Author Topic: Belly profile  (Read 569 times)

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Offline Kidder

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Belly profile
« on: January 24, 2021, 03:19:12 pm »
I understand that with woods that are weak in compression, such as black locust, itís important to have a perfectly flat belly. As I understand it this is to spread the compression forces across the belly as much as possible. However, is there a benefit to a d-shaped belly profile on compression strong woods such as yew or ERC? Iíve got to think there would be otherwise wouldnít we always just make a flat belly? Thanks!

Offline mmattockx

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Re: Belly profile
« Reply #1 on: January 24, 2021, 03:40:30 pm »
Using a D shaped belly on compression strong woods is the same as trapping the back on tension strong woods. It helps balance the two sides so that one is not drastically weaker than the other and improves performance by straining all parts of the limb to an equal percentage of their maximum capacity.


Mark

Offline Pat B

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Re: Belly profile
« Reply #2 on: January 24, 2021, 03:45:36 pm »
It does add most of the strain down the crown of the belly.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline Kidder

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Re: Belly profile
« Reply #3 on: January 24, 2021, 05:50:29 pm »
That makes sense. So a follow up then - a bamboo backed ERC - what limb profile would you choose? Bamboo is so tension strong what youíre saying tells me to do a flat belly...

Offline mmattockx

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Re: Belly profile
« Reply #4 on: January 24, 2021, 07:18:38 pm »
That makes sense. So a follow up then - a bamboo backed ERC - what limb profile would you choose? Bamboo is so tension strong what youíre saying tells me to do a flat belly...

I would do anything bamboo backed with a flat belly.


Mark

Offline tradcraftsman

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Re: Belly profile
« Reply #5 on: January 24, 2021, 07:22:01 pm »
I haven't used any boo, but I did learn on some ERC.  IMO it is not dense enough to pair with boo.

Offline Kidder

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Re: Belly profile
« Reply #6 on: January 24, 2021, 08:29:00 pm »
I haven't used any boo, but I did learn on some ERC.  IMO it is not dense enough to pair with boo.
Iíve seen some boo backed ERC from members on here that were stunning. Yes, they were some of the best bowyers out there. But Iíve got some really straight grained, knot free ERC boards I picked up for this very reason. Iím going to give it a try. And if you never see one posted or see me post problems you can chime in ďI told you so!Ē

Offline mmattockx

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Re: Belly profile
« Reply #7 on: January 24, 2021, 11:16:46 pm »
But Iíve got some really straight grained, knot free ERC boards I picked up for this very reason.

Instead of bamboo you could try it with maple or hickory.


Mark

Offline Kidder

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Re: Belly profile
« Reply #8 on: January 25, 2021, 01:05:04 am »
But Iíve got some really straight grained, knot free ERC boards I picked up for this very reason.

Instead of bamboo you could try it with maple or hickory.


Mark

Iíve got some good hickory that would work for a backing - Iíll probably try it with both and see what I can come up with. Itíll be fun - even if it does explode...just so long as I walk away relatively unscathed!

Offline Dances with squirrels

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Re: Belly profile
« Reply #9 on: January 25, 2021, 05:26:12 am »
I know my opinion differs from many, but that's pretty much all it is, my opinion. To me, it's never necessary to make a bow with a perfectly flat belly. In fact, it's important to me to make my bows anything but flat. I just don't like it, don't need it, and won't do it. There are other ways to adjust for lesser woods, but if a wood is so weak in compression resistance that I can't use it with a radiused belly by tweaking other attributes to my liking, I just won't use it. That said, I've not found it to be the limiting factor some claim.
Straight wood may make a better bow, but crooked wood makes a better bowyer

Offline RyanY

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Re: Belly profile
« Reply #10 on: January 25, 2021, 07:32:52 am »
You can find a few examples of boo backed ECR if you do a search. Simson made one a couple years ago and it was gorgeous. I don't have a problem making flat bellied bows and think a flat belly will probably give the best chance of survival. A couple of the examples had trapped backs with the bamboo.

Offline mmattockx

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Re: Belly profile
« Reply #11 on: January 25, 2021, 09:22:26 am »
Iíve got some good hickory that would work for a backing - Iíll probably try it with both and see what I can come up with. Itíll be fun - even if it does explode...just so long as I walk away relatively unscathed!

One of the benefits of using board wood instead of bamboo is you can make the back lam as thin as you want, with no limitations imposed by the crown on the bamboo. With a good backing it shouldn't explode, that usually requires a tension failure and you are more likely to overwhelm the ERC on the belly and end up with a lot of set or a buckled limb at worst.


In fact, it's important to me to make my bows anything but flat. I just don't like it, don't need it, and won't do it.

Why do you prefer a rounded belly?

It isn't a matter of opinion that a flat belly or back surface is the structural optimum, but there can always be other considerations you feel are more important.


Mark
« Last Edit: January 25, 2021, 09:28:40 am by mmattockx »

Offline Dances with squirrels

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Re: Belly profile
« Reply #12 on: January 25, 2021, 11:10:15 am »
Mark, yeah, I have plenty of considerations beyond 'structural optimum' in wooden bows.

As far as belly shape, I prefer a radiused belly for several reasons. I like the look. Flat bellies look unfinished and unrefined to me. It's just my preference, but I don't want a flat spot anywhere on my bow if I can help it. All rounded and curvy and smooth looks and feels more natural and attractive to me. I like how they better create a sense of 'flow' from end to end and all around, can't hardly tell where one part stops and another begins.

Imo, a perfectly flat belly shape can be harder to maintain during construction, more-so the more character a stave has. It's more difficult to navigate flatness around snakey grain with leans to and fro or humps and dips. Radiused bellies just seem to transition through that stuff with relative ease. They also mate better with my favorite handle design, which together allow added on handle pieces to be feathered in from working limb laterally as well as longitudinally, which I suspect in composite bows, distributes those stresses over more and different area and means less chance of a glue joint failing with no need for pedestals, powerlams, etc.

Speaking of thin hickory backing. I made a black cherry bow with quartersawn hickory backing, just 1/16" thick. Its cross section is squashed down compared to an osage bow but the belly is fully radiused, 1 5/8" wide, 68" ntn, and 58# @ 28". Still holds glued in reflex and cherry feels light as a feather. Even cherry doesn't 'have' to be flat.
Straight wood may make a better bow, but crooked wood makes a better bowyer

Offline mmattockx

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Re: Belly profile
« Reply #13 on: January 25, 2021, 11:16:47 am »
Mark, yeah, I have plenty of considerations beyond 'structural optimum' in wooden bows.

That's fair. There is lots of room to make whatever appeals to you. I can see your point about character staves as well. Trying to keep a flat belly on a twisty piece of osage would be very hard and it would look terrible as well. Radiused surfaces will look much better in that case.


Still holds glued in reflex and cherry feels light as a feather. Even cherry doesn't 'have' to be flat.

I bet that is a sweet bow. Nothing 'needs' to be flat, it is just the most efficient way to use the material. As long as the stresses are kept low enough (through limb length and/or width) most any cross section will work fine with any reasonable bow wood.


Mark
« Last Edit: January 25, 2021, 11:21:00 am by mmattockx »

Offline Dances with squirrels

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Re: Belly profile
« Reply #14 on: January 25, 2021, 11:24:14 am »
I agree.
Straight wood may make a better bow, but crooked wood makes a better bowyer