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Thread: Maximum holding weight of an M6 thumb screw

  1. #1
    Associate Engineer
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    Maximum holding weight of an M6 thumb screw

    What calculation should I use to calculate the maximum weight that can be carried by an M6 thumbscrew secured to a 12mm diameter rod? Please see attachment for orientation. Thanks!
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  2. #2
    Technical Fellow Kelly_Bramble's Avatar
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    It looks like a friction holding design - friction created by torque - axial force on the locking screw (unknown size) + friction between the contacting surfaces (unknown surface area) on unknown material holding the device static against gravity and the unknown static bending - friction forces.

    All you can do is estimate the torque created by your "Thumb Screw" and follow the math for the total friction created and then the force required to break the static friction.

    Lot's of unknowns and more than a simple calculation.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Associate Engineer
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    Ok, thanks. Will see how I go

  4. #4
    Technical Fellow jboggs's Avatar
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    As common as your approach is (a screw tightened down on a surface) for trying to achieve a clamping action, it is equally non-effective. Its only benefit is that its easy to make. But it rarely works very well for very long and inevitably ends up with scarred surfaces, stripped threads, and slippage. One reason is that it focuses all of the clamping force on an extremely small area of actual contact. That small area distorts, resulting lower force and permanent deformation.

    A more reliable method would involve clamping on the entire shaft surface, such as you would see in two-piece shaft collar.

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