Three-Legged Vertex Joint

On this page, you'll find the tutorial and process for creating a 3d printed joint to connect 3 pieces of wood at a vertex.

I built this joint with 3 main lines, each of which would hold 1 piece of wood, and 1 short line to close the pieces with a flat base.

For this particular design, the prongs are separated by 120 degrees, with the ends raised 40 degrees. This was to maintain radial symmetry and create a joint that could be 3d-printed without support, as the particular 3d-printer I would use requires support for overhangs steeper than 45 degrees. I set the initial length of these construction lines to 100mm, which was pretty arbitrary.

Next, I used the pipe function to create a cylinder around each of the prong construction lines separately, with 12mm for the radius of each base. This was designed for 10mm radius pieces of wood. Then, I added a short line at the base to close the gap at the bottom with a flat piece, and used pipe again, also with 12mm for the radius.

Next, I made a duplicate of the 3 pronged construction lines to represent the pieces of wood. I scaled them up with 0 as a base to make them longer than the joint structure, then drew a circle with a 20mm radius circle to trim the inside of the lines.

I applied the pipe function to each of these lines, using 10.1mm for each radius, to simulate the 10mm radius pieces of wood plus a .2mm total gap.

Then, I used the boolean difference function to subtract the wood pipes from the structure. Because of the way the construction lines were placed, this cuts out the place the pieces of wood can be slid in, with a clean edge to rest against at the end.

Finally, I used the boolean union function to connect the remaining pieces.

I created a sphere with radius 75mm, and trimmed the outside pieces to make the joint smaller without messing up any proportions or angles.

I exported the closed polysurface as an STL object and exported it to the 3d-printer. I printed the joint without support, and with relatively quick print settings for the prototype you see above. The shape held fairly well, except for a bit of drooping in the top parts of the joint legs. This could perhaps be solved with slower and more precise print settings, or by using support which would need to be removed afterward.

The file used has been attached.