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Hi! Could anyone of you post here a link to a webpage that actually

  1. Feb 1, 2007 #1
    Hi! Could anyone of you post here a link to a webpage that actually describes how a torque (of a screw) is transformed into a force that acts in the direction of the screw's axis, that makes is to screw in? Or could you briefly explain it? Any help would be highly appreciated.
  2. jcsd
  3. Feb 1, 2007 #2


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    Staff: Mentor

  4. Feb 1, 2007 #3
    I mean like.. what makes the screw to go down, to screw in. After I thought about it, I came up with this idea. When I rotate the "head" of the screw, the shaft (the lower part) rotates as well. Since a part of the shaft is already in the wood (where the thread has made a groove), the groove acts against this rotation - reacting with a force F. This force acts on an inclined plane (the thread) and it is possible to decompose it into two forces, F1 and F2. And it is the force F1 that makes the screw to screw in the wood (see the attached drawing).. Is this the appropriate explanation?

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  5. Feb 2, 2007 #4


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    inclined plane: http://en.wikipedia.org/wiki/Inclined_plane

    helically warped, but that is essentially what a screw is: http://en.wikipedia.org/wiki/Screw
    Last edited: Feb 2, 2007
  6. Feb 2, 2007 #5
    Yep, I know, so do you think that my drawing is correct?
  7. Feb 6, 2007 #6
    I would say you're pretty close. I think you need the equivalent of a "normal" force that is perpendicular to the angled thread. It gets pretty hard to get your head around the helical screw thread, so I did a quick analysis of a much simpler screw, which consists of a bolt with a small post that acts as the thread and a hole with a helical groove cut in it.

    The results of the free body diagram confirm the result you get from a "work balance" analysis:

    Fvert = 2*pi*T/d

    Where Fvert is the vertical force, T is the applied torque, and d is the thread pitch.

    This analysis ignores friction, which is a huge simplification. Hope this helps...

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