Wood Working (Basics)

WOOD

TREE ANATOMY

OUTER PROTECTION OF DEAD

BARK

INNER

LIVING BARK

(COMPOSED OF HOLLOW

LONGITUDINAL CELLS THAT CONDUCT NUTRIENTS FROM THE LEAVES TO THE ROOTS)

CAMBIUM LAYER -

TREE ANATOMY

THICK LAYER OF LIVING WOOD CELLS INSIDE THE CAMBIUM IS

CALLED THE

SAPWOOD

(THIS IS WHERE NUTRIENTS ARE STORED)

AT THE INNER EDGE OF THIS

RING, THE SAPWOOD DIES AND

BECOMES

HEARTWOOD

TREE ANATOMY

AT THE VERY CENTER OF THE

TREE IS THE

PITH

ZONE OF WOOD CELLS THAT WERE THE FIRST YEAR’S

TREE ANATOMY

WOOD IS MADE OF TUBULAR CELLS WHOSE LONG AXIS IS PARALLEL TO THE LONG AXIS OF THE TRUNK

CELLS ARE STRUCTURED OF TOUGH CELLULOSE

CELLS ARE BOUND TOGETHER WITH LIGNIN

TREE GROWTH

THE CAMBIUM

MANUFACTURES NEW SAPWOOD CELLS IN THE SPRING

GROWTH OCCURS RAPIDLY

DUE TO COLD TEMPERATURES AND AMPLE GROUND WATER

TREE GROWTH

GROWTH IS SLOWER IN THE SUMMER BECAUSE OF HIGH HEAT AND LOWER WATER

CELLS ARE MORE DENSE THAN SPRINGWOOD CELLS

THESE CELLS ARE “SUMMERWOOD” OR “LATEWOOD” CELLS

SOFTWOODS & HARDWOODS

SOFTWOOD

HARDWOOD

NAMES ARE DECEPTIVE

SOFTWOODS & HARDWOODS

SOFTWOOD TREES HAVE A SIMPLE MICROSTRUCTURE CONSISTING OF MAINLY

SOFTWOODS & HARDWOODS

HARDWOOD TREES ARE MORE COMPLEX IN STRUCTURE,

WITH A LARGER PERCENTAGE OF RAYS AND TWO DIFFERENT TYPES OF LONGITUDINAL

CELLS:

FIBERS (SMALL DIAMETER)

