Main Discussion Area > Bows
Stress and performance
Aussie Yeoman:
No, it shouldn't be. That's what I'm trying to say. No matter what the design, profile, drawn shape, draw length or draw force... a piece of wood should be used so that it has the same maximum stress.
It probably is the case that people doing it by feel often make some bows with higher or lower stress depending on the dimensions and whatnot. But in an ideal world, and with the help of some scientific and engineering principles, a crossbow prod pulling 200 lb at 12 inches should be subject to exactly the same working stress as a 72" longbow pulling 45# at 28".
bradsmith2010:
ok
Bob Barnes:
--- Quote from: Aussie Yeoman on June 24, 2022, 07:19:12 pm ---No, it shouldn't be. That's what I'm trying to say. No matter what the design, profile, drawn shape, draw length or draw force... a piece of wood should be used so that it has the same maximum stress.
It probably is the case that people doing it by feel often make some bows with higher or lower stress depending on the dimensions and whatnot. But in an ideal world, and with the help of some scientific and engineering principles, a crossbow prod pulling 200 lb at 12 inches should be subject to exactly the same working stress as a 72" longbow pulling 45# at 28".
--- End quote ---
So, if you have the formula, and if it's not a lot of work, could you explain using Brad's 2 bow example from the above post? I'm just guessing that your formula involves coming up with the ideal dimensions for a given bow/bow wood...? thanks.
sleek:
Mass distribution is more important than mass alone. That gets into surface area and pounds of stress per square inch. For a few years I have been on and off working on getting a formula for it. I have one that works well, but isn't exactly where I want it to be. I'm still trying to improve it.
Badger:
I think because all species and even individual samples of wood vary to such a large degree it is almost impossible to predetermine stress levels based on design beyond the standard rules of thumb we have come up with. You can fine-tune that a bit by monitoring set which is the ultimate practical limits of the bow anyway. But Ideally, I would agree that stress limits should be the same for any bow of any weight and design. Without engineering details on every piece of wood any practical useful chart to establish widths would be nothing more than the same estimates we use now.
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