Metalwork - Materials - Woods
Wood is a hard, tough substance that forms the trunks of trees, and has been used for thousands of years as a fuel and as a material for construction. Wood is a renewable material, however as the global demand for wood rises, increased timber production has developed in tropical countries and in the northern forests of Russia. The current deforestation in tropical rain forests has alarmed scientists concerned with the ecology. Forests play an important role in regulating the climate of the planet by removing carbon dioxide from the atmosphere. Scientists are therefore also increasingly concerned about the role that tropical deforestation may play in global warming. In many parts of the world, large areas of forest have been set aside and are managed primarily for the continued production of wood. The United States, Russia, Canada, Japan, Sweden, Germany, Poland, France, Finland, and Brazil are the chief timber producing countries in the world. In addition, many beautiful varieties of timber such as mahogany, ebony, and rosewood, used chiefly in furniture manufacture, are produced in tropical Asian, Latin American, and African countries.
Woods are classified as either Softwood or Hardwood, depending on the tree which they come from. Woods from Deciduous or broad-leaved trees, are called Hardwoods, and woods from Coniferous trees are called Softwoods, regardless of their actual hardness. Therefore many Softwoods are actually harder than some of the so-called Hardwoods. Hardwood is generally used for furniture and high-grade flooring, and Softwood is generally used for construction materials. If you would like to know which woods are Hardwood and which are Softwood goto the Varities of Woods page.
A Wood's appearance is one of the most important properties when the wood is being considered for some interior use such as furniture, floorboards or panelling. Certain woods, such as Walnut and Mahogany, have straight parallel graining, and a dark, attractive color which makes them highly desirable for furniture. 'Knotty' grains may also make attractive patterns, and with the wide variety of wood stains available today, unattractive woods can be made to look very attractive. The main physical Properties of wood are strength, hardness, stiffness, and density. Density is often an indication of the properties of the wood, as dense woods are usually hard and strong. In the case of strength, a wood that is high in one kind of strength may not be high in the others. The strength of a wood also varies with the state of dryness of the wood and with the direction of the grain. Wood is always much stronger when cut along the grain rather than across it. Generally wood has high compression strength, in some cases higher in proportion to its weight than steel; it has low tensile strength and moderate shear strength. You can see more about the different types of strength that a material can have on the Properties page. The toughness of a wood is a measure of resistant it is against sudden and repeated stress. Hickory and Ash are outstanding for their toughness and are used in baseball bats, axe handles and hurleys, because of this. Other less important properties may be critical for a particular use. The elasticity and resonance of Spruce make it the only material suitable for the sounding board of a fine piano. Wood is naturally a very durable substance. If not attacked by living organisms, such as dry rot of fungi, it will last for hundreds or even thousands of years.
There are many different varities of wood, used for different purposes. Goto the Varities of Woods page to get a list of different woods, their classification, appearance and uses.
Plywood is made up of an odd number of layers of wood bonded together by glue or synthetic resins The layers are laid with the grain of each at 90° to the next one. The resulting sheet of plywood is equally strong in all directions, which is an improvement on normal pieces of wood, which are only strong along the grain.
Only the layers on the outside of the plywood need have hardness and good appearance, the inner layers need only be strong, as they arte the ones that are seen and used. Fine and expensive woods, such as Mahogany, Satinwood, Ebony, and Zebrawood, are now commonly used in the form of plywood, with a thin layer of expensive wood covering several layers of strong but inexpensive ordinary wood such as Douglas Fir. In this way, the cost of the wood is greatly reduced, the appearance remains the same, and the strength and resistance to warping is greatly increased.
Veneer is thin pieces of richly grained or colored woods, glued in sheets, strips or many tiny pieces to the surfaces of inferior woods. Veneering makes use of many beautiful and expensive tropical woods. After being cut, veneers are pressed flat and dried. Veneer may be applied in large sheets, as on flat surfaces of walls, furniture, or the outer woodwork of most pianos. Veneering applied in small pieces of equal thickness over a surface to form a decorative design is known as Marquetry. The principle of veneering is used in the construction of Plywood.
Wood can be joined in a number of ways. Goto Types of Wood Joints if you would like to see different common methods of joining pieces of wood together. These joints are usually fixed together using screws and adhesives, and often both at the same time. Wood screws are self tapping which means that they do not have to have a hole drilled in the wood before they are inserted.
There is a wide range of wood cutting tools in use in the Woodwork room. Thay are classed as Hand Tools and Machine Tools. Goto Woodwork Hand Tools if you want to see some of the common Woodwork hand tools.