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Crossbow band lengths?


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Old 03-30-2016, 01:33 AM   #1
Shain77
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Default Crossbow band lengths?

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.

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Old 03-30-2016, 09:04 AM   #2
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Glad you are having fun. I will leave the crossbow bandlength question for the experts.


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Old 03-30-2016, 09:58 AM   #3
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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.
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Old 03-30-2016, 04:11 PM   #4
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Quote:
Originally Posted by JoergS View Post
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.
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?
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Old 03-30-2016, 04:19 PM   #5
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Quote:
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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?
Maybe because the bands have cooled off?
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Old 04-05-2016, 10:51 AM   #6
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Maybe because the bands have cooled off?
I have tried to shoot it under ten seconds from drawing out the bands. Still the same result :/
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Old 04-06-2016, 09:29 AM   #7
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I think you will get more power with full width untapered bands.


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