WOOD - Materials for Civil and Construction Engineers - page 404

FIGURE 10.7 Types of
board cut: (a) flat sawn, (b) rift
sawn, and (c) vertical- or
edge-sawn.

(a) (b) (c)

Flat-sawn boards have desirable exposure of grain for decorative appli-
cations. However, flat sawn boards tend to distort more than vertical-sawn
boards in response to moisture fluctuations. Hence, vertical-sawn boards are
generally better for structural applications.
The sawing pattern selected depends on the cross section of the tree, the
capability of the mill, and the desired product. Plain sawing is rapid and eco-
nomic, whereas quarter sawing maximizes the amount of vertical-sawn cuts.
Some of the advantages of the different sawing patterns are summarized in
Table 10.2 (USDA-FS, 1999).

■ 10.4.2 Seasoning

Green wood, in living trees, contains from 30% to 200% moisture by the
oven-dry weight. Seasoning removes the excess moisture from wood. For
structural wood, the recommended moisture content varies from 7% in the

T ABLE 10.2 Relative Advantages of Plain-sawn and Quarter-sawn Lumber

Plain-sawn Quarter-sawn

Shrinks and swells less in thickness Shrinks and swells less in width

Surface appearance less affected by Cups, surface checks, and splits

round or oval knots,compared to less in seasoning and in use

effect of spike knots in quartersawn
boards; boards with round or oval knots
not as weak as boards with spike knots
Shakes and pitch pockets, when

Raised grain caused by separation

present, extend through fewer boards in annual rings does not become as

pronounced

Figure patterns resulting from annual Figure patterns resulting from

rings and some other types of figure pronounced rays, interlocked grain,

brought out more conspicuously and wavy grain are brought out

more conspicuously

Less susceptible to collapse in drying Does not allow liquids to pass

through readily in some species

Costs less because it is easy to obtain Holds paint better in some species

Sapwood appears in boards at edges
and its width is limited by the
width of the log