2020 Flashcards
Tree coverage %
31%
Aus forest description
- Australia has one of the largest and most diverse forest ecosystem consisting of 125 million hectares.
- A large percentile is native with hardwood trees such as Eucalyptus dominating land coverage.
- 600 species of hardwood
Aspects of forest management
1) thinning = remove every 2nd tree as they grow
2) pruning = selectively removing parts of a plant
3) fire protection = remove potential fire fuel
Reafforestation
The replenishment of depleted forests and woodlands. This process often occurs after deforestation. Can happen through silviculture of dropping seeds.
Silviculture processes
Clear felling = felling the whole of the useable crop at the one time. Area is often cleared and trees replanted or natural growth can occur
Selection = Felting just the largest or specific trees as they mature, leaving smaller ones to develop.
Grouping = The process of not removing single trees but whole groups of trees. Up to 1 hectare
Hoop pine
- softwood
- light yellow to almost white
- even texture with no pronounced growth rings
- durable in wet conditions
used for interior joinery, cabinetwork and mouldings
Timbers commonly important into Australia
- Oregon
- Meranti
- Fijan mahogany
5 by-products of timber
Building Boards = particle board, hardboard, soft board, medium density fibreboard
Sawdust = can be used in fuel, insulation, packing, stuffing. Up to 20% is made into sawdust from aloy
Paper pulp = wood is cut into chips, ground and pulped in water and chemicals to bind fibres. Then compressed
Chemicals = Creosote, methanol etc. produced by distillation process.
Plastics = Source of cellulose from which plastic materials may be viewed.
Function of root system
1) anchor tree into ground to combat elements
2) extracts water and nutrients in form of mineral salts from the sail
The trunk
1) provides rigid support
2) carries water and food material to the crown
parts of a tree
- Cambium layer = food material travels to the branches, trunk and roots through this. it is responsible for growth in trunk thickness.
- Truewood = It provides necessary strength to support the tree. durable. made from dead cells
- bark
- sapwood = Water and mineral salts are conducted from the roots to other parts of the tree through this.
Photosynthesis
Photosynthesis forms sugar from CO2 and water in the presence of sunlight. This releases oxygen into the air..
requires chlorophyll
cross section of a tree
Outside to inside…
1) live bark
2) cambium layer
3) sapwood
4) growth rings
5) medullary rays = horizontal cells for food storage and conducting it radially. from the pith to out zones
6) truewood
7) pith = conducts food materials horizontally in the trunk of a tree .
Hardwood
Wood that contains large pores in its structure
tracheids
water carrier and bulk of wood substance
three substances present in cell structure
lignin
resins
gums
durability of wood
The ability of wood to resist decay, termites, borers and the weathering process. does not depend on hardness
texture
The property of wood that refers to the arrangement and relative size of cells.
figure
The pattern in timber caused by variations in colour, grain and texture
straight grain
when fibres are parallel to each other and parallel to the face or edge of a piece of timber
Cross Grain
When the direction of fibres is not parallel to a face of edge
interlocked grain
when the angle of fibres changes or reverses in alternate layers.
timber grading
when timber is categorised according to suitability for particular end uses. determined by number, size, type and position of knots, gum veins etc.
graded by standards association of australia
wood defects
Knots = branches embedded in the tree. cause change of grain direction and can be difficult to work with
Shakes = When adjoining layers of wood seperate either along medullar rays of growth rings. Can seperate.
Pipe = Absence of wood at the centre of the tree.
Gum veins = cavities in the timber which contain gum or resin substances. natural or physical force.
what factors (besides natural defects) tend to weaken timber
Strength of wood directly relates to how long the fibres are… Collapse, warping, bowing, springing, seasonal, handling, checks, splits, twisting, cupping
Slicing method
A blade which is the full length of wood stock and slices vertically.
Rotary cutting method
The wood is rotated as a blade advances towards the middle.
Plywood
High strength and stability.
High resistance to impact.
Resistance to water, chemicals, fire, and heat.
Flexibility in shape, size and thickness makes it fit for every requirement.
No shrinking, swelling and wrapping.
Durable.
