How Hardwood Lumber is Sized?
Unlike dimension lumber, which is milled to nominal thicknesses, widths and lengths, cabinet-quality stock comes in random widths and lengths to keep waste to an absolute minimum. In addition, because all furniture and other wood working projects have different dimensions, there’s no need for dimension stock.
Thickness, though has been standardized, and is expressed in different ways, such as 4/4 (1”), 5/4 (1-1/4”), 6/4 (1-1/2”), and so on. Don’t be confused by all this; just remember that the quarter designation and the nominal thickness are the same animal.
When you order cabinet-quality lumber; you’ll receive a board as long a or longer than and as wide as or wider than the item ordered. The thickness (if surfaced) to the lumber grades chart. When you purchase hardwood lumber, it’s by the board foot. If the dealer has the boards already priced, he arrived at those prices by figuring the number of board feet each contained.
A board foot, simply, equals 144 cubic inches of wood. Think of it as a piece 1 inch thick and 12 inches square. Because board footage always is calculated in quarters of an inch thickness, starting a no less than 1 inch (even if the order less than an inch, you’ll pay for 1 inch thickness), a 5/4 board 6 inches wide and 72 inches long would be figured like this: 1.25 (thickness) x 6 (width)x72 (length)=540. Divide 540 by 144 to determine the number of board feet in the stock. If the board length is stated in feet rather than inches, use the same method but divide your total by 12 instead of 144.
Understanding Moisture Content
All cabinet-grade lumber begins as a “green” board that’s mill-sawed from a freshly felled tree. The moisture content of a green board will be 28 percent or greater, making it unsuitable for woodworking because all wood shrinks, warps, and splits as it dries.
Air-drying reduces the moisture content naturally-worker stack the slabs in such a way that air circulates between the separated layers of boards.
Air-drying lowers the moisture level to between 12 and 17 percent. (This is acceptable for outdoor construction, but don’t make any interior projects using air dried material).
Kiln-drying takes over where air-drying leaves off. Large oven-like kilns with carefully controlled temperatures reduce the moisture content to between 6 and 9 percent, the ideal range for interior projects.
With few exceptions, retail hardwood dealers sell only kiln-dried lumber. It’s stored and sold indoors under a roof where the elements won’t affect it.
Kiln-dried lumber should be stored indoors lying flat on dry sticks of scrap or hardboard. Never lay it directly on concrete because it will absorb excessive moisture.
From the editors of Wood Magazine
Lumber Grading
Hardwoods are graded differently then softwood. Graders look at the wood at the wood to see what size rectangular shapes can be cut with no defects. This is called clear faced cutting. The waste and size of the clear cutting areas determines the grade. Grading goes like this:
FAS-First and seconds-No more than 16% waste and the worst side of the board is the side graded. The clear cutting cannot be smaller than 3 inches wide and 7 feet long or 4 inches wide and 5 feet long. The actual boards must be at least 6 inches wide and 8 feet long.
FAS-1 This grade is scored like FAS but on the best side of the board.
Selects are also similar but the boards can be as short as 6 feet and as narrow as 4 inches.
Number 1 Common can have 33% waste and clear cuttings are 4 inches wide and 2 feet long or 3 inches wide and 3 feet long. The length of the board must be at least 3 inches wide and 4 feet long.
Number 2 or 3 Common have even more waste and are usually not used in furniture.
Of course there are exceptions to everything and lumber grading is no different. Quarter sawn boards can be as narrow as 5 inches in walnut and butternut and still be classified as FAS.
The long and short of it is that hardwood is graded for useful wood and softwood is graded by appearance.