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Homework Help: Determining screw size

  1. Nov 13, 2015 #1
    1. The problem statement, all variables and given/known data
    Hello guys, I want to make a mounting for a display which 6 Kg weight. The display will be supported by two hollow square 30x30 with 2 mm thickness and bolted by 2 socket screw in each hollow. Base of the display are made from aluminium sheet 1 mm thick.

    2. Relevant equations
    What is the minimum screw size should use?

    3. The attempt at a solution
    the closest way is get the section area of the screw from a stress formula, but I'm not sure which stress formula
  2. jcsd
  3. Nov 16, 2015 #2


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    Can you do a drawing? It's not clear if the screws are in tension, compression or shear.
  4. Nov 20, 2015 #3
    Is there any way to edit my previous post? I've tried to find edit button but i couldn't find it.


  5. Nov 22, 2015 #4
    The bolts in your diagram would experience shear stress. First you could calculate the weight force of the display by using mass x gravity. Then since you have 4 bolts divide your weight force by 4 to get the force per bolt.

    Once you have that you need to pick the material of your bolts and look up the max shear stress allowed for that material. Once that is known you can use the equation stress = force / area. Use max shear stress in place of stress and force per bolt in place of force and write area as PI*D^2/4Then you can solve for D. It will most likely not be a standard bolt diameter, just pick the next largest size.
    Last edited: Nov 22, 2015
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