Crossbow band lengths?

Discussion in 'Slingshot Crossbows' started by Shain77, Mar 29, 2016.

  1. Shain77

    Shain77 New Member

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    What would be the calculation for spacing of the forks (band length) and centre of bow to lock for maximum efficiency? I would like to know how far to space the forks to have the rubber pre tensed with a 70 cm distance from the centre of the bow to the lock.

    This hobby is awesome. Since my theraband arrived on Friday, I have made a conventional, a slingrifle, a catchbox, and half a crossbow! This forum is also great, much more friendly than the other one I was looking at. Tons of good information.

    Thanks,
     
  2. bigdh2000

    bigdh2000 Administrator

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    Glad you are having fun. I will leave the crossbow bandlength question for the experts.
     

  3. JoergS

    JoergS Administrator

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    On crossbows, I use stretch factor 4 and no tapering. This way the bands will live long and the hysteresis effect (cooling bands) is less problematic.

    You will need plenty of rubber for good performance though. I recommend doubling the results of the calculator.
     
  4. JonS

    JonS New Member

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    With factor 4 I suppose you mean 400% elongation?
    I have made your bullpup slingshot crossbow, and banded it with 6 layers of TBG per side (tapered 3-2cm).
    The draw weight is 80 pounds, but when I shoot it it is weaker than my 15 pound child bow. Why is that?
     
  5. Redloesebob

    Redloesebob Slingshot Veteran

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    Maybe because the bands have cooled off? :confused:
     
  6. JonS

    JonS New Member

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    I have tried to shoot it under ten seconds from drawing out the bands. Still the same result :/
     
  7. Redloesebob

    Redloesebob Slingshot Veteran

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    I think you will get more power with full width untapered bands. :)