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Benefits of a lenticular crossection for white wood bows?
Aksel:
--- Quote from: RyanY on March 27, 2024, 08:12:46 pm ---I think this is likely difficult to determine and more than likely a matter of doing what works with what we’ve got. I don’t think a flat versus rounded belly makes enough of a practical difference for bowyers to notice and choose one over the other from both a performance and safety factor. I can’t say with certainty but it seems our knowledge of engineering and physics helped us understand that relationship more than discovery from trial and error in bows. As with evolution, if it works good enough it survives. Doesn’t have to mean that it is necessarily the best.
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True, could be so. But then I wonder why they did the lever bows since it is a more extreme and complicated design which takes more work and most likely was to make bows that would cast the arrow faster - they could have stayed with simple flat bows. And it might also be so that the rounded belly was advantageous in some way we´re not thinking of yet. I remember Tim Baker said in TBB4 when they measured arrow speed from different bow types that the bows with rounded belly performed unexpectedly good, despite more string follow -probably due to lower limb mass.
Aksel:
--- Quote from: Kidder on March 28, 2024, 12:06:25 am ---We should also remember that we are talking about a relatively small sample size - we probably have a few hundred (?) surviving examples (many of which are only partial examples) over a period of thousands of years where we have to assume that probably millions of examples were made by many thousands of bowyers. To take a single or even a few similar examples from a specific time period and location and extrapolate that to conclude that “bows of this period, or that location were ————“ is probably beyond what can actually be said. I think the only safe conclusion is where environmental limitations necessitated a particular design ie cable backed bows by the Inuit.
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Maybe 100 bows from early+late stone age in Europe. Tim Baker said in TBB about the Holmegård bow" it was preserved by a random act of nature and is therefore probably a random bow of it´s time". Not sure if that´s true but we have the material we have and there are patterns. But sure, we can never be sure. My main thinking on this question is that there can´t be anything random or only "fashionable" in something that has lasted for thousands of years. Must be something that works very well.
Aksel:
--- Quote from: Del the cat on March 28, 2024, 08:49:04 am ---Just a couple of thoughts...
'Flat' doesn't occur very often in nature ( although, some rocks cleave flat and Ice is pretty flat) , and you tend to need something flat to create another flat surface. I suggest the curve is simply a more natural shape resulting from the working practices.
from a technical stand point, I think a flat belly tends to become slightly concave as it is bent and concentrates stress on the edges?
Del
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Some things are flat in nature. The surface of a lake, the horizon and I have seen a tool box made from oak boards from Neolithic times. So surely they knew how to work wood and knew the concept of flat. But I see what you mean - you have a point, but evidently there are bows with perfectly flat surfaces. That a convex surface flattens or becomes concave when bent is true and an interesting thought, I will have to think more about it.
Aksel:
I have been looking a little closer on the finds and it seems there is, perhaps, a clue:
The bows with flat (or close to flat) belly all seem to come from a sapling of around 2 inches.
The bows with a lenticular cross section all come from larger trees, around 4 inches.
My first reaction was thinking: it´s probably to much work to work a thicker sapling flat, but they seem to have been looking for a symmetrical cross section. The bows with a more rounded belly are also worked on the back to get that symmetrical lenticular cross section, others have a rounded belly to match the crown of the back. You can see this in the images I posted in the previous page.
Does this seem logical and anyone got a clue why?
willie:
what seems illogical when looking at the top pic you posted in reply 4, is why, when working with an apparently larger diameter stave, the bowyer would create extra crown on the back by rounding the back edges so hard?
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