Intro to Wood Materials
TED 126
ENGINEERING MATERIALS AND
PRODUCT DESIGN
Classification of Woods
A tree is usually defined as a woody
plant which, when mature, is at least 20
feet tall, has a single trunk, unbranched
for at least several feet above the ground
and has a definite crown.
 Trees are divided into two biological
categories: softwoods and hardwoods.
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Classification of Woods
The terms softwood and hardwood do not refer
to the hardness or density of the wood.
Softwoods are not always soft, nor are
hardwoods always hard.
Mountain-grown Douglas fir, for example,
produces an extremely hard wood although it
is classified as a "softwood," and balsawood,
so useful in making toy models, is classified a
"hardwood" although it is very soft.
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Classification of Woods

Hardwoods are biologically called
angiosperms, which are trees that produce
seeds enclosed in a fruit or nut.
 The hardwood category includes the
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oaks, ashes, elms, maples, birches, cherry, walnut,
beeches and cottonwoods.
In contrast to softwoods, hardwood trees have
broad leaves and nearly all North American
hardwoods are deciduous, which means they drop
their leaves in the fall.
However, there are exceptions: holly, magnolia and
live oak are hardwoods that retain their leaves
year- round.
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Classification of Woods
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In biological terms, softwoods are called
gymnosperms, which are trees that produce "naked
seeds."
The most important group of softwoods are the
conifers or cone-bearing trees, which have seeds
that are usually visible inside opened cones.
All species of pine, spruce, hemlock, fir, cedar,
redwood and larch are softwoods.
Nearly all softwood trees have another common
characteristic: their leaves are actually needles or
scales and they remain on the tree throughout the
winter, which is why they are also called evergreen
trees. Exceptions are larch (or tamarack) and cypress
whose needles drop in the fall, leaving the tree bare
during winter.
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Classification of Woods

Giant coast redwoods
(Sequoia sempervirens)

The largest trees are
over 300 feet (91 m)
tall and 17 feet (5.2 m)
in diameter. They
sprouted from seeds
the size of oatmeal
flakes nearly 2000
years ago, and grew
into giants taller than
the Statue of Liberty
(from the foundation of
pedestal to torch).
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Classification of Woods
Ancient Bristlecone Pine
Bristlecone pines (Pinus longaeva and
Pinus aristata) are one of the best sources
of tree ring data because they live so long.
As a result of the matching and overlapping
of tree rings from different trees and sites,
bristlecone pine chronologies exist that
extend back to 9000 years ago.
Earth's oldest living inhabitant "Methuselah" at
4,767 years, has lived more than a millennium
longer than any other tree.
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Classification of Woods

Identification characteristic of woods:
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Color – Most timbers show variation in color
between species and within species. It can also
vary within a single piece. Color descriptions
usually relate to the heartwood of the species and
may be significantly different from that of the
sapwood. (Sapwood is always white to very light
brown.) Color can vary with use, age and by the
application of finishes. Timber exposed to light
will change color, and unprotected timber exposed
to the weather will eventually become silvery grey
in color.
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Classification of Woods
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Identification characteristic of woods:
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Texture – of timber may be described as being coarse, fine,
even or uneven.
The differentiation between coarse and fine texture is
determined by the size and arrangement of the wood cells.
Softwoods are usually fine textured, while hardwoods
may be either.
For example, mountain ash is a coarse textured hardwood,
but brush box is a fine textured hardwood. The main process
affecting texture of the timber is the finishing applied during
fabrication. Planing will produce a fine texture, sanding or
brushing – a fine to coarse texture, rough sawing or splitting a
coarse to uneven texture. Surface finishes will also affect the
texture, high build, smooth coatings will give the finest texture.
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Classification of Woods

Identification characteristic of woods:
Figure – refers to the pattern produced on the
surface of the timber. The pattern is determined by
the type of grain, the arrangement and size of cells,
color variations and sawing patterns.
Designers can use these features to produce striking
effects in different lights. Where particular grain
patterns are required, this will need to be
investigated very carefully with the supplier, and
may require special milling.
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Classification of Woods

Identification characteristic of woods:
Grain – refers to the general direction, size
and arrangement of wood fibers.
Grain can be described as sloping, straight,
spiral, irregular, wavy etc.
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Classification of Woods

