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Force Applied onto a Mounting Hole

  1. Jul 17, 2011 #1
    Hi everyone:

    I have an 0.1" thick aluminum plate. I am mounting a component to the plate using four 8-32 screws.

    During use, this component will see a torque of about 35 Ib.in applied onto a shaft that is connected to it.

    How do I determine the force that is applied onto the four mounting holes?

    I really want to make sure the plate thickness is sufficient.

    Thank you for any guidance.
  2. jcsd
  3. Jul 17, 2011 #2
    Assuming the screw holes are symmetrically arranged around the shaft's center-line at a radius of 'r', then the load on each would be Force = Torque / (r*4 holes). That assumes the forces on the screws will be equally divided, which is not likely. A more reasonable assumption would be to assume that only 2 screws react the torque, then the Force = Torque / (r*2 holes).
  4. Jul 17, 2011 #3
    Once you have found this force, you can check if the plate is thick enough (and the holes are far enough away from the edge) by computing the "bearing stress" and the "shear tear out" stress. Let me know if you need any help with these.
  5. Jul 19, 2011 #4
    Thanks very much for your response. Yes, I would like help with this.
  6. Jul 19, 2011 #5
    Thanks for your response. The hole are only symmetric about the horizontal axis.
  7. Jul 19, 2011 #6
    Compute the bearing stress as follows:

    bearing stress = force / ( screw diameter X plate thickness)

    Compute the shear tear out stress as follows:

    shear tear out stress = force / (2 X plate thickness X distance from hole edge to plate edge)

    Then limit these calculated stresses to 40% of the yield stength of the plate (typical for shear).
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