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How To De-magnetize Electronic Calipers

Discussion in 'QUESTIONS & ANSWERS (Get Help Fast Here!)' started by sanddan, Apr 12, 2015.

  1. sanddan

    sanddan Active User H-M Supporter-Premium

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    My Mitutoyo 6" digital calipers have become magnetized on the tips which is a pain when trying to measure parts. Is there a safe way to de-magnetize them? If so, what do I need to perform this job?

    Thanks
    Dan
     
  2. darkzero

    darkzero Global Moderator Staff Member H-M Supporter-Premium

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    I run my Mitutoyo digital calipers over a demagnetizer. I've seen talk where there are concerns about causing damage to it. Some recommend removing the battery. If you send calipers to Mitutoyo for repair, they automatically demagnetize them. I've never had a problem demagnetizing any of my calipers.
     
  3. higgite

    higgite General Manger - Proofreading Dept. Active Member

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    I've not tried this magnetizer/demagnetizer on calipers, but it works well on screwdrivers, Allen wrenches and such. I don't see why it wouldn't work on caliper blades. I think I got mine from Amazon.

    Tom
    images?q=tbn:ANd9GcTTnDeborYNFEZWJ_1UThamNh4XESjFgXDw0ni8526GRFqePjGOOw.jpg
     
  4. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    One method that I have used, if you have a soldering gun is to replace the standard tip with a piece of 10 awg. copper wire to make a loop of about 2" in diameter. Turn on the gun to the 140 watt position and pass the jaws of the calipers into and out of the loop. Do not release the trigger until you have removed the calipers from the vicinity of the loop. This should demagnetize them.

    The wire will heat up so act quickly and don't touch anything heat sensitive to the wire. I use 10 awg wire to make my own soldering tips rather than buying the pre-made tips.

    In theory, you should be able to make multiple loops of the same gauge wire since the magnetic flux is proportional to the number of turns times the current flowing and the resistance of the wire is proportional to the length of wire and therefore current will be inversely proportional to the number of turns so, for constant voltage, the flux is a constant.

    Another method involves an old CRT TV or monitor. They all had a degaussing circuit consisting of a coil of wire wrapped around the perimeter of the CRT which was energized when the set was turned on. One of those coils run with a Variac would enable you to degauss a larger item. Again, they were made for short term use so this is a get in/get out quickly kind of thing.

    Finally, I had an old cassette tape eraser that used a rotating permanent magnet.The rotation creates the changing magnetic field instead of the alternating current. To use, you start the magnet(s) rotating and slowly bring your tool in as close as possible and withdraw it slowly. Stop the rotation after the tool is removed from the vicinity. With some of the rare earth magnets available now, you could probably make a degausser by epoxying two magnets to a steel bar or plate that has an central axle you can mount in a lathe or mill. It would be best to put it magnets in a pocket or use other restraints to prevent them from being thrown out by centrifugal force and become unguided missiles. Based on the tape demagnetizer, you will not need high rpm. I would think that 200rpm would work.

    The principle behind all demagnetizers is that you have to use a spatially magnetic field strong enough to align the domains in opposition to the existing magnetism. By pulling the object out of the varying magnetic field, the domains are random ly aligned again and the object is demagnetized.
     
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  5. darkzero

    darkzero Global Moderator Staff Member H-M Supporter-Premium

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    I have a couple of those Wiha demagnetizers, the older dark green ones. They do work well on some screwdrivers, especially Wiha screwdrivers but that's about it. The generic copies suck.

    For larger tools & what I use for calipers, I use a cheap import demagnetizer from Enco (got it on sale for $40 + 20% off that). There's more expensive quality ones but this one hasn't failed me yet. It works very well, one wave across it & it's done. It has demagnetized everything I've needed to date.

    (You don't actually set parts on it to demagnetize, below was just for the pic when I took it)
    Img_0435.jpg
     
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  6. JimDawson

    JimDawson Global Moderator Staff Member Director

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    I have the same problem. I have been afraid to try it, I thought the scale was magnetic. I'll give it a try.
     
