Presentation drawing. Illustration by Richard Jones
In Chris’s blog post, “The 10 Worst Mistakes I Made as a Beginner,” one mistake he mentioned was “buying the hardware at the end.” I added a comment to his blog to say that when I was studying furniture design and making at college in the early 1980s, a visiting lecturer, and furniture designer and maker Rupert Williamson, cited the mantra, “Design from the handles back.” He added, “Nipping down to the hardware shop at the last moment to carelessly buy some pug ugly wooden knobs for the chest of drawers you’ve made is all wrong.”
I immediately thought, How obvious. Essentially, all Rupert was really saying was to consider carefully what the viewer first sees because that first look either draws the viewer in or repels them. Every other part of the design is important of course, including what’s not seen initially along with the technicalities of construction and the fulfillment of other design criteria whether they be aesthetic, practical, cost, material choices and so on. The first look evokes a reaction, e.g., “ooh nice,” “hmm?” or “eeyeuch!” leading to further examination, pausing and moving along.
Earlier in my career, an element of my production included designing furniture for display in galleries and furniture shows, and the cabinet used to illustrate this text is an example. Exhibition pieces project your design ability and style, generate commissions, and are themselves salable. The variation of the cabriole leg style used in this piece was the design motif that initiated the design development; this leg form had already featured in tables, chairs and beds but I wanted to see if it could be used successfully in a cabinet.
Designing for shows is both liberating and restricting; you can make anything you like, but will anyone else appreciate it? In this case, with just the leg form as a starting point, there were no pre-existing design constraints, apart from the piece potentially having appeal to categories such as homeowners, interior designers and so on. With speculative pieces, I find it helpful to invent a realistic end-use, perhaps a need of one’s own. Here I settled on “storage” as the vague generalised end function. This forced concentration on the storage role and discouraged flights of fancy which were filed in the “maybe for later” category.
General proportions, i.e., width, depth, plus incorporation of the cabriole leg profile were resolved first through a mixture of technical decisions and sketching. The early design development soon led to the decision that the cabinet would be a nest of drawers in a free-standing cabinet – drawers can always find a purpose. Technical decisions were required. How many drawers, and how should they move? Visible wooden drawer dividers between drawer fronts, or not? Proprietary drawer slides? Planted or integral drawer fronts? Exposed horizontal dividers visible between drawer fronts were ruled out to reduce the quantity of cluttered horizontal lines. Full-extension undermount metal drawer slides were chosen because they are quite inconspicuous and allow the drawer to fill most of the internal cabinet width; they also give full and clear access to the drawer box. There are always arguments for and against proprietary slides, but I concluded they were a good choice.
The cabriole leg form and the curves in it, long and sweeping below the shoulder, and above it short and tightly arced, informed other elements of the visual impact – for instance, the bottom 100mm or so of the leg’s inner face is also curved, as are the bottom edges of the lower front rail, and the bottom edge of the side panel. The top has a shallow bevel worked on the underside to show a slim edge, and the front edge is gently arced.
But what about the maxim to “design from the handles back?” This hadn’t been forgotten and I’d decided that proprietary pulls would be used rather than making wooden pulls. Several possibilities were considered with the eventual choice being a U-shaped bronzed pull that picks up the similar half U-shaped curve above the knee of the leg. The bronze colour worked well, in my judgement, with the chosen wood, i.e., the visible walnut and cherry. Alternative colours available for the pulls were black or bright chrome, which I rejected because the softer or mellow bronze worked subtly with the wood colours. As a side note, the drawer boxes were made of hard maple with maple veneered plywood drawer bottoms, primarily to present a clean and light interior.
View downwards of the cabinet drawer’s pulls.
Eventually, a presentation drawing was worked up, not drawn with meticulous care maybe, but good enough for me as the customer. This was followed by creating an orthographic projection, from which an estimate, a cutting list and hardware list were extracted. From there it was just a case of buying the materials and building the cabinet, which leads to another useful maxim: Never assume the hardware is available unless you have it in stock. I’ve known a few makers get into a bit of a pickle because they’ve built a piece thinking they’ll buy the chosen hardware at a later date, only to find, too late, that the selected item has been discontinued and no old stock is available.
