Glossary
Glossary of terms
This glossary of terms is designed to help you.
We are keeping all of this information on a single web page, so that you don’t have to load a different page for each letter of the alphabet, etc. If you cannot find what you are looking for, please let us know. (info@irishwoods.com).
Simply find the word you are looking for in the table below and click on it to find out more!
A
Air Drying: Also known as seasoning. Air dried timber has been allowed to dry in the open air or under cover until it is consistently dry throughout the piece of timber. (i.e. not just dry on the outside, but also in the centre). The boards are separated by “stickers” which allow the air to circulate around all surface of each board.
In Ireland, we can air dry timber to moisture levels of around 17 to 22% MC (moisture content), depending on the time of year, drying conditions and storage (in the open/under cover). For furniture making and many other uses, timber generally needs to be kiln dried, to reduce the moisture levels still further . (See Moisture Content (MC) for further information)
(Also see the “What We Do” section of our website, which gives more information on all of the processes involved in producing timber).
Annual Growth Ring: Every year a tree expands it’s diameter with a layer of fresh growth below the bark (see cambium). These layers are visible when a tree is felled, as concentric rings of alternating dark & light wood. The different colours are caused by the difference in the nature of the cells produced during the growing season. By counting these rings it is often possible to count the number of years that the tree has been growing for, and hence its age. When a log from a tree is sawn, these rings appear longitudinally as the grain of the timber.
Angiosperm: The botanical name for the group of trees that are broadleaved.
B
Back Sawn: This is where timber is sawn so that the growth rings are almost parallel to the face of the board.
Bark Pocket: Bark that has become trapped inside the tree as it has grown, and which can therefore appear in the timber sawn from that tree, often as a dark coloured and relatively soft.
Beam: A large piece of timber, usually sawn square or rectangular in cross section. Beams are often cut from the centre of a log, to maximise structural integrity. Beams support loads mainly by their internal resistance to bending.
Bevel: A tool used to make a rounded or inclined/smoothed/patterned edge along a square edge (which is also called a bevel). Also, see Router.
Birdseye/ Bird’s Eye: Circular markings on the surface of a board which add to the decorative value (especially in sycamore and maple). They look like small eyes.
Biscuit Joint: A method of joining two pieces of wood together, usually along the edges. A slot is “scooped” out of the side of each board (about 2 to 3″ wide) and a piece of beech (called a biscuit) is glued and inserted. The two boards are then clamped together, with glue along the edges. The biscuit holds the wood in place while the glue dries. The water from water based glues causes the biscuit to swell, which allows it to get a very tight grip on the pieces of wood, creating a good strong joint. (See also Lap Joint).
Bleeding: If there is sap/resin in the wood – particularly air dried softwoods, and especially through knots – it is (by it’s nature) a liquid… and it can therefore move. This can cause weeping through the surface of the wood, including through varnishes.
Blue Stain (Sap Stain): When timber is sawn and stacked with stickers for air drying, the wood can have a very high moisture content. The timber contains fungal spores that it has been gathering during growth. Occasionally the fungal spores “activate” in the wood while it is still damp. This can weaken the structural strength of the timber (the start of the rotting process). As the boards dry out the fungus cannot thrive. Once air dried (less than 22%), this process stops. In several cases, this process can produce a stunning effect on the look of timber, called spalting, especially in beech. The colours produced can vary, but is usually black with blue, red and green variants occasionally seen.
Board: A piece of sawn timber. Boards are sawn as square edged, waney edged or through-and-through. Boards vary in thickness, usually from 1″ to 3″, although thicker sections can be sawn for specific purposes, such as for mantelpieces or woodturning and carving.
(Also see the “What We Do” section of our website, which gives more information on all of the processes involved in producing timber)
Book Match/ Bookmatch: If a board is split in two and opened like book, the result is two asymmetrically opposite grain patterns facing each other. At the Lisnavagh Timber Project, all of our boards are numbered as they come off the saw bench which means that we can reunite “neighbouring” boards for bookmatching.
Bow: Boards sometimes bend, usually soon after sawmilling. This can be caused by bad stacking of the timber, or perhaps an inherent stress in the grain of the timber which might be due to the way the tree grew.
Boxed heart: The central core of the tree (the “pith“) can be quite soft timber. This can be “boxed” in or concealed by normal, harder wood. Boards like this might split or warp more often than other boards.
Broadleaves: Trees are grouped in several ways such as by the leaf shape (broadleaf/conifer), timber (hardwood/softwood) or whether they loose their leaves in winter (deciduous/evergreen.) Broadleaved trees are known botanically as “angiosperms” and have wide flat leaves (as opposed to conifers which have long thin needle-type leaves. The timber is usually, but not always, hardwood timber, and the trees are also usually, but not always, deciduous. Examples of broadleaf trees include oak, ash, beech, elm, birch, chestnut, cherry and lime. There are many more.
