Author Topic: Benefits of a lenticular crossection for white wood bows?  (Read 3609 times)

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Offline Aksel

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Benefits of a lenticular crossection for white wood bows?
« on: March 26, 2024, 06:14:40 pm »
 I always like to think about, and make historical replicas of old bows and I recently posted a flat bellied lever-tipped elm bow. The bow shoots really great and everyone seems to agree on flat bellies are the best for "white woods" to keep set low and speed up.

But when I look in my books on stone age bows -the golden age of self bows - I always wonder about all the bows with rounded bellies, because they existed parallell with others with flat bellies, some even found together.

The famous Möllegabet bow has rounded belly
Several of the Tybrind Vig bows (about 2 dozen lever tipped bows) have rounded bellies
The 2 most extreme AND refined lever tipped bows, the Hjärnö bow and the Maglemose Vange- bow (last one a 74" lever tipped bow) have lentil shaped bellies.
Also, several ordinary flatbows have rounded bellies.

If those superb bowmakers made the effort to shape rock-hard elm with stone tools into Lever tipped bows (and presumably understood the mechanics behind them), wouldn´t they also have understood the "benefits" of flat bellies -especially since they made others with flat bellies? I´m thinking there must be something over looked here... These bows existed over thousands of years over large areas.

I have made successful bows in the past with lentil shaped bellies, also with low set, but abandoned them due to "common wisdom" nowadays.

I´m curious on everybody´s thoughts on this!

« Last Edit: March 27, 2024, 05:06:38 pm by Aksel »
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Offline WhistlingBadger

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Re: Benefits of lentil-shaped crossection?
« Reply #1 on: March 26, 2024, 06:31:18 pm »
I've wondered about this too.  Chuck Loeffer, following Native American design, uses a lenticular cross-section in his juniper-sinew bows too, and I've never quite understood why.
Thomas
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Offline Hamish

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Re: Benefits of lentil-shaped crossection?
« Reply #2 on: March 26, 2024, 10:13:04 pm »
 I think at least part of the reason for a not totally flat belly, is due to primitive tools. It's easier to do a flatish lenticular cross section than a totally flat belly, even when using modern hand tools. Even a steel card scraper has trouble along a wide limb, removing wood evenly across the width, with one pass. Yes, it is achievable with rasps and scrapers but harder in my opinion.

Dean Torges book, Hunting the Osage Bow gives good reasoning for the faceted tillering approach, which delivers a lenticular cross section. How the bow bends along the limb is mainly controlled on the peak of the belly, and weight reduction and limb twist mainly on the outer edges of the belly.

Torges also thought the modern flatbow, came about with the availability of the stationary belt sander and drum sanders, in mass production. These tools automatically try and create a flat belly when used to tiller.

Offline willie

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Re: Benefits of lentil-shaped crossection?
« Reply #3 on: March 27, 2024, 01:15:47 am »
flat bellies stress the back more.
reliability trumps performance and a soft shooter works better than a broken back.
consider a whitewood bow that may get back dings and dried out over a fire sometimes.
« Last Edit: March 27, 2024, 01:22:12 am by willie »

Offline Aksel

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Re: Benefits of lentil-shaped crossection?
« Reply #4 on: March 27, 2024, 06:19:11 am »
I think at least part of the reason for a not totally flat belly, is due to primitive tools. It's easier to do a flatish lenticular cross section than a totally flat belly, even when using modern hand tools. Even a steel card scraper has trouble along a wide limb, removing wood evenly across the width, with one pass. Yes, it is achievable with rasps and scrapers but harder in my opinion.

Dean Torges book, Hunting the Osage Bow gives good reasoning for the faceted tillering approach, which delivers a lenticular cross section. How the bow bends along the limb is mainly controlled on the peak of the belly, and weight reduction and limb twist mainly on the outer edges of the belly.

Torges also thought the modern flatbow, came about with the availability of the stationary belt sander and drum sanders, in mass production. These tools automatically try and create a flat belly when used to tiller.

Facet tillering method makes some sense but doesn´t explain why they did some bellies flat and others not. One Holmegaard bow is +2" and has a perfectly flat belly. Other bows´ bellies are very deliberately shaped high with a well rounded belly. They also change the cross section of the lever part on several bows which makes me think there is logic behind it. You can see in the 2nd illustration how they even shaped the back of the bow to get that particullar cross section.
« Last Edit: March 27, 2024, 06:34:18 am by Aksel »
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Offline Aksel

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Re: Benefits of lentil-shaped crossection?
« Reply #5 on: March 27, 2024, 06:29:13 am »
flat bellies stress the back more.
reliability trumps performance and a soft shooter works better than a broken back.
consider a whitewood bow that may get back dings and dried out over a fire sometimes.