Close-up of the top of the cabinet showing a drawer open.
Is all of the above the recipe for successful design development? I’d say not really, but it does highlight the usefulness of the “design from the handles back” maxim. As to what happened to the cabinet? Well, it was exhibited at shows and galleries for a few years but never found a buyer. It did, however, generate several orders because people spotted it, liked it, and commissioned me to make something either based on it or very different. So, it earned its money for me and eventually I retired it from its exhibiting role and found a place in my own home – its drawers are stuffed with all sorts of things, so yes, drawers do always find a use.
Figure 8.1. Cross section of a board illustrating the three zones used to describe a moisture gradient, i.e., the core, intermediate zone and the shell. This is convenient but there aren’t actually distinct lines between each zone.
Richard Jones has spent his entire life as a professional woodworker and has dedicated himself to researching the technical details of wood in great depth, this material being the woodworker’s most important resource. The result is “Cut & Dried: A Woodworker’s Guide to Timber Technology” (from which the information below is an excerpt). In this book, Richard explores every aspect of the tree and its wood, from how it grows to how it is then cut, dried and delivered to your workshop.
In section 6.4 the drying and rewetting of wood was illustrated by using a sponge or towel to represent wood. An extension of this analogy serves as a preliminary introduction to terminology about the wood-seasoning process. Let’s say, for the sake of discussion, that you soak a very large and thick bath towel in a water bath. Lift up the sopping towel and wring it out as thoroughly as possible. Let us also assume you have the unlikely physical ability to wring out every drop of loose (free) water in the towel so the only water left is that bound within its fibres. This towel now stands for wood commonly and erroneously described as being at fibre saturation point (FSP), although the comments on FSP made in section 6.5 should be borne in mind. Fold the towel up three or four times into a long large sausage and hang it over a washing line. It’s a cool, dull, still, overcast day with, perhaps, intermittent, very light drizzle.
The towel will barely dry any further in the described weather conditions until either a breeze starts, the sun comes out or both changes happen together. It’s common knowledge that even if the sun doesn’t come out but a breeze starts the bundled-up towel will dry. Similarly, if there’s no breeze but the sun comes out the additional warmth causes water to evaporate from the towel’s fibres. In both cases described, the towel will eventually dry through. Put the two factors together, i.e., warmth and moving air, and the towel dries more rapidly than it will with either just a breeze or just extra warmth. Within the bundled-up drying towel there is a moisture gradient: As the towel dries it remains wetter in the middle of the bundle than near the surface. Assuming drying continues, the moisture content within the towel gradually evens out until it has an equal moisture content all through.
Without really knowing any science or terminology we know how to dry clothes quickly. Options include hanging them on a washing line on a warm, lightly breezy, sunny day, putting them out on a dull but dry and windy day, or hanging them over a warm radiator, and so on. Clothes fully opened and pegged on a line dry much quicker than clothes bunched up tightly.
What applies to drying clothes has similarities to the conditions that will dry wood. To dry wood quicker, heat air and move the hot air over it, although with wood, when it has dried to approximately 20 percent MC, the primary drivers for further drying are air temperature and humidity, not the speed at which the air passes over the wood. Thin boards dry faster than thick boards, which is analogous to opening clothes out to dry rather than leaving them bunched up. Fast drying of wood with very hot dry air will certainly accomplish the task, but it usually comes with an unacceptable price, i.e., degradation of one sort or another such as splitting, surface checking, case-hardening18, collapse (aka core collapse), honeycombing etc., making the wood unusable and unsellable. It’s imperative to control the speed at which wood dries in order to produce an acceptable end product.
The air’s RH must be low enough to absorb more water vapour. Air at 100 percent RH cannot absorb any more water vapour. Wet wood in RH conditions like this is comparable to my earlier description of hanging washing out to dry on a cool, damp, intermittently drizzly day – the clothes dry very slowly.
