Author Topic: Compression Woods?  (Read 11106 times)

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Offline gfugal

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Compression Woods?
« on: February 18, 2017, 10:10:01 am »
I'm convinced that there are two limiting factors in wood. Tension strength on the back of a bow is the limiting factor for a bow breaking. If you are making a self-bow this should be the main consideration when choosing a bow material. However, if you are making a backed bow, especially sinew, I feel the limiting factor is the wood's compressive ability. It will still probably break on the back before it brakes on the belly, but the reason compression is the limiting factor is because of set. Set represent internal damage to the cell walls in the wood. Once set occurs it is irreversible. It's theorized that set causes hysteresis. The more damage the more internal friction and less spring back capability. thus its compressive ability isn't limiting due to breaking, but its performance. That's why horn bows use horn. The large amounts of sinew allow the bow to bend great distances without breaking, but if it had a wood belly, it would undergo so much compressive damage that it would loose most of its elasticity.

So here's my question. I like backed bows (I might have a self bow phase after I get over my shorter backed bows), so I'm looking for good compressive woods. Does anyone have a list of woods that have great compressive abilities? I know off ipe, and I think I heard juniper is good, but I'm not sure. I don't think I'm quite ready for horn bows. I'm going to wait till I have more experience under my belt. I understand that set is going to happen, but I'm wanting to try and limit it as much as possible.

« Last Edit: February 21, 2017, 04:30:29 pm by gfugal »
Greg,
No risk, no gain. Expand the mold and try new things.

Offline Badger

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Re: Compressive Woods?
« Reply #1 on: February 18, 2017, 10:35:47 am »
 Osage, plum and yew are the best I know of. Ipe behaves very well but not as elastic as some other woods.

Offline Springbuck

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Re: Compressive Woods?
« Reply #2 on: February 18, 2017, 04:00:54 pm »
 Sinew backing makes woods compress LESS, not more.

  Second, I'm convinced a lot of bows that look like they failed in tension actually failed in tension when they break.  Set is absolutely an issue, but whenever I can't ID another cause like a bug hole or a nick, I wonder.  Whenever I see a fret, you can see also that there is a subtle kink or hinge, and that angle is where the back will get over-strained and pop a sliver, and it goes in the next second.

NOW, I was literally on this exact track once and let me tell you what I found out.  Tim Baker was right, design is king.  I was convinced that if I got super strong backings (bamboo), and super strong belly woods (ipe, bullletwood) that the back would never pop and the belly would never crush and we'd all live happily ever after. I bought brazilwood, granadillo, greenheart, massaranduba, jatoba, coyote, Peruvian walnut, osage orange, ipe, kingwood, pau-ferro, ebony, tropical bamboos, etc... and they all worked, but there was NO super-wood out there.

ANY WOOD CAN BE BACKED.  It's all a question of balance, limb width, trapping, and design.  I have seen red eolm backed with bamboo.  I have backed hickory with bamboo, etc...

Woods offer compressive STRENGTH, and compressive ELASTICITY.  Bamboo offers tension STRENGTH, sinew offers tension ELASTICITY.  The really important thing is figuring out how to best use the qualities.

Offline Badger

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Re: Compressive Woods?
« Reply #3 on: February 18, 2017, 05:54:31 pm »
   I agree with you springbuck. I honestly can't always tell if something fails in tension or compression first, I have heard they usually fail in compression but it can be hard to tell the difference.

