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Unexpected Magnetic Experiment Results

  1. Sep 3, 2009 #1
    Hello All!

    I read that placing a steel cup on one end of a permanent magnet will increase the "pull" at the opposite end. Having far too much time on my hands, I decided to perform my own test, to see how much the pull is increased. I found a neodymium cylinder magnet, 1 inch diameter and one inch long. I then machined a cup 2" diameter, 1-1/2" long, with a 7/8" deep x 1" diameter hole in one end. This gave me a steel cup with 1/2" wall and 1/2" floor. I attached a small steel rod to the strain guage and measured the results with a 3/8" air gap steel to magnet. Here are the results...

    Magent with no cup: 3lbs / 5oz.

    Magnet with cup: 2lbs / 8oz.

    The cup seems to have REDUCED the attraction!

    What gives?


  2. jcsd
  3. Nov 26, 2009 #2
    You made your hole diameter to small. It is shorting out your magnet. Make your hole 1- 1/4" in diameter. You will also need a bushing to keep the magnet in the center of the hole. Make your bushing out of plastic, wood, copper, aluminium, or anything else that is not attracked by the magnet. This will increase the pull of the magnet. Good Luck.
  4. Nov 26, 2009 #3
    How did you get the neodymium magnet out of the cup? I would have suggested a 1" deep by 1 1/2" or 1 3/4" dia hole. The cross section of the outer shell should be at least the cross section of the neodymium magnet, 0.785 square inches..
    Bob S
  5. Nov 28, 2009 #4
    Hi Bob!

    Thanks for the reply! When I milled the cup, I included a 1/4-20 tapped hole in the bottom to provide a means to push the magnet out. You're right, If not for the tapped hole, the magnet would still be in the cup (maybe forever).

    I'll try your suggestions. Thanks Again!


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