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Thread: Science of Magnets

  1. #1
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    Science of Magnets

    I was reading in the Lee Valley catalog that setting magnets into cups increases their holding power. What's the science behind this? Is it because you're increasing the surface area or some other magical reason?
    Confidence: The feeling you experience before you fully understand the situation

  2. #2
    The little metal bit around the magnet redirects the flux and allows it to reach maybe twice the strength as otherwise.
    It's kinda magic.

  3. #3
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    Iron cup, not wood or plastic.
    Bill D

  4. #4
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    Quote Originally Posted by Bill Dufour View Post
    Iron cup, not wood or plastic.
    Bill D
    Ironwood won't work?
    Confidence: The feeling you experience before you fully understand the situation

  5. #5
    Bought some RE magnets and cups from Lee Valley years ago. They suggested filing a notch in one side of the cup, so you could pry the magnet out if needed.

  6. #6
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    Quote Originally Posted by Steven Cooper2 View Post
    The little metal bit around the magnet redirects the flux and allows it to reach maybe twice the strength as otherwise.
    It's kinda magic.
    The iron cup concentrates the magnetic flux making the holding power increase. No magic is involved, just science.
    Lee Schierer
    USNA '71
    Go Navy!

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  7. #7
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    Quote Originally Posted by Lee Schierer View Post
    The iron cup concentrates the magnetic flux making the holding power increase. No magic is involved, just science.

    And then there is mhu metal.
    Ken

  8. #8
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    Mu metal..high nickel metal used for magnetic shieldimg. I had to look it up on Wikipedia.

  9. #9
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    Quote Originally Posted by Jerry Bruette View Post
    Ironwood won't work?
    Drop the mic and walk away, Jerry

    I laughed out loud. Well done.
    Beginning woodworker and amateur, proudly specializing in overly ornate, busy, ridiculously over-decorated, and garnished to the point of distaste details

  10. #10
    When a magnet is close enough to a piece of ferromagnetic material, the magnetic field of the magnet causes at least some of the atoms of the ferromagnetic material to align with the field of the magnet. The steel cup becomes magnetized. Normally the steel cup would have atoms arranged randomly. So you then have the original permanent magnet plus a temporarily magnetic cup. The magnetic properties of the cup are not permanent but will be present for awhile even if the magnet is removed.

  11. #11
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    If you work around high power magnets all iron stuff will get magnetized. My father always ha a small screwdriver and pocket scale in his shirt pocket. They were both magnetic from his job running a cyclotron. It had over 2,000 horsepower just for the steering magnets. Not including the main drive ones. I believe it had its own 12 KV switch yard to supply incoming power..
    Used special bronze wrenches and hammers. He said you could not swing a iron hammer in a straight blow. Welders hated working on it. Even gas welders had issues.
    BilL D

  12. #12
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    Quote Originally Posted by Bill Dufour View Post
    If you work around high power magnets all iron stuff will get magnetized. My father always ha a small screwdriver and pocket scale in his shirt pocket. They were both magnetic from his job running a cyclotron. It had over 2,000 horsepower just for the steering magnets. Not including the main drive ones. I believe it had its own 12 KV switch yard to supply incoming power..
    Used special bronze wrenches and hammers. He said you could not swing a iron hammer in a straight blow. Welders hated working on it. Even gas welders had issues.
    BilL D
    Did screwdrivers fly towards your father when he walked in your shop?
    - Its not that Im so smart, its just that I stay with problems longer. Albert Einstein
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  13. #13
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    Did screwdrivers fly towards your father when he walked in your shop?
    Reminds me of a story I heard when high-field NMR was a new thing. (NMR is a lab tool for chemical analysis that uses rf signals in a magnetic field; it's the technology behind MRI scanners.) The machines have liquid nitrogen-cooled electromagnets, typically decorated with signs warning users to keep metal objects away. A maintenance worker came in one night and didn't heed the signage. He was found the next morning, unhurt but unhappy, attached by his tool belt to the casing of the magnet.
    Last edited by Dave Fitzgerald; 06-10-2023 at 8:00 AM.

  14. #14
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    Back in the late 90's I worked at a computer store, and a few of the techs discovered rare earth magnets. I ordered a bunch of them (20 I think) and they came stacked together. They were about 3/4" x 1" x 1/4" or so. We were playing with them, marveling about how strong they were, and someone took the whole stack and walked past my workstation, close to my monitor, which was a 19" tube monitor. The magnets were so strong that they actually grabbed the shadow mask under the monitor's glass and pulled it out of adjustment. From then on, the screen had a moire pattern all the time, looking like it was slightly out of focus. Needless to say, we kept those magnets away from screens from then on.

  15. #15
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    If you want to experience some very powerful pound for pound magnets tear open an old computer hard drive. in the pivot structure of the disc reader arm you will find some kidney shaped magnets about 3/4 long by 1/2 wide and 1/8 thick. Stick two of them together and try to pull them apart. Even stick one to your table saw cast iron top and try to lift it.
    the power in this small form it amazing.
    calabrese55
    Let your hands tell the story of the passion in your heart

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