Simple software creates complex wooden joints

Carpentry is a practice as ancient as humanity itself. Equal parts art and engineering, it has figuratively and literally shaped the world around us. Yet despite its ubiquity, carpentry is a difficult and time-consuming skill, leading to relatively high prices for hand-crafted wooden items like furniture. For this reason, much wooden furniture around us is often, at least to some degree, made by machines. Some machines can be highly automated and programmed with designs created on computers by human designers. This in itself can be a very technical and creative challenge, out of reach to many, until now.

Researchers from the Department of Creative Informatics at the University of Tokyo have created a 3D design application to create structural wooden components quickly, easily and efficiently. They call it Tsugite, the Japanese word for joinery, and through a simple 3D interface, users with little or no prior experience in either woodworking or 3D design can create designs for functional wooden structures in minutes. These designs can then instruct milling machines to carve the structural components, which users can then piece together without the need for additional tools or adhesives, following on-screen instructions.

"Our intention was to make the art of joinery available to people without specific experience. When we tested the interface in a user study, people new to 3D modeling not only designed some complex structures, but also enjoyed doing so," said researcher Maria Larsson. "Tsugite is simple to use as it guides users through the process one step at a time, starting with a gallery of existing designs that can then be modified for different purposes. But more advanced users can jump straight to a manual editing mode for more freeform creativity."

Tsugite gives users a detailed view of wooden joints represented by what are known as voxels, essentially 3D pixels, in this case small cubes. These voxels can be moved around at one end of a component to be joined; this automatically adjusts the voxels at the end of the corresponding component such that they are guaranteed to fit together tightly without the need for nails or even glue. Two or more components can be joined and the software algorithm will adjust all accordingly. Different colors inform the user about properties of the joints such as how easily they will slide together, or problems such as potential weaknesses.

Something that makes Tsugite unique is that it will factor the fabrication process directly into the designs. This means that milling machines, which have physical limitations such as their degrees of freedom, tool size and so on, are only given designs they are able to create. Something that has plagued users of 3D printers, which share a common ancestry with milling machines, is that software for 3D printers cannot always be sure how the machine itself will behave which can lead to failed prints.

"There is some great research in the field of computer graphics on how to model a wide variety of joint geometries. But that approach often lacks the practical considerations of manufacturing and material properties," said Larsson. "Conversely, research in the fields of structural engineering and architecture may be very thorough in this regard, but they might only be concerned with a few kinds of joints. We saw the potential to combine the strengths of these approaches to create Tsugite. It can explore a large variety of joints and yet keeps them within realistic physical limits."

Another advantage of incorporating fabrication limitations into the design process is that Tsugite's underlying algorithms have an easier time navigating all the different possibilities they could present to users, as those that are physically impossible are simply not given as options. The researchers hope through further refinements and advancements that Tsugite can be scaled up to design not just furniture and small structures, but also entire buildings.

"According to the U.N., the building and construction industry is responsible for almost 40% of worldwide carbon dioxide emissions. Wood is perhaps the only natural and renewable building material that we have, and efficient joinery can add further sustainability benefits," said Larsson. "When connecting timbers with joinery, as opposed to metal fixings, for example, it reduces mixing materials. This is good for sorting and recycling. Also, unglued joints can be taken apart without destroying building components. This opens up the possibility for buildings to be disassembled and reassembled elsewhere. Or for defective parts to be replaced. This flexibility of reuse and repair adds sustainability benefits to wood."

This research is supported by JST ACT-I grant number JPMJPR17UT, JSPS KAKENHI grant number 17H00752, and JST CREST grant number JPMJCR17A1, Japan.