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these black dots on magnets annoy my mind

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  • these black dots on magnets annoy my mind

    please, can someone explain to me what these dot do on pickup magnets?
    I thought they are present only on Fender pickups, but I also meet them on other modern brands.
    It starts to annoy me because I don’t understand.
    these are not just dot from a pencil .. these are shock dot

    Click image for larger version

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  • #2
    Originally posted by vitaliikit View Post
    It starts to annoy me because I don’t understand. ]
    Man, you've got issues...
    Pepe aka Lt. Kojak
    Milano, Italy

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    • #3
      The dot appears from the photo to be an air bubble.
      When the end of the magnet was ground, it exposed the air bubble.
      If the black dot is a pit, or indention, then the bubble is the obvious answer.
      T
      "If Hitler invaded Hell, I would make at least a favourable reference of the Devil in the House of Commons." Winston Churchill
      Terry

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      • #4
        Originally posted by big_teee View Post
        The dot appears from the photo to be an air bubble.
        When the end of the magnet was ground, it exposed the air bubble.
        If the black dot is a pit, or indention, then the bubble is the obvious answer.
        T
        bubble ? no . here is a bit more pictures
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        Click image for larger version

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        as if hit spike and got a dent dot

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        • #5
          I still say it is due to the magnet casting process?
          Beyond that, just be annoyed!
          GL,
          T
          "If Hitler invaded Hell, I would make at least a favourable reference of the Devil in the House of Commons." Winston Churchill
          Terry

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          • #6
            20 years ago about 1/3rd of the alnico slugs had voids due to air bubbles or chips around the perimeter where they were cut on each end. Probably around 15 years ago they either started casting them differently or stepped up thier quality control. We rarely get anything more than an occasional pin hole anymore. Those are voids due to air pockets in the photos- no question.

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            • #7
              Thank you for idea Jason .
              I worked on this idea. but something does not fit.
              These points are always bottom side
              it is striking that these dots are mainly located in the center (or quite a bit from it) and very very rarely closer to the edges
              and they are always of shallow depth, almost the same. and almost always the right shape, like from a core hit
              I'm still in thoughts

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              • #8
                Originally posted by vitaliikit View Post
                I'm still in thoughts
                It's the nature of mind to find patterns - often seeing them where there is none. I might see unicorns or spaceships when I look at the clouds. Are they there by design? I can't deny that I see them.
                If it still won't get loud enough, it's probably broken. - Steve Conner
                If the thing works, stop fixing it. - Enzo
                We need more chaos in music, in art... I'm here to make it. - Justin Thomas
                MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey

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                • #9
                  Originally posted by vitaliikit View Post
                  it is striking that these dots are mainly located in the center (or quite a bit from it) and very very rarely closer to the edges
                  Castings cool from the outside and this increases the effective surface tension and the bubbles get pushed to the inside of the skin that first forms. That's why voids often only show up when machining and a casting can look perfect initially. This can be an expensive failure on (say) an engine cylinder head.

                  The magnets are perhaps gravity cast, which worsens the problem with gas inclusions - especially with small parts where the casting cools off very quickly and the gas doesn't have chance to escape upwards in time to clear the body of the casting.

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                  • #10
                    And it's important to note that aren't NEVER off center or ALWAYS uniform. Really, how large a control sample for consistency are we dealing with here?

                    If you examine the grainy nature of most cast metals it's pretty clear to me that these are inclusions from either air bubbles or somehow evaporated impurities. Mick's explanation of why they're typically located near center makes sense too. As to why they're usually located bottom side, well, if you're making pickups and you don't want your product to look like @$$ because of visible inclusions in the finished surfaces wouldn't you choose to put the inclusions on the bottom?
                    "Take two placebos, works twice as well." Enzo

                    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                    "If you're not interested in opinions and the experience of others, why even start a thread?
                    You can't just expect consent." Helmholtz

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                    • #11
                      you don't want your product to look like @$$ because of visible inclusions in the finished surfaces wouldn't you choose to put the inclusions on the bottom?

                      Tell em like it is

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                      • #12
                        Originally posted by Chuck H View Post
                        As to why they're usually located bottom side, well, if you're making pickups and you don't want your product to look like @$$ because of visible inclusions in the finished surfaces wouldn't you choose to put the inclusions on the bottom?
                        I did not mean the location of the points, but I meant that only on one side. if these bubbles are often on the one hand, then why are they not on the other? is it a careful selection of specimens?

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                        • #13
                          Originally posted by Lollar Jason View Post
                          20 years ago about 1/3rd of the alnico slugs had voids due to air bubbles or chips around the perimeter where they were cut on each end. Probably around 15 years ago they either started casting them differently or stepped up thier quality control. We rarely get anything more than an occasional pin hole anymore. Those are voids due to air pockets in the photos- no question.
                          But how to consider modern expensive pickups?
                          Click image for larger version

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                          Comment


                          • #14
                            Originally posted by vitaliikit View Post
                            But how to consider modern expensive pickups?
                            [ATTACH=CONFIG]56746[/ATTACH]
                            Have you asked the manufacturer of the pickups that have this birth mark on the bottom?
                            The guy that made the pickups, would be the one to answer these questions.
                            It may be something as simple, as a particular run of magnets.
                            If he bought them by the thousand, or more, it may take a while to work through them.
                            So I would go back to the pickup builder!
                            If I built the pickups, I could answer the questions.
                            T
                            "If Hitler invaded Hell, I would make at least a favourable reference of the Devil in the House of Commons." Winston Churchill
                            Terry

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                            • #15
                              They are 1000% caused by air bubbles in the castings.

                              If you've ever worked with casting metals before, this becomes very obvious very quickly.

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