Warm air transfers heat to the wood causing the moisture in it to evaporate into the air. Again, the RH of the air must be low enough to absorb the water vapour given off by the wood. Drying kilns add warm air to the drying chamber, which transfers heat energy to both the wood and the water within it. The difference in temperature between the introduced dry air and the wet wood is often, but not always, quite small at the beginning of the kilning process. Water in the wood converts to vapour and evaporates through the wood surface into the air introduced into the drying chamber. The air temperature within a kiln is high, e.g., at stages in the wood drying process temperatures of 65.5° C (150° F) or more are used. At this temperature if the air stays at 70 percent RH it will eventually dry wood to approximately 10.5 percent MC (see figure 8.2).
If the air becomes too humid to dry the wood effectively, one of two things must happen for the wood to continue drying. First, further raising the temperature of the air in the kiln reduces its RH. Hotter air is capable of holding additional moisture released from the wood. Second, moving the humid air out of the drying chamber and replacing it with drier air will continue the drying process. Raising the temperature of the air already in the chamber is the cheapest option, but too high a temperature may lead to faults in the wood, particularly in some species more than others, e.g., surface checking as described earlier.
As timber dries, a moisture gradient develops inside the wood much like the earlier-described folded-up towel hanging over a washing line. In a wood-drying kiln where air temperatures are artificially high, generally the greater the temperature of the air acting on the wood, the steeper the moisture gradient within it, and moisture moves out of the wood faster. This also leads to faster evaporation of moisture from the surface of wood. Conversely, when wood is air dried and therefore experiences normal weather conditions, or if the wood is in service in a typical environment found in habitable buildings, RH is the primary controller of the steepness of the wood’s moisture gradient – air temperature in these circumstances has only a small effect.
For green wet wood to dry, as freshly milled boards or planks, for example, air must be moving to carry moisture away from the wood’s surface; this creates a place for the water deeper in the wood to migrate to, where it will also be carried away by the flow of air. If only a small volume of stagnant dry air surrounds wet wood, that air quickly becomes fully saturated with evaporated water. At that point no further drying can occur until that pocket of air moves away and is replaced by drier air.
Moving air carries moisture away from the wood’s exterior, thus drying the wood. But the air molecules adjacent to the wood surface stick to it. Air molecules just above the surface collide with the stuck air molecules and their movement is disrupted and slowed down. In turn, these air molecules impede the flow of air molecules just above them. As distance from the wood surface increases, the collisions diminish until air movement is unimpeded and becomes free flowing. In effect there is a thin layer of viscous “fluid” near the surface where velocity changes from zero at the surface to free flowing some distance away from it. “Engineers call this layer the boundary layer because it occurs on the boundary of the fluid.”19 (Benson, 2009, p 1) Within the boundary layer next to the wood the air is wetter (because it’s picked up moisture from the wood) and travels slower than the air above the boundary layer – it tends to hold the moisture taken from the wood close to the wood’s surface. A faster-moving air stream reduces the effect of the boundary layer and it sweeps away the damp air with its high-vapour pressure. The damp air is replaced with new drier air, i.e. air with a lower vapour pressure better able to absorb further moisture from the wood.
Whether wood is air dried or kiln dried the air entering the wood stack from one end has a lower RH than the air leaving the stack at the far end. Moving air leaving a stack of drying wood is cooler than the air entering it. The air cools as it transfers heat to the wood, thus enabling the drying process. If the air continuously passes through a stack of wood in one direction, the wood at the “upwind” end of the stack always dries faster than the wood at the “downwind” end. This results in unevenly dried planks of wood where the downwind end of a stack might be 3 percent or 4 percent wetter than the upwind side. In more extreme cases, the difference in moisture content between the upwind and downwind side of a stack may be 8 percent to 10 percent MC if the wood is very wet at the start of the drying process – in this case one possible result is the stack of wood may lean toward the drier side. This effect is more evident in wide stacks of wood, e.g., greater than about 2 metres (~6′), than in narrow stacks. Natural changes in wind direction and speed cancel out this effect in stacks of air-dried wood. It is only if a kiln operator is drying a wide stack of wood, or some particularly difficult to dry woods, that there is a real need to regularly alternate the air flow direction within the chamber. To achieve this, the fan blade rotation is reversed at evenly spaced intervals, e.g., every two hours, four hours, 12 hours etc. This upwind and downwind disparity in the drying ability of moving air in a stack of wood limits the size of a stickered pile of planks. This is especially the case with air drying where the yard owner really has less control over temperature, wind speed or wind direction. However, it should be noted that air velocity in either a kiln or in an air-drying wood pile is most important at the initial drying stage of wet wood because of its role in carrying away moisture from the wood surface. As the wood dries the significance of air movement gradually diminishes until the wood reaches about 20 percent MC. At this MC the primary critical factors for further drying are humidity and temperature, with the importance of air movement reducing significantly the drier the wood becomes.