Identification characteristic of woods:
Hardness – refers to the resistance of the
timber to penetration.
 This is an important parameter for flooring,
with harder species wearing better and
requiring less maintenance than softer
species.
 It may also be an important parameter for
some cabinetry and joinery.
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Classification of Woods
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Identification characteristic of woods:
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Density – is influenced by cell structure and size,
thickness of the cell walls and moisture content.
The density of timber at a specific moisture content
(usually 12%) is the amount of wood substance in
a given volume, expressed as kilograms per cubic
meter.
Density is one of the most reliable indicators of
stiffness, joint strength, hardness, ease of
machining, fire resistance and drying
characteristics.
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Classification of Woods
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Identification characteristic of woods:
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Thermal properties – timber is a natural insulator.
Air pockets within its cellular structure make timber
a natural barrier to heat and cold.
As thermal conductivity increases with density,
lightweight timber is a better insulator than dense
timber.
Thermal conductivity also varies slightly with
moisture content, and natural characteristics such
as checks, knots and grain.
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Classification of Woods
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Identification characteristic of woods:
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Acoustic properties – an important property of
timber is its ability to damp vibrations.
Its cellular network of minute interlocking pores
converts sound energy into heat energy by
frictional and viscous resistance within these pores
and by vibration of their small fibers.
Because of this high internal friction, wood has
more damping capacity than most other
materials.
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Wood Structure

Cellulose (70%)… It forms the primary structural
component of green plants.
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The primary cell wall of green plants are made of
cellulose; the secondary wall contains cellulose with
variable amounts of lignin.
Lignin (25%) and cellulose, considered together,
are termed lignocellulose, which (as wood) is argued
to be one of the most common biopolymers on Earth.
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Wood Structure

Minerals, starches, oils, tannins,
coloring agents fats and waxes.
(5%)
 All plants have tube or straw
shaped channels ducts that
run the direction of the plant
called xylem. XYLEM,
(pronounced ZIE-lem) is a tissue
in plant stems and roots.
 Xylem transports water and
minerals upwards from the roots
to the stem, via capillary action.
 Xylem is strong and also
provides support to the plant.
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Wood Structure

The two most troubling characteristics of
juvenile wood are that:
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it shrinks and swells along the grain as
moisture content changes, and
strength is lower, and in some cases much
lower, than mature wood of the same tree.
This results in dimensional change not only in
tangential and radial directions, but also
along the grain when moisture is lost or
gained.
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Wood Structure
Seasoning of lumber
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Green is wood that just been cut from a log
 Once cut into individual boards they will be
stored in either vertical or horizontal racks.
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Wood Structure
Basic Methods of converting a log
 Plain sawn wood is the type most typically seen
today. When the log is cut in to planks all the cuts
are parallel to each other.
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Wood Structure
Basic Methods of
converting a log
 With Quarter sawn wood
the log is first quartered
(hence quarter sawn) and
then diagonally from the
center.
 This results in a grain that is
more vertical when looking
at the plank end on.
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Wood Structure
Air Drying (AD)
 To air dry, the lumber is arranged in layers, or
courses, with
 separating stickers, and built up into unit
packages and piles
 outdoors so that atmospheric air can circulate
through the
 piles and carry away moisture
 Reduces moisture to about 15 percent.
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Wood Structure
Force Drying
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In more complex drying processes, stickered
packages of
lumber are placed in closed buildings that
have fans to recirculate
heated air through the lumber piles. Both
forced air
dryers and predryers are commonly
considered low temperature,
forced-air circulation.
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Wood Structure
Kiln Drying (KD)
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To kiln dry, lumber is dried in a closed
chamber by controlling
the temperature, relative humidity, and air
circulation
until the wood reaches a predetermined
moisture content.
Seven percent moisture – four to five days.
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Wood Structure
Radio Frequency (RF)

Heat waves' unique technology utilizes
electromagnetic waves from the
 Radio Frequency spectrum to heat products
within a vacuum controlled environment.
 Heat waves' kilns use amplifier based power
generators to create the radio frequency field
which heats each load.

