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Calculating the force on a shaft

  1. Apr 11, 2012 #1
    I would like to attach bearings on a shaft, see: https://www.physicsforums.com/showthread.php?p=3856547#post3856547

    Therefore I would like to calculate the axial and radial force on the shaft, so I can select the right bearings.

    The picture looks a as following: http://i39.tinypic.com/kd1naq.jpg
    So I have a shaft, with a plate attached on it with a weight of 10kg. A load will be putted on the plate wit a weight of 37,5kg. Now I would like to calculate the axial and radial force on the shaft.


    Sum Fx to A = o

    Fxa = o

    Sum Fy to A = o

    (-375N x 0,625 x 0,3125) – (100 x (0,725/2)) + Fya x 0,725 = 0
    -73,2 - 37,6 + Fya x 0,725 = 0
    -110,8 + Fya x 0,725 = 0
    Fya = 110,8 / 0.725
    Fya = 153N

    Som M t.o.v. A = o
    M in a = 375 x (0,725 – 0,3125) + 100 x 0,3625
    M in a = (375 x 0,4125) + 36,25
    M in a = 191Nm

    The shaft would have an axial force of F = 153 N and radial momentus of M = 191 Nm according to this calcuation.

    Does this look ok, or should I calculate it completely differently?
  2. jcsd
  3. Apr 11, 2012 #2


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    You need to go back and shows the bearings in your FBD, and include their forces in your force and moment sums.

    Also, it is not entirely clear where some of your dimensions came from; can you identify them, please?
  4. Apr 16, 2012 #3
    What dimensions are not identified? Do you see the picture?
  5. Apr 16, 2012 #4


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    Yes, I saw the picture. One of the difficulties is that you have worked entirely with numerical values, rather than giving symbolic names to each of your dimensions. If you gave each of them a symbol, before plugging in the number, then it would be much easier to see where each item came from.

    Also, in the FBD, I do not see any reaction forces on the upright arm; why?
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