Figure 8.2. North American research showing the relationship between the EMC of (primarily) Sitka spruce samples in response to a range of temperature and atmospheric RH conditions.
A twisted Ligustrum sinense. This Chinese privet has the status of a Champion Tree in the U.K. It’s found at Thorp Perrow Arboretum, Bedale, North Yorkshire, and gained its Champion status through being the tallest and largest specimen in the country. In addition to these characteristics its status as a champion is surely derived from its most notable feature being the remarkably twisted trunk thought to be caused by a systemic fault.
I first learned about the Twin Oaks Community while working on “Cut & Dried” with Richard Jones. We needed an index. Members of Twin Oaks, an intentional community in rural central Virginia, make their living, in part, by indexing books. Additional income is generated by making hammocks and furniture and tofu, and seed growing. The Twin Oaks Community, comprised of about 90 adults and 15 children, are income-sharing. Members complete about 42 hours of business and domestic work a week, and in return receive housing, food, healthcare and personal spending money.
Rachel Nishan from Twin Oaks responded to my indexing query, and we agreed to work together. Indexing a technical book such as “Cut & Dried” is a rather monumental task, and just thinking about it made my eye twitch. Yet Rachel approached the project without an air of stress, asking detailed questions about tree types, specificity and British spellings. Throughout our correspondence one sentence has stayed with me, years later: “… a more technically-inclined reader could want to look through the index in a variety of different ways, so I have tried to be pretty redundant, which is the kindest for the user of the index.”
“Kindest for the user.” I think that’s the heart of bookmaking, no?
Richard and I sent hundreds of emails to each other while working together to turn his years of work into book form. And all of that correspondence, from image selection to epsilon size, was written with Rachel’s not-yet-said phrase in mind: kindest for the user.
I was nervous to begin work on this book. Honestly, I thought the content would be too technical for me to understand. But then I read it. And realized Richard used his genius to transform his scholarly work into easy reading. And Rachel made topics within the text easy to find. And Meghan designed the book to be easy on the eyes. All with kindness in mind.
Many woodworkers are initially reluctant to study trees in detail fearing the subject is dauntingly heavy. Whilst it’s true the subject can be studied with scientific precision it’s really only necessary to get to grips with the main elements to gain a firm basic knowledge. Wood isn’t created with the needs of the woodworker in mind. The creation of wood is necessary for trees’ survival. We simply use what nature provides. Understanding the original function of wood helps woodworkers use it sympathetically and successfully. One example of useful basic knowledge described earlier is to understand the essentials of Latin scientific classification resulting in precision and clarity in any discussion of the subject.
All trees are members of the plant family. Specifically, they are all spermatophytes meaning they are seed-bearing plants. Trees are generally characterised as being perennial seed-bearing vascular woody plants with a root system and (ordinarily) a single trunk supporting a crown of leaf-bearing branches. With exceptions (see mention of the Arctic willow, Salix arctica, earlier) they normally reach a minimum height at maturity of five m (15′) and survive for at least three years.
This basic classification then breaks trees down into two distinctive types – the angiosperms (covered seeds) and the gymnosperms (naked seeds). Alternative names for these two groups are hardwoods, deciduous or broad-leaved trees (angiosperms), and conifers or softwoods (gymnosperms). The terms hardwood and softwood can be misleading as not all hardwoods produce hard wood, e.g., soft balsa wood is the product of a hardwood tree whereas yew is hard and comes from a softwood tree.
Figure 3.1. Trees increase girth by adding growth rings annually. They increase in height by adding new growth at the tips of branches. Roots and root tips grow in the same manner.
