IGCSE DT
Timbers
Sources and Origins
Softwoods grow in temperate areas, such as alpine forests.
Hardwoods grow in European and Amazonian forests. These woods are the most sought after due to their colour and grain structure.
Forests can be a sustainable source of timber if managed correctly. To manage a forest, we can ensure that trees are replanted after they are felled with new seedlings
Trees and forestry emit carbon dioxide through a variety of ways
Cutting down the trees mean that they absorb less CO2.
Alongside this, the machinery used to cut down the timber produces CO2, and the methods of transport also emit CO2
Alongside this, trend forecasting can help identify future demands for timber, and allows us to account for it.
Types of wood, and properties.
Softwoods are coniferous trees, such as pine. They tend to be faster growing than hardwoods, so are cheaper.
hardwoods are sourced from deciduous trees like oak, birch, beech and ash. It is slower growing, and is more expensive.
All timber has a set of certain working properties.
Strength - its ability to withstand compression, tension and shear
Hardness - it's ability to withstand an impact without denting.
Toughness - it's ability to be not break or snap, and can absorb shock.
Malleability - how easy it is to bend or shape.
Ductility - can it be stretched into wires
Elasticity - it's ability to be stretched and then return to it's original shape
Ash is pale coloured, with a close grain. It is flexible and tough, and is used to make handles.
Beech has a pink tint, close grain, and is tough, durable and smooth to finish. It is often used for children's toys as it does not splinter.
Mahogany has a dark red colour, and a very close grain. It cuts and polishes easily, and is used for high quality furniture
Oak has a mid brown colour, and is used for quality furniture.
Balsa is a fast growing hardwood, and is very soft and easy to form, and is used to make models
Larch is pale coloured, with a contrasting darker grain. it has a lot of knots. It is durable, and easy to machine. It has good water resistance, and is used for external building and flooring.
Spruce is a pale cream colour, and is lightweight easy to form. It is used for construction and furniture
Pine is pale coloured with an aesthetically pleasing grain. It is lightweight, easy to form and used for construction and decking.
Manufactured timbers are usually made from timber waste and adhesives.
MDF is a smooth, light brown timber. It is smooth and easy to finish. it absorbs moisture, so is not suitable for outdoor use, and used for kitchens and flatpack furniture.
Plywood has an odd number of layers of veneer, glued at 90 degrees. It is very strong, and is used for shelving and construction
Chipboard is made of compacted wood chips, laminated with a variety of coverings. It is strong, but absorbent so is used for veneered worktops and flooring
Stock Forms
Timbers are sold in lengths known as:
Regular sections, such as planks, or blocks. These are known as stock sizes
Mouldings, a piece of timber that has a decorative pattern along it's length
Dowels, a thin long round piece of wood.
Sheets, often used for veneers
Reinforcing
Objects can be damaged by 3 main forces
Compression - a pushing force.
Tension - a pulling force
Shear - a force acting across the material
To strengthen timber, we can do a number of things
Timber has good tensile and compressive strength, but does not bend. To help this, we can "kerf" the material and cut lengths along it, and glue and compress it. This means that the wood can be bent and withstand the compressive force.
To strengthen a square or rectangle, we can put a diagonal strut or triangle across each corner.
We can laminate a plank, by having the layers at 90degrees to each other. The overlapping grains mean that it becomes harder to snap, and won't flex.
There are many processes which we can use to cut and shape timbers in quantity.
Routing
A router works by rotating a cutting bit at a high speed. They can plunge into material to cut holes, and can follow jigs or patterns. Routers can be CNC controlled to further help with accuracy
Sawing
Sawing machines can help cut timbers quickly. Circular saws and bandsaws are the most commonly found.
Mortising
A mortiser makes a square hole for a mortise and tenon joint
Bag press
A bag press is used to create curved shapes in laminated timber veneers. The bag is sealed, and veneers are pressed against a mould.
Core
Scales of Production
Batch
Batch production is where many items of the same product are produced. Money is saved when compared to the cost of a one-off product.
Mass Production
Mass produced products are manufactured in large volumes often on assembly lines, where standard components are just fit together
Continuous Production
Continuous production takes place 24 hours a day, 7 days a week. Timber products rarely have the demand to be produced like this, but stock sizes of timber and paper can be produced using this.
To shape timber, there are more things we can do to it.
We can cut it using:
A rip saw, for roughly cutting thicker planks and boards
tenon saw - for cutting straight lines with accuracy
Coping saws, for cutting thinner pieces of timber
Holes can be made using variety of drill bits
Twist drills, used to drill a hole of a fixed diameter into a piece of timber
countersink bits can profile a hole so the top of a screw sits flat.
forstner bits cut flat bottomed holes
hole saws cut large holes
Finally, timber can be shaped by:
chiselling, cutting away pieces of timber.
planing can smooth the edge of a piece , by running a sharp blade in the direction of the grain.
abrasion and sanding can help create a profiled shape or a flat piece of wood.
hand sanding
machines, like a belt, disc or orbital sander
files
rasps, which have larger teeth that leave marks
surforms, which are used for rough shaping
turning, using a lathe, creating a uniform circular pattern
Joining
To join pieces of timber, we can use:
Screws, which create a strong joint and can be unscrewed. We can drill a pilot hole which makes it easier for the screw to go in, and we can countersink it to ensure that the screw sits flush
Nails, which are just hammered into timber. They are faster than fitting a screw
Adhesives, such as CA and PVA are used. PVA is a wood glue that dries clear, and must be clamped. It produces a permanent and strong joint.
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There are also a set of physical characteristics
Knots are spots where the branch grew out of the tree. the grain swirls, and makes the part harder. Knots can also make the wood aesthetically pleasing.
Different woods have different colours.
Grain structure
Hardwoods have two long vessels known as fibres and pores. Softwoods have one cell called tracheids.
You can have close and open grained woods. Close grained woods have many growth rings packed closely together. Open grain woods have fewer growth rings spread apart more.
Finally, timbers have social footprints, and this must be considered
We can make use of trend forecasting, to invest in designing and making products for use in the future.
Logging can bring jobs and money to an area, but it also often pushes people out of ancestral honmes.
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Papers and Boards
Papers and boards have many aesthetic factors
The form, i.e the thickness, and physical properties.
Colour, which varies depending on the use of the product.
Texture, which can change how it is marketed.
Surface graphics,
a few examples are:
Solid white board, made from bleached wood pulp, which is expensive, but can be printed on. It is used for packaging and book covers.
Corrugated board are cri
folding box board, which is printable and can be folded easily and is used for boxes