Information about Wood Joints

History^{^[1]}

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 to make furniture or structures has a joinery tradition, wood joinery techniques have been especially well-documented, and are celebrated, in the Indian, Chinese, European, and Japanese traditions.

Because of the physical existence of Indian and Egyptian examples, we know that furniture from the first several dynasties shows the use of complex joints, like the Dovetail, over 5,000 years ago. This tradition continued in other later Western styles. In his comprehensive encyclopedia, the 18^th century writer Diderot included over 90 detailed illustrations of wood joints.^[2]

While Western techniques focused on the concealment of joinery, the Eastern societies later did not attempt to “hide” their joints. The Japanese and Chinese traditions particularly required using hundreds of types of joints. The reason was that the 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.^[3] Also, 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 with all trades, new developments have evolved to help speed, simplify, or improve joinery. These include “biscuit” and “domino” joints and pocket screw joinery.

Joinery skills became a recognised force in furniture construction during the 13^th century, with the first examples of clamped fronted chests. Their design used a long mortice and tenon to join wide uprights to a wide panel at right angles – to and between them^[4].

Picture Credit: “Dale Hodgins Joinery” by WorldSkills UK is licensed under CC BY 2.0.

Two ancient civilizations that used woodworking were the Egyptians and the Chinese. Woodworking is depicted in ancient Egyptian drawings, and a considerable amount of ancient Egyptian furniture (such as stools, chairs, tables, beds, chests and so on) has been preserved in tombs.

Microwear analysis of the Mousterian stone tools used by the Neanderthals shows that many were used to work wood^[5].

The Advantages of Wood Joints^[6]

Provide strength, flexibility, and toughness to the structure.
Reduce wood wastage during a project.
Cost-effective and increases durability.
Provides rigidity to the project and enhances its appearance.
Makes the parts stronger by using a mechanical fastener or adhesive.
Glue or fasteners add extra strength to the joints.
Some joints can be designed without glue or a fastener.

Carpentry and Joinery
Both Carpentry and Joinery are construction trades concerned with wood. To explain the difference in its simplest and traditional sense:

joiners join wood in a workshop,
carpenters construct the building elements on-site.

The skill in making construction components (such as windows, doors, trusses, stairs, etc.) is in the joints – this is where a joiner is specialised. But, carpenters normally work on-site, so their specialised skill is concerned with wood fixtures. A joiner is essentially someone who makes the product that a carpenter installs or repairs. Traditionally, joiners work in workshops, producing the components for carpenters to fix.^[7]

Common jobs for Carpenters include:	Common jobs for Joiners include:
Fitting floors	Making doors
Fitting staircases	Making window frames
Fixing window frames	Creating fitted furniture
Installing cupboards and shelving	Building stairs

Joinery often refers to the part of woodworking that involves joining pieces of wood, engineered timber or synthetic substitutes, such as laminates, to make more complex items. Traditional wood joinery techniques use the distinctive material properties of wood, often without mechanical fasteners such as glue or nails. There are different types of joinery for different structures: for example, the joinery used to build a house differs from that used to make cabinetry, furniture or toys, although some elements overlap.^[8]

Wood is strong when stressed along the grain (longitudinally) but weak across it (radially and tangentially). It expands and contracts in response to humidity. This change is very small longitudinally. It is considerable but unequal in the radial and tangential directions.^[9]

Ten Basic Joints^[10]

Butt Joint
A butt joint connects two squared-off pieces of wood, whether face to face, edge to edge, or at a corner. The important thing with a joint like this is ensuring they fit together tightly. In this case, a block plane can be used to smooth the end of the grain. Additionally, you can use either glue, nails, screws, or dowels to secure your butt joint.

Mitre Joint
As you may recognise from your mitre box or mitre gauge found on a table saw, mitre cuts are quite simply angle cuts. Another way of looking at it is that a mitre joint is a type of butt joint that connects the angled ends of two pieces. A classic example of this would be a picture frame, each with four butt joints in the corners, which are cut to a 45° angle. When fastening a mitre joint, you can use glue, nails, screws, dowels, and many other mechanical fasteners. There are two distinct advantages to using a mitre joint as opposed to a butt-corner joint:

No end grain shows (for aesthetic benefits)
Bigger surface area for glueing (for additional stability)

Dado Joint
Cutting a channel or groove into a wood piece away from the edge is called a dado. To make a dado joint, you set a second piece firmly into the groove using nails, glue, or other fasteners. You may hear some cabinetmakers differentiating between ‘groove’ and ‘dado joints’, saying that the grooves are cut with the grain, and dados must be cut across them. In any case, you can make these cuts using a dado head on a radial arm or a standard table saw. A great example of a dado joint in action is when setting bookshelves into uprights.

