Joinery

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Pocket-Hole Joinery being used in a simple butt joint.

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Detail of brace Mortise and tenon joints in a hand-hewn Timberframe.

A worker uses a mortising machine to shape Timber framing joints

A worker uses a large circular saw to cut joints.

Joinery is a 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,appearance, 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.

List of joints

Traditional woodworking joints

• Butt joint; the end of a piece of wood is butted against another piece of wood. This is the simplest and weakest joint.
• Miter joint; similar to a butt joint, but both pieces have been cut at a 45 degree angle.
• Lap joints; one piece of wood will overlap another.
• Box joint, also called a finger joint, used for the corners of boxes. It involves several lap joints at the ends of two boards.
• Dovetail joint; a form of box joint where the fingers are locked together by diagonal cuts.
• Edge joint; the edges of two boards are joined.
• Dado joint; a slot is cut across the grain in one piece for another piece to set into; shelves on a bookshelf having slots cut into the sides of the shelf, for example.
• Groover joint; the slot is cut with the grain.
• Tongue and groove. Each piece has a groove cut all along one edge, and a thin, deep ridge (the tongue) on the opposite edge. If the tongue is unattached, it is considered a spline joint.
• Mortise and tenon; a stub (the tenon) will fit tightly into a hole cut for it (the mortise). This is a hallmark of Mission Style furniture, and also the traditional method of jointing frame and panel members in doors, windows, and cabinets.
• Birdsmouth joint is used in roof construction. A V-shaped cut in the rafter connects the rafter to the wall-plate.

Nontraditional woodworking joints

• Pocket hole joinery; a hidden screw is driven into the joint at an angle.
• Joints using metal connectors, which attach to the frame with nails or screws.

Traditional ways of improving joints

• Dowels, where a small rod is used internal to a joint to both help align on glue up and permanently strengthen the joint. Traditional joints are used with natural timbers as they do not need any other materials other than the timber itself. for example: Butt joints. Dowel joints are also useful for pegging together weaker, cheaper composite materials such as laminate-faced chipboard, and where limited woodworking tools are available (since only simple drilled holes are needed to take the dowels).

Nontraditional ways of improving joints

• Biscuit joints, where a small 'biscuit' is used to help align an edge or butt joint on glue-up.
• Domino jointer, a trademarked tool similar to a biscuit jointer, where a piece larger than a biscuit has some of the advantages of dowels, and some of the advantages of biscuits.

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 nut sack 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 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, quartersawn lumber is preferred because its grain pattern is consistent and thus reacts less to humidity.

Materials used for joining

File:Timber Joint with Metal Plates.JPG

Metal plates are often incorporated into the design where the timber alone would not be strong enough for a given load.

• Joints can be designed to hold without the use of glue or fasteners; a pinned mortise and tenon is an example of this.
• Glue is highly effective for joining wood 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. However, glue is notably less effective on end-grain surfaces. Animal glue is soluble in water, producing joints that can be disassembled using steam to soften the glue.
• Various mechanical fasteners may be used, the simplest being nails and screws. Glue and fasteners can be used together.

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 some of these methods for over seven thousand years.

Nontraditional joinery

Methods that are not considered traditional joinery have come about in modern times, largely to attempt to simplify the job of the woodworker for various reasons. These include biscuit joints and pocket hole joinery.

See also

• Woodworking
• Cabinet making
• Building construction
• Chinese Wooden Architecture
• Timber framing

References

• Lee A. Jesberger (2007). Woodworking Terms and Joints. Pro Woodworking Tips.com
• Bernard Jones (Ed.) (1980). The Complete Woodworker. ISBN 0-89815-022-1
• Peter Korn (1993). Working with Wood. ISBN 1-56158-041-4
• Sam Allen (1990). Wood Joiner's Handbook. Sterling Publishing. ISBN 0-8069-6999-7
• Wolfram Graubner (1992). Encyclopedia of Wood Joints. Taunton Press. ISBN 1-56158-004-X

External links

• [1] Pro Woodworking Tips - Woodworking Terms and Joints
• DIYinfo.org's Carpentry Wiki - Practical information on creating various wood-working joints
• Dimensioning woodworking and carpentry joints Craftsmanspace