Main Joints in Furniture Construction
Cases are composed of a top, a bottom, and uprights between which are panels of wood or glass. The diagram shows a section of a cabinet with the parts separated so as to illustrate how it is constructed. The column forming the corner post is doweled to the base and cornice. The sides and back are panelled and are either doweled or rebated to the other parts. The bottom and top is composed of a frame surrounding a panel.
In order to build all parts together use is made of several kinds of joints. Though these are not always shown; on the drawings it is desirable that the draughtman be familiar with them. They may be arranged in three groups, comprising those commonly used in furniture construction; the butt, the angle, and the framing joint.
The butt-joint is employed when two pieces of wood are joined together in the same plane. The simplest form is when the edges of the two pieces are brought together and held by glue, no other connect-ing medium being used. This is often sufficient, and when properly made is quite strong. It is almost invisible in the majority o-f woods when made so the grain is parallel with the line of contact.
When a stronger method is required, and one side of the pieces joined is hidden from view, blocks are glued across the joint, on the unexposed surface, so as to stiffen it. The grain of these blocks must be parallel with that of the joined pieces that shrinkage may not loosen, or cause them to crack. More on glue joints.
Tongue & Groove Joint
Another way of uniting the edges of two boards is by the tongue and groove. A tongue, or projecting piece, along the middle of the edge of one piece is matched to a groove in the edge of the other. Sometimes in place of this, a groove is cut in the edge of each of the boards throughout their entire length. Into these grooves is then glued a hardwood strip, called the tongue or slip-feather, uniting the two pieces. More information on the tongue and groove joint.
The most popular joint with the cabinet-maker is the dowel-joint. It is, perhaps, the best where the wood is of sufficient thickness to permit its use. A dowel is a wooden pin used for fastening two pieces of wood together by inserting part of its length into one piece, the rest entering a corresponding hole in the other. Sometimes a number of dowels are fitted tightly into holes bored for them in one of the pieces to be joined and the other has corresponding holes bored in it, in which the dowels also fit tightly when the two pieces are glued together.
Angle joints are frequently mitred. That is the joined edges are cut at a bevel bisecting the angle between them when united. The union is made by butting the pieces and gluing them together. As this does not make a strong joint in itself it is stiffened in various ways. One method is to drive small bits of corrugated metal in the ends of the pieces, and across the joint, thus binding the parts together. At other times corner blocks are glued on the inner side of the mitred angle.
For rounded corners, or when a mitred angle is not wanted, the two pieces may be tongued and grooved together. The tongue is on the inner edge of one of the pieces so that as much wood as possible is retained outside the groove on the other. The best and strongest method of joining two pieces at an angle is by dovetailing. When the joint is made so the full thickness of .each piece joined is visible, and the shape of each dovetail can be seen, the joint is a plain dovetail. The lapped dovetail is constructed so the joint is seen at the side only, and is commonly used for fastening the sides and front of drawers together. When it is desirable to have all indications of the dovetailing hidden a combination of the mitre and dovetail is used in which the dovetails are cut in part of the thickness of the wood and the mitre in the remainder. Such a joint is a mitred dovetail.
The usual framing joints used by furniture makers are the dowel-joint ( see also dowel joint ), and the mortise and tenon.
Mortise & Tenon
The true mortise (cavity) is cut near the end of one piece to receive the tongue (tenon) of the other. The tenon is not always the full width of the piece on which it is cut but often is narrower. More on mortise and tenon.
When framing for a series of panels, a groove is sunk the whole length of two of the framing pieces (those extending horizontally, called rails), and those at right angles to them (vertical pieces between the panels, the stiles) have tenons cut on them which fit in the grooves. These grooves also receive the panels. This method avoids cutting a mortise for each tenon and the name given to the joint is stub tenon.
When two pieces are joined by cutting away half the thickness of each, and then lapping them together they are said to be halved. Such a joint is sometimes combined with a mitre so that where exposed to view it appears like any mitred joint. It is then said to be halved-mitred. More on halving joints.
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