Mortise and tenon joints are commonly used in woodworking to connect one piece of wood to another, usually at a 90 degree angle. The first piece of wood has a tenon which fits into the second pieces mortise. A tenon is a square extension off of the first piece of wood that is usually smaller then the rest of the piece of wood.

The mortise in the second piece of wood is a square notch or hole cut into the wood that the tenon fits into to form a secure joint which may be wedged or glued in place. In the simplest terms, a mortise and tenon joint is a square peg in a square hole.

Where to Use

Mortise and tenon joints are commonly used to make mirrors, bed frames, tables, doors, chairs, bookshelves and other furniture. They are usually used anywhere two pieces are joined together at a 90 degree angle.

In order to understand mortise and tenon joints better, you should understand more about the parts. The mortise is the square peg that fits into the tenon or the hole. Usually the mortise is on parts of furniture that are vertical such as table legs or bed posts. The tenon is normally a horizontal piece such as a rail or a shelf would be.

Tools Needed

• Hammer
• Chisel
• Router
• Drill
• Set of drill bits
• Router jig
• Lumber
• Glue

Making Mortise and Tenon Joints

Mortise and tenon joints can be made in many different sizes and slightly varying styles. For instance, you may choose to use a twin tenon on some wider joints. To make a normal(single) mortise and tenon joint, you want to make both the mortise and the tenon the exact same dimensions.

Some people make the mistake of undercutting to allow for a margin of error. The truth is there is not much room for error when making these types of joints, so take your time and do it right the first time. Messing one up can cause you to have to start over with a new piece of lumber.

Many craftsmen prefer to make their mortise and tenon joints entirely by hand. You may choose to use this method or you may decide to enlist the use of a drill and/or a router to assist you in making nice straight cuts.

When making mortise and tenon joints with lumber of equal thickness, be sure that your tenon is equal to the combined side wall thickness of the mortise. Then you want to be certain that your tenon is centered. The shoulders should be of equal size and everything should square up nicely.

Be sure to measure everything very carefully and cut with extreme care trying not to cut over any lines. Mark out all of your cuts in detail before you begin with the chisel.

A drill and/or router may be used to remove some of the wood, but it is sometimes necessary to do the intricate parts solely by hand with lots of care in order to get a perfect fitted joint. When the situation permits, a plunge router and router jig may be used to smooth and square the inside of your mortise. Here are some simple steps to making a mortise and tenon joint correctly:

1. Mark out all of your joint cuts for both the mortise and tenon.

2. Use the proper size drill bit to remove the majority of waste.

3. Use a plunge router and router jig on your mortise to square the surfaces to the work piece. Make sure all your walls are parallel.

4. Use your chisel to make all of your corners true and square.

Follow these instructions and remember: Practice makes perfect. As with many wood working techniques, you may not get it perfect on your first try, so practice on some wood scraps until you are confident in your ability before you go on to create your first piece of furniture with mortise and tenon joints.

Also there are different methods used to hold them together. You may use a glue or a wedge to hold your joints together. There are mortise and tenon joints where the mortise goes entirely through the piece of wood and there are ones that are hidden. Hidden joints have a mortise that generally only goes about half way through the wood.

Practice making some simple joints and get the technique down before going on to more complicated ones such as the twin tenon or joints on irregular pieces of lumber. This should be enough information to get you started.