Woodworking has so many facets to it that even dedicated craftsmen continue to learn about it throughout their lives. However, even acknowledged experts in any field of human activity have to start somewhere and this post is for those whose background to the craft is limited, and who are quite willing to call themselves beginners. Before we can use a material or handle tools competently we should learn something about them. Let us start with wood.
The best quality timber is cut from the heartwood ; this is usually darker in colour than the sap wood, which contains living cells and is not so dense. Heart-wood gives strength and support to the tree while new growth builds up around the sapwood, from the cambium layer beneath, and protected by, the bark.
Annual rings are formed each year: in the spring when sap is rising, and in the autumn when it is falling. Hence the names, spring wood and summer wood. The age of a tree can be calculated by counting the growth rings. Close annual rings indicate slow growth, wide ones indicate quick growth.
Growth rings of hardwoods are generally much closer than those of softwoods, and often less pronounced. Timber with close rings is usually more stable and less liable to distortion than wide ringed timber. Less than six rings to the inch in softwoods is often unacceptable for structural work.
Trees are divided into two classes: broadleaf trees usually shed their leaves in winter, although some are evergreen. Such trees produce hardwood. Class are the conifers, usually evergreen with needle-like leaves amongst which are produced cones. These are the softwoods.
The terms softwood and hardwood are rather inclined to be misnomers because balsa, the softest wood known and used for modelling, buoyancy aids, some stage furniture etc., is classified as a hardwood while yew, once used to make longbows and now used for fencing, furniture and decorative items, is dense, hard, and very durable; although it is a softwood. A point to observe in these classifications is that softwood and hardwood are each one word. When the term soft wood is used, it indicates a characteristic of the particular species, not its classification.
Newly felled timber is taken to the saw mill for conversion, as the initial sawing of the round log into plank and board form is called. The most common method of conversion is ‘slab’ sawing, also known as slash sawing or sawing through-and-through. The method of sawing and the part of the trunk sawn has some influence on the timber produced as shrinkage during drying or seasoning takes place. Plank would distort by cupping away from the heart side, as would plank.
Plank, referred to as a radial plank, would shrink in width but would remain fairly flat.
Planks sawn so that the growth rings meet the face at an angle of not less than 45 degrees are called quarter sawn, the most desirable timber for first class constructional work. When the growth rings are at an angle of less than 45 degrees the plank is described as plain sawn. These planks show the fine contour-line oval grain configurations. Plain sawing can therefore produce both types.
Before timber can be used for constructional purposes it has to be dried, or seasoned, to reduce the amount of moisture in the timber to suit the situation where the timber will be used. There are two methods of seasoning.
Here the sawn timber is stacked on level ground with spacers or ‘stickers’ between the planks, to allow a free circulation of air. This is the old way, but it is slow, taking about one year for each 25 mm of thickness of material. Ends of slabs may be painted or otherwise sealed to prevent too rapid drying and weights may be placed on top of the stack to prevent movement.
This is much quicker and a lower moisure content can be achieved by the carefully controlled conditions it is possible to create in the kiln. The stacking system is similar to that used in natural seasoning. This takes place in an enclosed chamber and by a combination of steam, dry air and fans the time of drying is reduced from years to weeks.
Often timber bought at a local merchant’s yard is only partially seasoned. This can lead to complications, especially with regard to shrinkage. Ideally, the timber should be carefully stacked, as for seasoning, in the place it will be used so that the moisture content can adjust to the environment. As stated earlier, timber shrinks unequally: lengthways, with the grain, nil; with the annual rings considerably; across the annual rings about half as much. Poor or inefficient seasoning can lead to splitting, warping, bowing and cupping. Leaning planks against a wall, ladderlike, for long times in sun, wind or rain can also cause bowing and warping, which is practically impossible to rectify.
Board is twisted and is bowed. A part waney edge is shown at. Waney edge is the outer part of the trunk covered, with bark. Some boards are sold with the waney edge for special use, such as cladding walls, but waney edges are not desirable on finished timber for structural use.