Offline gfugal

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Re: Compressive Woods?
« Reply #4 on: February 18, 2017, 06:28:06 pm »
Sinew backing makes woods compress LESS, not more.
Good catch. What I meant was that a piece of wood can bend much further with sinew than normal, so it can undergo more compression than it would have if it is bent further.
Second, I'm convinced a lot of bows that look like they failed in tension actually failed in tension when they break.
I assume you mean "that look like they failed in tension actually failed in compression"?
Tim Baker was right, design is king.  I was convinced that if I got super strong backings (bamboo), and super strong belly woods (ipe, bullletwood) that the back would never pop and the belly would never crush and we'd all live happily ever after. I bought brazilwood, granadillo, greenheart, massaranduba, jatoba, coyote, Peruvian walnut, osage orange, ipe, kingwood, pau-ferro, ebony, tropical bamboos, etc... and they all worked, but there was NO super-wood out there.
Wow you really took it seriously. I'm Impressed. Don't worry I'm not going to go all out and get exotic woods like that. I love the idea of usuing inferior woods. I was just curious if there was some common easily attainable woods that would be better suited for more stressful compact designs.
Woods offer compressive STRENGTH, and compressive ELASTICITY.  Bamboo offers tension STRENGTH, sinew offers tension ELASTICITY.  The really important thing is figuring out how to best use the qualities.
When you say compressive elasticity, do you mean its speed to spring back to its original shape?
Greg,
No risk, no gain. Expand the mold and try new things.

Offline Limbwalker

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Re: Compressive Woods?
« Reply #5 on: February 18, 2017, 07:17:01 pm »
Oh boy, remind me to keep this short. Disclaimer: I'm not the voice of experience for bow making.
With that said I do know a large amount about wood(s) and not just bow woods.Take what I say as food for thought, obviously everyone must form their own beliefs and from my experience common sense is my best friend. Sometimes I loose my friend, but I try to be mindful of my friend.

This is my approach. About 6 months ago I built my first bow. It was pretty awful. I don't watch TV and rarely Youtube, but I watched one video on a selfbow and I was off to the races. Well after my first aremlts I clearly needed to do more homework. That's how I found this place. I've read tons of threads. I love reading.

I knew nothing about dimensions and the forces at play really my first bow. I'm 6' tall and my draw length is 28". I decided to make my first bow 40", but it looked a little too long so I lopped off another two inches. Hickory self bow. Still have it. It's tiny. I was able to get the draw length to 19" before I thought it might fold. I know about leverage what was I thinking? I wasn't at first. Here is what I did learn.

The bow took very little set actually. I didn't know what set was though. Those hickory limbs are paper thin and the tips are more like pins. I didn't dare even try to bend it until I was near final dimensions. I think it pulls #30 something pounds. I didn't know it then, but not over building your bow and not bending the heck out of it while building it help keep the cells intact. This I can tell you, wood is wood. It is only so strong, resilient, elastic ect. What ever wood you do work with, give to it and it will give back and perform. Burden the wood with extra mass and cracking its spine a hundred times before it's braced and it will slouch, struggle and eventually break.

After this bow I read. I've made six and working on seven. I told myself I want to to build bows this way. I floor tiller enough to get a feel for the particular wood and then by feel, take it to near finished dimensions and if the belly needs toasting, I do all that before ever bending it. Now my bows have come back too light for what I was aiming for but not terrible. They made good gifts for my teenage nephews. I am determined to learn this way. Some feel like it is a bad way to go, but I am confident with my realatinship with 'wood' and as I get a better feel, I'm going to zero in and start producing good stuff.

Bowers say all bows set to some degree, I believe that because it's wood we are dealing with. Just keep exploring and forming your style and don't get down on yourself when you mess up. Reading is a good tool to help with learning curve, experience is knowledge so keep up the good work. I knew I couldn't keep it under three paragraphs, so I might as well tell you what I really think,

Cheers,

Of course I screw up all the time. All the time. I aim for the bullseye though. So there are superior compression woods, but if you don't have that wood, then what? It's all wood.

Offline ty_in_ND

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Re: Compressive Woods?
« Reply #6 on: February 18, 2017, 11:45:15 pm »
NOW, I was literally on this exact track once and let me tell you what I found out.  Tim Baker was right, design is king.  I was convinced that if I got super strong backings (bamboo), and super strong belly woods (ipe, bullletwood) that the back would never pop and the belly would never crush and we'd all live happily ever after. I bought brazilwood, granadillo, greenheart, massaranduba, jatoba, coyote, Peruvian walnut, osage orange, ipe, kingwood, pau-ferro, ebony, tropical bamboos, etc... and they all worked, but there was NO super-wood out there.