Burr: (In America this is called “Burl“) Occasionally trees have wart-like growths up the trunk and/or branches. These are basically where a large number of dormant budding points for twigs, or points of epicormic growth have grown on top of each other to cause a random looking swelling. The timber underneath is not straight grained timber as one would see in a “normal” board. When sawn though, the timber has swirling patterns of colour and grain which are extremely eye-catching and interesting to the observer. The wood has wonderful figure, and as a result, burred timber is highly sought after by all users of timber, especially woodturners and specialised furniture makers.
C
Cambium:This is thin layer of cells that form between the bark and the sapwood. Each year, new bark cells are formed on the outside of the layer and new sapwood cells are formed on the inside. It is this growth that creates the alternating light and dark rings, called annual growth rings.
Case-hardening: When timber dries it shrinks slightly, but if the centre of a piece of timber is still wet when the outside has completely dried, it will force the outside to stretch around the relatively swollen centre. This causes stress between the inside and outside parts of timber. The timber may not seem to have suffered, but when it is planed, resawn, or machined in some way, the stress can cause warping or splitting. Case hardening occurs where timber is dried too rapidly.
Cat’s Paw: Small knots in the timber which have the look of a cat’s paw print. This is a feature valued highly by furniture makers and is found in hardwood timber, especially oak (called pippyoak) and elm. Cat’s paw causes little or no structural instability.
Cellulose: The cells of wood are primarily made up of cellulose, which is a very strong carbohydrate.
Check: If the outside of the timber dries (and therefore shrinks) a lot quicker than the inside, it can mean that small shallow cracks occur on the outside of board, in line with the grain. Checking of timber is not the same as splitting. Splits tends to go right through the board and occurs singly, or in small numbers. Check is usually a few millimetres deep, and often appears in clusters.
Closed Knot: See Knot.
Collapse: If timber is dried too much, cells can collapse, or flatten, causing a rippled effect on the surface. The structural stability of the timber is reduced as a result.
Compression failure: If timber has had pressure along the grain (i.e. “end-on”) it can cause the fibres of the wood to buckle and deform. It can, for example, occur where a tree has bent over. Compression failure causes ripples to appear in planed timber.
Conifer: A grouping of trees (botanically known as gymnosperms) with needle or scale-like leaves (e.g. pine, fir, spruce, cypress). Most are evergreen trees, and most provide softwood timber.
Cross-cut: A cut across the grain. (i.e. sawing the end off a board is crosscutting it).
Crotch wood: Just below where a tree forks, the grain spreads in a fanlike pattern which is visible when the timber is sawn. It is highly sought after by wood turners.
Cup: Due to existing stresses in a piece of timber it can “cup”, especially when drying. The board is slightly U-shaped when looked at end-on.
Cup shake: Where the timber splits around a growth ring – also known as Ring shake.
D
Decay: The rotting or decomposition of wood initiated by fungi. The fungi break down the (otherwise indigestible) wood into a softer, lighter material which hundreds of species of insects are then able to make further use of. In woodland, other animals, such as woodpeckers, may then also become involved, searching for the insects, and causing further injuries to the tree in the process, thus hastening the rotting process further. Decaying wood loses strength, weight and colour.
Decking: A timber platform surface (for example for pedestrian/vehicular access across a bridge, or outside a house as a raised amenity.
Dehumidifier Kiln: A kiln which dries timber by way of heat (perhaps 40° C) and dehumidification. Such kilns take slightly longer than many other types of kilns to dry timber, but have the advantage of low capital investment & running costs and can result in less damage to the timber being dried.
(Also see the “What We Do” section of our website, which gives more information on all of the processes involved in producing timber).
Density: The weight of timber per unit of volume (kg/cu m) which is useful as a guide to the strength of the timber (the denser it is, the stronger it is – usually). For our page showing the densities of various species, click here.
Dowel: A round length of wood (or, less usually, metal) used (typically) to join two pieces of timber. A hole is drilled into each piece of timber and the dowel inserted into both pieces, usually with glue.
Doze: A phrase used to describe timber that has started to decay. The timber is pale looking, light to handle and soft enough to be indented by pressure from a thumbnail. Dozed wood is useless to woodworkers.
Drying: The removal of moisture from a piece of timber. See Air Drying and Kiln Drying.
Durability: A phrase to describe how resistant to decay a piece of wood is.
Dutch Elm Disease: A fungal disease (Ceratocystis ulmi) which effects elm trees. The fungus is transmitted from tree to tree by bark beetles. Originally discovered in Holland in 1919 – hence it’s name. It was in England by 1927, but in the 1960s a more aggressive strain took hold (coming from N. America) and wiped out half the elms in England by the mid-seventies. The disease is fatal and takes only a few weeks to kill even a large tree, apparently by blocking the vessels. Wych elm (Ireland’s native elm) is apparently more resistant to the disease.