Typical of deciduous trees in temperate climates is the loss of leaves during autumn as the tree loses vitality followed by a dormant winter period. As usual there are exceptions where many of the hollies (Ilex spp.) retain their spiky and waxy leaves throughout the year. Spring, with its longer daylight hours and warmer weather, heralds a new period of rapid growth with the emergence of new leaves, flowering and reproduction. This is not true of all hardwoods in all climates. Many equatorial living hardwoods are able to grow all year round and may never lose their leaves en masse. With these trees the cycle is continuous as old leaves reach the end of their useful life to be replaced by new ones.
Figure 3.2 . Dendritic (deliquescent) growth pattern of broad-leaved trees. The main trunk branches and rebranches.Figure 3.3. Excurrent form of coniferous Japanese larch. A single bole or trunk with subordinate branching. Larch is an exception to the rule because it loses its needles in winter. In this managed forest, juvenile Sitka spruce have established themselves between the planted larches. Dalby Forest, North Yorkshire, England.
Angiosperms (deciduous trees) from all climatic conditions have a characteristic growth pattern. Their form is deliquescent or dendritic, meaning there is branching and re-branching of a main trunk.
Gymnosperms (coniferous or evergreen) trees typically retain their leaves throughout the year, with larch being one exception to this trait. Their form is generally excurrent – the main trunk rises singly with lesser sideways branching. Broadleaved trees usually have large, relatively fragile, blade-like leaves and, to prevent dehydration of the tree resulting from their retention, they are lost before winter. Conifers on the other hand typically are able to resist dehydration because of their tough, needle-like waxy leaves, which stay on the tree through all the seasons. As with tropical hardwoods discussed earlier they lose leaves and replace them all year round. However, I’ve noticed even the much-despised fast growing leylandii (Cupressocyparis x leylandii) planted in my back garden by a previous owner loses more leaves in the winter than in the summer. Leylandii are, in truth, a very attractive tree grown where they have space. They grow very swiftly and are really too large in small British gardens – they rapidly exclude light and dominate these small spaces.
Figure 3.4. Scots pine (Pinus sylvestris). Needles (leaves) and seed cone. In common with broad-leaved trees conifers can be identified by a combination of factors – general form, bark, flowers, seeds and leaves. Scots pine needles, for example, occur in pairs, are bluish-green, twisted and about 50 mm (2″) long. They survive about four years before turning brown and dropping as a pair. Cones vary in size between 25 mm to 60 mm (1″ to 2-1/2″) in length and are usually rounded. The bark is distinctive being orange and flaky.
In common with hardwood trees living in cool temperate climates, evergreens have a dormant winter period.
Tree growth occurs in just three places. The first two are the tips of the branches and roots, which increases the tree’s height and the spread of the crown along with the range of the roots. The third place where growth occurs is in the girth of the trunk, branches and roots by the addition of an annual growth ring. Meristem or meristematic tissue refers to the growth tissue in trees. The growing tips of twigs and roots is the apical meristem. The lateral meristem is the cambium layer adding girth to the tree’s structure.
The cells produced by meristematic tissue, whether they are leaves, flowers, bark or wood, are largely of cellulose. Cellulose forms strong and stable long chain molecular structures. This, along with the lignin bonded with, or to it, is what gives wood its strength. Lignin is the “glue” holding wood together and is a complex mixture of polymers of phenolic acids. Lignin forms about 25 percent of wood’s composition and becomes elastic when heated. It is lignin’s flexible plastic property allowing wood cells to rearrange themselves that woodworkers use to their advantage during steam-bending wood into new shapes.
The majority of cells making up a tree’s structure are elongated longitudinal cells. Their long axis runs vertically up the trunk (and along the branches and roots). Some of these cells are short and stumpy and others are long and slender. The vascular function of the newly formed longitudinal cells is to conduct liquid raw essentials up the tree to the leaves and processed sugary food down the tree to nourish it. Spread through the wood are rays or medullary rays. These ray cells are also elongated but their long axis radiates from the centre of the tree toward the bark. They are stacked one upon the other throughout the length of the trunk in slender wavy bands.
In many wood species the rays are invisible to the naked eye but in others, such as numerous oaks and maples, they are usually highly visible because the groups of cells are large. Some ray cells – the parenchyma – store carbohydrates for use in cell development. The other primary purpose of the medullary rays is to transport nourishing sap toward the centre of the tree.
