For this learning module, you will need:
The first step in processing timber is separating the bark from the main part of the trunk. Logs are passed through a large cylinder known as a debarking drum. Inside the drum, logs spin and rub against each other until all of the bark is removed.
Pulp and Paper:
If destined to become pulp and/or paper, a debarked log is sent straight to the chipper. The chipper reduces the log into, you guessed it, chips. These are then mixed with chemicals and heated in big pressure cookers known as digesters. Digesting separates the cellulose fibers from the lignin. The soft, wet fibers, now known as pulp, are separated from the digesters, and washed and bleached to the proper shade of whiteness. From there, the fibers are mixed with water again and formed into large mats of pulp. These mats enter a series of rollers and presses that flatten the pulp into sheets and to extract water. Finally, a starch solution is added to both sides before the final drying process.
Higher-grade logs don't go to the chipper, but to the sawmill. It is here, a single log can become many different boards, planks and/or beams. The primary saw of any mill, the head rig, does the job of turning the log into rough sawn pieces.
After the head rig saws the log into sections, lumber is passed through an edger (which removes irregular edges and defects), and then through a trimmer (which squares off the ends at standard lengths). Finally, the lumber is sorted, stacked and dried in kilns.
Now let's take a closer look at the structure of wood...
This section will highlight some of the main features (and internal structures) of a tree and how this affects the timber we ultimately use to make things with.
Take a look at the stop-motion short film adjacent which gives you an inside look at a piece of raw wood as it goes through a milling machine. Notice the growth rings, knots and weathered spots that make each tree unique!
Let's start with the trunk. If you cut down a tree and look at the cross section, you will likely see the following:
The pith (or centre of the tree) is rarely used for woodworking as it is too soft and often has cracks around it. Bark is also removed, leaving the more desirable heartwood, and sapwood.
Sapwood is the part where sap flows up and down the tree and is vital to supporting the functions of a living tree. It contains a lot of moisture and is therefore more susceptible to cracking when dried. Sapwood is therefore less desirable than heartwood, although it is still commonly used.
Heartwood is the 'older' sapwood, and is drier and stronger than the 'newer' sapwood. Over time, sap no longer passes through the heartwood and its pores fill with organic materials. Heartwood also changes colour and composition over time, and is usually darker and more beautiful in appearance than sapwood.
In selecting timber for a project, things to consider should include moisture content, durability and workability...
In selecting which timber(s) to use in any project, it's important to first understand the differences between 'green' and otherwise 'dried' timber. Both have their pros and cons, so choose which is best for your project wisely.
Green wood refers to wood that has been recently cut down and hasn't yet had an opportunity to ‘season’. Seasoning refers to the drying of moisture present inside the wood. Green wood is considered to have 100% moisture content relative to air dried wood, which is roughly 20% by comparison.
The standard moisture content for furniture grade, kiln dried lumber is 8-12%
Green wood’s high moisture content means that it is flexible and soft, making it relatively easy to work with. It won't dull chisels, saw teeth or other hand tools as quickly for this reason.
However, green timbers are more likely to warp and/or crack as the moisture dries, ruining your project. It should only be used if you’re trying to achieve a particular aesthetic (or 'weathered look'), or are practicing your woodworking skills.
Below is an example of green wood, which has cracked as the moisture dries.
For construction and furniture making applications, green wood (and it's unstable nature) is definitely not the best choice.
In most cases, dried wood works, machines, and glues better than green timber... although there are some exceptions; for instance, green wood is often easier to turn than dry wood.
Paints and finishes last longer on dried timber too.
To achieve a wood product that has less than 20% moisture content, it must be dried (or seasoned). There are two processes that are used to do this, one is air drying, and the other is kiln drying. The ideal moisture content for making furniture is around 6-10%.
Kiln Dried Wood:
Kiln dried wood is wood that is sawn, placed in a kiln and dried using warm circulating air. Kiln drying is a much faster process compared to traditional air drying. This method also produces a much harder product, making it ideal for commercial building and construction applications.
In this process, timber is stacked in chambers, which are fitted with equipment to control atmospheric temperature, relative humidity and circulation rate. The vast majority of commercial timbers are dried in industrial kilns.
So which wood should you use?
As mentioned already, the moisture content of timbers should be selected depending on what the project is exactly.
Kiln dried wood is the industry standard for larger scale construction projects. It is the most consistently available commercial product, and offers many of the same advantages as air dried timbers.
