Introduction: Magnetic Hinge for Anatomical Models - TfCD

This small project shows the steps that I took to investigate the use of magnetic hinges with 3D printing.

One of the inspirations of this project was the Customizable Magnetic Hinge Box by Walter. See: http://www.thingiverse.com/thing:59332.

The goal of this experiment is to experience the feel and touch of using magnets as a hinge. I have tried four different sizes of magnets. The video shows the most optimal magnet size and a video of application in a experimental anatomical model of the human hand.

This experiment is part of the course TfCD, ACD, TUDelft, 2015.

Materials used:

  • Magnets (see next step for types)
  • Superglue
  • 3D printer (Ultimaker 2, PLA white plastic)
  • Drill
  • Mechanical Pencil (to hold the magnets)
  • Sanding paper (200 grain)

Step 1: The Magnets

These are the types of magnet that I have tested:

  • Neodymium Magnet ø2 height 1 mm. Force ± 0,13 kg.
  • Neodymium Magnet ø3 height 1 mm. Force ± 0,21 kg.
  • Neodymium Magnet ø3 height 2 mm. Force ± 0,25 kg.
  • Neodymium Magnet ø3,5 height 3 mm. Force ± 0,3 kg.

Of each type I have used three magnets. I did not test setups with different types of magnets (eg 2 ø3,5 and 1 ø2) This is something for the future.

The photo shows one magnet held using a mechanical pencil. This is very helpful as the magnets are very small and get lost easily. Especially when using superglue, you do not want to handle the magnets with your fingers.

Step 2: The 3D Printed Parts

Each hinge is made of three parts: 2x Base 1x Rod. The base part is printed twice.

The attached zip file contains all the parts (SolidWorks and STL).

After printing, I drilled out the holes with a cordless drill to assure a perfect fit for the magnets.

The Base parts contain a rod and a hole to be easily aligned. I found that those holes needed drilling as well, the accuracy of the Ultimaker 2 wasn't sufficient.

Attachments

Step 3: Adding the Magnets

Using the mechanical pencil and some glue, I pushed the magnets in place. With some sanding paper I got rid of the excess glue. This is important to reduce friction in the finished part.

A very important notice! Beware of the orientation of the magnets! The orientation should be NSNS (Or SNSN) but not NSSN or SNNS. Double check before you glue it in, otherwise the hinge won't work ;)

Step 4: Assembly of the Hinge

Using the glue I assembled the two base parts. It is not necessary to insert the rod, as this can be snapped and taken out later.

When dried I attached the rod and tested the different types.

Conclusion

My own experience is that magnet ø3 height 2 mm gave the most satisfying result, it had the best balance between holding force and effort to take apart. This is very dependent of the application of the hinge, however. They all worked nicely, snapping in place and rotating around the axis. The smallest one was a bit weak, it takes only a small force to take apart. It is however very small. In the pictures of the finger bones model, I used the smallest magnets for the distal phalanx, creating a detachable hinge of only a couple of millimeters in width.

My personal observation

Using magnetic hinges is a great technology to create very small, flexible hinges. Especially using the 3D printing technology magnets can prove to be an easy technology to create hinges. Large forces on the hinge will simply result in the hinge falling apart. After that, the hinge can be snapped back together, without any resulting damage. Application in robotics that has an interface with humans could be interesting. The robot can simply fall apart if it exercises a too large force. A broken (but easily re-assembled) robot instead of a broken finger is always a preferred outcome.

Thanks for reading! :)