If you've ever spent much time in a lumber yard, you've probably noticed customers examining each piece of stock by sighting down long axis of the piece. Are they looking for anything in particular, or are they just overly choosy about the stock that they choose to buy?
Well, it is probably both. What they're actually doing is looking for certain defects, to determine whether the piece of stock is acceptable for their woodworking project.
What defects should you look for when you buy your lumber?
Look for Defects First:
The easiest thing to spot when choosing your lumber is to inspect the four sides of the stock for visually obvious defects. A defect is usually caused by an imperfection in the log of the tree which may cause a problem with your woodworking project
when using the stock. These defects may be caused by knots, fungus, insects, lightning strikes, growth issues or improper drying or milling techniques. Typically, these defects are easy to learn to spot, as they simply don't look right.
Keep in mind, however, that a defect isn't always a problem. Some defects are actually beneficial, as they can lend character to a finished woodworking piece.
Case in point: a number of woodworkers like to recycle
long-leaf pine stock from old barns and houses. Once any nails and screw
s have been removed and the stock has been planed, there are likely to be some old nail holes remaining in the stock. In many cases, these defects are left to be visible in the finished piece, as they lend a lot of character to the project.
In the end, the choice of whether to use stock with a defect is purely up to you.
Finding a Bow:
If a piece of stock appears to be clear enough of defects to use, the next step is to check it for a bow. Pull the board from the stack and place one end on the floor or ground. Position yourself on the opposite end of the board and lift it to the point that you can look directly down the long axis of the stock.
Examine each of the four edges of the board. The board should be relatively straight. Any curving down the length of the stock is called a bow. A single bow in a piece may be acceptable depending upon the installation, but stock with more than one bow should probably be avoided.
While you're looking for bows, look also for twisting down the length of the stock. Twists are probably the most difficult type of warping to deal with, and should be avoided, particularly for structural members of your project.
One final defect to look for while examining the length of the stock is a crook. A crook is caused by the growth of the tree, and usually should be avoided. However, that isn't to say that the entire length of the stock is defective. In the case of a crook, if the stock is straight on either side of the crook, the piece can be cut into shorter pieces bypassing the crook.
If there are no appreciable twists or bows, look next for cupping. A cup is a type of warping where the board has a curve along the width of the board. Some cupping can be reduced by using a surface planer, but keep in mind that the cupping is likely being caused by the nature of the wood, and is enhanced by the method in which it was milled.
Cupping is quite common in one-inch thick stock. Often, the propensity for cupping can be determined by looking at the end grain
of the stock. Even if the board isn't cupping at the moment, if the end grain is curving, it is more likely to cup at some point in the future.
Checks and Cracks:
If all else appears acceptable, look at the ends of the board. You may see some areas in the stock with a check (a small crack) where the wood fibers are separating due to stresses caused by drying. If you buy stock that has small checks and isn't completely dried, those checks may become larger cracks as the stock reaches a state of equilibrium with the local environment. However, you may be able to cut off the checked ends and use the remainder of the stock acceptably.
One Final Item to Look For:
If you have a piece that appears to be usable based upon all of the aforementioned steps, try to determine the relative dryness of the stock. If you're overly concerned with the moisture content, you can use a portable moisture indication meter to determine the dryness of the stock.
A simpler method is to simply ask an employee how long the stock has been in house. Remember that the stock you choose should always be given time to acclimate to the local climate. If you buy relatively green lumber, you'll want to store the lumber for at least a few weeks before beginning your woodworking project.