ENCYCLOPEDIA OF WOOD

LUMBER CUTTING METHODS

LUMBER CUTTING METHODS

C

onverting a log into lumber requires certain compromises. Most logs are sawn in one of three basic ways. The sim­plest method squares the log and slices it into boards straight through from one side to the other. This technique, known as through-and-through sawing, results in stock cut tangentially to the annual growth rings. A second method, plain­sawing, is similar, except that the log is rotated as it is cut, and the low-quality pith is set aside for items such as pallets. Plain-sawn lumber is also known as flat­grained lumber.

The third method, called quarter­sawing or edge-grain sawing, divides the log into four quarters and cuts every board more or less radially. Quarter - sawn boards have their annual growth rings perpendicular to the face.

This orientation of the growth rings accounts for the dimensional stability of quartersawn boards. Wood shrinks and expands roughly twice as much tangen­tially to the rings as its does radially. When quartersawn boards swell or shrink they do so mostly in thickness, which is minimal, whereas a plain-sawn board changes across its width. A din­ing table made from plain-sawn pine boards, for example, can change as much as 1 inch in width; a similar table made from quartersawn boards would only swell or shrink by one-third as much.

THREE METHODS OF SAWING LOGS

LUMBER CUTTING METHODS

Choosing the best method

Cutting logs into lumber at a sawmill is a balance between intend­ed use, structural stability and esthetic appearance. Plain-saw­ing (above, left) produces boards of diminishing width as the log is rotated to make successive cuts. The more expensive method, called quartersawing (above, center), limits board width to the
radius of the log. But it produces more dimensionally stable lumber, making it ideal for drawer sides, tabletops and frame rails. Through-and-through sawing (above, right) yields the maximum number of usable boards from a log; the outer boards are plain-sawn, while the inner boards are quartersawn.

Подпись: The growth rings in this plain-sawn oak board appear on the face as an elliptical landscape figure. Plain-sawn stock is sliced from logs with most of the cuts tangent to the rings.LUMBER CUTTING METHODS

Quartersawing also offers an esthetic advantage: It exposes the medullary rays that radiate from the heart of a log like the spokes of a wheel. In most species the rays are only one cell thick, but in a few species, such as oak, the ray ceils are thicker and appear as vivid streaks scattered along the grain. Sycamore, poplar and basswood are also ideal candidates for quartersawing.

As the illustration at the bottom of page 24 shows, quartersawn lumber is not always cut perpendicular to the grain, and some through-and-through cut boards close to the center of a log will have quartersawn grain. Therefore, no matter how they are actually cut, boards with growth rings at angles between 45° and 90° to the wide surface are classified quartersawn, while boards
with rings at 0° to 45° angles to the wide surface are termed plain-sawn. Boards with growth rings at a 30° to 60° angle are also called rift-sawn or bastard-sawn.

In actual practice, sawyers use a myr­iad of sawing patterns, depending on the type of machinery being used, the intended use of the lumber, log diameter and the type of tree. For example, in vir­tually all trees the pith or central core of the heartwood is less desirable than and not as strong as the rest of the heartwood. Plain-sawing “boxes out the heart” by cutting around it to eliminate it.

ADVANTAGES OF PLAIN-SAWN AND QUARTERSAWN LUMBER

PLAIN-SAWN

QUARTERSAWN

Cheaper and easier to obtain

More dimensionally stable

Shrinks and swells less in thickness

Shrinks and swells less across the board

Usually comes in greater variety of widths

Twists and cups less

Less susceptible to collapse during drying; easier to kiln dry

Splits and checks less in seasoning and in use

Figure patterns resulting from the difference between earlywood and latewood in the growth rings are more conspicuous

Raised grain caused by the swelling of the earlywood in growth rings not as pronounced

Has more interesting figure

Figure due to pronounced rays more conspicuous

Round or oval knots that may occur have less effect on structural integrity

Holds finishes better in some species

Pockets of pitch extend through fewer boards

Sapwood in boards appears at the edges and is easily cut off

Not as susceptible to splitting when nails or screws driven through face

Wears more evenly

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