E
End Grain: The grain that is visible at the end of a board, where it has been cross cut.
Epicorm/Epicormic growth: Small branches on the sides of a tree that have grown from adventitious buds. The twigs start to grow, but die back, perhaps due to a lack of light? This growth causes “mini” knots to appear in the wood beneath and can result in highly figured timber which is prized by wood workers and furniture makers. (See also cat’s paw and burr)
Equilibrium moisture content (EMC): The moisture content of wood which has reached a steady balance with the immediate environment and where the relative humidity and temperature of the air is constant.
Exotic: A description used for non-native trees. That is, trees which have been introduced into a country, usually by man. A tree can only be called “exotic” in a country where it is not native – so, for example, an exotic species in England could be a “native” species in Ireland (e.g. the Strawberry Tree), and vice versa (e.g. Beech).
Extraction: This is the removal of felled trees or logs to a more accessible area on edge of a wood where they can be collected (by a lorry, for example). Methods of extraction include winching, mechanical towing, towing with ponies or using a forwarder.
F
Face: The widest surface of a piece of timber.
Fibre Saturation Point (FSP): When timber is drying out, water evaporates from the cell cavities first, and then the cell walls. The point at which the free water in the cell cavities has been lost, but the bound water in the cell walls remains is called Fibre Saturation Point, and the moisture content (MC) of the wood is typically between 25% & 30% at this stage. By taking the moisture content below FSP the timber will shrink in size.
Fiddleback: A wavy or ripple effect on the grain, typically in sycamore and maple and often used for the backs of violins and other musical instruments – hence the name. Also known as Tiger Stripe.
Figure: The word used to describe the features and patterns of a piece of wood and taking into account growth rings, medullary rays, grain, knots, catspaw, burr, colour and anything else that affects the “look” of the piece.
Fingerjoint: The joining of two pieces of wood where the ends of the pieces are cut to form wedge-shaped fingers which are then bonded with wood glue.
Finishing: The processes (usually sanding, polishing and perhaps oiling) that are carried out once the basic structure of the wooden item is completed.
Fissure: A generic term covering checks, splits, cracks, honeycomb and shakes along the grain or rays.
Forwarder:A forwarder (such as the one pictured) is used to extract timber from the wood or forest to the roadside or some other suitable point where it can be collected by a lorry. Forwarders can have tracks or large rubber wheels, and these allow them to “roam” in woodland, travelling over tree stumps and brash and with a greatly reduced chance of getting bogged down in wet ground.
Fungi: During the life of a tree, many types of fungal spores are continuously getting into the trunk and branches, but are (for the most part) harmless while the tree is healthy.
The spores enter though the roots, or damaged bark, broken branches, etc. The spores generally cannot cope with the high moisture content of the wood in a healthy tree, and only activate when the wood partly dries out or when the tree is dead or it’s defence systems are unable to prevent activation of the spores. Wood can dry out when there is a drought, or there is an injury to the tree.
When the spore is activated, a mycelium is produced which travels though the the sapwood, heartwood and/or just under the bark (see photo of mycelium under bark of pine).The only visible part of the fungus is generally the mushroom type growth which appears on the outside of the tree or wood – this is the reproductive centre of the fungus.
In some species, for example beech, the activation of the fungal spores, and spreading of mycelium, causes discolouration of the timber before the timber starts to soften. This is called spalting, and the timber from spalted wood is highly sought after by wood turners and other users of wood.
G
Glulam: Structural timber that is made up of several smaller sections of timber that are laminated together.
Grain: The main fibres in wood, as arranged in the annual growth rings, are referred to as the grain. Cuts of timber are usually described by referring to the grain – e.g. across the grain (cross cutting), or along the grain (as in ripping). The density of grain is often used as a description for the appearance of timber (e.g. wavy grained, close grained or open grained).
Green timber: Freshly felled or sawn timber which has not yet dried out at all. The moisture content will be in excess of the Fibre Saturation Point (FSP), and fairly consistent throughout.
Groove: See Tongue & Groove (T&G)
Growth Ring: See Annual Growth Rings.
H
Hardwood: This is a botanical description of timber, rather than a specific evaluation of hardness of timber. Generally, hardwood timber is from broadleaved tree species. There are some “softwoods” that are harder than “hardwoods”, but not many. (Also see our page ontimber densities)
Heartshake: A split in the timber that runs though or from the centre of the log towards the outside, crossing the growth rings. It can be caused by a tree landing too hard when it comes down.
Heartwood: This is the timber at the centre of the tree – between the pith in the middle and the softer sapwood towards the bark. As the tree grows & thickens, the cambium & sapwood are regenerated towards the edge or bark of the tree, leaving behind rings of fibres towards the centre which no longer need to carry nutrients or substances (sap). These fibres alter to become stronger and resistant to decay (and darken in colour). It is this hard material that gives trees such significant structural reinforcement at their centre that they can gain such notable heights.
