JC Wood Technology key terms

Timber from coniferous trees such as pine, spruce and Douglas fir, which have needles and cones. Their wood has no vessels, is usually lighter and contains resin; it forms most structural and construction timber.

Timber from broad-leaved flowering trees such as oak, ash, beech and mahogany. It contains vessels, is generally denser and more varied in colour and figure than softwood, and is used for furniture and joinery.

Natural long-chain carbohydrate that makes up the fibrous framework of every wood cell wall. Its fibres run mainly along the grain and give timber its tensile strength and flexibility.

Natural polymer laid down in wood cell walls that cements cellulose fibres together and stiffens the tree. It makes up roughly a quarter of dry wood and is largely removed in papermaking.

Band of wood produced by the cambium during one growing season, visible on a cross-section. The pale earlywood formed in spring is followed by darker, denser latewood in summer.

Outer zone of living wood that conducts water and minerals up the stem. It is usually pale, wetter and less durable than heartwood but is often easier to treat with preservative.

Inner, no-longer-active wood at the centre of the trunk. Extractives deposited in its cells darken it and usually make it more durable and more resistant to rot than sapwood.

Moisture content at which timber stops gaining or losing water to the air around it, depending on temperature and relative humidity. Indoor timber settles near 8-12% in a heated building.

Controlled drying of timber to a usable moisture content, either stacked in air or in a heated kiln. Correct seasoning reduces shrinkage, warping and fungal attack and prepares wood for machining and gluing.

Reduction in the size of timber as it dries. It is greatest around the growth rings (tangential) and least along the grain, which is why boards distort and joints must allow movement.

Piece of branch enclosed in the stem as the tree grows around it. The grain is deflected around it, so the wood may be harder, brittle and difficult to work; large loose knots weaken boards.

Any distortion of a board caused by uneven drying or grain, including bow (lengthwise curve), cup (crosswise curve), twist and spring. Warped timber cannot be planed true without losing thickness.

Converting a log by cutting it into quarters and then sawing boards radially. It is slower and more wasteful than through-and-through sawing, but boards are more stable and show straight grain and figure.

Manufactured board of thin wood veneers glued together with the grain alternating at right angles. This cross-lamination gives strength in both directions and makes the edges resistant to splitting.

Medium-density fibreboard: fine wood fibres bonded with resin and pressed into flat sheets. It has no grain, machines and finishes smoothly, but is heavy, soaks up water and creates fine dust.

Wood chisel with tapered, thinner edges so it can clean out the corners of dovetail and mortise joints without bruising the sides. The flat back must be kept dead flat.

Angle between the flat back of a blade and its ground bevel, usually about 25-30 degrees for chisels and plane irons. Too shallow weakens the edge; too steep makes it hard to push.

Abrasive block used with oil or water to hone a sharp edge after grinding. Coarse and fine grades, or a combination stone, produce a polished bevel and a clean, burr-free edge.

Simple wooden accessory that hooks over the bench edge, with a top stop for the work and a lower stop against the bench. It holds timber securely for cross-cutting and chiselling.

Hand-held power tool with a high-speed vertical spindle and interchangeable cutters for grooves, rebates and mouldings. Work or router must be fed against the cutter's rotation so it cannot run away.

Sudden, violent throwing back of the workpiece or the saw when a blade jams or is pinched in the kerf. Causes include ripping without a riving knife or twisting the work during the cut.

Fixed or rising steel plate immediately behind a circular saw blade and in line with it. It keeps the kerf open so the blade cannot be pinched, greatly reducing the risk of kickback.

Adjustable hood over the part of a circular saw blade that projects above the table, usually with dust extraction. It must be set close to the work and never removed while sawing.

Joint in which a projecting tongue (tenon) on one piece fits into a matching rectangular hole (mortise) in another. Glued and often pegged, it resists twisting and is standard in frames and furniture.

Corner joint of flared pins and tails cut so that they interlock and can only be pulled apart in one direction. Strong in tension, it is used for drawer boxes and carcass corners.

Groove cut across the face of one piece to take the end of another, usually a shelf or divider. The groove gives mechanical support and a large gluing area, and is often stopped at the front.

The box or body of a piece of furniture - sides, top, bottom and shelves - that gives it shape and rigidity. Doors, drawers and fittings are attached to the completed carcass.

Construction in which a solid panel sits in grooves in a surrounding frame but is not glued across its full width. The panel can then expand and contract with humidity without splitting the frame.

Water-based polyvinyl acetate glue used for wood-to-wood joints. It sets by loss of water and forms a strong bond on close-fitting joints; standard interior grades are not waterproof.

Number stating the particle size of an abrasive: low numbers such as 60 are coarse and remove material quickly; high numbers such as 240 are fine and leave a smooth surface ready for finishing.

Quick-drying lacquer applied to bare timber to seal open grain and stiffen raised fibres so they can be sanded off. It gives a flatter, smoother base for the finishing coat.

Volatile organic compounds: solvents that evaporate from paints, varnishes, adhesives and preservatives. They can cause headaches and long-term harm, so finishes need ventilation, extraction and suitable gloves or masks.

Drawing method showing an object as separate flat views - front elevation, plan and end elevation - projected at right angles. Each view gives true shape and sizes so the item can be made from the drawing.

Reference face, edge or line from which all measurements are taken when marking out or machining. Working from a single datum stops small errors adding up across a job.

The acceptable range of variation allowed on a stated dimension. Joints need clearance, a form of tolerance, so parts still fit together when sawing and machining are slightly inaccurate.

Local exhaust ventilation: extraction fitted close to the source of dust, such as a machine guard or bench hood, capturing particles before they reach the workshop air. It is the main control for wood dust.

Personal protective equipment - safety glasses, ear defenders, dust mask, apron and safety footwear - worn to protect the user. It is the last line of defence, after guards, extraction and safe working practices.

Forest Stewardship Council: international certification and labelling scheme for timber and board from forests managed to recognised environmental and social standards, traced through a chain of custody.

Harvesting timber no faster than the forest regrows it, so that the same woodland can keep producing indefinitely without being depleted or degraded.

Process by which growing trees absorb carbon dioxide from the air and store the carbon in wood; timber used in long-life products keeps that carbon out of the atmosphere.