3.1 Log Cross Section From the outside there is the outer bark (see figure 3.6), which is a protective insulating layer against weather, animal, fungal and insect attack. The bark has millions of tiny pores called lenticels through which necessary oxygen passes into the inner living cells beneath. In polluted atmospheres such as cities the lenticels clog with dirt. London plane (Platanus x hispanica) is well suited to city life because it sheds its bark regularly, exposing clear lenticels. The bark of all trees flakes off as the girth gets bigger.
Figure 3.5. Medullary rays in European oak. On the left they are visible as light-coloured flaky patches – the sought-after quartersawn oak figuring or “silver grain.” To the right where the horizontal bands of end grain show the rays are visible as thin, light-coloured vertical lines. The centre of the living tree in this example is toward the bottom of the photograph.
Inside the outer bark is phloem, bast or inner bark. The phloem is produced by the cambium layer and is a soft spongy liquid-conducting vascular tissue that carries processed food – sugary sap – from the leaves to the rest of the tree.
Figure 3.6. End section view of small yew log. Identifying the most significant structures visible to the naked eye.
Beneath this layer is cambium – the lateral meristem (growing tissue) that adds girth to the tree. The cambium is a slimy layer only one cell thick. These cells divide constantly when the tree is active. The cambium produces not only phloem towards the outside but, towards the centre, it produces xylem.
Xylem has two major functions. As sapwood it conducts water and minerals from the roots to the leaves. Sapwood contains both live tissue and dead tissue. Dead xylem, the heartwood, is the trees’ structural support. The longitudinal cells described earlier are organised to form water- and nutrient-conducting tracheids in gymnosperms or conifers, although some hardwoods also contain tracheids. In angiosperms (broad-leaved trees) the order is different. Vessels, which are continuous tubular structures, form a pipeline from the root tips to the leaves rather akin to drinking straws bundled and glued together. (Note, though, the comment I made about some hardwoods also containing tracheids.) In oaks, for example (see figure 3.7), the naked eye easily picks out the initial spring-laid vessels or pores. In other tree types magnification is required. Sapwood is often attacked by food-seeking life forms such as fungi, insect and animal life.
As sapwood xylem ages it loses its vitality through the loss of the living protoplasm within the cells and turns into heartwood. In some species the transition between living xylem and heartwood is abrupt and clearly visible as seen in the yew cross section at left. With others it is hard to distinguish between sapwood and heartwood. The sapwood can remain as living protoplasmic cells for several years but this period varies from species to species, and even within trees of the same species. The yew sample at left shows newly laid sapwood that took about 8 or 12 years to convert to heartwood.
Figure 3.7. Close-up of European oak end grain showing light-coloured medullary rays and spongy, adsorbent, open-pored spring growth and denser less-porous late growth – European oak is a ring-porous hardwood.
Heartwood is the column of xylem supporting the tree. It is dead because it has lost its active protoplasm. Whilst outer layers of the tree are intact – protecting the heartwood nourished by foodstuffs transported to it by the medullary rays – it will not decay. Heartwood is usually, but not always, distinct in colour from sapwood. Extractives cause the colour change. Extractives are trace elements imparting various combinations of characteristics to heartwood, such as colour, fungal- and bacterial-resistance, reduced permeability of the wood tissue, additional density of heartwood, and abrasive deposits.
Tyloses are bubble-like structures that develop in the tubular vessels of many hardwoods during the changeover from sapwood to heartwood. Tyloses block the previously open vessels, preventing free movement of liquid. Red oaks form very few tyloses whereas white oaks produce many and this explains why white oaks are preferred for barrels. It’s possible to blow through a stick of red oak submerged in water and create bubbles. Whisky distillers are well aware of the “Angels’ Share,” which is the part of the spirit, usually about 2 percent, that evaporates through the wood of the oak barrel (Whisky Magazine, 2008).
Growth rings are the result of the cambium layer adding new tissue year upon year. The cambium layer (in temperate climates) becomes active in spring, reacting to chemical signals produced in the tree brought about by warming temperatures and longer daylight hours. During its active period the cambium layer adds open, fast-grown porous tissue to cope with the rush of water and minerals required of the freshly opened leaves. As the summer approaches and the initial high demand for food subsides, the cambium lays down denser, harder latewood, which adds strength to the trunk and branches.
