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Design and Technology

Technical principles

1.2 Timber and wood

Specialist technical principles

Learning Outcomes

By the end of this unit you should have developed a knowledge and understanding of:

• the specific names and classifications of woods

• The processing from source into a usable material

• the performance characteristics of different types of timber

• why different types of timber are suitable for different applications

• stock forms of timber and wood

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Classification of woodsTimber comes in three main categories.

Woods

Softwoods Hardwoods Manufactured boards

Timber from coniferous trees

Timber from deciduous trees

Boards made from wood pulp, chips or

layers

Pine, Douglas Fir, Spruce

Oak, Beech, Mahogany, Teak, Ash

Chipboard, Conti board, MDF, Plywood,

Stirling board

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Woods can either be deciduous or coniferous.

Deciduous trees have broad green leaves which are shed in the autumn in a temperate (different seasons) climate. These are known as Hardwoods. Hardwoods grow in warm countries such as Africa, Asia and India and can take 100 years or more to mature although there are faster growing hardwoods. In tropical countries hardwoods often do not shed their leaves as there is often no noticeable change in the seasons like there is in the UK.

Coniferous trees have needle type leaves which stay on the tree all year round which is why they are known as Evergreens. These are Softwood trees. They generally grow in colder countries such as Russia and Scandinavia and take around 20 years to mature.

The UK has a temperate climate which is why so many different types of tree grow there and why some lose their leaves in winter.

Wood classification


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Sources and origins

The source of natural timber, paper, card and manufacturedboards is trees which grow in a variety of climates and Britain,with its temperate climate is able to support a wide variety ofdifferent trees.

Hardwoods tend to grow in warmer countries around theequator such as Africa, India and Asia.

Softwoods grow in countries nearer to the two poles such asScandinavia, Russia and the Baltics.

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Woods are fibrous materials made up of plant cells and resins. The mainsstructure is Cellulose fibres held together with Lignin which gives wood itsstrength but needs to be removed to make wood pulp for paper (see Paperand Boards)

Wood is a natural material and one that can be used in its green state i.e.when it has been recently felled or cut down.

Wood is hygroscopic meaning it gives up moisture in a dry environmentand takes in moisture in a wet environment. As a result Wood is alwaysprone to be unstable as it can shrink and expand depending on themoisture conditions.

Wood structure1

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Trees grow from the outside inwards making a new layer 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 the heartwood may begin to die and is know as deadwood.

Wood structure


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In order to use wood we inevitably need to cut down trees.

Trees are cut a few feet from the ground leaving a stump with the roots stillattached in the ground as it is much too hard to dig them up.

However, some trees can re-grow from their stumps and the process ofdoing this on purpose is known as coppicing.

The trees then have their branches removed and these are then chippedand used to make chipboard, paper and other wood-based products.Where the branches join the trunk, they leave a knot (a defect).

We are then left with the tree trunk ready to be converted into usablewood.

Wood conversion1

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Conversion of timberAs soon as possible after felling the tree should be converted into usable timber.

There are two main methods of converting timber:

Through and through (or Plain or Crown sawn) which produces tangential boards and

Quarter Sawn which produces radial boards.

The Quarter sawn is far more expensive because of the need to double (or more) handle the log. There is also more wastage. It is however more decorative and less prone to cup or distort. Note also there are two ways of sawing the quarter.

Through and through produces mostly tangentially sawn timber and some quarter sawn stuff. (see diagram) Tangential timber is the most economical to produce because of the relatively less repetitive production methods. It is used extensively in the building industry.

There are other ways but they are all variations of tangential and radial cuts to obtain the best or most economical boards for the use it is to be put. These basic cuts are not always able or need to be, on the exact tangent or radius of the trunk. The cuts, that fall between, crown and quarter are called 'rift' and between 'rift' and 'quarter' are identified as 'figured' - see below for explanation. Boxing the heart refers to eliminating the heartwood from the boards that would otherwise produce shakes, juvenile wood or may even be rotten

Wood conversion


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Wood is full of moisture when felled and is referred to as green timber. In order to make it stable and usable, it is necessary to reduce the moisture content in a controlled way. This is known as seasoning.

The traditional way of doing this is simply to allow air to pass around the wood in order to reduce the moisture content over time. The wood is stacked on bricks to keep the wood from wet floors and a roof is placed over so rain doesn’t reach the wood. Spacers between the planks of wood allow for circulation and the whole process requires little or no supervision.

However, it can take many years for the wood to season properly!

Seasoning


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Because wood is needed daily, it would be impossible to use traditional methods in industry as it would simply take too long for wood to become usable so a kiln drying method is used.