High speed steel (HSS): This is about 6 times harder than (normal) carbon steel. HSS tools should be ground on a ‘white’ (aluminium oxide grinding wheel).
Honeycomb: This is a serious problem, particularly in oak. Honeycombing is caused when the inside of a board has a relatively high moisture content, while the outside is being dried too rapidly. The result is that the outside “sets”. At this stage the outside of the board will not shrink any further. The core of the board then starts to dry, but, because the outside is set (or case hardened), the inside starts to split apart as it tries to shrink. Gaps open up in the wood inside the board and they tend to follow the medullary rays, rather than the grain of the wood. The result is a board that looks fine… at first. However, when the timber is planed to below the case hardened surface, the cracks/cavities inside the board become visible. It is said that if the moisture gradient exceeds 6%, then honeycombing is more likely to occur.
I
Irregular grain: Refers to grain that is not straight – for example, grain that bends around knots or twists.
J
Jamb: The piece of wood that runs up the side of an opening for a door or window.
Joinery: A term to describe the creation of fixtures, or the fixtures them selves, in buildings including doors, windows, cupboards, etc.
Joint: Where two boards meet and are fixed together. See Biscuit Joint, Lap Joint, Mortise and Tenon and Tongue and Groove.
Joist: A beam of timber that is used to support (usually) a floor or a ceiling and which rests on a loadbearing wall’s wall plate or some other support. Sometimes joists are incorporated into the design of a house so that they are visible and form a feature of the design.
K
Kiln: A chamber used for drying timber down to a required Moisture Content (MC). There are several different types of kiln, but they all work on the principle of artificially controlling the temperature and humidity in a way that reduces the moisture content as consistently as possible throughout each piece of timber. See Dehumidifier kiln
(Also see the “What We Do” section of our website, which gives more information on all of the processes involved in producing timber).
Kiln Drying: Artificially drying timber in a kiln using controlled levels of heat and humidity in order to reduce the Moisture Content (MC)to a required level.
(Also see the “Practices” section of our website, which gives more information on all of the processes involved in producing timber).
Knot: An area of wood which was originally part of a branch growing from the tree, but which has subsequently become incorporated into the main stem as it has grown and enlarged. In a board, most knots are seen in cross-section. Whilst knots can be regarded as features, depending on their nature, they are areas of irregular grain which can reduce the strength of the timber. Knots are usually darker in colour than the surrounding wood. An Open Knot is a knot where the substance of the wood has either opened up as a crack or dropped out completely. A Closed Knot is a knot where the substance of the wood is contiguous with, and fixed to, the surrounding material. (Also called a Sound Knot or Tight Knot). See also Cat’s Paw.
L
Laminated wood: Several pieces of wood glued or fixed together to form a larger, stronger piece.
Lap Joint: A method of joining two pieces of timber by partially overlapping them. This is done either by literally overlapping the two pieces and fixing them together (with glue, screws, etc.), or more neatly by cutting a rebate along each piece to be joined and then fixing them together. (Also see Biscuit Joint and mortise and tenon and Tongue& Groove).
Lignin: The “mortar” between the cells in wood. Lignin is the second most abundant constituent of wood.
Lumber: Another word for timber, principally used in North America.
M
MC: See Moisture Content
Medullary rays: These are groups of storage cells that run from the centre of the tree to the cambium (under the bark). In oak, for example, they can be very pronounced, especially in quarter-sawn material, and are considered a feature.
Moisture content (MC): The percentage of the weight of a piece of wood that is water.
The original (and possibly still the most reliable) method used to determine MC is to weigh a sample of the wood before and after drying it out thoroughly in an oven. The difference in the weight measurements is the water that has evaporated off during drying. Simply by dividing the weight of the water by the weight of the wood before drying, the percentage of water in the original sample (i.e. the moisture content) is determined. More usually moisture meters are used, and the best results are achieved using meters with a hammer probe, where the needles of the meter penetrate the wood to get readings at the centre of the piece.
The MC of timber is usually very important. Many uses of timber require the timber to be sufficiently dry throughout, and this is measured as %MC. For example (in Ireland at least) construction timbers usually need to be dried down to 20%MC, wood for furniture to 10-12%MC and floorboards, where under-floor heating is installed, down to 6%MC.
When a tree is initially felled, alive, it can have an MC reading of perhaps 100%. Most construction timbers are kiln dried immediately as big sawmills have a very large turnover and cannot wait for the timber to air dry. By air drying timber under cover, MCs of 17 to 22% are easily achieved in Ireland (being lower in summer than winter). The rule of thumb is that it takes 1 year for 1″ hardwood timber and 2 years for 2″ hardwood timber, although this depends on species, weather conditions and storage conditions. To dry timber further than this requires a kiln.