ANY WOOD CAN BE BACKED.  It's all a question of balance, limb width, trapping, and design.  I have seen red eolm backed with bamboo.  I have backed hickory with bamboo, etc...

Woods offer compressive STRENGTH, and compressive ELASTICITY.  Bamboo offers tension STRENGTH, sinew offers tension ELASTICITY.  The really important thing is figuring out how to best use the qualities.

2 of my most favorite bows I look back to on this site from time to time are "unconventional" combos: A maple backed black cherry bow (https://www.primitivearcher.com/smf/index.php/topic,30235.0.html) and a bamboo backed padauk bow Bubby made a few years ago (http://www.primitivearcher.com/smf/index.php?topic=50466.0).  There was even a thread from about a year ago about making bows from unconventional woods (cottonwood, poplar/aspen, etc... pretty sure Plan B made a cottonwood bow that looked pretty sweet).
"The best prize that life has to offer is the chance to work hard at work worth doing."

mikekeswick

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Re: Compressive Woods?
« Reply #7 on: February 19, 2017, 12:16:08 am »
Sinew backing makes woods compress LESS, not more.

  Second, I'm convinced a lot of bows that look like they failed in tension actually failed in tension when they break.  Set is absolutely an issue, but whenever I can't ID another cause like a bug hole or a nick, I wonder.  Whenever I see a fret, you can see also that there is a subtle kink or hinge, and that angle is where the back will get over-strained and pop a sliver, and it goes in the next second.

NOW, I was literally on this exact track once and let me tell you what I found out.  Tim Baker was right, design is king.  I was convinced that if I got super strong backings (bamboo), and super strong belly woods (ipe, bullletwood) that the back would never pop and the belly would never crush and we'd all live happily ever after. I bought brazilwood, granadillo, greenheart, massaranduba, jatoba, coyote, Peruvian walnut, osage orange, ipe, kingwood, pau-ferro, ebony, tropical bamboos, etc... and they all worked, but there was NO super-wood out there.


Me too! Been there done that. There is no magic wood! There are many variables but DESIGN IS KING.
However horn/maple/sinew is pretty close to magic. :) :) and lots of cultures worked that out a long time ago!

ANY WOOD CAN BE BACKED.  It's all a question of balance, limb width, trapping, and design.  I have seen red eolm backed with bamboo.  I have backed hickory with bamboo, etc...

Woods offer compressive STRENGTH, and compressive ELASTICITY.  Bamboo offers tension STRENGTH, sinew offers tension ELASTICITY.  The really important thing is figuring out how to best use the qualities.

Offline Limbit

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Re: Compressive Woods?
« Reply #8 on: February 19, 2017, 03:35:33 am »
Incense cedar is a great choice for a compression wood since it handles compression just as well as juniper, but actually grows straight...unlike juniper. Black Cherry is another wood that is considered a compression wood from what I have read. Like other people mentioned, plum is really great for compression and is just a great bow wood all around. The acacia that grows where I live (Acacia confusa) handles both compression and tension excellently and is very similar to rosewood in its properties. Then, there is always compression conifers like compression pine or compression spruce. I have no experience with either, but they were used traditionally by several cultures. If you haven't heard about these, there is plenty of info on compression conifers online and what causes them in nature. From conversations I have had with other bowers, many compression woods have a sluggish recovery time. I think this is another reason why prestressing the sinew into the design is an important factor for compression wood bows.

Offline Hrothgar

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Re: Compressive Woods?
« Reply #9 on: February 19, 2017, 06:17:21 am »
You can add locust and mulberry to your list also.
" To be, or not to be"...decisions, decisions, decisions.

Offline Springbuck

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Re: Compressive Woods?
« Reply #10 on: February 19, 2017, 11:30:32 am »
You can add locust and mulberry to your list also.