Amplifiers, as opposed to oscillators, allow for
absolute control of the RF field which allows us
to prevent any unwanted effects during the
process. Usually for hardwoods – 24 hours.
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Growth of a Tree
A tree grows two times during the year.

Spring Growth – largest growth ring, the lighter
colored ring
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Summer Growth – smaller growth ring, darker
colored ring.
1 light-colored ring + 1 dark-colored ring = 1 year.
This is called a "growth ring.
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Growth of a Tree
Rings
… the tree rings on the "Messiah" violin (photo ©
H.D. Grissino-Mayer).
The wood used by Antonio Stradivari and all
Cremonese violin makers for the violin top
was Norway spruce (Picea abies).
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Growth of a Tree
Rings
A cross section from an
eastern hemlock (Tsuga
canadensis) collected by
Rex Adams near Ashland,
Wisconsin (photo © H.D.
Grissino-Mayer and R.K.
Adams).
The rings are extremely clear
on this specimen.
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Growth of a Tree
Rings
….identify
Heartwood
Sapwood
Cambium
Outer Bark
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Growth of a Tree
Rings
Thickness:
How wide a ring is can tell
you if the environment
was good or bad for the
tree to grow in.
In years when the amount
of rain and temperature
were good a tree's rings
are wider.
In bad years a tree's rings
are thinner.
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Growth of a Tree
Rings
Shape:
If rings start to become
thinner on one side
than the other it
probably means the
tree is leaning over to
one side.
High winds or a big
storm can cause a
tree to lean.
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Growth of a Tree
Things scientists study to learn about climate
in the past include:
 Ice cores from the Antarctic and Greenland.
(They study bubbles of gas trapped in the ice.)
 Pollen from the bottom of lakes.
 Fossil records of insects.
 Growth rings of trees.
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Growth of a Tree
Dendrochronology: the study of tree rings
Dendrochronology
…means the measuring of time using trees –
dendro = trees, and
chronology = system of measuring time.
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Growth of a Tree
Extending a chronology based on
living trees further back
in time through
crossdating.
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Nature of Industrial Stock
Yard Lumber – mainly softwoods
Dimensional lumber is a term used in North America for
lumber that is finished/planed and cut to standardized
width and depth specified in inches. 1 x 12
Factory Lumber - Softwood lumber graded and used in the
factory for the manufacture of such items as doors,
sashes, moldings, and so on.
Shop lumber - Softwood lumber graded and used in the
factory for general cut-up purposes; similar to factory
lumber but of a lower grade.
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Nature of Industrial Stock
Yard Lumber – mainly softwoods
Structural lumber is light framing materials, such as 2 x 4
and widths up to six inches and wider for joist, rafters and
framing uses.
Rough Sawn Lumber – hardwoods and softwoods stock
used for manufacturing fine quality wood products.
Requires additional planing or surfacing.
Chip Form – making of particle boards, wafer board and
other sheet material.
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Nature of Industrial Stock
Yard Lumber……
OSB – Oriented Strand Board
Masonite
Hardboard – High Density Fiberboard
MDF – Medium Density Fiberboard
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Name of Industrial Stock
Lumber Measurement
The thickness of lumber is read in quarters of inches.
four-quarters
five-quarters
six-quarters
eight-quarters
4/4
5/4
6/4
8/4
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Name of Industrial Stock
Lumber Measurement
 In rough lumber (also called nominal thickness
or size) that has not been surfaced (planed smooth).
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4/4 rough=1” board thickness
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5/4 rough=11/4” board thickness
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6/4 rough=11/2” board thickness
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8/4 rough=2” board thickness
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Name of Industrial Stock
Lumber Measurement
 But surfaced lumber that has been planed
smooth may vary slightly in thickness.
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4/4 rough=3/4” to 13/16” board thickness
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5/4 rough=1” to 11/8” board thickness
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6/4 rough=11/4” to 13/8”board thickness
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8/4 rough=13/4” to 113/16”board thickness
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Wood Grades
Classified accordingly
to its quality.
The grade of lumber
refers to the
appearance,
strength and
lack of defects in the
wood stock.
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Wood Grades

