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 cause 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

• Dowel: A small rod is used internal to a joint both to help align and to strengthen the joint. Traditional joints such as butt joints are used with natural timbers as they do not need materials other than the timber itself. 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). The wood species of a dowel may be different from the overall piece to balance strength with cost, and some joinery may leave a dowel end visible as part of the piece's design.

• Biscuit joints: A small preformed wooden 'biscuit' is inserted in a pre-cut slot to help align an edge or butt joint when gluing.
• Domino joiner: A trademarked form of biscuit joiner, using a piece of preformed wood, larger than a traditional biscuit and referred to as a "domino"; has some of the advantages of dowels and of biscuits.

All reinforcements using wood as the introduced spanning material make use of the item's cellulose fibers to resist breakage. Biscuits or dominos may provide only slight strength improvement while still forming a strong alignment guide for the joint's pieces.

Types of wood joints

Traditional

Most-commonly referenced joints carried forward from historical Western traditions.

Modern

Joinery terms

When material is removed to create a woodworking joint, the resulting surfaces have the following names:

• Cheek, the flat surface parallel to the face of the joint member which exposes long grain
• Shoulder, the surface perpendicular to the face or edge of the joint member which exposes end grain

Joinery as a profession

A joiner is an artisan and tradesperson who builds things by joining pieces of wood, particularly lighter and more ornamental work than that done by a carpenter, including furniture and the "fittings" of a house, ship, etc. Joiners may work in a workshop, because the formation of various joints is made easier by the use of non-portable, powered machinery, or on job site. A joiner usually produces items such as interior and exterior doors, windows, stairs, tables, bookshelves, cabinets, furniture, etc. In shipbuilding a marine joiner may work with materials other than wood such as linoleum, fibreglass, hardware, and gaskets.

The terms joinery and joiner are in common use in Canada, UK, Australia, and New Zealand. The term is not in common use in America, although the main trade union for American carpenters is called the United Brotherhood of Carpenters and Joiners of America.

In the UK, an apprentice of wood occupations could choose to study bench joinery or site carpentry and joinery. Bench joinery is the preparation, setting out, and manufacture of joinery components while site carpentry and joinery focus on the installation of the joinery components, and on the setting out and fabrication of timber elements used in construction.

In Canada, joinery is considered a separate trade from carpentry. Both having their own apprenticeship path and red-seal certification.

History of joinery

In the history of technology in Europe, joinery was the medieval development of frame and panel construction, as a means of coping with timber's movement owing to moisture changes. Framed panel construction was utilised in furniture making. The development of joinery gave rise to "joyners", a group of woodworkers distinct from the carpenters and arkwrights (arks were an intermediate stage between a carpenter's boarded chest and a framed chest).

The original sense of joinery is only distantly related to the modern practice of woodworking joints, which are the work of carpenters. This new technique developed over several centuries and joiners started making more complex furniture and panelled rooms. Cabinetmaking became its own distinct furniture-making trade too, so joiners (under that name) became more associated with the room panelling trade.

By the height of craft woodworking (late 18th century), carpenters, joiners, and cabinetmakers were all distinct and would serve different apprenticeships.

In British English, a joiner is colloquially known as a "chippy".

Woodworking professions

The Institute of Carpenters recognizes the following professionals working in wood:

• Carpenters
• Furniture and cabinet makers
• Boat builders (woodworking skills)
• Joiners
• Shopfitter
• Structural post and beam carpenters (timber framing)
• Wheelwrights
• Wood carvers
• Wood turners