Jointing timber in width – Woodworking joints
This type of joint enables narrow boards to be built up to cover large areas (floor boards, cladding, etc.), or built up to form wider boards for shelving, cabinet work, table tops, etc.
This is the simplest and most common form of joint where the square edges of the pieces of timber are glued together (Fig.A). To strengthen the butt joint it can either be dowelled (Fig.B) or biscuited (Fig.C)
An improvement of the butt joint is tongued joint. Both pieces of timber are grooved out and a loose plywood tongue is inserted (Fig.D). This joint is used mainly for cabinet work and counter tops.
Tongue and groove joints
The tongue and groove (T&G) joint (Fig.E) is similar to the tongued joint, but rather than using a loose tongue, one of the pieces of timber to be jointed has a tongue cut onto it. Other variations of this joint include the tongued, grooved and veed (TG&V) joint (Fig.F) and the tongued, grooved and beaded joint (Fig.G). The joints can also be rebated (Fig.H) and rebated and filleted (Fig.I). A tongue and grooved joint is suitable for secret nailing (Fig.J) as it has a projection below the groove, which is more convenient for nailing. There are several modifications of this joint for secret nailing, but they have no special advantages. A rebated tongued and grooved joint (Fig.K) is one of this type.
Strengthening jointed boards
It is often necessary to strengthen jointed boards by placing battens on the rear. Three different methods are shown below that will allow for the movement of the boards whilst shrinking or expanding. This free movement is to prevent the joints from breaking or the boards from splitting.
The dovetailed batten or key (Fig.K) is an uncommon joint because it is difficult to fit the batten accurately in all the boards, so as to make it effective throughout (though when fitted well it is a efficient joint). The batten is fixed at the small end so the boards are free to contract. The batten can be driven further in, if necessary, when the boards are seasoned and refixed.
Several buttons engage with the batten and they are placed alternately on each side. It is common to make the buttons so that they can be swivelled when they are screwed in position. This makes the framing easy to take to pieces after fitting together.
The position of the screws in the slots depend upon the conditions. If they are intended to allow for shrinking only, the screws should be at the outside of the slots. If they are to allow for both expansion and contraction of the timber, then the screws should be in the centre of each slot (as shown above right). One or two fixed screws are placed at the centre of the batten without slotting, so that the boards may contract at each edge.
We shall conclude our series on woodworking joints in our next part by looking at hinging and shutting joints