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Thread: Demagnetizers

  1. #1
    Supporting Member mklotz's Avatar
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    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 If you do this, be sure to release the trigger as soon as the tool is fully withdrawn to prevent overheating the gun transformer.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.

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    Regards, Marv

    Home Shop Freeware

  2. The Following 11 Users Say Thank You to mklotz For This Useful Post:

    Beserkleyboy (Jul 13, 2018), bukwessul (Mar 18, 2018), Carnel (Aug 20, 2020), dbeierl (Mar 18, 2018), Inner (Jul 13, 2018), Jon (Mar 17, 2018), Paul Jones (Mar 20, 2018), rlm98253 (Mar 18, 2018), Saltfever (Aug 20, 2020), Seedtick (Mar 18, 2018), volodar (Mar 21, 2018)

  3. #2
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    Marv - These are great new ideas for a DIY demagnetizer. I like the idea of dedicating an old soldering gun to the task. These things frequently show up cheap at garage sales and flea markets. Leave it plugged in and hanging in it's own "holster" ready to grab and "shoot".
    There's still the old method of using a stator winding from a shaded pole fan motor. These devices are designed to be impedance protected with a rotor in place and not turning. But that protection works well enough with the rotor removed to be convenient to use for a demagnetizer. Simply disassembled from a table fan the wiring is exposed and the connection is fragile. So if I were starting a project I'd build a simple protective housing for it with a momentary on-off switch and pilot light and attach it permanently or with a screw clamp to a work bench in some out of the way corner like hanging from the end of a shelf where I could push the button with my left hand and withdraw the tool with my right.

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    Paul Jones (Mar 20, 2018)

  5. #3

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    Whenever U need to de-magnetize a screwdriver just wrap a piece of autumotive type electrical wire several wraps connected to a small battery then pull the tool out of the wire and wah-lah no more magnet. Just reverse the procedure without pulling it out .... only takes a second or two, stronger the battery (to a point) the stronger the magnet.

  6. #4
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    JJ -- This a great reminder of how simple the basic process is. Like experiment with all that wire and wall warts collecting dust in my shop. I have a good DVM so the experiments should be fun to put actual numbers on. I can't help but think this would be great stuff for a high school science teacher to mess with.

  7. #5
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    Thanks mklotz! We've added your Demagnetizer to our Miscellaneous category,
    as well as to your builder page: mklotz's Homemade Tools. Your receipt:

  8. #6
    Supporting Member Paul Jones's Avatar
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    Thank you for your advice for using Weller soldering gun as a de-magnetizing tool.

    I have my old Weller dual wattage soldering gun (100W and 140W) that my parents surprise me with during Christmas 1963. The reason I still know the date is because I filled out the Weller warranty card but left it in the original plastic carrying case and never mailed it in. The warranty wasn't necessary. I have used this soldering gun a lot since then and other than replacing the tips, the Weller product has worked very well during almost 55 years. I think the products were better built back then and we would expect our tools to keep going for years if we took care of them.

    Paul Jones
    Last edited by Paul Jones; Jul 15, 2018 at 07:19 AM.

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    Beserkleyboy (Jul 13, 2018), PJs (Mar 20, 2018), volodar (Mar 21, 2018)

  10. #7
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    Thanks for another use for my faithful Weller soldering gun. Never knew that.

  11. #8
    Supporting Member Beserkleyboy's Avatar
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    Paul, too true re quality manufacture. I got my Weller (exactly like Marv's) in 1965 when I started my DIY electrical learning. I got a Lafayette Radio Electronics 'kit" shortwave receiver (4 or 5 tubes..), used the Weller and a pencil iron and Voila! We lived on top of a hill in the neighbourhood and dad helped me run 120 and 60 ft copper wire at 90 angle. I got international stations all over the world. Even sent a request QSL to Radio Havana Cuba.....and promplty got their newsprint propaganda paper (Granma) monthly, for YEARS! This was about the time SSB came about, so back to Lafyette for a VFO, and I could listen in. I never got my licence, sadly. But the Weller was still going strong in 87 when I emigrated to AUS...Cheers
    Jim in Sunny South Coast NSW Australia

  12. #9
    Supporting Member Bony's Avatar
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    Thanks Marv. How would an ac spot welder or an older type transformer stick welder do as a demagnetizer for lerger items, like spanners? I appreciate it's not wise to let either or any welder effectively short circuit for more than a few seconds. I presume the effect would be the same?

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    olderdan (Jul 14, 2018)

  14. #10
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    Quote Originally Posted by Bony View Post
    Thanks Marv. How would an ac spot welder or an older type transformer stick welder do as a demagnetizer for lerger items, like spanners? I appreciate it's not wise to let either or any welder effectively short circuit for more than a few seconds. I presume the effect would be the same?
    You may like to have a look here

    This will easily demag spanners and larger items.

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    PJs (Jul 15, 2018)

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