Cost-effectiveness.
used in applications such as car-case construction, doors, panels, linings, shelves, cupboard backs, drawer bottoms.
Particle board
made from thinning and trimmings from pine plantations and whole trees
production process
plantation, logs and thinning to mill, billet cut, billets flaked, flakes milled to size, flakes dried, flakes sprayed with glue, mattress formed, mattresses pressed, sheets sanded and trimmed.
chemical treatment prevents growth of mould and prevents attack by termites and borers.
bonded by the glue: urea formaldehyde
Very little expansion and contraction takes place. less effected by conditions such as humidity
expands in rain and disintegrate. nails and screws cause chipping.
Hardboard
requires supporting frame in construction work. highly absorbant and may swell and/or shrink in humidity, dryness, heat. can be wet to stabelize
used in: wall sheetings in housing construction
Grain directon
relates to the direction of cell fibres in timber
we should work in the same direction as grain.
dressed timber
smooth, straight timber cut to the right width and thickness
tools to mark parrallel lines
try square
mortise gauge
marking gauge
timber laminating
The process of gluing together blocks or thin strips of timber into large members
strong due to multiple layers
visually appealing due to multi-colour layers
can be made larger than regular timber
used in: furniture, bridge constuction, flooring, framing
strips are called veneers
Cost factors
size quantity costing N.B Estimates Cubic metre
working time
relates to the adhesives used. Length of time available between setting glue and it drying
Efficiency
relates to planning and using assembly methods that produce quality of work in the shortest time.
planning methods
Use of formaldehydes
when long working times are need when working with resin.
PVA glue
flexible, delivers a very strong bond and, unlike many polymers, it is not acidic. PVA wood glue is most often used: as a wood adhesive. minimum cramping time of around 3 hours
Widening joint
widening joints produce wide boards by joining a number of narrow board edge to edge
1) Butt joint = Squared butted together and glued in place. clamped to hold surfaces together as glue dries. produces wide boards.
2) biscuit joint = similar to dowel joint but a biscuit shaped wedge which reacts with flue and expands providing a stronger joint
3) tongue and groove joint = A tongue on one piece of timber fits into a groove on the second piece to form this joint
Dowelled butt joint
can be used in a variety of applications such as frame construction, leg and rail construction or post and rail construction. Matching dowel holes are drilled in both pieces. Wooden dowels are glued into the holes in one piece and the joint is assembled with glue applied to the contact surfaces and the other dowel holes. The joints usually require cramping. They are a quick and cheap way to join timber. Shows end grain however joint itself is not visible.
biscuit joint
Used for reinforcing framing, widening and carcass joints. Small oval objects which are inserted into two separate pieces in order to join them together. Reinforced through gluing (usually with PVA). Optimal for gluing tabletops.
domino joint
Similar to a biscuit joint but instead of biscuits a domino shaped piece of timber is used which reacts with glue and expands providing a stronger joint. This joint is used where more strength is required normal used in joining legs to rails in table construction. Relatively easy to use however requires costly specialty equipment.
mitre joint
Mitre joints are constructed when two pieces of wood are connected at a 45° angle. Together, they form a ninety° corner angle and which makes them optimal for picture frames, skirting boards and mouldings for building construction. There are multiple metre joints including; metre (flat/edge), feathered metre, mitre halving, doweled metre, metre plate joint and knock down metre joint. These have various strengths and weaknesses. Ie knock down joints are complex but can be undone. Flat metre joints are quick but weak.
halving joint
Halving joints are a type of Lap joint where 2 pieces of timber have their thickness halved in order to overlap them. They are strong but can be tricky to achieve “flushness” especially when using hand tools such as saws and chisels. They are often used for strengthening rails in tables and chairs and for budget construction purposes.
mortise and tenon joint
The mortise and tenon joint is highly popular for woodworkers due too it being strong, flush and hidden. It is for connecting them at right angles by utilising a router and saw. The basic mortise and tenant joint are made up of the mortise hole and the tenant tongue. The joint may be glued, pinned or wedged to lock it in place. They are commonly used in frame construction due to their strength. Chairs and table often benefit from this joint as well.
