Da Vinci Bridge・6 long 3 short pure mechanical self-locking structure (3D printing no supports) supports up to 12 long 6 short (the more pressure, the more stable) short mortise and tenon Bailey Bridge Luban Bridge

The Bailey bridge, also known as Bailey bridge, is a type of modular steel truss bridge designed by British engineer Donald Bailey during World War II that can be quickly assembled. The main body of this bridge type is composed of pre-designed steel components, making it easy to transport and assemble on site

Bailey bridges were initially used for military river crossings and later expanded to disaster relief. They played an emergency transportation role in Taiwan's Typhoon Morakot disaster in 2009 and the damage to the Sunkoshi River bridge in Nepal in 2024. After three weeks of urgent repair, the Bailey bridge on Nepal's Arniko Highway resumed traffic in 2024. Authorities conducted vehicle load tests and recognized relevant personnel. Its structural principles are also used in popular science education, such as community activities where young people learn about bridge structures by building models with chopsticks

In the fields of engineering and mechanical structures, its official academic names are usually: self-locking bridge or tensegrity bridge

Why is it called this name

1. Bailey bridge: This is the most common name, derived from its unique mechanical principle. It is not fixed by cement or nails, but rather uses the squeezing force (multiplied force) generated by multiple layers of intersecting square rods to convert pressure into clamping force, becoming tighter with more pressure, thereby achieving self-locking
2. Da Vinci Bridge: Because this classic mechanical structure diagram first appeared in the manuscripts of Leonardo da Vinci, later generations often named it after him
3. Self-locking bridge: This name best describes its function. The entire structure has no connectors (such as screws or glue), relying entirely on the interlocking grooves of the parts themselves to lock

This model has been modified based on this. The cross-section of the long rods has been changed to square, while the cross-section of the short columns retains a circular design. Circular slot positions have been added to the long rods with mating clearances, fully considering the needs for symmetry, stability, and ease of assembly

Starting from 6x3 up to 12x6, a self-locking bridge structure can be built, as long as the number of long rods is twice the number of short columns

You can change the number of long rods and short columns in the model file as needed (the model contains 12 long rods and 6 short columns)

Because printing the rods vertically would greatly increase the number of print layers and time, we placed all long rods and short columns horizontally flat on the build plate. Actual tests showed no printing issues, and the cylindrical parts printed perfectly. To ensure print quality, a small amount of PVP glue can be sprayed on the contact points between the cylinders and the build plate to ensure model adhesion. No supports are needed throughout the printing process

For assembly, please refer to the image below and the GIF images, simply repeat the operations

Of course, although we have tried our best to modify the parameters to increase the model's strength, considering the material itself, it is recommended to start with one book and gradually experiment with increasing its load-bearing capacity (the load in the picture is approximately 350g+)

Using fewer parts can actually increase its strength and rigidity

If you want to increase material strength, you can also increase the sparse infill to 60% or even 100%

Happy printing