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Woodworking joints
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Joinery is that part of woodworking that involves joining together pieces of wood, to create furniture, structures, toys, and other items. Some wood joints employ fasteners, bindings, or adhesives, while others use only wood elements. The characteristics of wooden joints - strength, flexibility, toughness, etc. - derive from the properties of the joining materials and from how they are used in the joints.
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Joinery is that part of woodworking that involves joining together pieces of wood, to create furniture, structures, toys, and other items. Some wood joints employ fasteners, bindings, or adhesives, while others use only wood elements. The characteristics of wooden joints - strength, flexibility, toughness, etc. - derive from the properties of the joining materials and from how they are used in the joints. Therefore, different joinery techniques are used to meet differing requirements. For example, the joinery used to build a house is different from that used to make puzzle toys, although some concepts overlap.
Traditional Joinery
Many traditional wood joinery techniques use the distinctive material properties of wood, often without resorting to mechanical fasteners or adhesives. While every culture in which pieces of wood are joined together to make furniture or structures has a joinery tradition, wood joinery techniques have been especially well documented and celebrated in the Chinese, European, and Japanese traditions. The Japanese and Chinese traditions in particular include hundreds of types of joints, many of which do not use glue or nails. The Chinese have been using this method for the last seven thousand years.
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.
Joining wood parts together must take this into account, 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. Furniture from the 18th century, while made by master craftsmen, did not take this into account. The result is this masterful work suffers from broken bracket feet, which was often attached with a glue 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 used during that period.
In modern woodworking it is even more critical, as heating and air conditioning cause major changes in the moisture content of the wood. All woodworking joints must take these changes into account, and allow for the resulting movement.
Strength
Wood is stronger when stressed along the grain (longitudinally) than it is when stressed across the grain (radially and tangentially).
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 tissue still absorp 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, quartersawn lumber is preferred because its grain pattern is consistent and thus reacts less to humidity.
Materials used for joining
- Joints can be designed to hold without the use of glue or fasteners.
- Glue is highly effective for joining wood when both surfaces of the joint are edge grain. A properly glued joint may be as strong as a single piece of wood. However, glue is ineffective on end-grain surfaces. Compared to a mortise and tenon, a dowel joint is a poor joint because it does not address these properties. Much of the surface of the hole of a dowel joint is end-grain, to which glue adheres poorly. In a mortise and tenon, most of the surface of the joint is longitudinal-grain. Animal glue is soluble in water, producing joints that can be disassembled using steam to soften the glue.
- Various mechanical fasteners are used, the simplest being nails and screws. Glue and fasteners can be added together.
Types of joints
Some types of joints used include:
Images of different types of joints
See also
Footnotes
External links
- Pro Woodworking Tips - Woodworking Terms and Joints
- - Practical information on creating various wood-working joints
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