UNIT 3

WOOD AND ITS DERIVATIVES

Alumno ________________________________________ Grupo _________

1. Wood

Wood is a raw vegetable material. It comes from the trunks of trees and bushes.

It´s composed of:

Cellulose fibres like all vegetable matter

Lignin which makes it rigid and hard

The parts of a tree trunk you see when you make a horizontal cut:

Bark (exterior layer): protects the plant from external attack.

Cambium: a thin transparent layer

Sapwood (recent growth): not very strong, used for woodwork that needs soft

wood.

Heartwood: the strong part that keeps the trunk vertical; hard and dry,

extracted and processed for all types of woodworking.

Pith: the centre of the trunk; very weak, not generally used.

2. Properties of wood

Factors that influence the properties of wood:

Type of tree

Environment

Soil

Age of tree

Composition of the wood

2.1. Physical properties

Hardness: wood is hard, but can be penetrated by objects such as screws or

nails.

Density: wood is less dense tan water, so it floats.

Electrical insulation: dry wood provides good electrical insulation.

Thermal insulation: wood provides good termal insulation, but it burns easily.

Porosity: wood can absorb or emit liquids and gases because it has tiny holes,

called pores.

Mechanical resistance: wood has good mechanical resistance against the

forces of traction, compression and bending.

Colour and grain: wood has aesthetic qualities: a variety of colours and grains.

2.2. Ecological properties

Wood is a renewable raw material. New trees can grow all the time. But

desforestation causes serious damage to the balance of our ecosystem.

Wood is biodegradable. It descomposes as time passes.

Wood is recyclable. We can make others things from it, such as prefabricated

boards, paper and cardboard.

3. How to process wood

Cutting and pruning

The trees are cut down with chainsaws and the branches are the cut off.

Transport

The logs are transported by road, rail and water to their destination.

Removing the bark

This happens at the sawmill. A chain of rollers with metal teeth turns and removes

the bark.

Sawing

The logs are cut into planks or boards that are cut parallel to the axis of the log.

Drying

The wood is dried under pressure so that it doesn´t warp. Dry wood lasts longer and

it is lighter.

Planing

The wood is planed to make it smooth and evenly flat. This also gives it a good finish.

4. Classifying wood

Wood is classified as hardwood or softwood depending the tree it comes from.

Hardwood

Deciduous tree

They grow slowly and have thick trunks

They contein little resin

They can be in many different colours, are compact and are resistant

Type: beech, oak, cherry, mahogany.

Their most common uses: furniture, floor, handles, toys, rods, parquet, barrels,

musical instruments…

Softwood

Conifers (trees with needle-shaped leaves)

They grow quickly and have clear anual rings.

The wood is resinous and usually light-coloured.

It´s light and easy to work with because it´s less resistant.

Type: pine, white fir, red fir, White poplar.

Their most common uses: furniture, boats, electricity posts, floors, boxes, paper,

fencing, wood panelling, plywood…

5. The most important types of wood derivatives

Plywood

Source: Thin sheets of wood glued together and compressed.

Characteristics: Very sensitive to humidity and temperature changes. They can

warp and increase in thickness.

Uses: Joinery, doors, packing, agricultural construction and boats.

Chipboard

Source: Made with wood chips glued together (90% chips and 10% glue) and

compressed. Covered with a natural sheet of wood or with plastic.

Characteristics: Fragile and not easily deformed. Some of their components are

affected by changes in humidity and temperature.

Uses: Furnishings, doors, ceiling panels, insulation panels for prefabricated

buildings.

Fibreboard

Source: The fibres come from milling the wood chips. Tiny wood threads are

compressed and glued together to make a conglomerate. There are different

grades of density.

Characteristics: Compact, flexible and easy to work with.

Uses: Exterior covering (because it has a smooth surface), furniture, cabinets,

shelves and doors.

Hardboard

Source: Made from left over wood from the mill and unused pieces of wood.

Characteristics: Compact, flexible and easy to work with.

Uses: It is compressed together with glue to make lining for cupboards.

6. Safe ways to use woodworking tools

6.1. Safety rules

Before you start, check that tools are in good condition.

Secure the piece of wood properly with a clamp or bench vice, so that it can´t

move.

Be careful with sharp objects, e.g. an awl or punch.

Keep your hands well behind the cutting blades of the tools.

Don´t blow on the wood chips – they could go into your eyes. Use protective

glasses.

6.2. How to use a saw

1. Draw the cutting line onto the wood with a carpenter´s pencil.

2. Clamp the piece of wood down properly with the correct equipment so that it

can´t move or vibrate.

3. Make a small cut with the saw or a punch to mark the cutting line.

4. Hold the piece of wood with your free hand while cutting.

5. The saw should be at an angle of about 45° to the piece of wood.

6. Work with the complete length of the blade of the saw, at a moderate speed

and pressing down as you advance. Always cut back and forth in the same

direction.

6.3. How to use a fret saw

1. Choose the correct blade.

2. Loosen the two screws.

3. Put the blade on the bolt, next to the handle, with the teeth pointing away

from the saw, place the wing nut on the bolt, and tighten the nut with pliers or

pincers.

4. Tighten the blade and adjust the second wing nut .

5. Draw the cutting line on the piece of wood.

6. Clamp down the piece of wood so that it can´t move or vibrate.

7. Make a small cut with the fret saw to make a starting point before you make

the main cut.

8. Use the full length of the blade. Hold it perpendicular to the wood so that it

doesn´t break. Use constant and firm pressure.

9. To make an interior cut, make a hole, put the blade through and then fix the

saw onto the handle with the wing nut.

6.4. How to use a gimlet

1. Clamp the piece down and make a small hole with the punch or the gimlet to

mark the place where you want to make the hole.

2. Place the gimlet into the hole in a vertical position and turn clockwise.

6.5. How to use a sandpaper

1. Clamp down the piece of wood so that it can´t move.

2. Take a small piece of wood and wrap the sandpaper round it.

3. Sand the wood in the direction of the grain or fibres. Start with rough

sandpaper and continue with fine sandpaper to perfect the surface.

6.6. How to use a rasp

1. Clamp the piece of wood down to the workbench so that it can´t move.

2. Hold the handle with one hand (right hand, if you are right-handed; left hand if

you are left-handed) and hold the other end with the palm of your other hand.

3. Hold the rasp at about 45° to the piece of wood.

4. Use the full length of the rasp, a moderate speed, pressing down as you move

to file off some the wood; this way the sides of the rasp don´t break.

6.7. How to join objects

Nailing and screwing

1. Check the length of the nail or screw. It must be a little shorter than the piece

of wood you use.

2. Make a small hole with a punch before you use a nail or screw.

3. You should not put the nails and screws along a straight line aligned with the

fibres, but at intervals or back and forth so that the wood doesn´t split.

Gluing

1. First stir the adhesive well.

2. Make sure the surface is clean. Use a brush to wipe away dust.

3. Depending on the type of glue you are using, you have to wait a while for it to

dry, unless it´s a type that sticks immediately.

4. While the glue is drying, secure the pieces with: a clamp, a vice, a rope,

weights, etc.