At the centre of the tree cross section is the pith or medulla. The pith is the small core of soft spongy tissue forming the original trunk or branch.
3.2 Gymnosperms & Angiosperms – Differences 3.2.1 Gymnosperms Gymnosperms (conifers, softwoods) are simpler in structure than angiosperms. Gymnosperms evolved earlier than angiosperms and have some distinct structural characteristics. More than 90 percent of the wood’s volume is made of tracheids. Tracheids are long fibrous cellulosic8 cells approximately 100 times longer than their diameter. They range between about 2 mm and 6 mm (about 1/16″ to 1/4″) in length depending on the species.
The two main functions of tracheids are as structure for the tree and as conductors of sap – nourishment. Tracheids conduct liquid food up the tree after the living protoplasm has left. Water and minerals pass upward to the leaves from one tracheid to the next via osmosis. Osmosis is the process where liquid from a high water (weak) solution passes through a cell wall into a low water (strong) solution. In softwood trees water and minerals move upward from the roots initially through upward root pressure created by soil-borne water migration into the root tracheid cells. Secondly, there is also transpirational pull created by water evaporating from the leaves. This method of conducting foodstuffs is distinctly different to the method used in broad-leaved trees described later.
The cambium layer lays down different forms of tracheids at different times of year. In the spring, the tracheids laid down are thin walled with a large diameter and are lighter in colour. Late-growth tracheids are dark coloured, have thicker walls and a smaller diameter. The early-wood tracheids with their thin walls are better at conducting liquid than the later thick-walled tracheids. Both will conduct water, but a tree needs structure as well as the ability to transport liquid – there is a necessary balance struck between the two functions in tracheid cell structure.
A distinctive characteristic found in some gymnosperms is resin carried in resin canals. Pine, spruce, larch and Douglas fir have resin canals. These timbers have a characteristic scent when worked, and the resin can cause bleeding problems under paint and polishes. One way of setting the resin solid to reduce bleeding problems is to raise the temperature of the wood during kiln drying to 175º F for a sustained period. Genuine gum turpentine is a product of the resin from Southern yellow pine, a tree of the North American continent.
Medullary rays are narrow in conifers and invisible to the naked eye, so to see them it’s necessary to mount thin wood samples on a slide for examination under a microscope.
3.2.2 Angiosperms Hardwoods are more complex than gymnosperms. There are a number of specialised cells present in angiosperms absent from gymnosperms. For instance, the means of conducting liquid foodstuffs up and down the tree in nearly all cases is through the vascular tubular vessels. This is distinctly different to the liquid-conducting tracheids of conifers. The vessels in angiosperms form a bundle of pipes encircling the tree. The fibrous tracheids of hardwoods are much smaller than they are in conifers and because of their thick walls they are not well suited to conduct liquids. Unlike the softwoods, the rays of deciduous trees are often easily visible, e.g., in oaks, sycamore, maple, beech etc. Resin canals are rare in angiosperms, but some tropical plants such as the rubber tree produce gum and have gum ducts.
Seasoning and drying of wood describe the same thing: reducing the moisture content of boards or planks thus bringing them into a dry-enough condition to use.
Acclimatising already-dried wood (acclimating in U.S. parlance) to the conditions in your workshop, or bringing it to a condition where it suits its final location as a piece of furniture or woodwork, is a different process to seasoning or drying wood. This subject (is) covered in section 6.12, Allowing for Changes in Wood Moisture Content.
There are several advantages of using dried wood.
Drying wood:
• Reduces its weight.
• Increases its strength and stiffness.
• Pre-shrinks it.
• Makes it more pleasant to handle.
• Reduces the chance of insect pest infestation leading to wood damage.
• Reduces warp and distortion of the wood in service because the drying process largely reveals any such tendencies in advance of constructing furniture and other wooden artefacts.
• The resin of resinous softwoods is hardened during higher temperature stages of the drying process in conventional kilns, making the resin less likely to weep out onto the surface of finished work.
• The end result of most machine and hand-tool operations are more predictable.
• Paints and polishes adhere better to dry wood.
