With the launch of Norton Clipper’s new wood cutting range, we’ve decided to give a basic overview of wood. Here, we give our overview of this versatile and ubiquitously utilised natural resource.
Wood has been a crucially important material in the production of tooling and construction material throughout human history and demand is intrinsically linked to population growth. Whilst the methods for cutting and processing the material have changed over the millennia, wood consumption continues to grow year-on-year and it is almost impossible to imagine the world without it.
What is the difference between hardwood and softwood?
Starting at the beginning, wooden material can broadly be separated into two categories. The first is natural timber, which is made up of standard hardwoods and softwoods, the second, are artificially manufactured boards; particle board, fibre board, and plywood.
Broadly, hardwoods are made from deciduous trees; the ones that lose their leaves during the colder seasons. As the name suggests, these types of wood are generally hard (with some notable exceptions).
Conversely, softwood is derived from coniferous, evergreen trees. They generally grow faster and the timber is usually cheaper than their hardwood counterparts. Softwoods are the source of about 80% of the world’s lumber so when we talk about wood, more often than not, we're talking about softwood.
Before reaching the workshop
If you have ever purchased timber or wood products, the likelihood is that it once started its life growing in a forest in either Canada, USA, Sweden, Finland, or Germany (World’s leading wood exporters). Once imported and processed, it will then likely find its way into a timber or builder’s merchant or a DIY store.
Before that happens however, the raw timber needs to be sawn down into planks and dried to remove the natural moisture in the wood.
Trees retain a huge amount of water and the structural integrity and usefulness of the wood is reliant on its proper removal. Fluctuations in the moisture content of the timber can affect the wood’s width by up to 3cm, therefore it crucially important process to get right.
Seasoning and drying
What do we mean by seasoning?
It is the process of drying the wood – removing the moisture content from within the cellular structure of the timber. This done by one of two methods; either kiln drying or air drying (or a combination of both methods).
Kiln Drying the Wood
In kiln drying, the wood is stacked in a sealed, controlled environment known as a kiln. Within this enclosed system, both the temperature and humidity are carefully monitored and adjusted to optimum levels for seasoning.
Kiln drying is much the quicker method of seasoning as it only takes between 6-8 weeks to complete. Additionally, the wood is not exposed to fluctuating climate or weather conditions, or the fungal attacks seen in air drying methods.
The drawback however is the relatively high cost both from an initial setup perspective and with the ongoing expense. In turn, this pushes the unit price per plank up with kiln dried timber.
Air Drying the Wood
This method takes significantly more time, instead of the 6-8 weeks seen in kiln drying, air drying generally takes years. As a rough guide, a hardwood plank needs to be air dried for about one year per every inch of thickness.
Air drying consists of a stack of sawn timber separated by “stickers” on raised foundations, and stored in a clean, cool, dry and shady place. The wood is secured by strapping or a sheet of particle board weighed down by breeze blocks.
Air drying requires sufficient air flow between the planks and around the individual boards. Once complete, the wood is left to dry.
Does wood move?
Yes, wood expands and contracts in accordance with the ambient humidity of its surroundings. Even after seasoning, the wood is still subject to expansion and contraction in accordance with how much moisture is in the surrounding air.
The most noticeable area to observe this change is across the woodgrain itself, being observable at right angles to the direction of the grain. As the wood expands and contracts, both the width and thickness fluctuate.
Factors such as the species of the wood have a marked effect on the extent of these changes and woodworkers have to make this a key consideration when their designing products.
Acclimatising the Wood to Surroundings
Before using the wood, it should ideally be stored in the same room as it will eventually take up residence, however this may not always be practical.
It is important that the storage conditions reflect as closely to its final living space as possible, particularly where solid wood flooring or furniture is concerned. After several weeks the moisture content of the timber should have acclimatised and it can then be used.
Working with artificially manufactured board materials such as particle board, fibre board and plywood is generally much simpler than working with solid wood materials as dimensional stability is a fundamental consideration in their design.
Any expansion and contraction in man-made boards is minimal, which makes them ideal for use in structural applications.
Three Types of Man-Made Boards
Plywood is a wood based material manufactured from thin layers of wood veneer glued together with adjacent layers. Plywood has a ‘cross grain’ structure.
This is when the wood in a board is cut so that the growth lines are not parallel to the long edge of the board. The benefits of this structure are that it reduces the tendency of wood to split when nailed, there is also a reduction in the amount of expansion and contraction in the board, and cross graining also makes the strength of the panel consistent across all directions.
Particle boards are made up of small and irregularly sized wood chips that are bonded together using synthetic resins and pressed into sheets of varying sizes and thicknesses.
These boards are relatively cheap and are used commonly throughout the budget end of the furniture industry, particularly for kitchen laminate worktops and MFC (Melamine Faced Chipboard) cabinet carcasses.
The most commonly used form of fibre board is that mainstay of modern interior design: Medium Density Fibreboard (MDF).
This material is composed of softwoods that have been broken down into small fibres and fused together using resin glues. Fibreboard typically has a smooth, flat, continuous structure that is well suited to cutting with standard power tools and finishing.