Almost all these bows are made from elm which can handle stressed backs well, and some of them did have perfectly flat bellies. They obviously thought about peak performance with some of those extreme lever tipped bows - but made them with lenticular shaped bellies. Between this bow illustrated (Hjärnö) with rounded belly, and the older holmegaard bow with perfectly flat belly, there is apr. 5000 years! Makes you wonder...
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Offline Aksel

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Re: Benefits of lentil-shaped crossection?
« Reply #6 on: March 27, 2024, 06:38:24 am »
I've wondered about this too.  Chuck Loeffer, following Native American design, uses a lenticular cross-section in his juniper-sinew bows too, and I've never quite understood why.

I don´t know much about native american bows, even less of sinew backed bows. But I have worked with juniper, it´s nice and sof and easy to work. Maybe did they go for lenticular cross section because juniper is less tension strong?
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Offline Kidder

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Re: Benefits of lentil-shaped crossection?
« Reply #7 on: March 27, 2024, 07:14:50 am »
Ever notice how we all build different styles of bows? I can see a certain bow and tell you which member made it (some of the time). Maybe it’s the same throughout history with different builders having different design preferences. And then there are the bows built in a certain style because that was what the wood gave us. I imagine two bowyers sitting around a fire thousands of years ago having this same debate.

Offline Aksel

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Re: Benefits of lentil-shaped crossection?
« Reply #8 on: March 27, 2024, 07:48:59 am »
Haha yes that has of course some truth to it, but I don´t think, over thousands of years, the tried and tested designs they came up with has as much to do with taste as with functionality since they depended on those weapons. In Switzerland they made yew bows with concave bellies instead, which also must have had to do with performance and not taste.
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Offline willie

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Re: Benefits of lentil-shaped crossection?
« Reply #9 on: March 27, 2024, 07:53:04 am »
a question about the Hjarno a little off topic if you dont mind.

do you have or can point to any pics of a  hjarno style that show handle details or crossections?
thanks

Offline Aksel

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Re: Benefits of lentil-shaped crossection?
« Reply #10 on: March 27, 2024, 08:22:46 am »
willie: its handle is 29 mm thick and 24 mm wide. Looks comfortably rounded. Reported to be 120mm long. I do not have other details of the grip but there are pics: https://www.tradgang.com/tgsmf/index.php?topic=178571.0
« Last Edit: March 27, 2024, 12:00:50 pm by Aksel »
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Offline superdav95

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Re: Benefits of lentil-shaped crossection?
« Reply #11 on: March 27, 2024, 11:25:00 am »
Interesting post.  Now that I look back at my builds I can say that I tend to make my yew bows more rounded/ lenticular belly then I do with hardened white woods or Osage bows.  Not to say that I did this deliberately but more subconsciously I think.  Maybe more of a styling thing or by feel.  Not sure on this actually.  It just seemed like they looked and felt better made that way.  I cannot say that I’ve done enough testing of each shape to see a particular performance advantage either.  I think that kidder is onto something about personal preference factor and personal style of bow builds.  This being said we bow builders today still like to replicate things that we admire.  A personal reflection for me is the mollegabet style bows.  I’ve made several of them and have never claimed that they are replicas or dimensional copied even.  I make them loosely based I guess while adding my own flare to them.  Some may say this is subjective and varies wildly even in deliberate replicas.  I wonder if this is partly what has happened over time with bows that seem similar in style over time in this case thousands of years. 
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Offline Aksel

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Re: Benefits of lentil-shaped crossection?
« Reply #12 on: March 27, 2024, 05:01:01 pm »
Superdave, for sure can trends play a part in this, but i wouldn´t think they would last over 5 thousand years if performance didn´t play a big part in it also.

With the wooden bow revival -over the last 30 years or so - we keep "discovering" things stone age man knew 10´000 years ago; super skinny tips, sapling bows, lever tipped bows, Hollow limb design, probably fire hardening as well just on top of my head. I am convinced there are more things to discover, and cross sections are one of them.  ;)
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Offline Hamish

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Re: Benefits of a lenticular crossection for white wood bows?
« Reply #13 on: March 27, 2024, 06:29:03 pm »
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.


Offline willie

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Re: Benefits of a lenticular crossection for white wood bows?
« Reply #14 on: March 27, 2024, 07:08:36 pm »
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