In this method, wood is placed in a kiln and heated up using steam. This means that the wood does not dry out, but the moisture content can be reduced in a controlled way resulting in a process that can take days rather than years.

Seasoning


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Hardwoods are more expensive than softwoods for one main reason and that is the time it takes for a hardwood to reach maturity i.e. when the tree is fully grown and can provide the most quality wood.

Hardwoods typically take over 100 years to reach maturity although there are faster growing species such as bamboo.

Hardwoods


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Hardwood is more expensive than soft wood and is used in more quality joinery jobs, expensive flooring, or outside areas which are exposed to the weather like front doors. It's often used on expensive window frames as it looks great and last for years. On floors it's very hard wearing. Being harder it's much harder to work with but you can get a great finish on. It doesn't split nearly so easily as pine. Examples are beech, oak, mahogany and teak.

Hardwoods


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Applications for woodsCommon uses for hardwoods

Material Properties Applications

Oak Durable, hardwearing, attractive Quality furniture and

construction, flooring, barrels

Beech Small grain, hygienic, durable Chopping boards, mallets

Teak Naturally repels water, durable Garden furniture, boats

Ash Springy, strong in compression Sports goods

Mahogany Hardwearing, attractive, High quality furniture

Walnut Dark, dense, tight grained,

attractive

Gunstocks, flooring

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Softwood is the cheapest of the two varieties of timber and that is due to the fact that trees reach maturity in 25 years or less. Compare this to hardwoods which can take 4-5 times longer to grow and you can see a similar increase in prices. It also helps that the UK is geographically nearer to softwood producing countries so shipping costs would be less. The UK also produces a reasonable amount of softwood for its own use. All of these factors mean that softwoods are more readily available and therefore cost less.

Softwoods


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Softwood is used in a huge range of general constructional jobs. In the UK it's usually pine or spruce but other types include Douglas Fir and Western Red Cedar. It's cheap and very easy to work with, although some care is required to avoid it splitting when nailing, screwing into, sawing or drilling.It comes in several forms:

Rough Sawn treated -quite roughly presented

this is used for outdoor use and is pressure

treated with preservative to help prevent

rotting (tantalizing). Used in fencing a lot. You

can usually tell it's treated by it's slightly odd

colour usually a brown or green tinge to it

depending on the color of preservative.

Rough Sawn - quite roughly presented often

use where you won't see it like stud walls

which are covered with plasterboard.

Planed - nice smooth surface used for

precision joinery or where you see the

surface. e.g. door frames, skirting. Referred

to as PSE (Planed Square Edge).

Softwoods


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Common Softwoods include Parana Pine, Scots Pine, Cedar,

Fir and Spruce.

Softwoods


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Applications for woodsCommon uses for softwoods


Yellow Pine Affordable, readily available General construction,

carpentry frames, paneling

Spruce One of the most common building

materials

Soundboards for musical

instruments, construction

Cedar Fragrant wood, strong attractive Wardrobes, coat hangers,

sheds

Douglas Fir Excellent strength, workable Flooring, furniture, cabinets

Parana Pine Straight grain, uniform texture,

workable

Furniture, interior woodwork

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Answer the following questions

1. What are the two categories of woods?

2. Which type of trees grow in hotter countries?

3. Which type of wood doesn’t lose its leaves in winter?

4. Which is the more expensive category of wood?

5. What word describes turning a tree into planks of wood?

6. What word describes removing the moisture from wood?

7. What is a renewable material?

8. What gas does a tree provide us with?

9. What is the strongest part of the tree?

10. What is a knot?

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Check these answers against yours

1. Hardwood and Softwood.

2. Hardwood

3. Softwood

4. Hardwood

5. Conversion

6. Seasoning

7. A material that can be regrown

8. Oxygen

9. Heartwood

10. Where the branch joins the tree trunk

Now add up your scores out of 10

Applications for woods


Visual test on timber and wood.

What would be the most suitable wood for the following object and why?

Answer: Teak as it is naturally oily and will repel water.

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What would be the most suitable wood for the following object and why?

Answer: Beech as its tight grain makes it more hygienic for food use.

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What would be a suitable wood for the following object and why?

Answer: Ash as it’s springy and withstands impact.

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Answer: Oak as it’s a hardwearing, attractive and durable wood.

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Answer: Cedar as it’s a durable but relatively cheap softwood.

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Bonus question: What wood is this phone case made from?

Answer: Bamboo is a fast growing and renewable source of wood

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Various types are available and all usually come in thickness' of 4 mm,

6mm. 9mm. 12 mm. 15 mm. 18 mm. 24 mm.

A large sheet will be 8 feet x 4 feet which will be the size you get from a

builders merchant. DIY stores will usually supply smaller sizes as well.