Yes you can...

And, I really appreciate the link to those two cool bows.


  Actually, though, elasticity doesn't mean the speed with which wood it can return to shape.  That's more about hysteresis, which I don't understand very well.

  Compression elasticity really means simply that it WILL return to shape when squished.

   Some woods RESIST compression well, take a huge amount of pressure to physically compress, and store a lot of energy by being compressed only a little distance, but under great pressure.  That's ipe, for instance.  These woods are very stiff, and it doesn't take much of it to make a bow belly.

   Some woods willingly compress quite easily under moderate pressure, and will gladly squish down for you a good percentage.  They too store energy, but likewise readily spring back to full length once the pressure is relieved.  These woods are less stiff (easy to compress belly=easy to bend limb), but can often be used in deep, thick designs where the belly compresses a lot. Yew is classic, ERC and juniper follow.

  Someone mentioned black locust.  Well BL is great belly wood, BUT has a reputation for weakness in compression.  What's happening here, I believe, is that locust is STIFF like ipe, but won't hold together as well once it IS compressed.  So, locust is (almost) as hard to compress as ipe, but you have to compress it incrementally less, or it will fail.

 Take something like elm next.  Elm is much easier to compress than locust, but will only handle about the same AMOUNT of compression before it wants to stay squashed on the belly.

I think.

Offline Springbuck

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Re: Compressive Woods?
« Reply #11 on: February 19, 2017, 11:31:43 am »
And, correct, I did NOT mean "tension" twice!

Online DC

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Re: Compressive Woods?
« Reply #12 on: February 19, 2017, 11:41:14 am »
And I still think we need a sugar daddy to pay for tests as they relate to bow making :D
Vancouver Island
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Offline willie

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Re: Compressive Woods?
« Reply #13 on: February 19, 2017, 12:11:13 pm »
Springbuck, nice explanation of compression and response.

I guess that hysteresis understood in the classical way, is just the difference between energy in vs. energy out.

As far as launching an arrow goes, one understanding of hysteresis could be that some of the energy put into the limbs cannot be delivered fast enough upon release to contribute to the continued acceleration of the arrow. The arrow accelerates up to a point where limbs can not make it go any faster, and any remaining energy in the limb is "lost"



« Last Edit: February 19, 2017, 06:15:44 pm by willie »

Offline Limbwalker

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Re: Compressive Woods?
« Reply #14 on: February 19, 2017, 06:06:16 pm »
Here is an article I read the other day for work and thought some of you may find it useful, or not.
As you already know wood comes from trees and (some) bows come from wood, the article is fairly on topic.

I added another article for anyone interested, I understand some people here already may know this stuff, it can help to know some of the things discussed in the articles when your out collecting staves, or if using limb wood.

I'm getting at something, I'm not being extremely clear, but there is reason for that. Anyway when your out hunting for staves knowing what spieies you want is all fine and if you find a tree or limb that is straight and minimal knots, good. But those things don't mean your stave is going to be that good. As you know trees are living and they are outside every day and night, through every thunderstorm, wind storm, hurricane etc. They compensate on their own to deal with forces and compression is a force trees naturally deal with. Trees are stuck in the soil and cannot alter the soil to their needed PH. You can tell a lot by looking at many other things besides no knots and a straight piece. Learn how different species deal with compression/tension and use it in your bows. I agree some wood handles compression better than others. But if the cells are abused, having a "good" compression wood doesn't matter.

For me, the issue of finding the perfect wood and wood combinations doesn't carry much weight. If one is so intent on finding it, they should probably just make glass bows because wood will always be wood. Be well,

This is not directed at any one individual, simply some thoughts on the matter.

https://www.dropbox.com/sh/axohbuvobt976p8/AADuwA9miZa7L8nxbDMtmLqEa?dl=

« Last Edit: February 21, 2017, 06:51:41 pm by Limbwalker »