It can be very annoying if small tools such as punches, Allen wrenches, scales, etc. become magnetized and begin to grow swarf "whiskers". A means of demagnetizing them is a necessary, I would volunteer essential, device to have in the shop.
There are companies that would have you believe that this POJ...
will do the job. While I have been able to use it to magnetize tools, I've yet to successfully demagnetize anything with it. Perhaps I don't know the magic invocation that must accompany its use; more likely the thing just doesn't work very well.
To really demagnetize, you need an alternating magnetic field. If derived from a residential electric supply, this will flip the atomic magnets in the steel of the tool back and forth at a frequency equal to that of the power supply. Slowly withdrawing the tool from this field will effectively scramble the direction of the atomic magnets and render the tool demagnetized.
Most of the senior members of the forum will recognize the venerable soldering gun...
Not everyone is aware that the soldering gun is also an effective demagnetizer. When the trigger is pulled a large current flows through the tip to heat it. A large current implies a large magnetic field surrounding it and that field is oscillating at 60 Hz; exactly what we need. Hold the tool firmly in the gap in the tip, pull the trigger and slowly remove the tool to an arm's length away from the gun. Test the tool with some swarf. If not demagnetized, repeat the process.
I mentioned holding the tool firmly. The large magnetic field will exert a force on the tool when the trigger is pulled. While having the tool touch the tip probably isn't too critical, having it short across the tip is to be avoided in order to prevent damage to the tool and the transformer in the gun. It's never been a particular problem for me but, if you're concerned, I suppose the tool could be wrapped in some insulating material before attempting demag.
If the tool is too large to fit through the gun tip opening, you can substitute a loop of heavy gauge copper wire for the tip and shape the wire into a form that will accommodate the tool. If you do this, be sure to release the trigger as soon as the tool is fully withdrawn to prevent overheating the gun transformer.
If you're old enough to remember reel-to-reel tape recorders you will probably recognize a bulk tape eraser...
They show up at electronic swap meets and sometimes antique stores. I don't Ebay so can't say but they're probably there too.
Their use is similar to the soldering gun. Hold the tool under the eraser, press the trigger, slowly withdraw the tool and then release the trigger. These are not meant for continuous use which could cause overheating and damage. Observe the duty cycle instructions that come with them.
If you would rather build your own demagnetizer, there are scores of DIY articles on the web. Simply Google something like "build demagnetizer" and start reading. Most of these designs involve cannibalizing the transformer or motor coil from some donor electrical device and rewiring it to serve as a demagnetizer.
If you're not comfortable with electrical DIY, it is possible to generate alternating magnetic fields mechanically. Take a wooden disk and glue a circle of neodymium magnets to it. Arrange the magnets so that adjacent poles alternate, e.g., a NSNSNS... configuration around the circle. If I were doing it I'd spot drill shallow flat-bottomed holes for the magnets to help with keeping them separated while the glue dries.
Mount the disk in your drill press or hand drill and spin it. Voila!, a rapidly varying magnetic field. Proceed as described above to demagnetize tools.
