Force on a screw

Discussion in 'Physics & Math' started by Steve100, Jan 21, 2015.

  1. Steve100 O͓͍̯̬̯̙͈̟̥̳̩͒̆̿ͬ̑̀̓̿͋ͬ ̙̳ͅ ̫̪̳͔O Valued Senior Member

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    First time on sciforums for a long time, just wondering if anyone can help me out.

    Am i correct in thinking that the linear force from a screw is equal to the rotational force applied * the distance from screw center / 2 pi * screw pitch ?
     
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  3. theorist-constant12345 Banned Banned

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    The word you are looking for is torque.


    http://en.wikipedia.org/wiki/Torque
     
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  5. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    No it's not.
    Your link CLEARLY states that torque is rotational force.
    Thus it can't be the "linear force" that Steve100 is asking about.


    BTW, how's it going Steve, long time no see.
    You joined The Mob didn't you?
     
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  7. origin Heading towards oblivion Valued Senior Member

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    This should tell you what you need.
     
  8. theorist-constant12345 Banned Banned

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    What ever Dy, you have to apply linear twist to over come the force holding the screw, torque is the subject the person is asking about.

    ''torque is defined as the cross product of the lever-arm distance vector and the force vector, which tends to produce rotation.
     
  9. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Which means it's not the linear force, doesn't it?
    You're as ignorant on mechanics/ kinematics as you are on every other aspect of science.


    Might be worth looking here Steve.
    Or, further down, this:

    Please Register or Log in to view the hidden image!

     
  10. theorist-constant12345 Banned Banned

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    The person asked - '' the linear force from a screw is equal to the rotational force applied ''

    The rotational force applied is?
     
  11. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    If you don't want to speak of torque, one can consider a screw to be an incline plane wrapped around an axis, but that will not help much to know the torque as unlike the classical incline problem with point contact ball accelerating down it, the contact is mainly one dimensional and the distance from the axis, for wood screw, but not for machine screw, is a variable.

    About the only thing one can approximately calculate is the max torque or failure torque.
    The approach is to consider a 360 turn of the wrapped incline plane, and the base area of the thread against the solid tappered cone. The shearing of the thread off that base can be estimated from the shear strength of the metal. Do this for all turns and the easiest to shear off sets the torque limit.
     
    Last edited by a moderator: Jan 21, 2015
  12. Steve100 O͓͍̯̬̯̙͈̟̥̳̩͒̆̿ͬ̑̀̓̿͋ͬ ̙̳ͅ ̫̪̳͔O Valued Senior Member

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    Thanks
    Correct, if it were the torque I wished to discuss I wouldn't have included the distance from the screw center in my working.
    Admittedly I was rather drunk when I asked the original question, but on sober reflection it still makes perfect sense, and I am pretty sure I was correct.

    Going well Dywyddyr, you?
    5 years since I joined the Mob. This puzzle was actually to do with load testing an aircraft flight control bearing.
     
  13. Steve100 O͓͍̯̬̯̙͈̟̥̳̩͒̆̿ͬ̑̀̓̿͋ͬ ̙̳ͅ ̫̪̳͔O Valued Senior Member

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    Please Register or Log in to view the hidden image!


    Force on the bar vs force on the bearing is what I was after for clarification. (Awesome MS Paint skills included)
     

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