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  • Magnetic attraction threshold distance problem

    Discussion in 'Calculations' started by tmer1, Mar 26, 2015.

    1. tmer1

      tmer1 Member

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      Hello,

      I am trying to design a board game with magnetic pieces.
      The board is to be made of stainless steel and the pieces should be small disk Neodymium magnets.
      I need the pieces to be attracted to the board more strongly then they attract each other, so pieces don't jump out of position.

      The board will be quite small, each tile will be 16mm^2 so magnets will sit approx 16mm centre to centre.
      I would like that the magnetic pieces do not jump to each other unless they are very very close (maybe 2mm?)
      Is this possible ?

      The thickness of the board tiles is yet to be determined by cost options. They will either be 0.8,1.6 or 2.4 mm
      What is the recommended dimensions for the neodynum magnets for each of these three options?
      It is also important that the pieces grip the board adequately and don't unstick too easily.

      I am not an engineer so I don't know how to go about starting to calculate this, please help me understand how to solve this problem.

      Ty,

      Tom
       
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    3. tmer1

      tmer1 Member

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    4. 4t8

      4t8 New Member

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      Tom,
      FYI, not all stainless steel is magnetic.
      Have you considered making the board out of wood or aluminum, and then recessing an additional magnet at the center of each tile?
      Fred
       
    5. maniacal_engineer

      maniacal_engineer Well-Known Member

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      400 series stainless is magnetic, 300 series generally is not. Stainless is more expensive than a plain steel, but if you powdercoat the plain steel it will probably be adequately rust free for a board game type application. Using magnets for both the board and the pieces gets into polarity issues - sometimes they attract and sometimes they repel - which could be a disaster or a feature, depending on how you design the game. But using magnets would be more expensive than even stainless.

      You could do a really gnarly computer simulation of the magnetic attraction vs thickness etc... but really it would be easier and cheaper to buy a few magnets, get a few steel scraps, and see what feels right.

      In looking at you cubical board on the other thread I have some comments there too.
       
    6. Bill @ ERG

      Bill @ ERG Member

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      Consider using a cup style magnet assembly (circular steel cup with magnet inside). Not only does it increase the holding power, but it also reduces the stray magnetic flux that would cause the magnets to attract each other. If all north poles are aligned (say down relative to the board) then they also don't tend to snap together when not attached to the board - avoiding the possible impact damage. If a thin film of rubber or soft urethane is applied, it would also increase the coefficient of friction, further reducing the likelihood of magnets moving on the board.
       
    7. maniacal_engineer

      maniacal_engineer Well-Known Member

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      a thin rubbery coating is even better than powdercoat.
       
    8. jameswang

      jameswang New Member

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      Hi Tmer1, are you based in AU or USA? If you are based in USA, I can probably send you some free small magnets to test out. :)
       
    9. tmer1

      tmer1 Member

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      What is idea with "cups" can you explain it a bit further ?

      thanks for all replies:)

      I live in Au, but its ok I will buy a bunch of magnets and test them out... thanks though!
       
    10. Jefflucasart

      Jefflucasart Member

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      The problem is that most SST is non-magnetic. The simple solution is to use 17-4 stainless steel, which is magnetic.
       
    11. Bill @ ERG

      Bill @ ERG Member

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      Cup style magnet assemblies have a magnet with a steel cup around the magnet, leaving one edge nominally flush with the face of the magnet. Locally we can get a cup magnet with a 6mm diameter rare-earth magnet that can be pressed or glued into a 3/8" hole. The cup increases the holding force by up to 4X, while reducing the flux on all but the open side of the assembly. For the 6mm magnet, this would represent a maximum force of about 10 lbs with cup and suitable surface.

      A local supplier has a link to their website http://www.leevalley.com/en/Hardware/page.aspx?p=58750&cat=3,42363,42348&ap=1

      This is a link explaining how they work, and showing the difference in flux density. https://www.kjmagnetics.com/blog.asp?p=mounting-magnets

      I am assuming that similar assemblies are available in your location. You could try specialty hardware stores, scientific / educational supply stores, hobby shops etc. The
       
      Last edited: Mar 27, 2015

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