Good Design: Japanese Wood Joinery
As a manufacturing engineer, I love learning about how things are made. A process I have been fascinated with for a long time is Japanese wood joinery, also called sashimono [1]. This incredible example of design is found in furniture, artistic pieces, and even buildings, all of which are exclusively made of wood and completely devoid of fasteners. The masters of this technique produce work that can last for decades, standing as a testament to the effectiveness, quality, and durability of sashimono.
A classic example of a sashimono cabinet piece | Traditional Crafts of Tokyo
History of Sashimono
Simply defined as “the tradition of making furniture without the use of nails or screws of any kind [2],” this technique is evidence of ancient ingenuity. The earliest origins of sashimono date back to the Heian period of Japanese history, between 794 and 1185. It rose to further popularity, particularly with fabrication specialists making ceremonial tea chests, during the Muromachi era, between 1382 and 1573 [3]. In Japan, everything from kitchen utensils to Buddhist shrines have been constructed through sashimono techniques. Today, unfortunately, demand for sashimono furniture has decreased. In order to keep his craft alive, Mogami Yutuka, a sashimono craftsmen in Taito City, said that he challenges himself to “create a wide variety of things [for] the modern lifestyle that can be made with sashimono technique [4].”
Mogami Yukuta in his workshop, showing off a piece he made, in the background are more works of his | Taito City Craftsmen
There is a reverence surrounding this craft, with specific, almost sacred, materials and tools reserved for its manufacture. Masters can spend a lifetime honing their art, will produce marvelous pieces, all while still being humble and wise. One such master, George Nakashima, wrote in his book, The Soul of a Tree: A Woodworker’s Reflections, “We work with this material [speaking of a particular type of wood] as an instrument, to fashion useful objects, possibly if so willed a thing of beauty. In any case, a joining of the rhythms of nature to fulfill its own destiny and ours [5].” Through the process of sashimono, masters will play the wooden instrument and create a chair or cabinet that can only be described as melodic. As with the great composers of Baroque classical music, we can count sashimono masters among the greatest artists of the human race.
Design Lessons from Sashimono
Good Design is everywhere around us. The greats of every field of design, art, and engineering leave us with vast troves of knowledge and experience. Sashimono masters do no less in their work. From them, I believe that there are two design lessons we can learn and strive to implement in our own practice. Because of my own experience, I have chosen to classify these lessons within fields of Design for X (DfX, see note).
Design for Manufacturing and Assembly (DFMA)
Designing for Manufacturing and Assembly causes designers to think about what processes go into making their projects. They need to think about the tools, technicians, and space available to them and their clients. Though it is complex and intricate, Sashimono is an example of a 100% successful implementation of DFMA. Sashimono masters utilize only the tools they have on hand – a mix of planers, chisels, and saws – to manually make each cut. Each prospective design, therefore, needs to have enough room for the tools and hands of the craftsmen.
After the cuts are made, the parts are assembled, all without the aid of nails and screws. Angles, mortises, tenons, and tight tolerances all work together to create incredibly strong joints that are often invisible from the outside. Though externally hidden, the joints and connections are works of art from the inside. There are even techniques to make hinges out of two pieces of wood, while still making the seam and joinery invisible to the outside. Sashimono is defined by the capabilities of the craftsman. Whatever they are capable of making and assembling is the resulting complexity of their designs.
Images of different kinds of sashimono joints, including an invisible hinge on the far right, a cantilever compression joint in the middle, two different types of dovetail joints in the bottom left, and a series of 90° connector methods in the top left. | Mohamed Helali on LinkedIn and The Guardian
Design for Reliability (DfR)
Considering design for reliability creates products that will endure for a long time. Key features of these designs are high-quality materials, multiple mechanical safeties, and proven track records. Sashimono is traditionally done with Japanese wood species with pronounced grains, high strength-to-weight ratios, and resistance to harsh environments. The quality of the wood is enhanced in the way that it is cut, treated, and finished, making the wood heat and moisture-resistant, as well as enhancing the natural beauty of the wood grain.
The complex joint geometries are the most impressive feature of sashimono joinery. These joints are hand-carved and still fit together perfectly. The edges and faces all work together so that, when the joints are placed under certain stresses, they remain immovable. As you can see in the following video, the way parts are inserted together slowly eliminates degrees of freedom within the joint, until no degrees remain and the joint is fixed. This, coupled with the tight manufacturing tolerances, creates multiple redundancies, resulting in incredibly reliable connections.
The above video is an animated rendering of a sashimono joint, courtesy of The Joinery social media page, which has 105 different joint animations.
Reliable designs also need to be tested and proven. Sashimono joints have stood for decades, with most craftsmen expecting their constructions to last 100 years. Since this crafting technique has been around since the eighth century, it has very obviously passed every test thrown at it. When assembled, the tight tolerances used in sashimono joints produce strong enough forces that require a mallet to be released. Some sashimono pieces are even able to endure earthquakes.
This is Horyu-ji, the oldest standing wooden building in the world, which is constructed with a scaled-up version of sashimono, miyadaiku. The main structure of Horyu-ji is a modified post-and-lintel system that uses intricate brackets to transfer the weight of the ceiling down through the columns, into the base of the structure [2]. Some of the structures in the Horyu-ji complex have stood since the late seventh century, proving the durability of its construction. The track record of sashimono joinery, and its derivatives, leaves viewers in awe and provides reassurance that the design will be worth whatever the associated costs.
How to apply in our designs
What can you do to design as a Sashimono master craftsman? First, like the sashimono masters, you need to ensure that all of your pieces can be manufactured by your available processes. If you don’t have access to a laser cutter, you should plan to use different tools to fabricate your design, otherwise manufacturing it will be incredibly difficult. Second, your designs should be easy to assemble. Sashimono has zero fasteners, using only mechanical advantage to hold multiple pieces together. You can include some redundancies like bosses that stop nuts from travelling, overlapping inserts that prevent vibration on coverings, and fasteners in different directions to provide opposing forces. And third, you need to ensure reliability. Sashimono experts know what joints to employ to get the best outcome, allowing them to build pieces that can last decades and centuries. Learn from experts in your fields and the best practices they use to create successful products.
Conclusions
There is so much we can learn from Japanese wood joinery. I could include sections on sashimono aesthetics (how they hide the joints completely from sight), on tool usage (the plethora of tools that a master can amass is astounding), and on sashimono traditions (specific woods and techniques revered by the masters). As such, I encourage you, reader, to broaden your horizons and look into this beautiful blend of art, engineering, and design. Maybe you will pick up an incredible new skill and be able to add sashimono tools to your designer toolbox.
Note
DfX is a widely used definition that allows designers and engineers to focus on a specific aspect of their designs. The X can stand for cost, environment, manufacturability, assembly, testability, sustainability, quality, and more. To learn more about DfX principles, you can visit the following link: https://fractory.com/design-for-x-dfx/
Sources
[1] https://japanwoodcraftassociation.com/traditions/techniques/sashimono/.
[2] https://interestingengineering.com/culture/sashimono-the-subtle-art-of-japanese-wood-joinery
[3] https://kougeihin.jp/en/craft/0619/
[4] https://craft.city.taito.lg.jp/en/craftsmaker/2268/
[5] The Soul of a Tree: A Woodworkers Reflection, book by George Nakashima
To cite this article:
Cousins, Andrew. “Good Design: Japanese Wood Joinery.” The BYU Design Review, 24 Mar. 2025, https://www.designreview.byu.edu/collections/good-design-japanese-wood-joinery.