SOFTWOODS

SOFTWOOD LUMBER HAS AN UNINTERESTING GRAIN

STRUCTURE

MOST LUMBER FOR BUILDING FRAMING COMES FROM

SOFTWOODS

HARDWOODS

HARDWOOD LUMBER HAS BEAUTIFUL GRAIN

STRUCTURE

USED FOR FINE FURNITURE

AND INTERIOR FINISH DETAILS

CERTIFIED WOOD

CERTIFIED WOOD COMES FROM FORESTS THAT ARE

MANAGED FOR THEIR LONG-TERM ECOLOGICAL

SUSTAINABILITY AND ECONOMIC VIABILITY

FOREST STEWARDSHIP

LUMBER

1. BEGINS WITH THE FELLING OF TREES AND THE

TRANSPORTATION OF LOGS TO THE SAWMILL

2. EACH LOG IS STRIPPED OF BARK

3. PASSED THROUGH A

LUMBER

4. THE SAWYER (WITH

COMPUTER HELP) JUDGES HOW TO OBTAIN THE

MAXIMUM MARKETABLE WOOD FROM EACH LOG

5. USING HYDRAULIC

MACHINERY TO ROTATE AND ADVANCE THE LOG, THE

LUMBER

6. A CONVEYOR BELT CARIES

THE SAWED OFF PIECES AWAY TO SMALLER SAWS WHERE THEY ARE REDUCED TO

PLAINSAWING

THE SEQUENCE AND PATTERN WITH WHICH THE LOG IS

SAWN AFFECT THE

ORIENTATION OF THE GRAIN WITHIN THE FINISHED PIECES

PLAINSAWN

PLAINSAWING

THE ORIENTATION OF THE GROWTH RINGS VARIES

ALONG THE BOARD’S WIDTH

A LARGE PORTION OF THE

BOARD’S WIDER FACE HAS A GRAIN PATTERN IN WHICH THE ANNUAL RINGS ARE ORIENTED CLOSE TO

PARALLEL WITH THE FACE

PLAINSAWING

“FLAT-GRAIN” LUMBER HAS A TENDENCY TO WARP OR

QUARTERSAWING

QUARTERSAWN

PRODUCE EDGE-GRAIN OR VERTICAL GRAIN LUMBER

TYPICAL FOR STRUCTURAL LUMBER

ANNUAL GROWTH RINGS RUN MORE CONSISTENTLY

QUARTERSAWING

VERTICAL GRAIN BOARDS TEND TO REMAIN FLAT DESPITE CHANGES IN MOISTURE CONTENT

SEASONING

GROWING WOOD CONTAINS WATER

THIS CAN RANGE FROM 30% TO 300% OF THE OVEN DRY WEIGHT OF THE WOOD

AFTER A TREE IS CUT, WATER STARTS TO EVAPORATE

SEASONING

WHEN THE FREE WATER IS GONE, THE TREE STILL CONTAINS 26-32% MOISTURE

THIS “BOUND WATER” IS HELD WITHIN THE CELL WALLS

AS THE BOUND WATER EVAPORATES, THE WOOD STARTS TO SHRINK

SEASONING

WOOD CAN BE DRIED TO ANY DESIRED MOISTURE CONTENT

FRAMING LUMBER IS CONSIDERED SEASONED WHEN IT HAS A MOISTURE CONTENT OF 19%

SEASONING

WOOD WILL MAINTAIN AN EQUILIBRIUM WITH THE SURROUNDING AIR

MOISTURE

IT IS THEREFORE OF LITTLE USE TO HAVE FRAMING

LUMBER WITH A MOISTURE CONTENT BELOW 13%

FINISH CARPENTRY & ARCHITECTURAL

SEASONING

MOST LUMBER IS SEASONED AT THE SAWMILL

CAN BE AIR DRIED IN LOOSE STACKS FOR A PERIOD OF MONTHS

SHRINKAGE

WOOD DOES NOT SHRINK AND SWELL UNIFORMLY WITH CHANGES IN MOISTURE

SHRINKAGE ALONG THE LENGTH OF THE LOG

SHRINKAGE

SHRINKAGE IN THE RADIAL DIRECTION (

RADIAL

SHRINKAGE

SHRINKAGE AROUND THE CIRCUMFERENCE OF THE LOG (

TANGENTIAL SHRINKAGE

SHRINKAGE

IF A LOG IS SEASONED

WHOLE, IT WILL NOT SHRINK MUCH ALONG THE LENGTH (LONGITUDINAL), BUT WILL SHRINK IN DIAMETER

SHRINKAGE

DISTORTION OF A BOARD

SAWN FROM A LOG VARIES

SURFACING

LUMBER IS SURFACED TO MAKE IT SMOOTH AND MORE DIMENSIONALLY PRECISE

ROUGH (UNSURFACED) LUMBER IS ALSO AVAILABLE

MOST LUMBER IS SURFACED ON 4 SIDES (S4S)

LUMBER DEFECTS

DEFECTS CAN COME FROM:

GROWTH CHARACTERISTICS (DEFECTS CAUSED BY THE GROWTH OF THE TREE)

LUMBER DEFECTS

TYPES OF “GROWTH

CHARACTERISTICS” DEFECTS

KNOTHOLES

DECAY

LUMBER DEFECTS

TYPES OF “MANUFACTURING CHARACTERISTICS” DEFECTS:

