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Benefits of a lenticular crossection for white wood bows?

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Aksel:
 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!

WhistlingBadger:
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.

Hamish:
 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.

willie:
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.

Aksel:

--- Quote from: Hamish 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.

--- End quote ---

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.

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