Moisture Gradient: This is the variation in moisture content from the centre of piece of wood to the edge. For example, a piece of wood which is 23%MC on the outside and 28%MC at the centre has a moisture gradient of 5% (i.e. 28 minus 23). A high moisture gradient might occur in timber that has part air dried, for example. When kiln drying, high moisture gradients (6%+) can cause serious problems, especially with oak, and can result in case hardening and/or honeycombing of the timber.
Moisture Meter:An instrument used to determine Moisture Content (MC). In order to measure the MC of the inside of a piece of wood, a hammer probe is used. The two pins of the hammer probe penetrate the wood to a required depth (usually one third of the depth of the sample being tested).
Mortise and Tenon joint: A method of joining two pieces of timber. In one piece a slot is formed (the mortise/mortice), and in the the other piece a key to fit the mortise is cut (the tenon). The tenon should fit snugly into the mortise to make a firm joint. These joints are usually secured using wood glue and/or other pieces of wood such as dowels.
N
Native: A native species is one which is indigenous to a country. In other words it has not been introduced from abroad. However, labelling a species as “native” can be controversial, as most of the species in any country have been introduced from another country at some point in time, however long ago, and not necessarily by man. Or, to offer another argument, seeds from monkey puzzle trees have been found in the soil under Lough Derg (from beefier the Ice Age), so does this mean the monkey puzzle is one of our native Irish trees?!
Natural Regeneration: This occurs when seedlings grow without any direct assistance from humans. It can start from a seed or from the suckers of another tree. Seeds are carried by animals, birds or the wind. In many woodlands, natural regeneration is now encouraged, especially where the trees themselves are of a good provenance (genetic quality)
The birch pictured above are in one of our woodlands here at Lisnavagh.
They naturally regenerated in a wood that was planted with sitka spruce.
The spruce were not doing well, and were thinned out to let the birch grow on.
It was a good decision, as the wood is now regarded as one of the finest stands of birch in Ireland
O
Olive Ash: Older ash trees can develop a stained heartwood. Compared to the cream colour of ash in younger trees, olive ash is a dark brown colour.
Open Grain: A wood that has large pores is called open grained.
Open Knot: See Knot.
Oven Dry Weight: The weight of a piece of wood after all of the available water has been evaporated off. This is done in an oven at 100 to 105°C. The Oven Dry Weight can be compared to the weight before drying to give a very accurate measurement of the Moisture Content (MC) of the undried wood.
P
Palmate: Leaves that have lobes shaped like the fingers of the hand, e.g., Horse Chestnut.
Phytophthora kernovii: In early 2004, some trees in Cornwall (UK) were discovered to have a new disease – so new that the name has yet to be scientifically formalised (at the time of writing). Phytophthora are fungi – and usually harmless in their natural habitat. On the other hand, it also from the same genus of organisms that led to the potato blight (Phytphthora infestans) causing the famines.
The first outbreak of the disease in the UK was discovered near Redruth in Cornwall and was initially found to be infecting rhododendrons and a beech tree. However, 30 beech trees and two pedunculate oaks were subsequently found to be suffering from the disease as well, which has caused real concern as it would be an uncomfortably close relative of the dreaded Sudden Oak Death (seePhytophthora ramorum, below) of America which has also found it’s way into this part of Britain. A 6-mile exclusion zone has been set up in the area in the biggest excercise of it’s type ever undertaken.
Rhododendenron would appear to be the main carrier of the disease, and it succombs in just a few weeks.
It was initially hoped that native species, such as oak, would be resistant to the disease, and some extensive research in the UK appeared to prove this to be the case with Sudden Oak Death. However, the infection of two peduncualte oak trees with the new variation of the fungus is a worrying discovery.
Phytophthora ramorum: Also known as Sudden Oak Death, the fungus has caused widespread blight amongst American oak species. It was discovered in Califronia in 1995. It was first found in Ireland in 2002.
The following text is from a Dail Debate in June 2003 and a question put to the then Minister for Agriculture & Food, Joe Walsh:
Tuesday, 10 June 2003
235. Mr. Deasy asked the Minister for Agriculture and Food if plants can be imported without a phytosanitary certificate; if his attention has been drawn to any cases here of phytophthora ramorum (sudden oak death); the efforts being made to ensure that this disease does not come here; and if he will make a statement on the matter. [15260/03]
Minister for Agriculture and Food (Mr. Walsh): Plants, planted or intended for planting, that arrive in the European Union from third countries are required to be covered by a plant health certificate issued by the plant protection service of the country of export. Each consignment must be inspected by the plant protection service of the member state of introduction and found to conform to EU plant health requirements before it can be released into free circulation in the EU.
