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Bows by the numbers - modelling a bow before cutting timber
Aussie Yeoman:
--- Quote ---Reducing set is the goal, not getting a lower draw weight. I'm asking g what the program would show had you built the bows to the same dimension but with lower draw weight.
--- End quote ---
Ah yes, I'm picking up what you're putting down now. Unfortnately the bulk of my bend test data is currently on a dead laptop, and I've not yet been able to rescue the data.
I can't remember if theres a linear or exponential relationship between working strain and set. Woodbear might know off the top of his head. Reducing the working strain by making the limbs thinner would definitely reduce set. However you'd have to make the limbs wider to bring the draw weight back up again.
You'd know this already of course but I'm pointing this out for the benefit of digital archaeologists who will excavate the internet hundreds or even scores of years from now.
Zugul:
--- Quote from: sleek on September 09, 2024, 03:45:40 am ---I just want to point this out.. Thats exactly how folks should be doing it, you reduce the thickness of the bow to reach your draw length, not to reduce the draw weight. Too many people think wrong when tillering and that's what leads to set very often. The bows over all width is what makes the bows draw weight. I'm sure you knew this already, but felt it's important enough to highlight and not let it be glossed over.
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Wait wait wait... So after nearly 4 years of me being on this forum pretty much daily I learn this TODAY??? I mean, I know the wider the limbs, the thinner they have get to accomodate for a certain draw length, but I have never thought about it in that way! It all makes so much more sense now! (A)
willie:
--- Quote from: Woodbear on September 09, 2024, 03:15:41 am --- does the modeling accommodate non-rectangular cross sections?
--- End quote ---
Hi Dave,
Stefans Virtualbow app only accomadates retangular sections, but lets you easily design multi lamination bows with different materiels ("Traditional" cored "glass" Bows). I think one could approximate a non-retangular crossection by creating layers with differing stiffnesses, the MOE of a layer being proportional to the desired width in the crossection
sleek:
Absolutely! Glad you saw the thread then! Yes, the verbiage that describes tillering is very wrong and leads to incorrect conclusions when people say things like, "tillering the bow down" implying a drop in weight, when what they are actually doing is decreasing the bows bend radius allowing for a longer draw. It's a key element in bow making and why I say that most folks tiller a bow wrong, and as a side note, often make their bows to narrow and or short, due to being over poundage for the bows dimensions.
--- Quote from: Zugul on September 09, 2024, 06:07:53 am ---
--- Quote from: sleek on September 09, 2024, 03:45:40 am ---I just want to point this out.. Thats exactly how folks should be doing it, you reduce the thickness of the bow to reach your draw length, not to reduce the draw weight. Too many people think wrong when tillering and that's what leads to set very often. The bows over all width is what makes the bows draw weight. I'm sure you knew this already, but felt it's important enough to highlight and not let it be glossed over.
--- End quote ---
Wait wait wait... So after nearly 4 years of me being on this forum pretty much daily I learn this TODAY??? I mean, I know the wider the limbs, the thinner they have get to accomodate for a certain draw length, but I have never thought about it in that way! It all makes so much more sense now! (A)
--- End quote ---
Hamish:
Set in the limbs looks pretty good. Simplicity and effectiveness, and speed of manufacture vs perfection there is always a trade off. I agree you could tweak the design so it doesn't take as much set up near the fades, but that defeats the purpose of your experiment. I would be really happy with your results, and I'm sure any student in your bow building class would be too.
I have made bows from the charts in Elmer's Target Archery, which were mathematically designed, too. They have a similar distribution of set, ie slightly more set near the fades than I would find ideal. Nonetheless they are very good bows, and still have relatively low set overall, shoot really well.
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