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  • Tamperproof screw for harsh environment

    Discussion in 'Joining & fabrication' started by GarethW, May 18, 2015.

    1. GarethW

      GarethW Chief Clicker Staff Member

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      I'm looking for a way of tamperproofing an M4 machine screw. Under normal circumstances I'd just recess it into a counterbore and stick a "warranty void" label over the top. However, this is for harsh environment and a label would obviously be unsuitable.

      I don't want to use a screw with a fancy "tamperproof" head because anybody can simply buy the appropriate driver.

      What I need is some kind of plastic cap that gets fitted over the screw head and is impossible to remove without destroying. I can't seem to find a suitable product anywhere...

      Any ideas where I can get hold of such a thing?
       
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    3. CPPMable

      CPPMable Well-Known Member

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      What are you considering a "harsh environment". Is this a temperature, water, chemical, or other type of environment?
       
    4. GarethW

      GarethW Chief Clicker Staff Member

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      -45 to +80 deg C temperature range. 1000hrs salt spray resistance.
       
    5. K.I.S.S.

      K.I.S.S. Well-Known Member

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      Hi Gareth,
      Without knowing too much detail, does the screw have the requirement to be recessed or can it stand proud?
      Also, would it be possible to use a thread type that can be driven in and screwed out?
      If the need justifies it, you could always fill in the slot of (for example) a Posidrive screw with a suitable resin mixed with a little 'magic water' - that's the U.K. trade name for the unique chemical they can supply to you that you paint on valuables, which can then be traced back to the owner.
      Of course, you could always add a couple of little tabs with a hole in them and apply a numbered pull tight security seal, if the design allows?
      K.I.S.S.
       
    6. GarethW

      GarethW Chief Clicker Staff Member

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      Hi K.I.S.S, thanks for your reply. The screw should stand proud and should be removable somehow for rework. The resin idea is novel, but we want to avoid adhesives and such on the production line. The pull tight security seal is also a nice idea thanks, but the geometry of the enclosure does not allow it. A special screw with cap that has to be destroyed to be removed is still my ideal solution. If only I could find one... In the meantime I've done my own design of special screw and cap and I'm getting a quote!
       
    7. K.I.S.S.

      K.I.S.S. Well-Known Member

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      No problem Gareth,
      Good luck with the design - I've also designed a few security seals in the past, and I've had a lot of experience in this field, including the bypassing of them. Let me know if you'd like some unbiased advice - you'd be amazed at some of the tricks people will try to overcome them, including (and I'm not kidding) urinating on them in a cold environment to make the polypropelene expand (that's why a polyethelene insert is sometimes a good idea..)
      K.I.S.S.
       

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