Rugby School Thailand - Design and Technology

Woods

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Topic 1.2.1 (Wood Classification)

Categories of Wood and Timber:

Sources and Origins:

Wood Structure:

Anatomy of a tree:

Conversion & Seasoning:

Common Hardwoods:

Types of Softwoods:

Common Softwoods:

Wood is a natural material that is grown all over the world and has been used for building work, furniture, and decorative items for thousands of years.

Categories of Wood and Timber:

Softwoods

Timbers that are made from coniferous trees.

Pine, Cedar, Spruce, Douglas Fir

Hardwoods

Timbers that are made from deciduous trees

Oak,, Ash, Beech, Mahogany, Teak

Manufactured Boards

Boards made from wood pulp, chips, or layers.

Chipboard, MDF, Conti board

Coniferous Trees

Coniferous trees are also known as 'Evergreens'. They have a cone-bearing structure and needle-like leaves varying in size, shape, and colors that stay on the tree all year round throughout the year while remaining green in all seasons because the leaves love for several years.

Softwood generally grows in the colder countries of the Baltic region (including Scandinavia and Russia), North America, and China; taking around 20 years to mature.

Deciduous Trees

Deciduous trees are giant flowering plants also known as 'Harwood Trees'. They have broad leaves that typically fall off in the autumn months, in temperate climates, and are fast growing.

Hardwoods are usually found in temperate and tropical forests around the world such as Africa, Asia, and India. It can take 100 years or more for the wood to mature. In ore tropical regions, hardwoods do not shed their leaves as often since seasonal changes are less noticeable in those regions (e.g. UK)

Sources and Origins:

Woods used in the design are derived from various tree species. The source of the natural timber, paper, card, and manufactured boards is trees which grow in a variety of climates and regions around the world.

Softwoods

Softwoods, derived from gymnospermous trees, their source and origin rooted in coniferous forests. They are widespread across the Northern Hemisphere, thriving in boreal (northern regions) nearer to the two poles such as Scandinavia, Russia, and other temperate regions.

Hardwoods

Hardwoods originate from angiosperm trees which have flowering plants that produce seeds enclosed in fruits or nuts. They can be sources from both temperate and tropical climates, growing in the warmer countries around the equator; countries such as Africa, India, and Asia.

Wood Structure:

Woods are fibrous materials made up of plant cells and resins.

The main structure of the woos is Cellulose fibers held together with Lignin (a natural binder) which gives strength. This needs to be removed before making paper. At a microscopic level, wood exhibits distinct grain patterns that represent the alignment if long fibers r cells along the trunk oof a tree

Anatomy of a tree:

The tree consists of three main parts: the roots, trunk, and branches. The roots anchor the tree in the soil, absorbing water and nutrients essential for growth. The trunk, composed of layers of bark, cambium, sapwood, and heartwood, provides structural support and transports water and nutrients between the roots and leaves. The branches extend from the trunk, supporting the foliage where photosynthesis occurs. Trees grow from the outside inwards making new layers each year (hence annual rings). As a result, the weakest wood is just inside the bark while the heartwood is the most stable and dense section of the tree. Eventually, when the heartwood may begin to die and is known as dead wood.

--> Wood is a natural material that can be used in its green state (wood that has been recently cut and therefore has bit has an opportunity to season/dry by evaporation of the internal moisture).

Wood is hygroscopic meaning it gives up moisture in a dry environment and takes in moisture when in wet environments causing it to be prone to warping as it shrinks or expands in different moisture conditions.

As a result, woos is always prone to being unstable.

Conversion & Seasoning:

In order to convert trees into timbers for us to use, they need to go through the process of conversion and seasoning.

Harvesting

Trees are cut down, leaving a stump behind (leaving a few feet from the ground with the roots still attached to the ground because it is hard to dig them up)

Some trees can regrow from their stumps and the process of doing this on purpose is known as coppicing. Sustainable forestry practices aim to minimize environmental impact and promote the long-term health of the forest. Once harvested the logs are transported to a sawmill or processing facility.

Once harvested the logs are transported to a sawmill or processing facility. Logs are scaled to determine their volume and value. They are then sorted based on size, species, and quality, as these factors influence the resulting lumber's characteristics.

The trees then have their branches removed and these are then chipped and used to make chipboard, paper, and other wood-based products. The logs may undergo a debarking process to remove the outer bark. This can be done mechanically or chemically, depending on the mill's equipment and preferences.

