Joinery is a part of woodworking that involves joining pieces of wood, engineered lumber, or synthetic substitutes (such as laminate), to produce more complex items. Some woodworking joints employ mechanical fasteners, bindings, or adhesives, while others use only wood elements (such as dowels or plain mortise and tenon fittings). The characteristics of wooden joints—strength, flexibility, toughness, appearance, etc.—derive from the properties of the materials involved and the purpose of the joint. Therefore, different joinery techniques are used to meet differing requirements. For example, the joinery used to construct a house can be different from that used to make cabinetry or furniture, although some concepts overlap. In British English joinery is distinguished from carpentry, which is considered to be a form of structural timber work; in other locales joinery is considered a form of carpentry.
History
Many traditional wood joinery techniques use the distinctive material properties of wood, often without resorting to mechanical fasteners or adhesives. While every culture of woodworking has a joinery tradition, joinery techniques have been especially well-documented, and are celebrated, in the Indian, Chinese, European, and Japanese traditions. Surviving Indian and Egyptian furniture from the first several dynasties show the use of complex joints, such as the dovetail joint, more than 5,000 years ago. This tradition continued to other later Western styles. The 18th-century writer Denis Diderot included more than 90 detailed illustrations of wood joints for building structures alone, in his comprehensive Encyclopédie published in 1765. While Western techniques focused on concealment of joinery, joiners in the Eastern societies traditionally did not attempt to "hide" their joints. The Japanese and Chinese traditions in particular required the use of hundreds of types of joints. The reason was that nails and glues used did not stand up well to the vastly fluctuating temperatures and humid weather conditions in most of Central and South-East Asia. In addition, the highly resinous woods used in traditional Chinese furniture do not glue well, even if they are cleaned with solvents and attached using modern glues. As the trade , new developments have evolved to help speed, simplify, or improve joinery. Alongside the integration of different glue formulations, newer mechanical joinery techniques include "biscuit" and "domino" joints, and pocket screw joinery.
Properties of wood Many wood joinery techniques either depend upon or compensate for the fact that wood is anisotropic: its material properties are different along different dimensions. This must be taken into account when joining wood parts together, otherwise the joint is destined to fail. Gluing boards with the grain running perpendicular to each other is often the reason for split boards, or broken joints. Some furniture from the 18th century, while made by master craftsmen, did not take this into account. The result is a masterful work that may suffer from broken bracket feet, which was often attached with a glued block, which ran perpendicular to the base pieces. The glue blocks were fastened with both glue and nails, resulting in unequal expansion and contraction between the pieces. This was also the cause of splitting of wide boards, which were commonly available and used during that period. In modern woodworking it is even more critical, as heating and air conditioning causes more severe respiration demands between the environment and the wood's interior fibers. All woodworking joints must take these changes into account, and allow for the resulting movement. Each wood species has a general respiration rate; a generally-assumed time length for acclimating a board to its locale is 1 year per inch of thickness. In preparing raw wood for eventual usage as furniture or structures, one must account for uneven respiration and changes in the wood's dimensions, as well as cracking or checking.
Strength Wood is stronger when stressed along the grain (longitudinally) than it is when stressed across the grain (radially and tangentially). Wood is a natural composite material; parallel strands of cellulose fibers are held together by a lignin binder. These long chains of fibers make the wood exceptionally strong by resisting stress and spreading the load over the length of the board. Furthermore, cellulose is tougher than lignin, a fact demonstrated by the relative ease with which wood can be split along the grain compared to across it. Different species of wood have different strength levels, and the exact strength may vary from sample to sample. Species also may differ on their length, density and parallelism of their cellulose strands.
Dimensional stability Timber expands and contracts in response to humidity, usually much less so longitudinally than in the radial and tangential directions. As tracheophytes, trees have lignified tissues which transport resources such as water, minerals and photosynthetic products up and down the plant. While lumber from a harvested tree is no longer alive, these tissues still absorb and expel water causing swelling and shrinkage of the wood in kind with change in humidity. When the dimensional stability of the wood is paramount, quarter-sawn or rift-sawn lumber is preferred because its grain pattern is consistent and thus reacts less to humidity.
Materials used for joining
Dowels can secure wood joints hold without the use of glue or mechanical fasteners, as in a pinned mortise and tenon. Glue is highly effective for joining timber when both surfaces of the joint are edge grain. A properly glued joint may be as strong or stronger than a single piece of wood. Animal glue is soluble in water, producing joints that can be disassembled using steam to soften the bond. Various mechanical fasteners may be used, the simplest being nails and screws. Glue and fasteners can be used together.
Reinforcing joints
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