Demagnetizer that mounts in a drill

Did you accidentally magnetize your nice calipers while measuring a magnet? Unintentionally magnetize some other tool and now it collects iron filings? This will help you fix them. Works well on hand tools like screwdrivers, pliers, calipers, scissors, etc.

Requires two additional pieces of hardware:

• 1/4 inch hex socket adapter, like this or this. You could probably modify the design to have a printed piece that goes into the chuck, but I wanted something a bit stronger since the layer lines are weakest in the direction that's easiest to print.
• 3/8 x 3/8 inch axially magnetized neodymium magnet (preferably N52), like this

To use:

1. Print the parts. Since these are functional tools, I recommend using a stronger material like PETG or an engineering plastic.
2. Insert the magnet into the larger hole.
3. Snap the cap over it.
4. Push the hex socket adapter into the smaller hole.
5. Insert the hex adapter into a drill and tighten the chuck.
6. Hold the curved side (not the flat end) of the demagnetizer close to the item to be demagnetized.
7. Turn on the drill. I've had best results with a reasonably (but not recklessly) high speed.
8. Gradually pull the drill away from the item to be demagnetized while the drill is running.
9. Repeat as needed, moving to different areas of the part if it is large.

Why this works:

• When you hold a strong magnet next to a ferrous material, it orients the magnetic field of the material to align with the magnet's field. This is how things get magnetized. The strength of the field drops off with distance from the magnet.
• When you slowly pull the demagnetizer away from an object while the drill is running, the polarity of the magnetic field that the item experiences changes rapidly.
• While it doesn't quite work this way, you can think of it like the demagnetizer magnetizing layers of the object in alternating directions as it spins (and thus its polarity changes) as you pull it away from the item.
• This results in the item's magnetic field being randomly “scrambled” with different polarities. When this happens, different parts of the item's magnetic field cancel each other out, resulting in a net zero magnetic field.

Disclaimer: power tools can be dangerous, and so can strong magnets. Be careful using this tool. You could injure people (including yourself) or damage items using it, including by catching your hair or clothing or by flinging metal objects. Use at your own risk.

Here's the model in OnShape in case you want to modify it.