Commission Decision 2002/757/EC of 19 September 2002 on provisional emergency phytosanitary measures to prevent the introduction into and the spread within the Community of phytophthora ramorum Werres, De Cock & Man in ‘t Veld sp. Nov., was agreed in response to the threat posed by this new organism and its measures became operative on 1 November 2002. Phytophthora ramorum has been found in Ireland on a number of occasions. It has also been found in at least nine other member states, including all of our main trading partners. All infected plants that have been found have been destroyed.
Host plants of the disease – plants of rhododendron and viburnum species – within two meters of infected plants have also been destroyed as required under EU legislation. In addition, host plants within ten meters of infected plants are required to be quarantined for three months. A survey for the organism is being carried out in all member states. The survey results are to be forwarded to the Commission by 1 November 2003 and the decision must be reviewed by 31 December this year at the latest.
Joe Walsh, TD, subsequently introduced regulations to reduce the risk of infection in Ireland in September 2004. (See http://www.agriculture.ie/legislation/SI2004/s578-04f.pdf for details)
PEG: See Polyethylene Glycol.
Pedunculate: Fruits which are borne on a stalk, as in pedunculate oak.
Pin Joint: A hinge-like of joint.
Pippy: e.g. oak – see Cat’s Paw
Pith: This is the central core or heart of the tree. Pith wood can be quite soft, and therefore prone to splitting when drying. It can have a deeper colour than the wood around it.
Planer thicknesser: A planer thicknesser is a machine that has two functions, both based around the same blades (usually two or three blades mounted on a spinning cylinder).
- The first function is as a planer, where timber is passed (on the top table) over the blades to give a flat planed surface on one face of a board, or along the edge of a board. Where planing the edge, a fence allows the timber to be placed either at 90 degrees (i.e. square) to the blades or at an angle to the blade. Usually up to 3mm can be removed in a single pass over the planer.
- The second function, as a thicknesser, allows timber to be passed underneath the blades. The timber moves over a table whose distance from the blades can be very precisely adjusted by the operator. When a board is put into the thicknesser, powered rollers grip the board and pass it under the blade at a preset speed. The board is usually passed through the thicknesser several times, with the table being raised slightly each time (a mm or two at most usually) and that thickness being removed from the thickness of the board until the exact desired thickness is aquired.
Plank: See Board
Pocket: An area where the timber has closed in around other material such as bark or resin/pitch.
Pollarding: A way of cutting trees so that they sprout upward growing branches. The trees are cut at around eight feet in height.
Polyethylene Glycol (PEG): A chemical which replaces the water within the pores of the wood by a process of osmosis. It is frequently used by wood workers to stabilise green wood. It also has the advantage of acting as a lubricant by reducing friction in coarse open grained wood. The wood is immersed in a PEG solution and allowed to soak. Works better with planks, than with logs. PEG is sold in solid and liquid forms.
Polytetrafluoroethylene: See PTFE.
Pores: These are tiny holes (occurring in hardwood timber) which are at the end of vessels running along the grain. They are most prominent in the end grain (where timber is cross cut), but also appear obliquely in the sides and faces of timber.
Preservative: Chemicals used to protect wood from decay. (We do not use preservatives on our timber. Air drying is enough to kill fungi and kiln drying will kill insects present.)
Propagation: Regeneration of new plants by means other than seeds, e.g., rooting, cuttings. (See also Natural Regeneration)
PTFE: (Polytetrafluoroethylene). This is a chemically inert flouroplastic polymer that is able to withstand high temperatures and which causes little friction. It is probably best known for it’s non-stick uses in kitchen wares, where it usually takes the form of Teflon. It is also well known to plumbers who use the tape for sealing joints on pipes. However, PTFE also has it’s uses in woodworking machinery, such as planer thicknessers and saw tables or wherever there is potential for friction between the machine and the wood. PTFE (which is available in aerosol form) allows the wood to “glide” over metal surfaces easily. It can also prevent machines clogging up with wood shavings and sawdust, for example planer blades). PTFE has relatively low flammability. It is quite expensive, but a tin goes a long way and can make a very noticeable difference to the smoothness of an operation.
Purlin: One of a series of horizontal framing timbers supporting the rafters or spanning between trusses or frames and supporting the roof. Purlins usually span at right angles to the slope of the roof.
Q
Quarter-sawn timber (edge grain): Timber sawn so that the annual growth ringsare at an angle less than 45° to the face of each board. The timber is stronger as a result, but the practice is usually carried out to enhance the presence of medullary rays, which are a very desirable feature in oak furniture.
The first picture (above right) shows the easier method of quarter sawing. (Also shown in the photographs below) The log is quartered into four sections. Each section is then propped at an angle and sliced through-and-though.
The second picture (left) shows True Quarter Sawing. As above, the log is sawn into four sections, or quarters. But this time, instead of being sawn though-and-through, the section is placed with one face square to the blade. The section is rotated through 90 degrees for each saw cut.
