Types of Wood for Carpentry

Choosing Wood – What About Species?

Types of Wood for Carpentry Trees are classified in two categories, hardwoods and softwoods. But don’t rely just on the name, because a softwood like Douglas fir is actually harder than basswood, which is known as a hardwood.

Commercially available softwoods include pines, spruces, firs, and redwood. Hardwoods harvested for market include oak, birch, maple, cherry, and walnut. These woods are not only cut into strips and boards to sell, but are also sliced to face panels such as plywood, and are chipped up to manufacture fiberboard and particleboard.

All wood is made up of cellulose (the cell framework), lignin (the cement between the cells), organic extractives (which give the wood its color, density, scent, and rot resistance), and trace minerals.

Variations in these elements make the difference between hard and soft woods, stiff and flexible woods, and woods that are light or dark. The makeup of each species is fairly constant, so a wood’s species has come to serve as a guideline in choosing wood for one purpose or another.

For general construction, softwoods are good because they’re available, reasonably priced, and easy to work with. Most lumberyards or home improvement centers should have a dimensional lumber on hand for framing and finishing all the projects you’d want to build.

The hardwoods — used for cabinet and furniture manufacture — are more expensive and not as easy to come by, though some retail outlets supply them for home use. Hardwood is a bit more difficult to work with than softwood because it’s more dense. That’s compensated for to some degree by the fact that hardwoods offer a cleaner cut, are usually stronger, and have better appearance quality than softwoods in general.


Wood Size and Dimensions

Lumber is sized and priced by its rough-sawn dimensions. But when the rough stock is planed for the market, the overall size can be reduced by 25% or more. The original sawn dimension is called its nominal size — after planing, the piece is sold by its actual dimension. This, if you’ve ever wondered, is why a 2 x 4 really measures only 1-1/2″ by 3-1/2″. A piece of lumber less than 1″ thick and between 2″ and 6″ wide is called a strip. Stock less than 2″ thick and up to 16″ wide is a board. Dimension lumber measures from 2″ to 4-1/2″ thick and up to 16″ wide. Standard lengths range from 6′ to 16′, in 2-foot increments.

Hardwoods are sized differently. Boards come in random widths up to 6″, though wider boards can be custom-cut. Standard lengths run from 4′ to 16′. Thickness is generally measured in 1/4″ graduations, from 1″ to 4″, and is expressed as a fraction — for example, a 5/4″ board measures 1-1/4″ before it’s planed.

Wood is sold commercially in volume by the board foot, a long-established standard by which each unit is equivalent to a rough board measuring 1″ thick by 12″ wide by 12″ long, or 144 cubic inches of wood altogether. The rules are that any stock less than an inch thick is counted as a full inch, and anything over 1″ is figured to the next larger 1/4″.

In the market, 4 board feet could be a twelve-foot 1 x 4 or a 16-foot piece measuring 1-1/2″ x 2″. To calculate board feet, multiply thickness by width in inches, then multiply by length in feet and divide by 12.


Sheet and Panel Products

Solid lumber for both commercial and home use is steadily being supplanted by manufactured sheet goods. At one time, plywood was about the only panel product readily available, but today there are several kinds of panels that can be used to make good-looking and highly functional projects and furniture pieces.

Plywood — made of thin veneers glued so that the grain of adjacent layers run perpendicular to one another — comes in a standard 4′ x 8′ panel. There is a 3/16″ thick panel, then sizes run from 1/4″ to 3/4″ in 1/8″ increments. The quality and cost of the board increases as more layers are used (regardless of finished thickness), because multiple layers improve the consistency and flatness of the sheets. Veneer plywood is stable and holds screws extremely well. It can be faced in a variety of wood types for finish and underlayment use.

Lumber-core plywood is a costly variant of its common cousin which isn’t in general use. Its core stock is softwood or hardwood lumber rather than thin veneers, and although it stays flatter than regular plywood and has the same characteristics, it’s really not worth the extra expense.

