Want to learn what makes great lumber? Take a sawmill tour and find out firsthand.

Jim Pierce, owner of Pierce Lumber Company, has spent a lifetime learning how to turn a stack of logs, such as these red-oak behemoths sitting in his mill yard, into the top-quality lumber he stands alongside.

Most woodworkers buy wood already milled into boards, ready to cut up and make into projects. But a surprising few understand the complex processes used to create those boards. Learn how it's done, though, and you'll get higher-quality stock every time, and be able to spot deals, whether you buy from a retailer or directly from a mill.

To get the full story, we recently visited Pierce Lumber Company in Belle Plaine, Iowa. In this high-tech operation, owner Jim Pierce and his employees produce about 350,000 board feet of top-quality hardwood lumber monthly. Jim grew up in the mill business, and knows that creating great lumber requires careful attention to detail at every stage of production.

Although many smaller operations occur in sawmills, four key areas warrant close examination: log selection, efficient milling, drying techniques, and proper grading. Let's see how Jim ensures that his mill makes the most of every board. Also check out Jim's top 5 tips for buying hardwood (sidebar at end of this article).

Great boards come from good trees

Creating top-quality boards requires a topnotch tree. Jim and his buyers can judge a specimen quickly, before it's ever cut down, to determine whether it's worth making into lumber, or it it's destined to become pallet stock. So just how do they know this, and why should you?

You need this knowledge because the tree's location, condition, and size all combine to determine the quantity and quality of lumber it will yield and, therefore, the price that you'll ultimately pay. Plus, if you own a tree that you've considered processing into lumber—perhaps one from your yard that was damaged in a storm—you'll be able to evaluate whether it's worth sawing up.

The most desirable trees grow in rural areas, preferably in large stands, and distanced from roads or fencerows. Trees growing in urban areas or near homesteads may contain metals that can destroy a sawmill's expensive blades. The same metal stains wood and invites damaging viruses and bacteria that can cause a raft of problems with milling and drying.

A buyer looks also for straight trees, and not just because they yield longer boards. A curved trunk contains "reaction wood" that has uneven distribution of the wood cells and fibers. This wood will likely warp, bow, or twist over time.

Curves are easy to see, but many indicators are tougher to see, until you learn to "read" the bark. "Learn to do this, and you'll know what's inside the log," Jim says. These subtle cues include remnants of long-overgrown branches. Called "cat's faces," shown in the photo below, these areas disappear only after years of growth-ring layering over the branch site.

This roughly circular interruption in the bark's straight lines marks the former location of a branch. Though no visible branch butt remains, the wood below will contain knots.

Jim can even differentiate between related trees by examining the bark on cut logs. The logs seen in the opening photo, for example, all are classified as "red oak." Jim points out, though, that the pile contains true red oak, black oak, pin oak, and hybrids.

Each of these logs will produce oak with slightly different color and grain characteristics. Some sawmills lump it all together, which means you may get hard-to-match boards. Jim's employees sort milled oak boards by color and appearance.

A tree's health also ranks as an important indicator of its lumber value. Dead sections, splits, and discolored leaves may indicate rot or infection. Those conditions reduce the yield, produce discolored boards, or boards that won't dry properly. Jim also warns against "over-mature" trees, which often have internal problems that remain invisible on the surface.

Only after the tree is cut can some internal problems be diagnosed, usually by looking at the log's butt end.

The tree in the photo below, for example, shows several typical problems. First, checks (splits radiating from the center) are forming. "It needs to be milled soon before those advance, or we'll only be able to produce shorter boards," Jim notes.

The butt of this log shows a few ills, but an experienced eye can tell the log remains suitable for milling. If these conditions progress, though, much of the wood will go to waste.

The log also has a rotted pith (center portion), and a condition known as "ring shake." This occurs when a tree that has been weakened by infection gets flexed enough by wind, or another force, to break apart cells between the growth rings.

Once a log lands in the yard, Jim tries to mill it as soon as possible. "People are often told to let a log sit on the ground and season for six to 12 months before milling. But that's a bad idea," he says. "During warm months, I don't keep logs in the yard for more than 60 to 90 days." Heat causes more problems than moisture because it encourages growth of fungus, bacteria, and insects.

Proper milling produces lovely lumber

Examining the exterior of a log gives a good idea of what lies inside, but nobody knows for sure until the log enters the sawmill. (Read the sidebar "A run through the mill," at the end of this article, to see firsthand how the high-tech mill at Pierce Lumber Company operates.)

Every mill employee needs to understand the lumber-production process. The headsaw operator, for example, has to rotate the log to decide how to best saw it for maximum yield. The resaw operators (two at this mill) then judge the log's figure and appearance, and slice the log to garner the best yield.

Should anybody misjudge the log, the boards they produce won't be as large or look as good as they could. In the end, that means you'll find fewer superior boards in your lumber retailer's bins.

