Author Topic: rounded belly  (Read 694 times)

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Offline gfugal

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rounded belly
« on: November 09, 2017, 08:39:47 am »
So I'm trying to have an open mind, but I'm not seeing how a rounded belly (other than rounded corners) is more beneficial than a flat bow? Enlighten me. From a physics standpoint, by rounding the belly your essentially doing the same thing as a crowned back. It causes the middle fibers to be further from the neutral plane and thus under more stress. Wouldn't it be better to evenly distribute the load between as many fibers as possible? In fact, If you have a crowned back wouldn't you want to hollow out the belly?

If the reason is aesthetic, then I'm okay with that. As long as it's in the realms of what the material can take then who cares right? but if you're going to tell me it's better mechanically I'm going to need you to convince me. Also, I heard that ELB were designed the way they were so they could get more bows out of the yew they had, so that's always another reason but that's not really an issue today as we aren't chopping all the yew trees for our military anymore.
Greg,
No risk, no gain. Expand the mold and try new things.

Offline gfugal

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Re: rounded belly
« Reply #1 on: November 09, 2017, 08:41:06 am »
Sorry if this opens an old can of worms
Greg,
No risk, no gain. Expand the mold and try new things.

Online bradsmith2010

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Re: rounded belly
« Reply #2 on: November 09, 2017, 09:12:30 am »
I am not sure most think it is more beneficial ,, it does work,, there are other designs that work as well,, and from what i know it really depends on the kind of wood as well,, Badger mentioned he made a english long bow for someone that set flight shooting record,, and I think that says alot,,, I dont make them so it is out of my area of expertise and have relied on the documentaion of others to make my opinion,, ok well a long time ago I made a semi rounded belly bow and shot a buffalo with it,,, but I think any well made bow would have worked..

Offline High-Desert

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Re: rounded belly
« Reply #3 on: November 09, 2017, 09:22:37 am »
If everything is perfect and there is absolutely no misalignment in the limbs, a squared off corner would techniqually be better and distribute the load better, but this is not the case. Corners concentrate the energy and become areas that will splinter out, so by giving the corners a radius, it distributes the stresses over the radius and not at a difined point, and helps against splintering, in addition to a radius's look better than squared off corners....that's for glass bows.
Eric

Offline mikekeswick

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Re: rounded belly
« Reply #4 on: November 09, 2017, 09:39:16 am »
Yes the rectangular section is the 'best' for even distribution of strain but the rounded (subjective...how rounded?) belly section doesn't lose much to it. However when it comes to heavily ring porous woods like osage, ash, oaks etc a dead flat belly  with a thickness taper leaves a wide section of earlywood on the belly and it is easy to make a series of hinges each time you go down through a latewood ring into the earlywood. A gently rounded belly eliminates this potential problem by feathering the rings termination.
There is also the poisson effect to take into consideration with extreme thin/wide cross sections. The effect being more strain on the upturned backs edges. Of course this isn't a big deal on wooden bows but something to consider.

Offline gfugal

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Re: rounded belly
« Reply #5 on: November 09, 2017, 11:15:52 am »
Yes the rectangular section is the 'best' for even distribution of strain but the rounded (subjective...how rounded?) belly section doesn't lose much to it. However when it comes to heavily ring porous woods like osage, ash, oaks etc a dead flat belly  with a thickness taper leaves a wide section of earlywood on the belly and it is easy to make a series of hinges each time you go down through a latewood ring into the earlywood. A gently rounded belly eliminates this potential problem by feathering the rings termination.
There is also the poisson effect to take into consideration with extreme thin/wide cross sections. The effect being more strain on the upturned backs edges. Of course this isn't a big deal on wooden bows but something to consider.
The difference between growth rings is a valid point! and so is the corner rounding but that's not really what I'm wondering. I'm talking about like the deliberate crowning of the belly. such as depicted in this sketch
Greg,
No risk, no gain. Expand the mold and try new things.

Offline Stick Bender

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Re: rounded belly
« Reply #6 on: November 09, 2017, 11:16:35 am »
That was a interesting comment on poison effect but I'm wondering how much it really plays out on all wood bows that are well built maybe more so on hi stressed sinew bows or under built wood bows to be honest I never considered when making wooden bows but some thing to think about !
If you fear failure you will never Try !

Offline gfugal

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Re: rounded belly
« Reply #7 on: November 09, 2017, 11:19:25 am »
I feel like I'm missing something. What's the poison effect?
Greg,
No risk, no gain. Expand the mold and try new things.

Offline Stick Bender

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Re: rounded belly
« Reply #8 on: November 09, 2017, 11:30:39 am »
Basically in very simple explanation in a thin wide limb or a high stressed back the limbs warp on the outer edges it can cause failure ! Something that's not discussed in all wood bows often !
If you fear failure you will never Try !

Offline High-Desert

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Re: rounded belly
« Reply #9 on: November 09, 2017, 11:31:29 am »
The picture with rounded belly is most likely an older photo, my guess is that's from the time they made bows based off of the ELB design, in the time when the only good woods were yew, Osage and lemonwood.
The poissen effect just says that a material that is compressed will expand perpendicular to the applied force and contract when under tension. Since the back is under tension, the material borrows while the belly expands causing the upturned edges mikekeswick mentioned. Which would cause some concentration of forces.
Eric

Offline PatM

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Re: rounded belly
« Reply #10 on: November 09, 2017, 11:49:07 am »
 During the heyday of the rounded belly the woods used could take that shape. They were not limited to The "big three" either.  Many tropical woods were available then and the British bowyers of the time used them all.   Lancewood, Snakewood, Ruby Wood, Fustic etc.

 Logically a fishing rod and a whip and trees themselves are round and bend a lot so there's no reason to think a bow can't just be made the same.

Online bradsmith2010

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Re: rounded belly
« Reply #11 on: November 09, 2017, 11:52:48 am »
those guys that wanted a bow to shoot further would just shoot a heavier bow,,

Offline willie

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Re: rounded belly
« Reply #12 on: November 09, 2017, 12:08:40 pm »
Quote
I feel like I'm missing something. What's the poison effect?
if you bend a square pencil eraser, you can see cupping on the back that necessitates the need for the corner radius (on the back). Of course the opposite happens on the belly, and the belly tend to become more rounder.
I once heard an explanation about some belly wood being overly strained is an acceptable tradeoff from performance, if the strain on the back can be reduced. Makes more sense if your in a situation where your life depends on keeping a working bow.

Offline Dances with squirrels

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Re: rounded belly
« Reply #13 on: November 09, 2017, 12:49:13 pm »
I have YET to make a wooden bow with a board-flat belly. All are fully radiused... ELB, flatbows, d/r, recurves, all of em. Generally, the lesser the wood, the wider and thinner and/or longer the limbs, and so by default... the more subtle the radius... but it's radiused.

Flat bellies just ain't done yet  ;)

Offline DC

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Re: rounded belly
« Reply #14 on: November 09, 2017, 12:51:01 pm »
I can't get a flat belly on me, so I put then on my bows ;D ;D ;D
Vancouver Island