CHANGES RESULTING FROM DIFFERING RATES OF SHRINKAGE

LUMBER GRADING

GRADES OCCUR FOR APPEARANCE OR FOR STRUCTURAL STRENGTH/APPEARANCE

(DEPENDING ON INTENDED USE)

LUMBER GRADING

MAIN BEAMS OR STRUCTURAL MEMBERS ARE OFTEN A HIGH GRADE/HIGH COST

REMAINING MEMBERS ARE OFTEN INTERMEDIATE GRADE/LOWER COST

LUMBER GRADING

STRUCTURAL GRADING CAN BE DONE BY MACHINE OR BY PERSON

VISUAL GRADING (BY PERSON) ALLOWS A PERSON TO JUDGE QUALITY AND STAMP IT WITH A GRADE IN

LUMBER GRADING

IN MACHINE GRADING, AN AUTOMATIC DEVICE ASSESSES THE STRUCTURAL PROPERTIES OF THE WOOD AND

STAMPS A GRADE AUTOMATICALLY ON THE PIECE.

LUMBER GRADING

STRUCTURAL PROPERTIES OF

WOOD

WOOD IS USUALLY:

STRONGER IN COMPRESSION THAN IN TENSION

STRONGER PARALLEL TO THE GRAIN THAN PERPENDICULAR TO THE GRAIN

LUMBER DIMENSIONS

LUMBER SIZES ARE GIVEN IN

NOMINAL DIMENSIONS

SUCH AS 2 X 4 (TWO BY FOUR)

TRUE SIZES ARE LESS THAN THESE NOMINAL DIMENSIONS

LUMBER TERMINOLOGY

PIECES OF LUMBER THAT ARE LESS THAN 2 INCHES IN

NOMINAL THICKNESS ARE CALLED

BOARDS

PIECES FROM 2 TO 4 INCHES IN THICKNESS ARE

REFERRED TO AS

DIMENSION LUMBER

PIECES NOMINALLY 5 INCHES AND MORE IN THICKNESS

LUMBER TERMINOLOGY

LUMBER IS COMMONLY SUPPLIED IN 2’ INCREMENTS, 8’, 10’, 12’, 14’, 16’

RAFTER MATERIALS ARE OFTEN STOCKED IN SIZES UP TO 24’

LUMBER IS PRICED BY THE BOARD FOOT - A

BOARD FOOT

A BOARD FOOT OF LUMBER IS DEFINED AS A SOLID VOLUME OF 12 SQUARE INCHES IN NOMINAL CROSS SECTIONAL AREA AND ONE FOOT LONG

WOOD PRODUCTS

MUCH OF THE WOOD USED IN CONSTRUCTION TODAY IS PROCESSED INTO MANUFACTURED PRODUCTS

DESIGNED TO:

OVERCOME SHORTCOMINGS OF REGULAR WOOD

GLUE-LAMINATED LUMBER

JOINING TOGETHER SMALLER STRIPS OF WOOD TO FORM A LARGER STRUCTURAL MEMBER

JOINING OCCURS WITH GLUE

LAMINATE BECAUSE:

SIZE

SHAPE

GLUE-LAMINATED LUMBER

VIRTUALLY ANY SIZE STRUCTURAL MEMBER CAN BE MADE BY LAMINATING (UP TO MACHINERY LIMITS)

CAN BE LAMINATED INTO SHAPES LIKE CURVES, ANGLES AND VARYING CROSS SECTIONS

GLUE-LAMINATED LUMBER

INDIVIDUAL LAMINATIONS ARE COMMONLY 1.5 INCHES THICK (EXCEPT IN SMALL RADIUS CURVES WHICH ARE 0.75 INCHES THICK)

END JOINTS ARE EITHER FINGER JOINTED OR SCARF JOINTED

HYBRID GLULAM BEAMS

SUBSTITUTE COMPOSITE LAMINATED VENEER LUMBER (LVL) FOR USUAL SOLID WOOD TOP AND BOTTOM

ENGINEERED LUMBER

(STRUCTURAL COMPOSITE)

