modified: Friday 1 May 2020
Project: Tool demagnetiser
This thing works absolutely brilliantly:
The box provides a very strong, oscillating magnetic field between the two green zip ties when you hold the button down. You demagnetise your tools by slowly removing them from the oscillating magnetic field.
Make sure to demagnetise your whole tool, not just the tips! Many tools (such as side-cutters) have steel inside the handles that retains magnetism.
Inside the box is a re-arranged transformer, a fuse and a capacitor to reduce arcing on the switch:
Normal steel transformers (as you find them in old-fashioned plugpacks) are designed to keep as much magnetic field inside them as possible. To make this device I intentionally "cut" the iron core so that the strong field would exit it on one side. This is relatively easy to do -- you just split the steel core into its E and I sections, then throw away all of the I-sections and re-assemble. Example guide.
The switch is a "22mm panel button" from eBay. They're mains rated and otherwise really nice apart from their large size. I printed and installed my own logo for the button.
I found a guide on the web suggesting that spinning some alternating magnets in a drill could provide an oscillating magnetic field good enough for demagnetising tools. I couldn't get this to work, I suspect my magnets were not strong (large) enough.