Timber Joints - Frame
It is often required to build timber frames and there are a number of simple joints which can be used to make them. Where frames are used, they are often clad with plywood or other man man boards. The use of a frame adds strength to the structure so that relatively thin board can be used - thus save in both weight and cost..
The area of contact for this basic of all joints is limited to the end of the one piece of timber that butts against the surface of the second piece. It is the weakest type of joint and is not really of practical use for a thin frame.
For a mitre joint, the ends of two pieces of wood are cut at a 45 degree angle. The mitre, which is only marginally stronger than the butt, is used almost exclusively for appearance sake as the joint conceals the exposed end grain of both pieces of timber. It is the standard type for picture frames and small decorative finishes.
With thin material, the mitres can be cut using a handsaw although using a power circular saw with a guide or jig will produce a more accurate cut.
Stronger than the simple mitre, the half mitre still has the advantage of concealing the end grain of one piece of timber.
Place one piece of timber in a mitre box (or guide) and cut the mitre angle (45 degrees) to half the timber thickness. Place the timber vertically in a vice and tenon saw the mitre angle to remove the waste.
Place the other piece of timber in the mitre box (or guide) and cut the end off at 45 degrees. Measure the width of the timber from the peak of the mitre and mark squarely across, cut down this line to half the timber thickness. Place the timber vertically in a vice and remove the waste using a tenon saw. For a perfect joint, care needs to be taken.
The first of the halving joints where half the thickness of the timber is removed from each piece so that they interlock.
Carefully mark out the end of each piece of timber including the depth. Make all cuts using a tenon saw. Secure the timber to a bench when cutting across the timber and place it in a vice when cutting from the end.
Mainly used where an intermediate timber meets an edge timber. It is formed by fitting the end of one piece of wood into the recess in the other, with half the thickness removed from the area shared by the two pieces.
Mark out the width and depth of the recess in the edge timber and cut squarely to the depth line with a tenon saw. Use a chisel or pre-set router to remove the surplus material from between the cuts. The depth should be cut twice, the first time to remove the bulk of the material, the second time to carefully take it down to the correct level.
Mark and cut the other piece as if it were for a corner halving joint.
Similar to the T halving but used for intermediate framework. Half the thickness is removed from both pieces of timber where the cross. Mark out the width and depth of the recess in both pieces of timber and cut squarely to the depth line with a tenon saw. Use a chisel or pre-set router to remove the surplus material from between the cuts.
For use where a stronger joint is required than the simple T halving joint. The sides of each half of the joint are cut at an angle of about 30 degrees so that when the joint is assembled, the separate pieces are locked together.
Mark out the width and depth of the recess in the edge timber as for a T halving joint. Then mark the angle for the dove tail, this can be achieved by using an adjustable square or by measurement. Cut the angled sides of the dovetail down to the depth line with a tenon saw. Use a chisel or pre-set router to remove the surplus material from between the cuts.
Mark and cut the other piece as if it were for a corner halving joint. Then mark each side of the projecting piece with the same dove tail angle down to the shoulder line. With the timber secured in a vice, carefully cut the angle down each side to the shoulder line, reposition the timber and cut the sides along the shoulder line to remove the waste material.
- Lay out the timber before you start marking out - you may need to reposition the timber to avoid a knot that may coincide with a joint.
- Decide upon the 'presentation face' of each piece of timber - it may not matter which face this is but you need to make all depth measurements from the same side of the finished frame.
- Mark out all the joints before you start any sawing.
- Especially with half joints, mark the 'waste' material with a cross after you have marked it out - it's very easy to pick up a piece of marked timber and make the cut in the wrong place.
- Always cut on the waste side of the marked line.
- Measure twice (or thrice) and then cut accurately once.
- Use glasspaper to smooth each joint and remove any splinters.
- Assemble the joints using a good quality wood adhesive; apply it to all mating faces. Wipe away any surplus adhesive before it dries.
- Where the thickness of the timber allows, secure each joint with a nail or two, drive them in at an angle so they lock the timbers together.
- Clamp or apply pressure to each joint until the adhesive has dried, in humid conditions allow additional time.