Both methods are extremely time consuming and laborious, but especially true quarter sawing, and as a result quarter sawn timber is rare and expensive.
The log is sawn into four equal quarters or sections. Because of the amount of time it takes to quarter saw logs, the practice is reserved for the best logs only. It is most commonly seen in oak. | On the saw bench, the sections are placed at an angle to keep the growth rings virtually at right angles to the saw blade. (The blade in the picture is a horizontal one). | The boards are sawn from the top down, and stacked as usual. This method of sawing results in very narrow boards from the top & bottom of the section being sawn, with the wider ones being from the middle of the section. |
R
Radial: A line along the radius of a log. (i.e from the centre to the outside.)
Radially Sawn: Radially sawn timber has been sawn along the radius, producing a wedge or triangular shaped piece of wood. The cut is at right angles to the growth rings.
Radial Arm Saw: A saw used for cross-cutting pieces of timber at very specific points and angles. The angles can be sawn with horizontal and vertical variations. The saw blade slides back and forth to allow wide cuts and non-vertical cuts. (N.B. The word “Radial” refers to the saw itself, rather than the the way the timber is cut)
Rays: Bands of soft tissue vertically aligned and radiating from the centre of the tree; insignificant in softwoods and variable in hardwoods – if broad can produce distinctive figure – e.g. silver grain in oak. (See Medullary Rays)
Relative humidity (RH): The ratio of the amount of water vapour present in air to the amount which the air would hold if saturated at the same temperature.
Regeneration: The production of new trees by natural seeding. (See also Natural Regeneration)
Ring shake: Where the timber splits around a growth ring – also known as cup shake.
Rip: To saw timber along the grain.
Ripple: A wavy or ripple effect on the grain, typically in sycamore and maple and often used for the backs of violins – also known as fiddleback.
Rot: Decay or decomposition of wood, initiated by fungi. See decay or fungi.
Rough Sawn: A description of timber that has been sawn in a sawmill. It has not yet been sawn accurately, nor planed. The width (especially) of rough sawn boards may vary, particularly after drying/seasoning.
Router: A machine used to gouge out timber. For example it may be used along the edge of an otherwise finished piece of wood to produce a bevelled edge, or it can be used for occasional morticing work.
S
Sapwood: This is the wood from the outer growth rings, extending from the heartwood to the cambium. Sapwood contains living cells, with carbohydrate food reserves, and conducts the sap up the tree. It is generally lighter in colour and wetter than heartwood when freshly felled, and is generally more perishable.
Sap Stain: See Blue Stain
Saw Cuts: Timber can be sawn from a log in several ways:
Sealing: A sealer is applied to wood to stop water or other materials from getting into the timber and staining it or increasing moisture levels.
Seasoning or drying: The process of removing moisture from timber. Seasoning often refers to drying in the atmosphere (air drying), or kiln drying by accelerated drying under controlled conditions in a kiln.
(Also see the “Practices” section of our website, which gives more information on all of the processes involved in producing timber).
Shake: A separation or splitting of the fibres along the grain, usually between the annual rings (see Cup shake/Ring Shake), or radially (see Star Shake)
Shrinkage: The reduction in size of a piece of timber as a result of the removal of water. A 12″ wide board might shrink by perhaps 1/2″ during the drying process. The amount of shrinkage depends on the moisture levels before and after drying, density of the material, etc.
Softwood: This is timber from (usually) conifer trees. The term relates to the botanical grouping of the trees and not to the hardness of the wood ( some softwoods, e.g. yew, are harder than some hardwoods).
Sound Knot: See knot.
Spalting: Spalted wood is sought after because of the patterns, colours and appearance. The spalting is caused by fungal decay, representing the early stages of the entirely natural process of “rotting” that occurs in timber. Whilst spalted wood can have soft areas, the ideal piece of spalted wood has been dried just before the wood has started to soften too much and the patterns caused by the fungal decay are at their peak. (Fungal decay stops when timber reaches 20% MC or less.) Spalting occurs in most hardwood timbers, but is most commonly found in beech.
Species: This is a biological classification, below “genus”. Organisms that can interbreed with each other and produce fertile offspring are (usually, but not always) of the same species.
Spiral grain: Growth of fibres in a spiral direction around the trunk of the tree. It may cause twisting of timber during drying.
Split: If a log of timber has tension, or stress in it (which can occur for multiple reasons), then sawmilling or drying the timber can bring that stress to the point where the fibres in the wood pull apart to release the tension, and thereby cause a split (also known as shake). Drying timber can exaggerate the stresses and sawing or planing the timber can reduce the strength of the wood to resist splitting, so timber can split during any of these processes. Small shallow cracks on the surface are called checking, and occur during drying timber. Shallow check is generally not a problem as they are machined out during planing.
Spring: A curve along the edge of a plank; normally due to growth stress.
