Mechanically Switchable Magnet ~ 2021

One common task in a machine shop is indicating parts or equipment to be aligned with the machine's working axis. While the indicator is the important tool, affixing the indicator in a rigid, yet accessible way can be a challenge.

With that said, a saving grace is that most machines have readily available cast iron surfaces. Cast iron is ferrous, allowing a strong attachment of permanent magnets.

Permanent magnets, sized properly, satisfy the initial requirement of rigid attachment, but do not satisfy the accessibility factor I wanted. My design incorporates two permanent magnets housed in an enclosure where one magnet is rigidly held, and the other is able to be rotated. By joining the magnetic field of these magnets with two steel plates, the magnetic flux can be directed to a desired region — the base of the mount.

When the magnets align their poles — north with north and south with south on the same steel plates — the magnetic flux wants to find a path to complete the flux external to the base. This directed flux will result in a strong attachment force to any ferrous metal.

The key part to this is that when one magnet stays stationary and the other is rotated 180 degrees, the flux now wants to travel within the steel plates from one magnet's north to the other magnet's south. This purposeful redirection of the flux means that the base, which was previously strongly magnetic, has minimal attraction to ferrous objects.

To develop this design in a form factor that works for my equipment, I began with FDM 3D printed prototypes to identify the proper spacing of the magnets and steel plates to achieve a reasonable force in the constrained size. Once I was content with the performance of the 3D printed prototypes, I made manufacturing drawings to tune the prototype into a finished part made from a combination of 1018 steel and 6061 aluminum.