Educational Model of Cardan Universal Joint

My Educational Mechanical Examples Series

This model is one of my educational mechanical mechanism examples on 80mm x 80mm base plates.
You can find all models in the series in this collection => [Mechanical Mechanism Examples]

The present model

This is an educational model of the Cardan Universal Joint.

Brief Description

A universal joint is used to transmit rotational motion from one shaft to another when the shafts are not aligned in a straight line.

This educational model shows the most simple universal joint, Cardan joint, in which two intersecting shafts are connected by a cross-shaped component, often called a spider. With this structure, the rotation of one shaft is smoothly transmitted to the other at any crossing angle, as long as the angle is not too large.

However, as can be seen in the animation, in a Cardan universal joint, the output shaft does not rotate at a constant speed even if the input shaft does. Its rotational speed varies periodically depending on the input angle, and the effect becomes more pronounced as the joint angle increases.

Therefore, in applications where a constant rotational speed is required, double-Cardan joints or other constant-velocity (CV) joints are used instead.

Case

This model is compatible with the case included in my first set.

Printing

• Use the models named ???-printable.stl for printing.
  The models named ???-assembled.stl are provided just to show how they should be assembled.
   
• Use well-dried PETG to have better dimensional accuracy.
• Use 0.1 mm or 0.08 mm layer height to have smoother surfaces.
• Use slow printing speed for overhangs.
• Select “Random” seam position to have smoother rotation.
  Randomly distributed seam should be easily worn out after some wearing.Printing

Sanding and Filing

Sometimes, the gears suffer from the stringing effect and/or elephant foot effect, resulting in a too tight fit to the shafts (they are designed with a 0.15 mm radial clearance). 

If you see rough surface on the shafts due to stringing, sand off the roughness with a small piece of sand paper.

If you feel the gears do not rotate smoothly due to an elephant effect, widen the hole slightly by using a thin round bar file.

Without those issues, the parts should rotate very smoothly with minimal friction.

Assembly

No glue is needed, in theory. 

Just snap assemble the parts.

Mounting the two shafts on the bearings is sometimes a little tricky because the bearing might be printed fragile if your filament has absorbed moisture. So, be careful not to break them when pushing the shafts in.

If your print shows stringing, it is a sign of highly moisturized filament.

Other examples

You may also be interested in the models in my educational mechanical mechanism examples.

Find them in this collection:
https://www.printables.com/@osamutake_3341417/collections/2728214

Happy printing!

Updates

• 2025-11-06  (v94)
  • Reduced the play between the shaft and the bearing because I found too much play makes rotation not smooth. 
  • Made the bearing even more flexible to prevent it from breaking when inserting the shaft,
     
• 2025-10-29  (v89)
  • Made the bearing more flexible to prevent it from breaking when inserting the shaft.

Acknowledgement

I got into gears thanks to K.$uzuki's amazing articles and YouTube videos. Many of the mechanisms shown in this series came from the introductions on his website. He also makes excellent gear models himself. This series wouldn’t have existed without his inspiration.

I learned a lot about technical detail of designing gear tooth profiles from Haguruma-No-Hanashi website. I’m truly grateful for that.