1. Chipboard

2. Conti Board

3. Plywood

4. MDF

Manufactured boards


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Chipboard is similarly to MDF but from actual wood chips. Used widely by kitchen

manufactures who cover it with a laminate.

Also used widely for low cost flooring You can buy flooring packs in different sizes

which come tongue and grooved which allows each section to slot together with the

next before screwing or nailing down.

If used for shelving, it's fairly weak so needs well supported. It doesn't paint very

well and the edges are quite rough. Rarely used these days for shelving, though it is

very cheap.

Conti board is laminated chipboard available in white or various other colours and

finishes. Used widely in kitchen carcasses You can usually buy it in 6 feet lengths of

various widths. Can be use for shelving but will need plenty of support. Inexpensive.

Manufactured boards


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Plywood This is made from thin laminates of wood glued together each

layer at right angle to the grain of the other. It is very strong but also quite

flexible, especially if you get thinner sheets.

It's used widely in the building industry as it's so strong. Used for things

like boxing in, sub floors prior to tiling, and general construction.

It's tougher to work with and the edges tend to fray a bit when sawn. It

doesn't paint up very well. Best used where it's not seen. It's quite

expensive, especially if you buy the most expensive, marine ply, which is

very good quality and relatively water-proof.

Manufactured boards


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MDF (medium density fiberboard) very popular these days. It's made from

powdered wood which is bonding with glue and compressed to form the

sheets. Used widely for interior projects especially cupboards and shelving.

It's quite soft and very easy to work with. It cuts and sands very easily and

you can get a great paint finish on it. It's not particularly strong when cut in

thin strips for shelving so will need support if you want long lengths.

It gets' very dusty when sanding it so you'll need to wear a dust mask. It

hates moisture and will swell up if it gets wet. Don't ever use outside or

areas likely to get damp. You can MDF with a wood veneer like cherry, oak,etc. These are quite expensive but do look great.

Manufactured boards


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Sterling Board can be thought of as somewhere between chipboard and

Plywood. It is made of compressed fragments of wood which are bigger

than those found in chipboard but is lacks the laminates and exterior

veneers (and the higher cost) of Plywood. It is increasingly used for

flooring in sheds and lofts as well as in building due to its high load bearingstrength.

Manufactured boards


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FlexiPly is a relatively modern development of Plywood and consists of two

outer layers of wood which are scored to allow them to flex without

splitting. The two layers sandwich a thin layer of silicon which allows the

whole sheet to flex without damage. Flexiply can either be fixed to a curved

or shaped frame where it will follow the contour of the frame or it can be

laminated (two or more layers of FlexiPly) with glue in between the layers.

If wrapped around a former and left to dry the FlexiPly will keep the shape

of the former when removed. It is much more expensive than traditional

Plywood.

Manufactured boards


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Flexible MDF works in a similar way to FlexiPly but the boards are kerfed

(grooved) allowing the material to collapse into the grooves when flexed

and allows the MDF to be curved while retaining a nice smooth and

consistent surface on the outside.

Note that FlexiPly has the same surface on both sides while Flexi MDF will

have only one smooth side.

Manufactured boards


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Aero ply is a modern plywood which was developed for the aircraft industry

as its name implies. It is very thin yet very strong and flexible and is still

used in glider and airplane construction. It can also be laser cut for use in

jewelry.

Manufactured boards


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Maplex is a relatively new material designed to replace MDF since, although

it is made from wood fibres, it does not contain potentially toxic resins. It is

made from 100% pressed wood fibres with no binding agents and has

similar working properties to MDF. It is also completely recyclable.

Manufactured boards


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Veneers are thin slices of real wood but are often put on manufactured

boards to make them look more expensive. They are ‘peeled’ off the trunk

of a tree much like you peel toilet paper off a roll!

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Hexaboard is an exterior quality birch plywood with a hard phenolic resin

laminated surface. This hard-wearing surface has been embossed with a

hexagonal pattern making it safer to walk on making it particularly suitablefor flooring in commercial vehicles and aircraft etc.

Manufactured boards


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Applications for woodsCommon uses for manufactured boards


Stirling board Large sheets, cheap Shed and loft flooring

Chipboard Good compressive strength Flooring, furniture (laminated)

Conti board Same as chipboard but with a

heatproof and wipeable surface

Kitchen cabinets, bookcases

MDF Large sheets, smooth surface

finish

Furniture, cabinet doors

(often laminated or veneered)

Plywood Large sheets, strong, attractive

surface finish

Construction, paneling,

furniture carcasses

Aero ply Strong, flexible, lightweight Jewelry, aircraft bodies

Flexi-ply/MDF Flexible, large sheets Curved furniture, wall

cladding

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Visual test on manufacture boards.


