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Making a self winding spool

  1. Sep 2, 2017 #1
    sorry bout long lead up

    retractable cords, pet/id leashes and tape measuers work the same way
    they have a really long metal band coiled inside, anchored on 2 seperate pieces
    this coiled up band of metal gets tighter as you pull, and tries to uncoil when let go

    my questions/problems are as such

    the many feet of metal band take up a decent amount of space
    dealing with many feet of coiled metal is relatively dangerous (if it "pops out")
    the coil has relatively little power (in thier original state)

    im fairly certian this type of coil is used because of the " lenght of travel"
    (if you want to pull out 20ft of cord, that spool needs to spin many many times)

    i believe the strenght would be increased just by exchanging the metal band, for wire
    coiling could be made safer, with use of a zip-tie
    but were still talking many feet of loose metal

    if i have a much smaller lenght of travel, is there a more efficient coil or other mechanism for winding the spool?
    how can i get more resistance (resists removal of cord or "unspooling")

    lets say this device is metal, and the approximate size of a roll/spool of teflon tape
    (1" > inner dia, 2" dia flange)

    the coil needs to fit the inner dia.
    spool only needs to rotate a few dozen or so times

    then i would need to find a calculator online for determining coil make and power
    (i remember finding one for compression/extension springs, but not sure about coils)
  2. jcsd
  3. Sep 3, 2017 #2


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  4. Sep 3, 2017 #3
    yes, it was meant to be a question (was going to try editing the OP to clear up but cant do that here)

    im trying to make spool "self wind"
    the problem is i want a greater resistance in a smaller form, if possible

    i just had a revelation, but cant find an explaination of the mechanism on the internet

    wind up live traps (mouse trap)
    the mechanism is near impossible to get to w/o destroying the unit (you can only see the stopper mech, which ive no interest in)
    but appears to be closer to what i want
    all you can see and infer of the mech proper, is that its a rod/tube and includes a coil or spring

    anyone happen to know what the mech likely is, and how it works (so i could make it)

    i think if i only needed it to spin partialy, itd use one of those omega shaped springs
    but since i need more travel, it wont work
  5. Sep 3, 2017 #4


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    All engineers want that. There are many “clockwork” solutions that involve springs. The energy stored is the force employed multiplied by the distance travelled. The volume of spring material needed will be proportional to the total energy storage needed. So using a long thin wire spring or a short roll of flat spring tape is decided by how much force you need to apply and over what length you need it to act. Self retracting tapes are reasonably close to optimum. You could scale those designs to suit your application.

    You have not specified the application, force, turns, or the length of filament that the spool must hold. That is not the best way to get assistance.
  6. Sep 4, 2017 #5
    *deleted hours rambling, sad excuse for communication

    lets say i can steal the guts from a tape mesure, and have it work for what i need
    since i need far less rotations than the measure, could i subtract some lenght from the coil, and "increase power" that way?

    or is my best bet just to get some music wire, and make a coil randomly and work from there?
    since i cant realy explain what im doing?

    since the other dimension change depending how small or large a coil i can/need to use
    all i can state for sure is im tring to achieve about 10lbs of resistance

    (i mean i know what im trying to do, and can do it safely, but damned if i can express it cohereantly)
  7. Sep 4, 2017 #6


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    eBay search 'Spring Balancer Tool Holder'
    Small ones are like a retracting tape and cost less than $20, bigger ones have a fusee.

    You might find a retracting tape that gives about 10 lbs of pull, then if you only need x% of the retraction length, keep a little more than an x% length of the internal clock spring.

    Two clock springs wound together will pull twice as hard as one.
    If you cut a clock spring down the middle, one half will have half the pull of the original.
  8. Sep 5, 2017 #7


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    If you need only a short straight pull, you can use a piston in a cylinder.

    When a gas is compressed in a cylinder, the force on the piston increases as the compressed volume reduces. But if you draw a vacuum with a piston in a cylinder, (or with a syringe), you have a constant pulling force on the piston.

    Given atmospheric pressure across the piston and a need for about 10 lbs of pull, you could use a syringe with an internal cylinder diameter of about 0.94”.
  9. Sep 5, 2017 #8
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