Already we have used terms which may be unfamiliar. Some of them are illustrated by the drawings but the following simple glossary will introduce a few more. It is good sense to learn the language of woodworking; you will then know what your supplier is talking about and, very importantly, he will know what you mean.
Air-dried Seasoned as previously described, in open air conditions. Such timber will have a relatively high moisture content at least equal to the ambient climatic humidity. If used indoors and especially in heated rooms, such timber may shrink or deform unless carefully used. Generally such timber is satisfactory for normal constructional use such as roofing timbers, but during long periods of damp weather air-dried timber, and indeed any timber stored under normal climatic conditions during such periods, will have a high moisture content.
Board Converted timber around 51 mm or greater thickness. Manufactured product in sheet form.
Clean Free from knots.
Clear Free from visible defects and imperfections.
Density Weight per unit volume such as lb per cubic ft or g per cubic cm.
Edge Narrow side of square sawn timber.
End Cross-cut surface of square sawn timber.
Face Broad side of square sawn timber.
Ornamental markings, seen on cut surface of timber, formed by structural features of the wood.
Grain General direction or arrangement of fibres. Plane of the cut surface, e.g. edge-grain, end-grain.
Lumber Imported square edged sawn hardwood of random width. Also refers to all forms of sawn timber.
Machined Having a surface or dimension that has been subject to machine operation after initial conversion.
Nominal Size before planing. Planing will reduce the nominal thickness of a sawn board by about 3 mm and width by up to 6 mm.
PIE Planed one edge. P2E, planed two edges.
PIS Planed one side. P2S, planed two sides.
PIS IE Planed one side and one edge.
P4S Planed four sides.
P.A.R. Planed all round.
P.T.G. Planed, tongued and grooved.
T. and G. Much used for flooring. Un-edged Plank with both edges waney.
Various composite boards are manufactured by quite involved processes requiring complicated machinery, intricate production lines and well organised factories. Probably the most common is fibreboard, which includes the ubiquitous hardboard, so well known it needs no description. Fibreboards range from fairly thick low density boards through various medium density boards to standard hardboard and finally oil-tempered hardboard, which is so dense that it can be used for external cladding and floor surfacing.
This is made from wood and other ligneous materials after they have been reduced to a fibrous pulp. This pulp is carefully graded, spread on ‘mats’ to a predetermined thickness, pressed, dried and trimmed to standard size sheets. Various refinements in the general process described are added to produce the different qualities or grades.
This is made from three or more thin laminations of wood bonded together so that the grain of one ply is at right angles to its neighbour. Many grades are available according to type of wood used, whether surfaced with a decorative veneer or not, thickness of laminations, quality of exterior surface, and type of glue used. Marine grade is made from best quality materials with water- and boil-proof glue.
Block-board, lamin-board and batten-board
These are composite boards with cores of solid softwood in the form of strips. The narrower the strips the less chance there is of distortion and surface undulations. It usually has birch faces and is frequently sold in veneered form.
Chipboard or particle board
In simple terms this is a board made from graded wood chips bonded together with an adhesive under great pressure and heat. Many manufacturers offer this material with veneered faces and edges in two or more standard lengths and up to ten widths from 152 mm upwards. It is also available with melamine and other plastics surfaces. Chipboard, unveneered, is used for constructional work, including floors, and is manufactured to specific standards.
Lamin-board is considered the best and most stable of the composite boards. The core strips, not more than 6mm wide, are bonded together with the heart sides alternating. Lamin-board may have one or two outer plies. Block-board has strips up to about 19 mm wide and also has one or two outer plies. Batten-board has strips up to 76 mm wide.
Often chips are graded from large ones in the centre to fine particles on the face. A point to watch is that in large particles screw-holding may be affected when edge fixing so it is advisable to use plugs specially made for chipboard.