Lap Joint
A lap joint is formed by joining two pieces of wood that have had recesses cut into them:

One recess in the top of the surface of the first piece
The other recess in the lower surface of the second piece

When removing the waste material from the recess, it is typically half the thickness of the original stock, meaning that when the lap joint is connected, the top and bottom of the joint arc are flush with each other. Lap joints can be cut using dado heads on standard circular sawblades or radial arms, and table saws. These joints can be glued or joined using other fasteners such as dowels or wooden pins.

Rabbet Joint (or Rebate)
This is a type of joint that comes in the form of a lip or channel cut from the edge of your workpiece. A standard rabbet joint is made when a second piece is joined to the primary piece, set against the rabbet. A rabbet joint is most commonly used when recessing cabinet backs into the sides, or when wanting to reduce the amount of ‘end grain’ that is visible on a corner. It is considerably stronger than an average butt joint and can easily be made using two radial-arm saw cuts (one into the face and the other into the end grain or edge). You can also use a plow plane or a router to cut a rabbet joint. Glue, nails, or screws can be used to fasten the rabbet joint properly.

Spline Joint
Typically, a spline is a thin strip of wood that fits perfectly into grooves on surfaces to be joined. For example, mitre and other joints may often incorporate splines in them. When the surfaces are cut to be joined to fit, you can then use a table saw to cut matching kerfs. When using a spline, it can add rigidity to the joint, whilst also increasing the glueing area. Most splines are thin, so they are more commonly made out of plywood or hardwood.

Mortise and Tenon Joint
A mortise and tenon (occasionally mortice and tenon) joint connects two pieces of wood or other material. Woodworkers around the world have used it for thousands of years to join pieces of wood, mainly when the adjoining pieces connect at right angles. Typically, mortise and tenon are straight in shape, though round tenons and mortises can also be applied. Whilst this type of joint is much harder to shape than the other simpler joints, it provides a great deal more structural rigidity.

Tongue and Groove Joint
Tongue and groove is a method of fitting similar objects together, edge to edge, used mainly with wood, in flooring, parquetry, panelling, and similar constructions. Tongue and groove joints allow two flat pieces to be joined strongly together to make a single flat surface. Before plywood became commonplace, tongue and groove boards were used to cover buildings and construct concrete formwork.

Finger Joint
The finger joint (aka drawer or box joint) is the most common type of joint found in drawers. The interlocking rectangular ‘fingers’ are cut into the end grain of drawer ends and sides. Of course, while precise cutting is essential, a finger joint only requires simple 90° cuts, which can be made either by hand or using a router or table saw / radial arm.

Dovetail Joint
A dovetail joint or simply a dovetail is a joinery technique most commonly used in woodworking joinery, including furniture, cabinets, log buildings, and traditional timber framing. It is noted for its resistance to being pulled apart, the dovetail joint is commonly used to join the sides of a drawer to the front.

The Properties of Wood^[11]Many wood joinery techniques either depend upon or compensate for the fact that wood is anisotropic^[12]: its material properties are different along different dimensions and must be taken into account when joining wood parts together, or the joint is destined to fail.

Glueing boards with the grain running perpendicular to each other is often the reason for split boards, or broken joints. Furniture from the 18^th century, although made by master craftsmen, failed to take this into account. This masterful work suffers from broken or unsteady bracket feet, often attached with a glue block that ran perpendicular to the base pieces. The glue blocks were fastened with glue and nails, resulting in unequal expansion and contraction between the pieces. It was also the cause of splitting in the wide boards 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. Woodworking joints must take these changes into account and allow for the resulting movement.^[13]

Traditional Wood Joints^[14]

[1] Explanation: Mission Style Furniture is a style of furniture that originated in the US in the late 19^th century. It traces its origins to a chair made by A.J. Forbes around 1894 for San Francisco’s Swedenborgian Church. The term mission furniture was first popularised by Joseph P. McHugh of New York, a furniture manufacturer and retailer who copied chairs and offered a line of stylistically related furnishings by 1898. The word mission references the Spanish missions throughout colonial California, though the design of most Mission Style Furniture owed little to the original furnishings of these missions. The style became increasingly popular following the 1901 Pan-American Exposition in Buffalo and was popularly associated with the American Arts and Crafts movement. Source: https://en.wikipedia.org/wiki/Mission_Style_Furniture

[2] Source: “Miscellaneous Joints”. sawdustmaking.com.

Picture Credit: “Collection of old woodworking tools” by quinet is licensed under CC BY 2.0.