Softwood lumber is graded using the
American Lumber Standards, which are
based on the structural integrity of a board.
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These grades consider the size and location
of defects as well as the slope of grain in
order to predict the load bearing capacity of
the board.
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Wood Grades
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Softwood lumber is graded using the American
Lumber Standards, which are based on the
structural integrity of a board.
These factors are used to determine the percentage
of clear wood in the board that in turn determines
the grade. Several of the most common grades and
their clear wood requirements are:
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Select - at least 80% clear wood
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Graded A to D. With A presenting the best quality
surface appearance.
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Wood Grades

Softwood lumber is graded using the American
Lumber Standards, which are based on the
structural integrity of a board.
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Common - graded by number, ranging from 1-4.
With 1 being the best grade , no knots.
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#1 Structural - at least 75% clear wood
#2 Structural - at least 66% clear wood
#3 Structural - at least 50% clear wood
Construction Grade - at least 57% clear wood
Standard Grade - at least 43% clear wood
Utility Grade - at least 29% clear wood
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Wood Grades
Hardwood Grades

An FAS(First and Second) board must be at least
6" wide and 8' long. 83 1/3% of the board must be
clear.
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F1F (FAS One Face) If a board face is graded to FAS but the
reverse face is not, the board drops in grade. If the reverse
face of a board can be graded as #1 Common, the entire
board is graded as F1F.
 For example, if a board face grades to FAS but the reverse
face only yields 82% clear the entire board is graded to at
best F1F.

If a board reverse face cannot be graded to #1 Common the
board is not F1F.
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Wood Grades
Hardwood Grades
 Select
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A select board is graded exactly like FAS.
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The only difference is that the minimum size
of a Select board is 4" x 6' (whereas an FAS
board must be at least 6" x 8').

The reverse face of a Select board can be
either Select or #1 Common.
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Wood Grades
Hardwood Grades
 #1 Common (Number 1 - 4)
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A #1 Common board must be at least 3" wide and 4' long. 66 2/3% of
the board must be clear.
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The maximum number of imaginary cuts is one-third of the board
measure plus one. Surface area after each imaginary cut must be at
least 4" x 2' or 3" x 3'.
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For example, a board 6" x 8' is 4 board measure. One third of 4 +
1 is 1. If a single imaginary cut in the board yields 66 2/3% clear
where the uncut area is at least 4" x 2' or 3" x 3', the board is
graded as #1 Common.
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An additional cut in the board is allowed if the resulting clear yield is at
least 75%. This applies to boards between 3 and 10 board measure.The
reverse face of a #1 Common board is always #1 Common.
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Wood Grades
Hardwood Grades
 #2 Common… #2 Common board must be at least 3" wide and
4' long, just like #1 Common.
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The clear yield of a board can be as low as 50% after cuts equal to
half of the board measure. Surface area after each imaginary cut
must be at least 3" x 2'.
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For example, a board 6" x 8 is 4 board measure and can be cut twice,
half of four. The resulting clear area of the board must be at least 3" x 2'
and at least 50% clear.

An additional cut is allowed in boards between 2 and 7 board measure if
the yield is 66 2/3% clear.

The reverse face of a #2 Common board can be #2 Common or
better.

If the reverse face of a board is #3 Common then the entire board
becomes #3 Common.
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Wood Grades
Abbreviations
HDWD - hardwood
M - thousand
SAP - sapwood
SD - seasoned
S1E - surface one edge
S1S - surface one side
S1S2E -……….
CLR - clear
BTR - better
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Wood Defects
Bark Pockets - a patch of bark partially or whole …enclosed in the wood.
Peck - a channeled or pitted area or pocket
Decay - disintegration of wood fiber.
Shake - a crack between and parallel to the rings of annual growth rings.
Stain - a discoloration that penetrates the wood fibers.
Wormholes - caused by insects or beetles.
Knots - piece of sawed lumber which is either a portion of a branch or limb
of a tree.
Pitch - an accumulation of resinous materials.
Wane - the presence of bark or absence of wood on corners of a piece of
lumber.
Warp - is any variation from a true surface.
Bow - a curve along the face of a board that usually runs from end to end.
Twist - warping in lumber where the ends twist in opposite directions..
Cup - warping along face of a board from edge to edge.
Crook -warping along the edge from one end to the other.
THE END
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