Square edged: A description of a board that has been sawn with both sides cut square (i.e. the bark/wane has been removed). Because of the way that timber moves during drying, the square edges can distort. The phrase refers to the way the timber has been cut, rather than how it will appear after drying. Square edged timber needs to be resawn or trimmed after drying to get a truly square edge.
Star Shake: Where cracks radiate from the pith to the outside of the tree.
Straight grained: Where the grain (fibres) of the piece run almost perfectly parallel to the pith with little distortion.
Streaks: (e.g. mineral) Staining of the wood from the take-up of minerals in the ground surrounding the tree.
Stress: The applied force per unit area or volume. The primary stresses are tensile, compression and shear. A combination of all three occurs in bending.
Stickers: Length of wood used to aid the drying process. Stickers are placed at regular intervals across a board of wood. Another board is then placed on top of the stickers, this is continued to form a stack of boards. The stickers are very important as they allow air to circulate between the boards, thereby helping the boards to dry evenly. It is important to use the correct size of sticker. For difficult woods like oak the stickers should not be thicker than 13mm. For woods such as pine, beech, etc. they should be 25mm, for 25mm boards. For thicker boards the stickers should be 13mm (6mm for thick oak).
(Also see the “Practices” section of our website, which gives more information on all of the processes involved in producing timber).
Structural timber: Timber used for specific tasks in construction where it needs to be of a minimum strength.
Sudden Oak Death – see Phytophthora ramorum
Swirl Figure: Where the grain in wood is irregular and has a whirlpool type appearance, usually around a knot.
T
T&G: See Tongue and Groove
Taper: For example, where a board’s width is narrower at one end than the other, it’s width would be tapered.
Tenon: See Mortise and Tenon
Tension wood: This occurs in hardwood trees that are leaning against other trees. The upper side of the trunk becomes compressed, and as a result the timber from this part of the trunk is prone to distortion.
Through-and-through: (Also known as T&T or T/T) Where a log is sawn from top to bottom without being squared off, so that the bark (or wane) is showing along both sides of the board. This is a quick way to saw a log, but if the bark or wane is not wanted for the final end-use of the timber, then valuable storage space and and drying costs are being applied to what is (effectively) waste material.
(Also see the “What We Do” section of our website, which gives more information on all of the processes involved in producing timber).
Through Check: This is where a crack/split runs right through a board from one face to the other.
Tie: To ‘tie’ is a method of securing thin or short grain parts of a carving. This is done by linking one part of a carving to another in such a way that it strengthens the thin bit while not being obvious. For example, you could link the stems of flowers by having them criss cross each other thereby providing great support for both stems, or having fragile leaves lie on top of one another, again adding support. As both these happen in nature, you would provide support whilst keeping within the context of the piece.
Tiger Stripe: See Fiddleback.
Tight knot: See Knot
Timber: A term to describe wood in the form of (for example) trees, logs, boards or beams.
Tongue and groove (T&G): A method of joining two boards side by side. One board has a groove cut, or routed, along the edge to be joined. The other board has a tongue(formed by creating two rebates either side of it) along the matching edge. The two boards are then slotted together. They can be glued in place, or left free to move (to allow for expansion/contraction of the wood). T&G boards are used for flooring where they are free to move at the same time as forming a dust proof barrier.
True Quarter Sawing: See Quarter Sawing.
Twist: This is where one corner of a board moves out of the general plane of the rest of the board. See warp.
U
Unseasoned Timber: Timber that has not been dried (seasoned), and typically with a moisture content exceeding 25%.
V
Veneer: A very thin slice of wood. It is usually applied to another material (chipboard, composite material, softwood, etc.) in order to give the appearance of being a solid piece of wood of the veneer’s species.
W
Wane: The original rounded surface of a tree that remains (with or without bark) on a board after sawmilling.
Waney Edged: A description of a board where (usually) one side of a board is sawn square , and the other side is not sawn at all, thus retaining the edge of the tree, or wane. This type of board might be used, for example, by a furniture maker who wants to give a rustic and uneven appearance to furniture along an edge.
(Also see the “What We Do” section of our website, which gives more information on all of the processes involved in producing timber).
Warp: A twist in a board resulting from movement of the timber caused by the release of tension and stresses in the wood fibres. These stresses can be released by sawmilling, drying or planing the wood. With the stresses released, the wood fibres “relax” and can cause considerable movement in a piece of timber.
Wild Grain: See Irregular Grain
- The material which is produced by a tree, and of which that tree substantially comprises. Wood is made up of fibres (small vessels) through which nutrients are supplied to the growing parts of the tree by capillary action. The active fibres are in the sapwood. See also Sapwood, Heartwood, Cambium and Pith.
- An area of ground in which several trees are growing – i.e. Woodland, forest.
Workability: The ease with which wood can be worked.
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