LAMINATED STRAND LUMBER (LSL)

ORIENTED STRAND LUMBER (OSL)

MADE FROM SHREDDED WOOD STRANDS THAT ARE COATED WITH ADHESIVE THEN PRESSED INTO A

RECTANGULAR CROSS SECTION AND CURED UNDER HEAT AND PRESSURE

LSL STRANDS ARE LONGER THAN OSL STRANDS

LEAST EXPENSIVE OF COMPOSITE PRODUCTS

LAMINATED VENEER LUMBER (LVL)

MADE FROM THIN WOOD VENEER SHEETS (AS WIDE AS

THE MEMBER IS DEEP) THAT ARE GLUED AND LAMINATED INTO THICKER MEMBERS

LVLS ARE SIMILAR TO PLYWOOD IN LOOK, BUT WITHOUT THE CROSSBANDS

PARALLEL STRAND LUMBER (PSL)

MADE FROM LONG THIN STRIPS OF WOOD VENEER THAT

ARE GLUED AND PRESSED IN A PROCESS SIMILAR TO THAT FOR LSL AND OSL BUT WITH THE UNIFORM STRIPS

ARRANGED IN A MORE UNIFORMLY PARALLEL MANNER

HEAVIEST, STRONGEST AND MOST EXPENSIVE

I-JOISTS

FLANGES OF MEMBERS MAY BE SOLID WOOD, LVL OR LSL

WEBS ARE TYPICALLY OSB OR PLYWOOD

USE WOOD MORE EFFICIENTLY THAN

TRADITIONAL LUMBER & CAN SPAN FARTHER

STRUCTURAL FINGER-JOINTED

LUMBER

SHORT LENGTHS OF SOLID LUMBER SCRAP ARE FINGER-JOINTED END-TO-END INTO LONGER LENGTHS

OFTEN USED FOR STUDS AND POSTS

ADVANTAGES/DISADVANTAGES OF

ENGINEERED LUMBER

ADVANTAGES:

PRODUCTIVE USE OF WOOD MATERIALS

USE OF RAPIDLY

RENEWABLE MATERIALS

DIMENSIONAL STABILITY

STRUCTURAL STRENGTH

LARGE SIZES AND LONG

DISADVANTAGES:

ADHESIVES OFF-GASSING

WOOD-PLASTIC COMPOSITE

DECKING

MADE FROM WOOD FIBERS AND PLASTICS OF VARIOUS

TYPES THAT, WITH OTHER CHEMICALS, ARE MOLDED INTO BOARD LIKE SHAPES

CONSISTENT MATERIAL QUALITY

NON-STRUCTURAL COMPOSITE

LUMBER

MADE FROM BLENDS OF PLASTIC AND WOOD AND QUALITY VARIES WIDELY BY SPECIFIC PRODUCT

OFTEN USED FOR TRIM & SHELVING AND OTHER PAINTABLE SURFACES

PLASTIC LUMBER

MADE FROM 50% OR MORE PLASTIC CONTENT

MADE FROM RECYCLED CONSUMER WASTE (BOTTLES, MILK JUGS, ETC.)

LESS STRUCTURAL VALUE

RESISTANT TO WATER, INSECTS, FADING, ETC.

WOOD PANEL PRODUCTS

PANEL DIMENSIONS ARE USUALLY 4’X8’

REQUIRE LESS LABOR TO

INSTALL BECAUSE THEY ARE IN LARGER PIECES

RESIST SHRINKING, SWELLING, CHECKING AND SPLITTING

STRUCTURAL WOOD PANEL

PRODUCTS

3 TYPES:

PLYWOOD

COMPOSITE PANELS

PLYWOOD

MADE OF THIN LAYERS OF WOOD (VENEERS) GLUED TOGETHER

GRAIN ON FRONT AND BACK RUN IN THE LONG DIRECTION

ONE OR MORE OF THE INTERIOR CROSSBANDS HAS THE GRAIN RUNNING IN THE OPPOSITE

DIRECTION

COMPOSITE PANELS

HAVE TWO PARALLEL FACE VENEERS BONDED TO A CORE OF RECONSTITUTED WOOD

NONVENEERED PANELS

ORIENTED STRAND BOARD (OSB)

