Wood
Technology
January 4, 2007
Woodworking
Mr. Wecas
Lumber Classifications
Hardwood Softwood
• Broadleaved • Evergreen
– Deciduous – Conifers
• Shed leaves at • Cone bearing
the end of a • Needle bearing
growing season
Grades of Lumber
• The quality or grade of lumber
depends upon the pieces and
amount of clear cuttings they
contain.
• Standards are established by
associations of lumber
producers.
Softwood Grades
• Based on American Softwood
Lumber Standards PS 20-70.
• Established by US Department
of Commerce.
• Detailed rules are developed
and applied by the various
associations of lumber
producers.
Softwood Grades
• Lumber is classified into three
categories
– Boards
– Dimension Lumber
– Timbers
• Each classification has several
grades within it.
• Another classification is called
Factory or Shop Lumber
– Used for doors, windows, moldings and
other trim items.
Softwood Lumber
classifications and
grades
Hardwood Grades
• Grades for hardwood are
established by the National
Hardwood Lumber Association
• Founded in 1898
• Members include lumber
producers as well as lumber
retailers
Hardwood Grades
• FAS (Firsts and Seconds)
– Not less than 6” in width
– Not less than 8’ in length
– 83 1/3 % clear cuttings
• Selects (FAS 1 Face)
– 4” wide by 6’ long
– More defects on second or back
face
Hardwood Grades
• No. 1 Common
– Permits smaller pieces
– 66 2/3% clear cuttings
• No. 2 Common
– 50% clear cuttings
• No. 3 Common
– 33 1/3” clear cuttings
Hardwood Grades
• No. 2 & No. 3 common are not
usually listed in hardwood
catalogs.
• Retailers usually cut out
defects and sell these as Shorts
Lumber Defects
Knots Embedded limbs or branches
Splits/Checks Grain separations, along and across grain
Shakes Separations along annual growth rings
Pitch Pocket Internal pocket of solid or liquid pitch
Honeycombing Separations of wood fibers, rays
Wane Presence of bark on edge of board
Blue Stain Discoloration caused by mold-like fungus
Decay Disintegration of wood fibers, Fungi
Holes Lumber handling or worms
Warp Variation from true or plain surface
Types of Warp
• Cup
– Edge to edge
• Bow
– End to end
• Crook
– End to end along edge
• Twist (Wind)
Seasoning Lumber
• Green Lumber
– Fresh cut lumber
– Excessive moisture
– Must be removed before use
• Air Dried (AD)
– Simple exposure to air over a period of
time
– Moisture Content reduced to 12 to 18
percent
Seasoning Lumber
• Kiln Dried (KD)
– Lumber dried in huge ovens
– Temp and humidity carefully
controlled
– Moisture content reduced to 7 to
10%
• Free from internal stress
• Fewer defects from drying
Seasoning Lumber
• Electrostatic Drying
– Microwave type ovens
– Better control of Moisture content
– Ideal for small run batches
– Faster removal of moisture
– Fewer defects
– Louisville Slugger (Baseball Bats)
Cutting Methods
• Flat-Grained (Softwood)
• Plain Sawed (Hardwood)
• Cut from a log at angles of less
than 45 degrees
• Most common means of cutting
• More likely to warp
Cutting Methods
• Edge-grained (Softwood)
• Quarter Sawed (Hardwood)
• Cut from the log at angles of more
than 45 degrees
• More difficult to cut from log
• More waste
• Less likely to warp
• Produces attractive grain patterns
Surface and Size
• Softwoods are surfaced on all
four faces and edges is called
S4S (Surfaced Four Sides)
• Hardwoods are purchased as
– RGH (Rough)
– S2S (Surfaced Two Sides)
– Not cut to standard width (RW&L)
Composite Board
• Hardboard
– Standard or Tempered
• Refined wood fibers and resins
pressed together to produce a
hard dense material
• 1/8”, ¼”, and 3/16” thick
• 4’ x 8’, 10’, 12’ or 16’ lengths
Composite Board
• Particle Board
• Wood flakes and chips bonded
together with adhesives
• Large particles in the center for
strength, small particles on surface
for smoothness
• Base or core for plastic laminate
counter tops
• Thickness from ¼ to 1 7/8”
• 4’ x 8’ or 49” x 97”
Composite Board
• Waferboard
• Flakes about 1 ½ square
• Bonded together under heat and
pressure with adhesive
• ¼” to ¾” thickness
• 4’ x 8’ sheets
Composite Board
• Oriented Strand Board
• Similar to Waferboard
• Fibers arranged in layers at
right angles to one another
Plywood
• Constructed from thin veneers
of wood glued together
• Grain direction is turned 90
degrees in successive layers
• Odd number of plies so that the
face grain is the same on both
sides.
Plywood
• Varying core materials
– Veneer core
– Lumber core
– Composite core
• Thickness from 1/8” to more
than 1”
• Common sizes: ¼, 3/8, ½, 5/8
and 3/4