Benefits of a lenticular crossection for white wood bows?

[RyanY]

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.

[Kidder]

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.

[Del the cat]

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

[Aksel]

Hey Aksel, I don't doubt there are paleolithic bows out there with really flat bellies, It would just be harder to make them flat, vs lenticular, especially with stone, or bone tools
The cross sections that you show are lenticular in the working portion of the limb(wide), one is flat on the narrow non working or barely working portion.
That makes sense to me as very little tillering needs to be done on the levers, once you have initially roughed in the intended dimensions . The width is very narrow here, so it matters less if its flat or rounded, as its not as difficult to get the intended result. The wide working portion is a different matter.

The lenticular cross section lessens the chance of twist, as the centre of the belly acts as a keel. Over a 2" wide working limb, it still acts as virtually flat, without the difficulty of achieving a perfectly flat belly. Even though the bellies on these bows are not truly flat, I've always seen them referred to as flatbows.

The concept of flatness, or straightness, especially in pre modern times was relative. Design was organic, with no dimensions other than hands, finger widths, spans etc. If it achieved the desired result, with less work, then that's likely to  be more common.

I agree that it might be harder to make a flat surface than a rounded with stone/bone tools. But I have made one elm bow with stone/bone tools and I managed to make the belly flat without much effort (especially since I am not a flintknapper, only with broken up flint stone). I also think modern people tend to under estimate the skill of the people of olden days. Also is the way we value/measure time completely different to theirs. But sure it make sense what you´re saying, although I don´t think (in general) they would take the "lazy" time saving route before the better more time consuming one and compromise with performance. But that´s only my feeling. Nice though to think about it and hear everybodys thoughts on this.

[Aksel]

I always like to think about,

and in the Americas, rectangular cross sections developed in similar cultures, but maybe after contact with metal tools?
the sudbury,  of course might represent a more "traditional" NA design

it would be interesting to see if there are any surviving examples of pre-migration Asian bows

Yes, I´d be interesting to find this out

[Aksel]

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.

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]

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.

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]

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

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?

[Aksel]

willie, yes it´s a bit mysterious. Especially on such a bow where the maker was trying to push the stave to max performance with really long stiff-ish levers. But it´s deliberate and seems he wanted that symmetrical thick lenticular cross-section. That bow is estimated to 74 inches btw...

[willie]

TBB 3

North Andaman Island bow staves were selected from small-diameter trees having a natural reflex in what would be the mid upper limb only. The stave was decrowned, back and belly, creating a wide, flat lenticular — therefore very flexible—finished limb. South Andaman Island limbs were straighter. Longman reported a similar design in the New Hebrides.

although maybe lenticular in this description referred to width profile rather than crossection profile

pics showing crossection with flat belly
https://www.tapatalk.com/groups/paleoplanet69529/some-details-of-a-south-andaman-bow-t38355.html

[Aksel]

Willie, yes I´ve seen those on PP.

Fascinating bows and proves that "primitive" people went to great lengths making very sophisticated bows with simple tools and didn´t settle for something only good enough.

Those incisions in the pictures btw resemble some found on mesolithic bows. Interesting.

[Selfbowman]

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.

Very true! I’ve played with this for twenty years now with Osage. Flat belly’s , long and skinny, rounded belly’s , wide flat belly’s, trapping the backs, narrow tips , reflex,deflex, and a SHELF ,all the time trying to achieve a faster smoother bow. And I keep going back to the bow you see me post so often. Bowyers of a thousand years ago were no different I’m sure.

[willie]

And I keep going back to the bow you see me post so often. Bowyers of a thousand years ago were no different I’m sure.

And I would like to think that any number of good designs would suffice, and at some point, a more deciding factor is the skill of the bowyer to execute exceptional tiller