Conversion:

The trunks are then ready to be converted into usable wood. Logs are sawn into rough lumber using various sawing techniques. Common methods include plain sawing, and quarter sawing, each producing lumber with different grain patterns. The rough-sawn lumber is then edged and trimmed to achieve the desired dimensions and remove defects such as knots (where branches join the trunk) or irregularities.

Plainsawn

Plainsawn also known as through and through produces mostly tangentially sawn timber. Tangential timber is the most economical to produce because of the relatively less repetitive production method that is used extensively in the building industry.

Plainsawn contains the least amount of wasted material and is the cheapest to purchase. They have an inconsistent grain.

Quartersawn

Quartersawn wastes more product compared to other sawing methods making them more expensive.

It involves cutting the log into quarters before sawing. This results in a more consistent grain pattern so the end product is more stable. The end grain of the wood ends up largely perpendicular to the boards.

It is more decorative and less prone to distortion.

Seasoning:

Wood is full of moisture when felled and is referred to as green timber (recently cut timber). In order to make it stable and usable, it is necessary to reduce the moisture content in a controlled way to prevent warping or cracking. After sawing, the timbers go through either Air or Kiln seasoning.

Air Seasoning

Air seasoning, also known as air drying or natural drying, is a traditional method of reducing the moisture content of wood by exposing it to the surrounding air. This process allows moisture to evaporate gradually from the wood, resulting in lumber with a lower moisture content. Timbers are stacked on top of bricks and under a roof to prevent them from having contact with water, each layers are stacked with spacing sticks allowing air to pass around the wood (allow circulation). The process requires little or no supervision but it is very time-consuming - it takes years for the wood to be seasoned properly.

Kiln Seasoning

Kiln seasoning, also known as kiln drying, is a controlled process used to reduce the moisture content of wood in a more efficient and controlled manner than air drying. This method involves placing freshly sawn or green lumber into a specially designed kiln, which is a large, heated chamber where the temperature, humidity, and circulation are carefully regulated using steam. This creates a condition where the wood does not dry out quickly, but the moisture content can be reduced in a controlled way resulting in a much shorter time period taking days or weeks.

Common Hardwoods:

Hardwoods are more expensive than softwoods because it takes more time to reach maturity (trees that are fully grown an can provide quality wood). They usually take around 100 years to reach maturity although there are faster growing species such as bamboo.

Beech

Mahogany

Oak

Walnut

Teak

Ash

Cherry

Zebranno

Applications for Hardwoods:

Types of Softwoods:

Softwood is the cheapest out of the two varieties of timber because the trees reach maturity at a younger age of about 25 years or less. Compared to hardwood which takes about 4 to 5 times longer to grow. UK is geographically nearer to softwood-producing countries so shipping costs would be less. The UK produces a reasonable amount of softwood - softwood is more readily available and therefore costs less in the UK.

Softwoods are used in a variety of general construction jobs.

In the UK it's usually Pine or Spruce but other types include Douglas Fir and Red Cedar. They are some of the cheap options which are easy to work with although they still have to be careful so the woods don't split when nailing, screwing, sawing, or drilling. Softwood comes in several forms:

Rough Sawn Treated

Rough Sawn Treated typically refers to wood that has undergone a specific treatment process and retains a rough-sawn or textured surface where the wood has gone through preservative treatments to enhance its resistance to decay, insects, and other environmental factors (tantalizing).

It is often used in fencing. You can tell it's treated by its slightly odd colour which is usually brown or green tinge to it depending on the colour of the preservatives.

Rough Sawn

Rough Sawn refers to wood that has been cut from the log and processed to achieve a relatively unfinished or "rough" surface. This applies to wood that has undergone primary sawing but has not undergone additional planing or finishing processes. The resulting wood typically retains its natural texture and may have variations in thickness and surface irregularities.

Often used where you won't see it like stud allows which are covered in plasterboard

Planed

The process of smoothing and leveling the surface of a piece of wood using a tool called a plane. A plane is a hand tool or a machine equipped with a cutting blade that shaves thin layers of wood to create a flat, even surface. Planing is an essential step in woodworking and is used to achieve a smooth finish, remove imperfections, and prepare the wood for further finishing or joinery.

E.g. door frames, and skirting. Referred to as PSE (Planned Square Edge).