Air Dried Wood:
Air dried wood is exactly that. It’s wood that has been left to dry in the air, as opposed to applying heat to dry it. It is the more traditional method of drying wood and gives the timber a little more flexibility.
The technique of air drying consists mainly of making a stack of sawn timber (with the layers of boards separated by 'stickers') on raised foundations, in a clean, cool and dry location. The rate of drying largely depends on climatic conditions, and the movement of air (or exposure to the wind). For successful air drying, a continuous and uniform flow of air throughout the pile needs to be achieved.
Pros: air drying often produces a higher quality, more easily workable wood than with kiln drying.
Cons: Depending on the climate, it takes several months to a number of years to properly air-dry wood.
Air dried timber is a woodworkers best friend. It’s easier to work with and is more stable than other kiln dried options (...because it dries at a slower, more natural pace).
Air dried wood contains slightly more moisture than the more forcible method of kiln drying too. It’s this latent moisture content which makes it a little easier to work with, and less prone to damage hand tools. Air dried timber is said to have richer colour and grain clarity
The Janka Hardness Test measures the resistance of a sample of wood to damage and wear. It measures the force required to embed an 11.28 millimeter (0.444 in) diameter steel ball halfway into a sample of wood. Janka hardness ratings are most commonly used to determine whether a species is suitable for use as flooring and the like.
Testing is carried out on heartwood samples, clear of knots and with a 12% moisture content
Important: the hardness of wood varies according to the direction of the grain.
End grain hardness is generally higher than side grain in softer woods but in the denser hardwoods there is often little difference.
Australia has an abundance of both native timbers, as well as exotics, available to the budding woodworker.
Timber can be classified as either a softwood or hardwood. This distinction doesn’t mean one is necessarily harder than the other, but instead refers to its physical structure and form. Balsa, for example, is classified as a hardwood despite being very soft.
Hardwood: comes from angiosperm (or flowering trees) such as oak, maple or walnut.
Softwood: comes from gymnosperm, evergreen conifers such as pine or spruce.
Softwoods are lighter, and generally simpler in structure, whereas hardwoods are harder and more complex.
Being one of the more common species in Australia, the eucalyptus species contain many different types of sub species such as Tasmanian Oak, Blackbutt, Spotted Gum and Jarrah. This timber is commonly used for furniture making.
Western red is the most common type of cedar and is used for furniture, deck handrails, wall cladding and window frames as it has good weather-resistant properties.
Often referred to as Douglas Fir or Oregan. The reddish brown wood is imported from North America and is used as a rafter material.
Coming in several varieties the main ones in Australia is Radiata, Cypress and Hoop pine. This timber is commonly used as framing for housing,
Being a white to pale brown this type of timber is used in furniture production.
Being native to Sweden, Denmark and Norway, beech can be used from firewood to furniture and flooring.
This timber comes in two varieties: yellow and white. It is a fairly hard timber which can used for furniture and plywood. It is one of the most economical hardwoods and used extensively with flat pack furniture.
Very common in antique furniture but due to it’s availability its not commonly used today.
Available in two varieties: hard and soft. Hard maple is a very durable timber and can be used for high traffic flooring. Soft maple is used mainly for boxes and pallets.
This is one of the most sought after timbers and has been used for centuries. Available in 2 colours; red and white. It has a high resistant to moisture allowing it to be used for outdoor furniture.
Used extensively in boats and outdoor furniture as it is the best timber to resist sun and rain.
A fairly expensive hardwood that is normally only available in narrow boards. It is used extensively in furniture making and as a veneer.
Timber has long had a place in the built environment. As manufacturing processes and technologies improve, so does its versatility and scope or applications.
Today, engineered timber has become one of the most common types of wood products used globally. Due to its versatility, it's often used for many surfaces and applications such as cladding and joinery.
Durability was also dramatically improved, and continues to improve, with the introduction of engineered timber. The layered construction that characterises engineered timber provides stability in volatile environments that solid timber cannot.
The introduction of engineered timber into the market place further improved the ranges of colour and finishes available for timber flooring. These ranges continue to increase rapidly due to advancements in manufacturing technologies.
Engineered wood is a very prominent advance in the manufacturing of building materials. Engineered wood has many comparative benefits over natural wood. It is sustainable as the wood waste is used in manufacturing them. Since it is engineered they are perfect for specific purposes and have specific related properties, especially improved strength, custom thickness and density. They can be easily manipulated, cut and used with basic skill and tools. On the other hand, the adhesives used in making the boards, especially formaldehyde, are not entirely friendly. There are, however, other new resins, though comparatively expensive, that decrease that effect. So here are the basic types of engineered wood.
