulting "face" of the log then, would produce the widest pieces of lumber, and subsequent narrower lumber would be produced as the log is turned. In the photograph above, the sawyer, or the computer he operated, determined that the best first cut would be on what is the top of the log in the picture. The cut was made just at the edges of the top piece of bark, producing a "slab" from which the top two narrow boards were re-sawn in a downstream operation. Then, once the slab was sent on its way, the two-by-six and two-by-eight pieces (the third and fourth boards from the top) were sawn and sent on to and "edger" where the square edges of the boards were formed as the rounded corners were sawn away. The log was then rotated and sawing continued on the next face, with most of the pieces in this case being sent on to a "re-saw" or a "gang-saw" to produce the narrower strips you see.
Not long after the computerized saws were capable of producing the highest amount of lumber, or "yield" from a log, technologists figured out how to allow the mill operators to assign market values to the different sizes of lumber in "value tables" built into the software. This allowed the mill operator to then produce not the highest "yield" of lumber in board feet (one board foot is equal to a square piece of wood 12 inches long, 12 inches wide, and 1 inch thinck), but the highest value of lumber in dollars based on ever-changing current lumber market values.
This system works well for softwood lumber, for which most of the value is determined by the dimension of each piece. But in hardwood lumber production, the real value of the lumber is determined by the internal characteristics of the log...the number and size of knots and other defects, the coloring and figuring of the wood, and the surface area of "clear units" in each piece of lumber. These characteristics are determined again by the sawing technique used for each log. the three most common methods of sawing hardwood logs are called "plain- or flat-sawn" (the most common and highest yielding method), "quarter-sawn" (the most popular for certain applications where highly figured wood is desired), and "rift-sawn" (used when straight-grained lumber is highly desired).
The following is an excellent high-quality educational video from the folks at Frank Miller Lumber Company, an Indiana lumber producer that specializes in quarter-sawn hardwood. It provides a nice way to visualize the sawing process one has to try to imagine when looking at a piece of quarter-sawn lumber.
And that's how it's done. Show the video to your kids, and then take them to the nearest lumberyard. You might be surprised how much fun you'll have. And you'll all realize that lumber just doesn't come from Home Depot.