The terms softwood and hardwood cause an unfortunate amount of confusion.The builder uses these terms to describe the relative ease of working with different timbers, whereas a botanist would apply the terms in relation the cell structure of a given timber species.
Timbers are classified into two groups, hardwood or softwoods.
Timbers are classified into two groups, hardwood or softwoods.
Trees are either
A) DECIDUOUS: trees that lose their leaves in autumn and winter, and develop flat leaves in spring; also referred to as HARDWOODS
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B) CONIFEROUS: ever-green, bears cones and have needle shaped leaves that stay green all year wound; also referred to as SOFT WOODS
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Structure of Softwood
Softwoods are light in weight and easy to work with, however they are generally not as durable as hardwood.
The diagram represents the cell structure of a small block of softwood about 1mm high. The upper surface of the diagram represents sections through cells which form water carriers called Tracheids. The walls of the tracheids constitute the bulk of the wood substance. Tracheids are actually long thin cells, much smaller than the pores in hardwood. The diagram also shows a group of horizontal cells which form the medullary rays which store food and conduct it radially. Medullary rays run horizontally from the pith to the outer zones of the tree. |
Structure of Hardwood
Hardwood are strong, heavy, durable and hard to work with.
The following diagram represents the cell structure of a small block of hardwood about 1mm high. Hardwoods, or pored woods, consist of large tube-like vessels (pores), which vary in size and, in some species, are visible to the naked eye. Short cells are joined together forming a continuous conduit for food materials. The smaller, thick-walled cells shown in the diagram are wood fibres which make up the bulk of the wood substance. Medullary rays have the same function in softwood as they do in hardwood. |
Hardwood VS Softwood
HARDWOODS |
SOFTWOODS |
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Botanical Classification |
Angiosperms – ‘enclosed seed’ plants. The flowers produce seeds enclosed in fruit. |
Gymnosperms – ‘naked seed’ planes. There are no flowers, instead the cones produce seeds. |
Leaves |
Leaves are usually broad and flat. Many hardwoods are deciduous – they shed their leaves in autumn. |
Leaves are needle like. Most softwoods are evergreens – they do not shed their leaves. |
Cell Structure |
Pored wood, with two types of cells: · Large, tube like pores or vessels. These carry sap. · Smaller thick walled fibres. These support the tree. |
Non-pored wood, with only one type of cell: · Long thin cells call tracheids. These carry sap and support the tree. |
Geographical Location |
Best suited to more temperate or tropical climates. |
Best suited to cooler climates. |
Properties of Timber
Nature has provided many different species of wood with different characteristics and properties. The selection of a suitable timber for a particular job is usually determined by the suitability of the properties of that timber. Some of the main characteristics of timber are listed below.
`Density (weight) is related to the size and thickness of cell walls and also the quantity of lignin, resins and gums present in the cell structure.
Durability depends to some extent on moisture content but mainly on the presence in the cells of naturally occurring chemicals which provide resistance to fungus and insect attack. Durability can be stated simply as the ability of wood to resist decay, termites, borers and the weathering process and does not depend on hardness. The durability of some species can be improved by impregnation with chemical preservatives.
Early Wood The part of the wood in the growth ring of a tree that is produced earlier in the growing season. The cells of early wood are larger and have thinner walls than those produced later in the growing season.
Figure is the pattern in the timber caused by variations in colour, grain and texture.
Grain refers to the general direction of fibres relative to the longitudinal axis of a piece of timber and may be described as:
· 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 or edge;
· interlocked grain when the angle of fibres changes or reverses in alternate layers.
`Density (weight) is related to the size and thickness of cell walls and also the quantity of lignin, resins and gums present in the cell structure.
Durability depends to some extent on moisture content but mainly on the presence in the cells of naturally occurring chemicals which provide resistance to fungus and insect attack. Durability can be stated simply as the ability of wood to resist decay, termites, borers and the weathering process and does not depend on hardness. The durability of some species can be improved by impregnation with chemical preservatives.
Early Wood The part of the wood in the growth ring of a tree that is produced earlier in the growing season. The cells of early wood are larger and have thinner walls than those produced later in the growing season.
Figure is the pattern in the timber caused by variations in colour, grain and texture.
Grain refers to the general direction of fibres relative to the longitudinal axis of a piece of timber and may be described as:
· 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 or edge;
· interlocked grain when the angle of fibres changes or reverses in alternate layers.