Wringing out the water

The process of drying the wood to a workable level (usually between 6% and 10% moisture content for hardwoods) represents the final phase of lumber production. Moisture must be removed at just the right rate—which varies by species and board thickness—to prevent problems.

"Drying is a balancing act," says Jim. "If boards dry too quickly, checks (cracks parallel to the grain) appear." Some checks are inevitable at the ends of boards. Checking can become severe, though, if a board's exterior dries too rapidly. In many cases, the exterior wood shrinks, but the still-wet core doesn't, causing the surface to tear open. Occasionally, the exterior stays together and crushes the cells of the interior wood.

If you find boards that show excessive cracking on their faces, put them back. They'll cause such problems as splitting, warping, difficulty machining, and even inability to successfully accept glue, stain, and finish.

The drying process begins by stacking the boards on 34 "-thick spacers called stickers. These allow air to flow through the stack so that the boards dry evenly.

The stickered boards then head for a building called a predryer, shown in the photo below. "We expose boards to 80° temperature and circulate air through them for 30 to 45 days," Jim says. "This process gently takes the boards from green (where they retain all of their moisture) to a moisture content of 15 to 20%."


(Walnut boards actually make one extra stop between the mill and the predryer. Read the sidebar "Getting steamed about walnut,"below, to learn why.)

Once predried, boards head for the dry kiln, shown below. Jim runs four kilns to increase capacity and because different woods require varying combinations of time, airflow, temperature, and humidity to dry properly. The process takes 10 to 12 days. Samples are pulled daily to check their appearance and moisture content.


Some samples get cut into two-pronged wafers that are dried in an oven, below, to check for internal tensions in the wood. After checking the samples, the operator adjusts kiln settings accordingly.


Getting steamed about walnut

Walnut ranks as one of the most expensive, desirable hardwoods. "Unfortunately, walnut logs are smaller in diameter than many others, and always contain a thick layer of white sapwood," Jim Pierce explains.

Because of this, mill operators place the milled walnut boards inside a chamber and pump in hot steam for four to five days. This causes a chemical reaction that darkens the sapwood to a color that mimics the heartwood, as seen below, and produces more usable lumber in each board. On the downside, many feel the process dulls the natural variations in tone and purple hues that are common in the heartwood.


Making the grade

As freshly milled boards exit the mill, they arrive at the first of two grading stations. There, the boards are quickly judged by width and length, and examined for knots or other defects that will reduce their yield of clear lumber.

Because grading ranks so critically in determining the price the mill will receive for its stock, Pierce Lumber Company, and many other mills, grade the boards again after kiln drying, below. They measure the width of each board to check for shrinkage, and again look for knots and defects.


One key thing to remember is that grades aren't determined by appearance, only by yield. As grade level increases, a board's size and its percentage of clear (knot- and defect-free) area increase.

In fact, you'll often find lower-grade boards—No. 1 or No. 2 Common for example—that look just as good as those bearing the highest grades of Selects or FAS (Firsts and Seconds). You may also find completely clear boards graded as No. 1 Common only because they're smaller than needed to achieve Selects or FAS status. What's the payoff for the extra effort of working with this stock? A cost savings of 30% or more over FAS-grade stock.

After receiving their final grade, boards are either bundled for shipping in rough form, or surfaced and edged before they get shipped to become cabinets; flooring; furniture; or, the stock at your lumber dealer.

A run through the mill

When a log slips into the mill at Pierce Lumber Company, it enters a high-tech, high-power world. Taking every inch of a 27,000-square-foot building, the mill and its two main bandsaws are immense. The whole works sits elevated 10' above the concrete floor so that workers can move underneath to clear jams and perform maintenance. Logs and boards travel on conveyors that run in all directions, while catwalks allow the twelve workers who run this monster machine to travel between stations. Let's follow a log through to see how it's processed.


The yield factor

Even the most perfect log won't get milled entirely into the boards you buy for projects. Jim Pierce says that as little as 60% of many logs meet standards for the highest grades. So, the mill owner only makes top dollar on a portion of the wood, but has to purchase and process the entire log. This means the mill has to charge more for top-grade lumber to recover its costs.

The other 40% of the log, which includes the unstable center (called the pith) and areas with unworkable defects, doesn't go to waste, though. Much of it goes to manufacturers of pallets, crates, and railroad ties. The remainder gets chipped up to fuel the sawmill's kilns and furnaces.

Jim's top 5 tips for  buying hardwood

1. Know the wood color, grain figure, dimensions, and quantity you want so you're not left guessing while selecting stock.
2. Purchase No. 1 Common stock if you can get it. You can work around the defects, and you'll save up to 30 percent.
3. Closely examine each board for checks, cracks and uneven surfaces, which may be signs of improper drying.
4. Buy your boards from a sawmill that sells directly to the public. You may have to purchase a minimum quantity (100 or more board feet), and you won't be able to select your stock by hand. But, if you clearly communicate what you need, and you're knowledgeable and easy to work with, you'll get good stock at a great price.
5. Make sure the dealer is reputable and stands behind their product.