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Thread: GD&T floating Fastener Formula question

  1. #1
    Associate Engineer
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    Feb 2017
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    GD&T floating Fastener Formula question

    Good Morning Folks,
    Hopefully my question is an easy one concerning the “floating Fastener Formula”. I understand the FF formula as it applies to the typical joining of two surfaces such as a simple joint assembly where a clamping force is required from a floating fastener (T = H - F). However, my question is concerning scenarios where multiple layers, or great than two, come into play such as a telescopic tubing assembly. The fastener goes through at least four layers of material. In cases such as that, does that need to be factored into the FF formula? Would the resultant tolerance need to be divided by the amount of layers?


    Thank you!


  2. #2
    Administrator Kelly Bramble's Avatar
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    Feb 2011
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    Quote Originally Posted by james_kashuba View Post
    Good Morning Folks,
    Hopefully my question is an easy one concerning the “floating Fastener Formula”. I understand the FF formula as it applies to the typical joining of two surfaces such as a simple joint assembly where a clamping force is required from a floating fastener (T = H - F). However, my question is concerning scenarios where multiple layers, or great than two, come into play such as a telescopic tubing assembly. The fastener goes through at least four layers of material. In cases such as that, does that need to be factored into the FF formula? Would the resultant tolerance need to be divided by the amount of layers?

    No, each layer "floats" because the features are clearance holes / features. Just like with two floating parts assembled by a through fastener the four features may require full assembly with all fasteners un-tighened to ensure assembly.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Associate Engineer
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    Feb 2017
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    Thank you Kelly! I needed that confirmation

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