Double ball joint

A double ball joint is a very simple mechanical assembly. Threaded balls are sandwiched between two plates and the pressure is adjusted with a screw. Rods connect the balls which can be directed and more or less braked firmly. They are usually made of steel and are widely used in the animation industry.

The Phluux version

Photo of the DBj-20 and DBJ-16 joints.
The DBJ-20 and DBJ-16 joints

Since I like to reinvent the wheel, I've been looking for ways to make them without using steel. A nice solution - which requires printing a 3D part - is to create a cup that serves as an intermediary between the plates and the balls. This cup increases the contact surface compared to a simple chamfer and the flexibility of PLA* allows it to absorb irregularities. This solution leaves more choice in the materials used for the balls or the plates.

A diagram illustrating the interest of a cup between the ball and the plates of a joint
The interest of using a cup in a joint

Wood is the material I most like to work with. I chose it for plates as it is easy to recover small quantities of wood in the workshop scrap. The latter must be rigid enough to resist the clamping force.

As threaded balls, I found some drawer knobs at my favorite hardware store. The result is a lightweight joint that is perfect for orienting small projectors.

This articulation is the one I use in the "Nomad" projector and has been approved by actors in various situations where it is necessary to quickly reorient a projector. Of course, it is less suitable for an installation that requires a strong or permanent lock.

Photo of the "Nomad" projector using the dbj-20 joint
The "Nomad" projector with the DBJ-20 joint

I've been using quality filleted knobs because on stage the actors deserved this kind of comfort but in other situations, a simple nut is enough and costs much less. That's the beauty of DIY: you can always adapt a design to your needs.

Take care of your joints

A technical drawing showing the different parts of the "Double Ball Joint".
Overview of the pdf double_ball_joint_001

I promised in previous posts that I would document my work and share my designs. This model lends itself well to the exercise because it is very simple to draw and the ** Openscad file with which you can set up new cups is very short.

A screenshot of the Openscad file in which a cup is modeled. On the left we see a part of the script and on the right the rendering of the dbj-20.
The Openscad script for parametric bowls.

Content of the file:

  • A PDF with measurements and material references
  • STLs of both cup sizes (16 and 20 mm).
  • Openscad script to set up new ones
  • DXF of the plates for CNC cutting.
  • SVG of the plates to export your own DXF.

The whole is made available under a CC-BY-SA license.

* PLA (polylactic acid) is the most commonly used material for 3D printing

** Openscad is the software I use to model parts for 3D printing.