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Homework Help: Threaded screws

  1. Oct 19, 2005 #1
    Im having problems solving this problem.

    A C-Clamp is used to clamp a piece of wood to a workbench. its double square threads have a mean diameter of 3/8 in. and a pitch of 1/10in. The static friction coefficient between the threads is 0.25. If a torque of 30lb/in isapplied in thightening the clamp, determine (a) the compressive force on the wood and (b) the torque required to loosen.

    I need help getting started. I think this is the order and formulas I have to use.

    1)Lead angle= tan-1(np/2*3.14*R)
    which ends up being tan-1 ( n*.375/2*3.14*.375)
    I know n is the number of threads but i dont know how to calculate it.

    2)Loading Torque
    M=Wrtan(static friction angle - lead angle)
    How do you calculate the static friction angle?

    3)Mechanical advantage M.A=W/F=....

    4)Compressive force? how do i calculate this?

    Sorry for the long post. Thanks in advance

    The image is here
    http://img349.imageshack.us/img349/6807/untitled9db.png [Broken]
    Last edited by a moderator: May 2, 2017
  2. jcsd
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