• Modern adhesives formulations, in nearly every case, work best on dry wood.
• Wood preservatives and fire retardants penetrate dry wood better.
• Dry wood doesn’t spread damp to adjacent materials and objects.
• There is no fungal activity in wood dried to below 22 percent MC.
Cross section of a board illustrating the three zones used to describe a moisture gradient, i.e., the core, intermediate zone and the shell. This is convenient but there aren’t actually distinct lines between each zone.
Apart from traditional green woodworking briefly described in section 6.9, there are some situations where undried wood has distinct advantages:
• It’s easier to drive screws, staples and nails into undried wood, and the wood is also less likely to split during nailing, although wood shrinkage may later lead to splitting.
• Screws, staples and nails driven into wet wood go rusty and this increases their holding power. Pallet and potato box manufacturers use partially dried wood for this reason.
• Cutting, shaping and working the wood requires less power, a characteristic often taken advantage of by carvers, turners, in steam bending, green woodworking etc.
The preferred moisture content of wood varies with its planned end use (see section 6.10) but to summarise, about 19 percent MC suits outdoor wooden artefacts; wood for internal furniture in the U.K. should generally be made out of material between about 7 and 12 percent MC. This MC range suits typical seasonal RH values for most British habitable buildings, i.e., about 35 percent RH in winter to 65 percent RH in summer. These numbers are similar to those experienced in coastal regions of North America. On the other hand, in central and northern areas of North America, the typical RH of habitable buildings tends to be somewhat lower at about 20 percent RH in winter (which assumes no artificial humidification system is installed in the building to maintain higher RH values) to 50 percent RH in summer, equating to wood MC values of 5 percent to 9 percent MC. Wood at various moisture contents between 12 percent and 18 percent is suitable for a variety of construction work and joinery in heated sheltered locations, sheltered unheated locations and for exterior joinery.
The two most common methods for drying wood are air drying and kiln drying. The methods are often used in conjunction. For example, it’s a common practice to partially air dry and follow up with a kiln-drying cycle. Within the two broad categories of air drying and kiln drying there are sub-categories. Air drying, for instance, breaks down into traditional air drying, accelerated air drying, forced air drying, low-temperature warehouse pre-drying and drying in climate chambers.
End racking. Sycamore planks “end reared” and well-spaced apart. Sycamore is very prone to fungal growth if surface moisture is present so this practice of rearing the planks immediately after conversion into boards is quite common. Stickering the planks horizontally in piles straight after conversion may lead to the stickers trapping water and staining is the likely end result. Sticker-stained planks are unusable for show parts of furniture and sell at much-reduced prices to the upholstered furniture market.
Kiln dryer configurations and types are varied. Conventional medium-temperature kiln drying is the first and predominant form. Conventional kilns, by definition, operate at temperatures below 100 degrees C or 212 degrees F. The second most common kiln type is the low-temperature dehumidification drying kiln. The smallest versions of this type can generally only reach a high temperature of about 115 degrees F (46 degrees C), but large units will easily achieve 150 degrees F (65.5 degrees C). Thirdly, there is solar kiln drying. Lastly there are progressive kilns, which are uncommon – the only working ones I am aware of in the U.K. at the time of writing are owned by BSW Timber. With the exception of progressive kilns, a kiln is loaded and closed. A drying cycle is run through and then the kiln is emptied, ready for another batch.
“Every now and then there comes a work of exceptional importance for a wide range of woodworkers,” writes J. Norman Reid in a review of “Cut & Dried: A Woodworker’s Guide to Timber Technology” by Richard Jones. “This volume, by British cabinetmaker Richard Jones, is such a book. In “Cut and Dried,” Jones examines a broad spectrum of issues concerning the character, qualities, and uses of wood, with particular emphasis on its application to cabinetmaking.”
After a thorough review of the book’s contents, Reid writes, “Cut & Dried” is one of the most complete and detailed works on wood and wood technology available to non-specialist cabinetmakers. For this reason, it merits a place on the reference shelves of all serious woodworkers. I highly recommend this important book.”
Thank you, Norman, for the kind review. You can read the entire review here. You can learn more about “Cut & Dried,” and purchase it, here.
