In woodworking, wood assembly by traditional means without nails or screws yields a more natural, attractive and professional finish. The joining method is chosen according to available tools, knowledge, habits and project, although the same method may be used for various types of projects.
Popular among cabinetmakers for joining parts of equal thickness when making furniture. A mortise is a cut made to a stud (female part), whereas a tenon is a part that projects on the end of a rail (male part) and is inserted in the cut.
Mortise chisel (specially designed wood scissors, thicker than they are wide)
Shoulders are surfaces located on 1, 2, 3 or 4 sides of the tenon, to prevent the latter from pushing in beyond a certain depth, and to stabilize the joint while hiding the contours of the mortise.
To provide maximum hold, the tenon may completely pass through the stud, but the end of the tenon will then be apparent, which may be unattractive for some furniture. For an invisible joint, the mortise will not be drilled completely through the stud, so as to hide the end of the tenon (blind tenon).
If the parts to be joined are thick or large (e.g.: bed rail), it is possible to make a double tenon (two tenons on the same part), which is sturdier than a single big tenon.
It is also possible to make mortises in the two parts to be joined, with the latter connected by a tenon-shaped part. This variation, named “false tenon”, can also be considered as a variation of the dowel joint.
The sizing of a four-shoulder tenon must comply with certain rules to ensure joint strength and stability. Thus, the tenon’s thickness corresponds to one-third (1/3 = 0.33) of the thickness of the wooden part, its width corresponds to the part’s width less two portions of one-third of the thickness (2 x 1/3 = 0.66), and its length corresponds to three-quarters (3/4 = 0.75) of the part’s width. The measurements and cuts must be made with precision.
Example of rail A secure to stud B.
1.1 Measure the width of A and multiply by 0.75. The result will give you the required length of the tenon.
1.2 Using a square, carry over this measurement to all the sides of A, while measuring from its end.
1.3 Trace four lines on the end of A, each line being parallel to one of the end’s four rims. The distance from a line to its rim is equal to one-third of A’s thickness. The rectangle visible at the centre will be the tenon.
1.4 Extend each line on the rail’s adjacent sides, up to the line traced in point 1.
2.1 Indicate with precision, on stud B, the location where A will be secured, so as to have a “representation” of A on B.
2.2 Report lines and measurements from rail A to stud B. The rectangle at the centre represents the cut (the mortise).
2.3 Secure the stud in a vice (between two pieces of wood, to protect the stud).
2.4 Using the mortise chisel, drill the mortise to a depth corresponding to the length of the tenon plus 1/16". The tenon must not lean on the end of the mortise.
2.5 Check the depth regularly by inserting a measuring tape.
2.6 You can also use a mortiser to make the mortise, or pre-shape it with a drill press, then use the mortise chisel to finalize the shape of the mortise.
3.1 Secure the rail in a vice (between two pieces of wood), with the head facing upward.
3.2 Using the back saw, cut along the lines up to the line indicating the tenon’s length. Don’t cut on the lines themselves but on the outside, i.e., cut in the wood parts to be rejected.
3.3 Remove the rail from the vice and place it flat.
3.4 Saw along the line indicating the tenon’s depth, on all sides, while being careful not to saw the tenon.
4.1 Insert the tenon in the mortise to check the adjustment; you should be able to insert it with a slight push, but without having to hit it. Adjust the tenon as necessary, by sanding it.
4.2 Remove the tenon, put wood glue in the mortise.
4.3 Insert the tenon again and allow time for the glue to dry.
4.4 If, for some reason, the tenon is too narrow and thus not secured tightly enough in the mortise, plane a piece of wood to make a chip, and insert the latter simultaneously with the tenon.