Particleboards are made by bonding sawdust and shavings with resin. The result is a less dense and inexpensive flat board (compared to fiberboards). Usually used in low-end furniture for it’s low-cost manufacturing. Manufacturers typically add a veneer surface to make the material more resistant to stains, and to enhance the furniture’s overall look.
Fiberboards are made by reducing the wood into small chips and then heated to become fibers, and these fibers are then dried and bonded together using a synthetic resin adhesive. The result is a much denser board, less prone to chipping and breaking.
Strand boards are made by gluing together flakes of wood using a resin and bonding them together under pressure and temperature. There are different types of strand boards. Oriented strand boards (OSB) are made by glue and wood strands oriented in specific angles which are then subjected to high pressures. This type is mostly used in sheathing and constructing buildings that need to bear a lot of load. Parallel Strand Boards (PSL) are made using method similar to OSB but with the strands aligned in parallel. This helps them bear a lot of load in single direction and hence can be used as beams, columns and such.
The most popular type of fiberboard, this type of wood is durable thanks to its strong and dense structure. It is also cheaper compared to solidwood, so it is usually used for flat surfaces, like dining and office tables.
Medium Density Fiberboard (MDF)
MDF is manufactured by gluing sawdust, wood shavings, chippings or even any organic fiber together and pressing under high pressure to create fiber boards. There are different types of fiber boards depending on the strength and density – particle board, fiberboard, laminated board and veneer board. These are cheaper than natural wood and plywood, though not as durable and strong. They are easy to deal with and are used almost everywhere from commercial to residential buildings.
Plywood is very strong thanks to how it is manufactured. Produced by sandwiching multiple layers of wood veneers to create a smooth, sturdy and solid board. Popular in flooring industries due to its strength and resistance to warping.
Plywood is manufactured by gluing together a few plies, layers of wood veneer, together at different angles to create a single sheet of wood. The plies are glued at right angles if the plywood is of low quality and at 45 degrees angle to each sheet to create high quality plywood that is strong at all axes. The plies are almost always used in odd numbers to give it strength not to bend at right angles and prevent warping. Plywood has many applications from aircraft, marine and automobiles to residential indoor furnishing. There are various types of plywood and each is has its own application – softwood, hardwood, tropical, aircraft, marine and other decorative types.
Laminated wood is usually made by fusing layers of wood together and applying pressure to strengthen it. Glued Laminated Timber is made by gluing several layers of parallel timber together using adhesives that are resistant to moisture which makes it perfect for beams and columns. It can also be produced in curved shapes and hence offers more flexibility or use. Cross Laminated Timber on the other hand has layers of timber glued across the other layer to improve strength. Laminated Veneer Lumber is made by gluing several thin layers of wood veneer with the grain aligned along the length making it strong in that direction and so right for beams, columns and such.
When timber is milled from a section of the tree, the grain pattern that is visible depends on the angle that the growth rings intersect the cut surface. There are three different ways to cut a log;- plain sawn (or flat sawn), rift sawn and quarter sawn. The most common (and cheapest) is plain sawn, with rift sawn being the most expensive.
Plain Sawn/Flat Sawn:
Most common, least expensive
Plain sawn, also commonly called flat sawn, is the most common lumber you will find. This is the most inexpensive way to manufacture logs into lumber. Plain sawn lumber is the most common type of cut. The annular rings are generally 30 degrees or less to the face of the board; this is often referred to as tangential grain. The resulting wood displays a cathedral pattern on the face of the board.
More expensive than plain sawn material
Quarter sawn wood has an amazing straight grain pattern that lends itself to design. Quarter sawn lumber is defined as wood where the annular growth rings intersect the face of the board at a 60 to 90 degree angle. When cutting this lumber at the sawmill, each log is sawed at a radial angle into four quarters, hence the name. Dramatic flecking is also present in red oak and white oak.
Most expensive, least common
Rift sawn wood can be manufactured either as a compliment to quarter sawn lumber or logs can be cut specifically as rift sawn. In rift sawn lumber the annual rings are typically between 30-60 degrees, with 45 degrees being optimum. Manufactured by milling perpendicular to the log’s growth rings producing a linear grain pattern with no flecking. This method produces the most waste, increasing the cost of this lumber. Rift sawn lumber is very dimensionally stable and has a unique linear appearance.
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