Tenon and mortise joint

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.

It is possible to insert the rail directly in the mortise (i.e., without giving the rail any particular shape), but usually the rail is sculpted to give it shoulders. The latter 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, to hide the end of the tenon (blind tenon).
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When
The tools
How
1. Determine the tenon's length
2. Trace the lines
3. Extend each line
4. Indicate the mortise's location
5. Make the mortise
6. Make the tenon
7. Check the adjustment
8. Assemble and adjust, if needed
9. Variations
10. To strengthen joints

When

Popular among cabinetmakers for joining parts of equal thickness when making furniture.

The tools

Vice, back saw, square, pencil, mortise chisel (specially designed wood scissors, thicker than they are wide) and mallet.

How

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 × 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.

In this example, rail A will be secured to stud B.

1. Determine the tenon's length

First measure the width of A and multiply by 0.75, which will give you the required length of the tenon. Using a square, carry over this measurement to all the sides of A, while measuring from its end.

2. Trace the lines

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.

3. Extend each line

Then extend each line on the rail’s adjacent sides, up to the line traced in point 1.
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