Grain Direction
As someone with some woodworking experience already, you have probably already discovered that timber can be more easily worked in one direction than in the other. This is due to the direction of cell fibres in the timber which is usually called the grain direction. When seen under the microscope, cell fibres look like a bunch of hollow tubes glued together and all running in much the same direction. They were the parts of the tree that conducted food when it was alive. Working across these fibres tends to break them apart. This is called working across the grain and should be avoided as it often causes the timber to split. Working in a direction opposite to that in which they lie causes the fibres to lift and tear. This is called working against the grain. |
We should always work in the direction of the grain when we can. This cuts through the cell fibres more neatly and gives a smoother finish which requires little or no sanding when sharp tools are used.
One of the biggest mistakes made by beginning woodworkers is to try and use blunt tools. These tend to pull out the fibres instead of slicing neatly through them.
Hardness and softness are characteristics which are related to density and refer to the ability of wood to resist bruising and indentation.
Late Wood The part of the wood in a growth ring of a tree that is produced later in the growing season. The cells of late wood are smaller and have thicker cell walls than those produced earlier in the season. Within a growth ring, the change of early wood to late wood is gradual, but each layer of early wood from the next growing season makes an abrupt contrast with the late wood before it, thus leading to the perception of rings.
Medullary Rays radial sheets or ribbons extending vertically through the tree across and perpendicular to the growth rings.
Pores a minute opening in tissue, as in the skin of an animal, serving as an outlet for perspiration, or in a plant leaf or stem, serving as a means of absorption and transpiration.
Strength is directly related to cellular structure of the wood and is not always related to the weight. The length of fibres is a very important factor in cell structure which characterises strong timber. For example Oregon and Pine have very long fibres which give the timber excellent load bearing qualities.
Texture generally refers to the arrangement and relative size of cells. Texture could be described as coarse, medium or fine.
Tracheids are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts. Tracheids are one of two types of tracheary elements, vessel elements being the other. All tracheary elements develop a thick lignified cell wall, and at maturity the protoplast has broken down and disappeared. The presence of tracheary elements is the defining characteristic of vascular plants to differentiate them from non-vascular plants. Tracheid build varies by location.
The two major functions that tracheids may fulfill are:
- part of the transport system, mainly transporting water
- structural support
One of the biggest mistakes made by beginning woodworkers is to try and use blunt tools. These tend to pull out the fibres instead of slicing neatly through them.
Hardness and softness are characteristics which are related to density and refer to the ability of wood to resist bruising and indentation.
Late Wood The part of the wood in a growth ring of a tree that is produced later in the growing season. The cells of late wood are smaller and have thicker cell walls than those produced earlier in the season. Within a growth ring, the change of early wood to late wood is gradual, but each layer of early wood from the next growing season makes an abrupt contrast with the late wood before it, thus leading to the perception of rings.
Medullary Rays radial sheets or ribbons extending vertically through the tree across and perpendicular to the growth rings.
Pores a minute opening in tissue, as in the skin of an animal, serving as an outlet for perspiration, or in a plant leaf or stem, serving as a means of absorption and transpiration.
Strength is directly related to cellular structure of the wood and is not always related to the weight. The length of fibres is a very important factor in cell structure which characterises strong timber. For example Oregon and Pine have very long fibres which give the timber excellent load bearing qualities.
Texture generally refers to the arrangement and relative size of cells. Texture could be described as coarse, medium or fine.
Tracheids are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts. Tracheids are one of two types of tracheary elements, vessel elements being the other. All tracheary elements develop a thick lignified cell wall, and at maturity the protoplast has broken down and disappeared. The presence of tracheary elements is the defining characteristic of vascular plants to differentiate them from non-vascular plants. Tracheid build varies by location.
The two major functions that tracheids may fulfill are:
- part of the transport system, mainly transporting water
- structural support
PEEL ACTIVITY
COMPARE THE MICROSCOPIC STRUCTURE OF SOFTWOOD AND HARDWOOD.
DISCUSS THE ADVANTAGES AND DISADVANTAGES OF USING THESE TYPES OF WOOD.
(Expected length: 300 words)
DISCUSS THE ADVANTAGES AND DISADVANTAGES OF USING THESE TYPES OF WOOD.
(Expected length: 300 words)
Do not forget to use the PEEL Structure when completing this activity.
POINT |
What is the point you are trying to get across? Perhaps start with an introductory sentence which will tell your reader what you are writing about. |
EXAMPLE |
What are examples of Hardwood and Softwoods |
EXPLANATION |
At a microscopic level, what are the differences in the structures of hardwood and softwoods. Explain the advantages and disadvantages of these structures, relative to its end use. |
LINK |
Based on your arguments above, determine which classification of timber properties would be the most beneficial for your laminated cutting board. |