Has mortise and tenon joinery really been 'ruined'? Let's talk about 12 mortise and tenon structures suitable for CNC machining

　　Recently, I saw a post titled "Traditional mortise and tenon craftsmanship is being ruined" on a woodworking enthusiast website forum. The post mentioned that a red wood manufacturer's attempt to showcase mortise and tenon techniques ended up "ruining" the traditional craftsmanship, sparking heated discussions among woodworking enthusiasts.

　　Two woodworking enthusiasts believe that antique furniture for collection should strictly adhere to ancient methods, but for mass-produced household furniture, "mortise and tenon" should be cleverly used, regardless of orthodoxy. I agree with the two enthusiasts. The "mortise and tenon" structure is a type of concave-convex connection. Our ancestors explored and experimented in this area, leaving behind unparalleled wooden buildings and furniture that embody the spirit of Chinese craftsmanship.

　　With technological advancements, production tools have become increasingly sophisticated. The styles of "mortise and tenon" structures should also change with the evolution of production tools. Below, I will share some knowledge about "mortise and tenon" culture and woodworking CNC, and discuss 12 "mortise and tenon" structures suitable for CNC machining.

　　"Mortise and tenon" is not a Chinese "patent"

　　"Mortise and tenon" is not a Chinese "patent." "Mortise and tenon" is an abbreviation for tenon and mortise, a method of joining two or more components in traditional woodworking. The protruding part of the component is called the tenon, and the recessed part is called the mortise.

　　"Mortise and tenon" is an ingenious way to connect wooden structures. We have always had a misconception that "mortise and tenon" is a Chinese "patent," but this is not true. Many different civilizations around the world have spontaneously developed their own unique "mortise and tenon" culture. Ancient "mortise and tenon structures" appeared as early as 7000 years ago. The first example is the "bone" joint, discovered in a well near Leipzig—the world's oldest complete wooden structure, made of old oak planks and beams assembled using mortise and tenon joints. The second example is the "Khufu ship," sealed in a pit in the Giza pyramid complex around 2500 BC. The ship, 43.6 meters long and 5.9 meters wide, has planks connected using mortise and tenon structures, making it one of the oldest, largest, and best-preserved ships in the world.

　　In 1973, at the Hemudu site of the Neolithic culture, dating back six to seven thousand years, Chinese archaeologists discovered a large number of wooden components with "mortise and tenon" structures, mainly used in the construction of Hemudu stilt houses. The "mortise and tenon" structure is the main structural method for ancient Chinese buildings, furniture, and other wooden tools. The most famous example of architecture is the Yingxian Wooden Pagoda, which uses an all-wooden "mortise and tenon" structure. The entire pagoda is built without nails or rivets, and has withstood numerous strong earthquakes unscathed, a miracle in architectural history. Ming and Qing furniture took the "mortise and tenon" structure to the extreme. This exquisitely ingenious structure makes red wood furniture sturdy and durable, highlighting the "five beauties" of classical red wood furniture: beauty of wood, beauty of shape, beauty of structure, beauty of carving, and beauty of decoration.

　　(Yingxian Wooden Pagoda)

　　(Yingxian Wooden Pagoda—A Wonder of the World)

　　The application of mortise and tenon structures in wooden buildings and furniture has many advantages, but also some problems and disadvantages: Firstly, some structures are irreversible, although they achieve a nailless design, they require glue (fish bladder glue in ancient times) during assembly and are difficult to repair and reassemble; secondly, red wood furniture using mortise and tenon structures is relatively heavy and not light; thirdly, manual craftsmanship is not suitable for modern mass production.

　　Modern Woodworking Processes

　　1. Woodworking CNC Machine Tools

　　Modern woodworking processes use CNC machine tools, which are automated machine tools equipped with program control systems. My studio uses a woodworking carving machine with a processing size of 2.44 * 1.22m, which can quickly cut materials and carve, but the problem is that it can only perform top and bottom processing, making it impossible to process complex "mortise and tenon" structures. I recently found a multi-sided processing CNC system on a foreign website called TenonCam woodworking manufacturing system, which consists of a special milling head and software, used to form nested mortises and tenons on a flat CNC milling machine. It can be used to produce one-time milling of cabinet, drawer, and toe-board parts without auxiliary operations or auxiliary machinery. One-time processing, no double processing or secondary processing.

　　The image above shows the TenonCam milling head, showing the process of cutting the tenon at the bottom. The software allows cutting the tenon at any position in the nest.

　　2. Some of the most common cutting methods performed on CNC machines

　　(Diagram showing outside line cutting)

　　Outside line cutting: The tool cuts along the outside line, which can cut circles or squares.

　　Inside line cutting: The tool cuts along the inside line. When cutting squares, the tool used on the CNC machine is round and rotates along the axis, meaning it is impossible to cut sharp inside corners. Instead, the tool must leave a semicircle on the inner edge matching its diameter. This is also a drawback of CNC machines in processing grooves, affecting the aesthetics of the furniture.

　　Chamfer cutting: Using a chamfer tool cuts to the required depth and extends along an open or closed line, leaving a beveled edge.

　　Round corner cutting: Using a round corner tool cuts to the required depth and extends along an open or closed line, leaving a rounded corner.

　　Drilling: Find the center and drill to the required depth at the required diameter.

　　Engraving: Use a smaller diameter tool to cut to a shallower depth along the set path.

　　12 Mortise and Tenon Structures Suitable for CNC Machining

　　Before using digital manufacturing tools, complex joints could only be made by experienced carpenters, taking a lot of time to complete. Now, highly complex connections can be built in minutes, from classic mortise and tenon joints to unusual V-shaped interlocking mortise and tenon structures. Below are 12 "mortise and tenon" structures suitable for CNC machining.

　　1. Beam mortise and tenon: Used to install beams into the vertical posts of table legs, the tenon is not visible from the side.

　　2. Hook tenon: Usually used to install beams into vertical posts, the tenon is visible from the side.

　　3. Concealed tenon: Used to join panels together at a 90-degree angle.

　　4. Lap joint: A simple joining solution for boards connecting at right angles.

　　5. Blind finger joint: Conceals the joining structure, reducing visible end grain.

　　6. Finger joint: A simple and strong mortise and tenon joint.

　　7. Clamp lock joint: Can be used to lock parts together for regular assembly and disassembly.

　　(Clamp lock structure demonstration diagram)

　　8. Wedge joint: A mortise and tenon joint that creates tension when the wedge is squeezed through the hole.

　　9. T-shaped clamp lock joint: A mortise and tenon joint that locks parts together.

　　10. V-shaped clamp lock joint: A hidden locking joint structure.

　　11. Keyhole lock joint: An interesting mortise and tenon joint that can be used as a coat hook after locking.

　　12. Hinge joint: A simple CNC hinge solution where a square tenon rotates within a circular recess.

　　The above 12 types of mortise and tenon structures are suitable for CNC machining, providing solutions for modern furniture modular design. They enable nailless and glueless installation, especially allowing for repeatable installation. However, they do have certain requirements for wood material and thickness; birch plywood or other plywood is generally used, with thicknesses of 12mm and 18mm being preferable.