  7. David S

    David S Canada Active User H-M Supporter-Premium

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    Here is what I use. I made a number of turns on a form so that heating wouldn't be an issue. Works great.

    demagnitizer from old soldering gun.jpg

    David
     
  8. John Hasler

    John Hasler United States Active User H-M Supporter-Premium

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    Excellent! How many turns?
     
  9. JimDawson

    JimDawson Global Moderator Staff Member Director

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    I'm happy to report that my calipers are demagnetized and suffered no damage in the process.
     
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  10. David S

    David S Canada Active User H-M Supporter-Premium

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    ID of form in is 1.75" 6 turns of 16 awg solid.

    David
     
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  11. sanddan

    sanddan Active User H-M Supporter-Premium

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    Thanks DZ, knowing it won't kill my calipers is encouraging.
     
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  12. sanddan

    sanddan Active User H-M Supporter-Premium

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    Which process did you use? I like the soldering gun method but I don't have that version.
     
  13. sanddan

    sanddan Active User H-M Supporter-Premium

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    I saw this on Enco's web site this morning. I'll have to wait for a good sale and get one.
     
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  14. John Hasler

    John Hasler United States Active User H-M Supporter-Premium

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    Just made one. Works fine.
     
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  15. sanddan

    sanddan Active User H-M Supporter-Premium

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    Just as a follow up, I ordered the same one as darkzero and it worked great. I was a little startled the first time as it tends to suck the tool into the surface of the demagnetizer but not a problem now that I know it's coming. Thanks for all of the ideas.
     
  16. Tozguy

    Tozguy Active User H-M Supporter-Premium

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    Just a few questions if I may;

    David or John, can I make one of those with insulated wire or does the wire have to be bare?

    RJ, if I spin this in a 4 jaw would it work like you described?
    IMG_0165.JPG
    Those are four rectangular rare earth magnets held with super glue, strong little buggers.

    Anybody, can a digital calliper be demagnetized without scrambling the brains in it?
     
  17. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    It should work but you will magnetize your four jaw. I would mount the magnets on a shaft so the chuck isn't close ti the magnetic field.

    On the use of a soldering gun: A soldering gun is a transformer with a low voltage/high amperage secondary. The secondary coil is essentially a single turn. The magnetic field is proportional to the current x the number of turns in the demagnetizing coil but the resistance is proportional to the length of the coil which is proportional to the diameter of the coil x the number of turns and the current is inversely proportional to the resistance.
    The bottom line is that the magnetic field is essentially independent of the number of turns used for a given wire gauge and coil diameter. To increase the magnetic field, you have to reduce the coil diameter or use a smaller gauge (larger diameter) wire.

    One thing to remember in using a demagnetizer is that the demagnetized object must be removed slowly from the proximity to the changing magnetic field. The residual magnetism in the object is continuously reversed by the changing field but becomes weaker as it is moved away.
     
  18. David S

    David S Canada Active User H-M Supporter-Premium

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    I am using a transformer based soldering iron for my demagnetizer. To add to what RJ has said. Your explanation is correct IF the transformer voltage is constant. In my case the coil terminal voltage with one turn of #16 awg wire was 0.34 volts, with 6 turns the terminal voltage was 0.5 volts. So in this case the 6 turns provided more magnetic field than a single turn. Approximately 240 AT vs 140 AT.

    David
     
  19. Tozguy

    Tozguy Active User H-M Supporter-Premium

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    Turns out to be simple with a soldering gun. On the strength of what you kind folks have contributed here, I ran my calliper jaws slowly into the loop of a soldering gun tip at the high setting (140 watts). I just used the standard soldering tip because the opening was big enough to swallow a single jaw right down to the beam. Bingo, one pass and no more magnetism. So I did all my callipers and without burning myself.

    Although I'm a happy camper now it leaves me wondering how my calipers got magnetized to start with.
     

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