GLUED INTO THREE TO FIVE LAYERS

OSB STRANDS ARE ORIENTED IS THE SAME MANNER AS THE GRAIN IN PLYWOOD

NONVENEERED PANELS

PARTICLEBOARD

MANUFACTURED IN DIFFERENT DENSITY RANGES

NONVENEERED PANELS

FIBERBOARD

INTENDED FOR INTERIOR USE ONLY

DIMENSIONALLY MORE STABLE THAN PARTICLEBOARD, STIFFER AND BETTER ABLE TO HOLD FASTENERS

PLYWOOD PRODUCTION

VENEERS FOR PLYWOOD ARE ROTARY SLICED:

1. LOGS ARE SOAKED IN HOT WATER TO SOFTEN THE

WOOD

2. LOGS ARE ROTATED ON A LATHE AGAINST A KNIFE THAT PEELS OFF A THIN

PLYWOOD PRODUCTION

3. STRIP OF VENEER IS CLIPPED AND SENT THROUGH A

DRYING KILN (MOISTURE DROPS TO 5%)

4. SHEETS ARE ASSEMBLED INTO LARGER SHEETS AND DEFECTS ARE REPAIRED

(PATCHED)

PLYWOOD PRODUCTION

6. PRESSES COMPRESS THE

STACK WITH PRESSURE AND HEAT TO CREATE DENSE,

FLAT PANELS

PLYWOOD

PLYWOOD COMES IN

THICKNESSES OF .25” TO 1.125”

TYPICALLY 4 X 8 FEET IN SIZE, THOUGH USUALLY .125” (1/8) SMALLER THAN NOMINAL

MEDIUM-DENSITY OVERLAY

(MDO)PLYWOOD

FOR AN ESPECIALLY SMOOTH AND DURABLE SURFACE, A RESIN TREATED OVERLAY MAY BE APPLIED ON ONE OR

BOTH SIDES

MEDIUM-DENSITY OVERLAY

(MDO)PLYWOOD

UNLIKE STRUCTURAL PANEL VENEERS, HARDWOOD PLYWOODS INTENDED FOR INTERIOR USE ARE SLICED FROM SQUARE BLOCKS OF WOOD CALLED FITCHES

FITCHED SLICED VENEERS ARE ANALOGOUS TO

PRESSURE PRESERVATIVE-TREATED

LUMBER

DESIGNED TO COUNTERACT SUSCEPTIBILITY TO ATTACK BY DECAY AND INSECTS

PREVIOUSLY CREOSOTE WAS USED (AN OILY DERIVATIVE OF COAL) BUT ODOR, TOXICITY & UNPAINTABILITY HAVE

CAUSED IT TO BE

PRESSURE PRESERVATIVE-TREATED

LUMBER

CHROMATED COPPER ARSENATE (CCA) WAS ALSO COMMONLY

USED, THOUGH RECENT

DISCOVERY OF ITS TOXICITY HAS CAUSED IT TO BE PHASED OUT IN FAVOR OF LUMBER TREATED

WITH SALTS THAT DO NOT CONTAIN ARSENIC

LONG TERM PROTECTION (30+

YEARS) COMES FROM PRESSURE IMPREGNATION WHICH DRIVES

WOOD FASTENERS

FASTENERS HAVE ALWAYS BEEN THE WEAK LINK IN WOOD

CONSTRUCTION

WOOD FASTENERS: NAILS

SHARP POINTED METAL PINS THAT ARE DRIVEN INTO WOOD

WITH A HAMMER OR MECHANICAL NAIL GUN

SUSTAINABILITY OF WOOD?