Revision:Joints

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Butt joints and Mitre joints

The simplest form of flat frame joint is the but joint. This is relatively weak having only a small gluing area. It is often adequate, however particularly if the frame is covered with a plywood or a hardboard panel using glue and panel pins. Picture frames are usually mitred so that the shape of the picture frames moulding flows around the corner without interruption. Mitres must be accurately cut at 45 to ensure a good gluing area. This is not a very strong joint, but can be strengthened by nailing, or on heavy frames by applying a thin plywood reinforcing plate.

Halving joints and Bridle joints

Halving joints are cut by removing half of the materials thickness from each piece of wood to be joined. This is carried out by using a tenon saw and a firmer or level edged chisel. This process can be applied to corners joints, tee joints, and cross joints. This is stronger than Butt joining and the strength can be further increased using screws or dowels. Bridles for corner joints and tee joints have an increased gluing area compared with halving joints and are therefore stronger. Screws or dowels can also be added to increase the strength.

Doweled joints

Dowel is circular sectioned hardwood, usually ramin or beech. Doweled joints are really Butt joints reinforced with dowels and they are very strong. They are straightforward to make providing that you are careful. Holes, usually two are drilled in the end of one piece and the side of another in order to form both corner joints and tee joints. Glue is then applied and short lengths of dowel are inserted. It is important to use the dowelling jig to position the holes. Dowels will enter more easy if the ends are chamfered slightly using a dowel bit in a carpenter's ratchet brace. A groove along the length of the dowel will allow air and surplus glue to escape from the hole. When strengthening Halving and bridle Joints using dowel, it is necessary to drill a hole through the joint. A length of dowel is then glued into the hole when the joint is being assembled. Any protruding dowel should be cleaned off after the glue has dried.

Mortise and tenon joints

The traditional strong joint, the Mortise and Tenon joint is well worth mastering. The basic mortise and tenon is a Tee joint either through or stopped. This is cut using a tenon saw and a mortise chisel, and it requires careful marking out using a mortise gauge. It can be strengthened using dowel in the same manner as a Tee bridle or halving joint. Alternatively, the through mortise can be wedged by sawing slits in the tenon, tapering the mortise and driving wooden wedges in. On a corner, a haunched mortise and tenon joint can be used, either square or sloping. This enables a mortise to be used near to the end of the length of wood. Sloping haunches are used where the top of the frame is visible. If this is not critical then a square haunch is adequate.

Edging and Edge joining

The edges of manufactured boards are not very attractive, they are vulnerable to damage and allow absorption of moisture. Where the edge will not be subject to physical knocks, a wood veneer can be applied. Pre-glued edging veneer is available in widths and woods to match veneered chipboard. The glue is heat activated using a hot cloths iron, alternatively contract adhesive can be used. Melamine edging strip is also available to suit melamine faced chipboard. For a harder wearing edge a solid hardwood strip can be applied. It is best to mitre the corners so that the end grain is exposed. Solid edges ore fixed by Butt jointing or by using a tongue and groove. The tongue may be part of the edge or alternatively a loose plywood strip. All methods should be securely cramped until the glue has set. Tongued edging is stronger than Butt jointing is.

Edge jointing

Joining solid wood edge to edge is dependent upon carefully planed, flat and square edges. The methods of joining are similar to those applied to edging, Butt jointing, tongue and grooving or by using a loose plywood tongue. Another alternative is to use dowels.

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