Timbers Flashcards
What are the three timber classifications
Hardwood, Softwood, Manufactured board
Hardwood (classifications)
slow growing, close grain, deciduous
Softwood (classifications)
fast growing, wide grain, coniferous
Manufactured Boards (classifications)
Man made timber using reconstituted wood and adhesives
what are the stock forms of timber ( describe them)
Rough Saw: timber direct from seasoning, has nominal sizes instead of accurate finishes
Planed square edge: only has one accurate edge
Planed all round: all edges are planed, square and level
natural wood: timber direct from trees, maximum size is the size of the tree
Manufactured boards: man made timber in large sheets
Mouldings: pre-made shapes and profiles (e.g. skirting boards)
Air seasoning
leave wood in a sheltered location as moisture slowly leaves the material. (cheap and easy but slow)
kiln seasoning
stack planks in a kiln where temperature and humidity are controlled to quickly remove moisture (fast but expensive)
Material properties of timber
strong along grain but weak across it
biodegradable
generally strong and widely available
generally good aesthetics
needs extensive finishing and seasoning to prevent decay and corrosion
generally easy to work with
Seasoning (benifits)
removes 80-90% of moisture
prevents defects and deformation
gives better immunity to decay
prevents corrosion of metals
helps preservatives penetrate
lamination
wood veneers are glued together over a bent former
clamps apply pressure forcing the timber to take the shape of the former
When the adhesive dries the veneers fuse into the shape of the former
steam bending
heat and steam weakens lignin in the timber
the timber is more pliable and can be shaped around a former
when it cools and dries its strength is restored in the new shape
Turning
a work piece is rotated at high speed and a cutting tool removes the surface material
used for shaping cylindrical or spherical objects
Milling
a small rotating bit is used to cut complex shapes out of the timber. it can be manipulated by hand or with computers in CNC
Routering
used to machine slots, holes or mouldings in timber
can be done by hand or with CNC
Knock down fittings
removable joins often used in flatpack furniture
they are simple to install with limited skill and expertise while being strong and long lasting
types of knock down fittings
modesty blocks
barrel and bolt nuts
Cam-lock connectors
wood screws
Coach bolts
resins and laminations
used in manufactured boards to enhance the useable parts of a tree (sawdust, chips, fibres ect) to give multidirectional strength and no size limit
Fire retardant resins
resins impregnated into the timber to limit flammability
laminations
surface veneers which are added to other boards to improve their aesthetics
preservatives
protect timber from fugal and bacterial attack
often timber is pretreated with a copper based chemical to kill fungi
Pigmentation (timbers)
chemicals added to timber to change the aesthetics or make cheap softwood look like expensive hardwood
polysaccharide
this chemical impregnated and cures inside wood cells to increase hardness, toughness and stability
SCL (structural composite lumber)
strands of timber are layered and glued together with resins such as urea formaldehyde.
LVL ( laminated veneer lumber)
veneers of timber are glued with urea formaldehyde with heat and pressure
benefits and drawbacks of LVL and SCL
BENIFITS
unlimited length
high strength
less defects, splitting or shrinkage
better load bearing
DRAWBACKS
urea formaldehyde is a carcinogen
