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Material Basics
Timber and Wood Products
Basic material properties andcharacteristics.
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The nature of timber
Timber is a naturalproduct, drawn fromthe wood in thetrunks of trees.
Its character isconsistent with thespecies of tree andthe form and growth
over time of thewood in it.
Regrowth in a native forest
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Tree growth
New wood on outside of tree oldest wood on the inside
youngest wood on the outside
diameter largest at the base
one ring (layer) per growing season
Tree in forest grows toward light trunk is straight
lower branches die
leaving small knots in wood
Bark protects wood from damage the tree sheds bark each year
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Production of wood
Cambium - growth cells wood cells created on the inside bark cells created on the outside
Sapwood - newest wood on the outside of tree (~ 1-3 cm) takes nutrients from root to leaves
Heartwood - older wood cells closed - cant pass nutrients storage for waste - extractives
Pith - the start of growth in the tree the original sapling
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Variation: fibre & grain
The cell structure is designed to serve particularfunctions in a tree.
Its properties vary in different directions.
rays
rays
cellsfibres
vessels
hardwood earlywoodrays
latewood
softwood
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Variation: species & growth
Species andgenetics:
selected stock ornatural seed.
Climate: wet or dry, cold or
warm.
Arrangement:
native forest orplantation.
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Each piece is unique
Myrtle burl veneer
Quarter sawn hardwood
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Properties are variable
Drying (seasoning) & shrinkage Strength & hardness
Durability
Appearance
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Moisture and drying in wood cells
removedboundwaterSeasoned
timber15% MC
100% MC
Unseasonedtimber
Growingtree
free water
25% MC
fibre saturation
bound waterPartiallyseasoned
timber
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Benefits of drying
Drying timberincreases its: strength;
stiffness;
stability
durability; &
ease of fastening.
It is ideally dried to amoisture content inequilibrium with itsservice environment.
Checking the moisture content
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Timber shrinks as it dries
It shrinks at different rates in
different directions.
Once dry, it will expand &contract to be in equilibriumwith changing local conditions.
Shrinkage from 12% to 25% MC
Radiata pine Rad 3.5% Tang 4%Hoop pine Rad 2.5% Tang 3.5%Cypress Rad 3.5% Tang 4%
Spotted gum Rad 4.5% Tang 6%Karri Rad 4.5% Tang 10%Sydney blue gumRad 5% Tang 9%Grey Ironbark Rad 5.5% Tang 7.5%Mountain ash Rad 6.5% Tang 13%
Tangentialshrinkage
Radialshrinkage
Longitudinalshrinkage
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Shrinkage in sawn sections
Tangential shrinkageis the highest;
So, the growth ringstend to shorten as the
timber dries.
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Timber dries at different rates
Pines have a porous cell structure: They can be dried very quickly.
Turnaround time from saw to store canbe as low as a week.
Hardwoods have a non-porous cellstructure: The moisture must diffuse through the
cell wall.
Drying can be very slow.
It must be done carefully.
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Grain, strength & stiffness
Direction of grain
Strong parallel to grain & stiff parallel to grain
Weak perpendicular to grain
Properties of the grain
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Summary of characteristics
Timber is a natural material
Each piece is unique in fibre, texture andcolour
Its strength is dependant on the
properties of the wood and the slope ofthe grain
It takes up and gives up moisture
It expands and shrinks as it does so It deteriorates in line with exposure
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Timber products
Timber is available in a wide range ofproducts and species including:
Solid sawn, moulded and laminated timber;
Veneer;
Plywood; and
Wood panels.
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Timber products: sawn
Hardwood orsoftwood.
Solid timber cut froma log and dried.
It is a versatilematerial used formoulding, frames andexposed structures.
Size is restricted.
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Timber products: mouldings
Hardwood orsoftwood.
Solid seasonedtimber milled to a
wide variety ofshapes.
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Timber products: glue laminated
Small pieces oftimber gluedtogether to form alarger element.
Used as both astructural andfinishing element.
Size is limited only
by transportcapacity.
bench top
beam
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Timber products: curved glulam
Glue laminatedmaterial can becurved.
Curved bar
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Timber products: veneer
Thin layers of solid
wood sliced from aflitch or peeled from alog and dried.
High quality materialis used as adecorative finish.
Lower grade materialis used to makeplywood, LVL andsimilar products.
Veneer leaf
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Timber products: plywood
Layers of veneer
glued together sothat the graindirection alternatesbetween layers.
Usually produced insheets.
Very good in astructure, as a liningand as a flooringsurface.
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Timber products: wood panels
Panels made fromwood or wood fibresbound together withglue, or other binder:
Particleboard Medium Density
Fibreboard (MDF)
Hardboard
Core board
MDF sheet
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Appearance grading
Production processof sorting productsinto groups withsimilar
characteristics &properties.
Timber identified bycalling up a specific
grade.
Visual grading
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Grading standards
AS 1810-1995 Timber - Seasonedcypress pine - Milled products
AS 2796-1999 Timber - Hardwood -Sawn and milled products
AS 4785-2002 Timber - Softwood -Sawn and milled products
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AS 2796 Hardwood - Sawn & milled
This standard defines the requirementsfor hardwood used for visualapplications: architectural (flooring, etc),lining & cladding; &
It is in two main sections:
product requirements; &
visual grades.
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Appearance grading - rules
Establish permissible limits on: gum vein
knot size & frequency (location unimportant)
splits, cracks, checks (size and frequency)
stain (colour), grain uniformity
utility: want, wane, cup, bow, spring, twist
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Grade range
From selectgrade uniform wood with
few natural features
Through to highfeaturegrade including lively
natural feature aspart of a desirableaesthetic.
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AS 2796 Hardwood - Sawn & milled
Tolerances are established for the majorproduct groups (not grades):
Joinery and dressed boards;
Strip and overlay flooring, mouldings, sawn
boards for feedstock; &
Light decking, lining boards, cladding, facia,bargeboards.
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AS 2796 Part 1 - distortion
Bow - depends onthickness
Spring - dependent onwidth
Twist - separate limitsfor less or more than25 mm thick
Cup - 1mm per 100mm width
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AS 2796 Part 1
No lyctid susceptible sapwood isallowed. (Lyctids are small wood eating insects.)
MC anywhere in a piece must bebetween:
9-14% for most products including flooring.
8-13% for parquet & furniture components.
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AS 2796 Hardwood - Sawn & milled
The standard recognises feature as adesirable visual characteristic;
Therefore, distortion and machiningtolerances are associated with product,not grade; &
The timber can then be specified withthe desired appearance for any function.
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AS 4785 Softwood - Sawn & milled
Layout is similar to AS 2796 with productrequirements & visual grades;
Visual grades are Clear, Appearance,Select, Standard, Utility Grade;
With radiata, there is a much greater useof industry grades; &
Terms can vary between companies.
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Jointing
Timber is a highlyversatile materialthat can be shapedand joined easily.
Mortice and tenon Housed
Half housed
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Jointing methods
Overlap Fixing blocks
DowelBiscuit
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Conclusions
Timber is a natural product.
It has been used for centuries.
Skilled use and understanding of the
material can yield excellent results.
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