Answer: Plywood as it can be made into complex shapes when formed


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Answer: Chipboard as is cheap but flat and easy to lay for sub-flooring


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Answer: MDF as it is flat, comes in large sheets and easy to paint


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Stock forms of timberWood can be obtained in a variety of forms from the raw material (the tree itself) to various shapes and sizes of processed timber.

However, a single piece of wood can be no bigger than the tree it comes from unless it is engineered or laminated.

Common forms include planks, beams, square and rectangular section, dowel and various manufactured boards which are usually available in sizes up to 8’ x 4’ (sometimes even larger). Wood can also come in mouldings or profiles.

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Ecological and social footprint

You should have a knowledge and understanding of the ecological and social footprint left by designers:

• the effect of deforestation, mining, drilling and farming on social communities and on the environment

• mileage of product from raw material source, distribution, user location and final disposal

• the effect of carbon being produced during the manufacture of products

• the six R’s and their relevance to this material group

• safe working conditions; reducing oceanic/atmospheric pollution and reducing the detrimental (negative) impact on others

• any other current or topical concern relating to the material group studied and their effect directly or indirectly on the environment

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Ecological and social footprint• A collection of trees is called a forest and forests cover 30% of the earth.

There are around 3 trillion trees with most in tropical countries. That’saround 400 trees for every person but 12,000 years ago there were twiceas many trees and we are cutting down millions of trees every day.

• Trees provide the following:

• Trees convert carbon dioxide (our bad breath) into oxygen which allhumans and most animals need to survive.

• They provide materials for building.

• Pulp from wood is used to make paper and card.

• They provide food for humans and animals; nuts and fruit.

• Trees provide shelter for humans and habitats for animals and birds.

• The wood can also be burnt for fuel.

• Replanting two trees for every one we cut down will help to replace thedwindling tree population on the earth.

• Using alternative materials may reduce deforestation but may causeother ecological problems such as use of fossil fuels, mining for ores etc.

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• Trees are a sustainable and renewable source of energy andmaterials.

• Sustainable means we can keep supplies of a material going byrecycling, repairing or reusing them. Wood is sustainable but it isalso renewable because we can grow more.

• In contrast, Metal and Plastic are not renewable as their sources(ores and oil) are finite (running out) and you cannot make more.Other than recycling metal and plastic….when they run out theyare gone forever!!

• In order to make sure we have enough wood we have a system ofreplanting which means that for every tree we cut down we planttwo more. We have been doing this for around 50 years now butwe are nowhere near replacing all the trees we cut down overthousands of years.

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Summary of the unit

• Solid timber can be classed as either Hardwoods or Softwoods but thesewoods can be processed and combined to make manufactured boards.

• Wood is a natural material and therefore timber (wood in its natural state)is prone to changes in shape and size but manufactured boards are morestable and available in larger sheets.

• Wood is a sustainable material as we can grow more as long as we manageforests correctly. Due to its organic nature every piece of wood, likehumans, is unique in its size, grain and colour.

• Plywood is made from real layers of woods stuck together. This is calledlaminating.

• Manufactured boards can be covered in very thin layers of more expensivewood. These are called veneers.

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You should have a chart like this in your book. Complete each

section as you learn more woods. It will be a good revision guide.Trees (source)

Types of Wood

Hardwoods (Hot countries)

Slow growing (100 years)

Softwoods (Cold countries) Fast growing (25 years) Manufactured Boards(Processed Woods)

Type Use Type Use Type Use

OakHigh Quality

Expensive

Pine PlywoodLarge Sheets

Real wood layers

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Revision notes

For timber and woods, you should be familiar with theclassification, properties and stock forms available for eachmaterial.

You should be able to refer to the physical and mechanicalproperties of woods and why those properties make themsuitable for the particular application.

We will also look at the workshop tests undertaken to identifythe mechanical properties of timbers and woods.

In a later unit we will look at how timber can be enhanced andfinished in the production of products and components.

In your exam answers you will be expected to make referenceto the physical and mechanical properties of woods whereappropriate.

Make your own chart which puts timbers into categories withkey properties and common applications.

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AssessmentPlease read through the relevant section in the AQA textbook to support your notes and this presentation. You can find questions relevant to this section in the following past papers:

2010

2011 Q1

2012

2013

2014

2015

2016

2017

2018

2019 Q1, 3, 4, 9, 18

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Prep

Please attempt the past paper for next lesson and we will go through the answers together to see where you may have made a mistake or where you can improve your answers.

Please write in your homework planner:

Complete Q1-3 from AQA PROD1 Summer 2013

Next lesson: Metals and alloys

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