Medium-density fiberboard (MDF) is manufactured from small wood fibers bound together by resins with heat and pressure. It’s less costly than either type of plywood and takes very well to cutting and routing. It also holds a screw nearly as well as plywood, though it does better with a sheet-metal thread — style fastener than with a regular wood screw and must use a pilot hole.

MDF is somewhat heavy and comes in sizes from 3/16″ to over 1″ in standard fractional dimensions. It’s also made in 4′ and 5′ widths and in lengths up to 20′. One very attractive feature of these panels is that they can be ordered with a thin veneer of wood surface (these are called MDF-core plywood), which can be stained and finished like any other veneer. Otherwise, the unfinished panels, which are extremely smooth, can be covered with laminate or painted with excellent results.

Particleboard is also called chipboard. It’s made of small wood particles and fibers bonded in the same fashion as MDF. It comes either as a core sheet or as a plywood panel with a wood face and back. It’s heavy but less expensive than any of the other sheets, and comes in the same standard sizes as medium-density fiberboard. Drawbacks? The sheets don’t always cut cleanly and don’t hold a fastener as well as the other products. On the other hand, particleboard is more readily available than MDF.


Lumber Grades

When a log is harvested, the lumber varies in quality. To assure that buyers get a product that’s suited to their needs, the lumber is graded into standardized categories.

The grade is based on the size of the wood and the number and significance of defects (knots, pitch pockets, decay) that affect the strength, utility, or durability of the finished product. Hardwood and softwood are each graded further by use, which takes species, appearance, and structural integrity into account.

Softwood grades for construction fall into five different categories. No. 1 has tight knots and minor blemishes, and is used for finish work; No. 2 has larger knots and noticeable blemishes, and is suitable for paneling; No. 3 contains knotholes and visible flaws, fine for sheathing. Nos. 4 and 5 are low-quality boards.

Appearance lumber isn’t graded for strength but has visual appeal for finish work. Select grades are described by letters and numbers: B & Btr (1 and 2 Clear) is a higher-quality product than C Select, which contains limited defects. D Select grade has minor surface imperfections.

Hardwood lumber is graded into categories, mainly for manufacturing. “Firsts and seconds” (FAS) is a combination of the two best grades — the boards must be at least 6″ wide and 8′ long. “Selects” are FAS-quality boards at least 4″ wide and 6′ in length.

Plywood panels can be made of softwood (Douglas fir, western hemlock, and pine) or hardwood (birch, oak, cherry, and walnut). The grades are established by the quality of the face and back veneers. The inspection stamps on the back of each panel show the grade of both sides, the wood species group number (lower numbers indicate stiffer panels), application for interior or exterior use, and the mill and test marks.

Softwood panels are graded by letter: N — suitable for a natural finish and free of open defects; A — smooth and paintable, limited to 18 neatly made repairs; B — solid surfaced, with circular repair plugs and tight knots; C — knotholes up to 1″ and tight knots to 1-1/2″, with limited splits allowed.

Hardwood panels use number grades: 1-premium — matched grain with only minor defects; 1 — good, but unmatched grain and minor defects; 2 — sound, suitable for painting, with appearance defects and smooth patches.


Making the Best Choice

In lumberyard stock, the better grades will be free of major defects, but it’s always a good idea to visually inspect the lumber you want before you buy it. Some places try to discourage “handpicking,” but you shouldn’t accept poor quality.

Things to be critical of in a piece of wood are knotholes, checks, wane (flat or rounded edges), and warpage — either a bend or a twist in the wood. If appearance is a prime concern, as in hardwoods, stains or insect holes can affect your choice.

Workability is important, but with sharp-bladed tools problems can be reduced. A dense softwood such as Southern pine will cut and work well; hardwoods, especially oak, are tough on tool edges but have the same good qualities. The species to avoid are those that tear easily, are prone to split and warp, and give a ragged cut. The manufacturers of MDF panels recommend that table saws be equipped with sharp, all-purpose combination blades with high rake angles and a high tooth count (a minimum of 50 on a 10″ blade).

07. December 2010 by admin
Categories: Hand Tools, Home Maintenance | Tags: | Comments Off on Types of Wood for Carpentry

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