If you are working on a big project, it may be necessary to join two pieces of timber together to gain a longer length. Smaller projects also often require a section of wood grafting. There are several methods of joining timber, dependent on the strength and finish required.
For a strong face to face joint use coach bolts in conjunction with timber connectors (metal washers with toothed edges). Drill three holes along the centre of the sides of both timbers, aligning with the adjoining timber. Use the timber connectors between the two pieces of timber to be joined. Insert the bolts making sure the timber connectors are on the bolts when pushed between the two timbers. Use washers and nuts at the other end to tighten the joint. The timber connectors bite into the wood as the joint is tightened, increasing the strength of the union.
If the two timbers to be joined are meeting end on end, use two wooden plates to hold the union together like a sandwich. The two wooden plates must be strong enough to support the join. Measure the width of the timber to be joined. Use timber plates that are 4 times longer than that width. The timber plates should be the same width as the timber but half its thickness. Glue all the surfaces together before drilling holes in the construction and either screw or coach bolt the whole section together in strategic points staggered across the surface of the plates.
This type of joint is more suitable for lengthening lighter structures and is the easiest method of joining two timbers. Measure the timbers and mark the halfway positions on each. The laps should be cut to half the thickness of the timber, one cut reflecting the other in the second timber. The two shoulders made must butt exactly against the end of the joining pieces. Glue all the surfaces together before drilling holes in the construction and screw the sections together in strategic points staggered across the surface grain to avoid splitting.
This type of joint is only suitable for lengthening lighter structures such as in cabinet making. For the greatest strength, make the scarf length 8 times longer than the width of the timber. Measure the timbers and mark the scarf positions on each. The splayed faces must be measured, cut and planed accurately to perfect the bond. The faces must butt exactly together. Glue all the surfaces together and screw the sections together for added strength.
This type of joint is a variation on the lapped joint. The difference is that the lap is cut in the thickness of the timber instead of the width of the timber. The splayed lap joint is suitable for joining timber directly onto a joist or timber wall, giving it extra support. It is suitable for use when the timbers need to keep a straight edge in order to be used to support hardboard or chipboard sheeting. The length of the joint should be equal to the width of the timber. To help resist the chance of the joint being pulled apart, cut the splays along the grain of the wood. Check that they butt together exactly before securing. Nail the lower section of timber diagonally through to the joist or timber wall. Butt the joining length of timber into position and nail it diagonally through the top.
This type of joint is used when appearance is of prime importance, particularly in furniture repairs. Use a fine tooth saw to cut a ‘V’ shape in one section of wood. The joining section must be cut and planed to make a perfect fit if the repair is to be successful. It is worth spending time getting the exact fit before fixing the two pieces together. When ready glue and clamp the pieces together until the glue sets. If the join is in a vulnerable location, screws can be used to add extra strength.
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