Author Topic: Compression Woods?  (Read 25192 times)

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Limbit

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Re: Compressive Woods?
« Reply #30 on: February 21, 2017, 11:06:20 pm »
I'm going to relist the woods suggested earlier:
Yew, Osage, Ipe, Black Locust, Plum, Juniper/ERC, Incense Ceder, Black Cherry, Padauk, Mulberry.
(Sorry SpringBuck, I didn't include your long list of exotic woods. I also didn't include very hard to come by, unfamiliar exotic woods in the following list either).
 
I also am going to propose some potential candidates for good compression woods based off my research from the wood database. They are:
Wenge, Olive, Lemonwood, Hickory, Dogwood, Indian Rosewood, Turkey Oak, Chinaberry, Muninga, Hophornbeam/European Hornbeam, Black Walnut/English Walnut, Blue Ash, American Beech, Yellow Birch, and Slash Pine.

Do any of you have it on good wisdom that any of these woods would make a bad compression wood for bows?

Some time ago, I did an attempt at deducing bow wood properties (tension and compression) from the wood database. See this post (and especially the graphs added) http://www.primitivearcher.com/smf/index.php/topic,50571.msg692147.html#msg692147

Meanwhile, I expanded the list (and figures) to some 100 wood species, and also compiled data for other materials such as bamboo, silk, horn, sinew, flax, jute, sisal, cotton, dacron, steel, ... even fibergl*ss)

Do take this with a good grain of salt (as the primary data may be a bit iffy at times with very limited tests per species, or strongly depending on test conditions such as wood MC), and remember (otherwise Jim Davis will correct me on this): the test on osage was done on green specimens and extrapolated to seasoned wood. So it likely represents an underestimation of its true properties.

But I fully concur with Springbuck: any wood can give good bows, but design (not osage) is king. I once made a shooter out of a board of scots pine at 0.35 SG...

Joachim
   

I was literally making a spreadsheet when you posted this haha. Thats cool man I'm going to have to look it over. I noticed that you have a "compression before set" value. How did you get that value, since the wood database doesn't have a measurement for it? Did you use the crushing strength value? When I was coming up with that list above I took into consideration the max crushing value, the ratio of MOR/MOE, as well as a new ratio of crushing strength/MOE. The last value isn't a real value but an arbitrary one I came up with, since the wood database doesn't specify a stress modulus of elasticity, wood would not have the same value like most materials. But I figured it would be somewhat proportional. To be considered the list the wood had to score high in all three areas (CS, MOR/MOE, and CS/MOE).

Chinaberry isn't really a compression wood of any notice...in fact it is hardly a bow wood of any notice despite have a good value on the bow wood index. I've worked with it several times and was never able to get a bow out of it. I think it may be a better wood in different growing conditions than what I deal with here.

Limbit

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Re: Compression Woods?
« Reply #31 on: February 21, 2017, 11:08:38 pm »
Oh, and Rosewood is an excellent compression wood, but good luck affording a piece of it. I made a black ebony bow some time back and it also made a nice bow, but I was never able to afford to try stressing the design to find out if it is weak in either tension or compression due to the cost of the wood. Like I said before also, Acacia is a great belly wood for compression.

Offline Selfbowman

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Re: Compression Woods?
« Reply #32 on: February 22, 2017, 12:59:22 am »
You can try lots of different woods but I suggest using one good wood and trying different designs . That's what I am doing. All wood is different even in the same tree. Placement of mass is what makes a good bow. Light on the ends ,width, thickness, length.  Using one wood will get you there faster in my opinion.  O:) but I am asking questions on here just like you.  ;D Osage does both well. For me it's selfbows not backed bows at this time. Good luck with you adventure. Arvin
Well I'll say!!  Osage is king!!

Offline loon

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Re: Compression Woods?
« Reply #33 on: February 22, 2017, 01:00:00 am »
Since I practice Korean archery, I'd like to know that it's doable to make a bow that does something similar to the synthetic Korean bows without using horn, but [still] with natural materials. I definitely like the much smoother feel of longer static recurve bows, though...

Could incense cedar sapwood or heartwood, sinew backed, be elastic enough to handle a 32" draw with a 50"ntn static recurve? (Korean design). Oh, and with something like 12" of resting reflex.
Sinew backed bamboo - yes, I saw one... but it's a bit strange since bamboo is so much stiffer in compression than sinew is in tension? Or is it? While horn seems to have similar stiffness in compression than sinew in tension.

Look at this crazy thing. It bends so much. Wonder how much hysterisis it has.
Code: [Select]
https://www.youtube.com/watch?v=mjd5gQx5uQU#t=1m9s
Would something that has a stiffness similar to sinew not be able to bend more, if sinew backed, than something stiffer?... .. Wouldn't materials with different stiffness, laminated, result in more shear force? So could incense cedar or juniper be better than bamboo sinew backed? (unless bamboo is less stiff in compression than I think)
« Last Edit: February 22, 2017, 05:08:54 pm by loon »

Offline willie

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Re: Compression Woods?
« Reply #34 on: February 22, 2017, 01:13:26 am »
Greg

Quote
Unfortunately, there isn't really a good value out there that's been maticoulsly measured in wood.


Yes , I agree. At least not a value that tells us bowyers much about energy storage before set reaches an unacceptable level.
I have found listings for "work to maximum load" or WML in some of the older data. It seems that when wood was used in applications where it was commonly strained to the point of failure, (mine timbers and vehicle parts come to mind), the WML was useful. I have not yet found a good (mathematical) explanation of how the value was obtained, but quite a bit of testing was done at one time, and  if a way was found to examine those values and perhaps make an adjustment  for more moderate levels of strains, the "obsolete" data might be useful for our purposes.

A recent thread where  WML is discussed some.

http://www.primitivearcher.com/smf/index.php/topic,59651.msg828984.html#msg828984
« Last Edit: February 22, 2017, 01:27:19 am by willie »

Limbit

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Re: Compression Woods?
« Reply #35 on: February 22, 2017, 07:40:41 am »
Since I practice Korean archery, I'd like to know that it's doable to make a bow that does something similar to the synthetic Korean bows without using horn, but with natural materials. I definitely like the much smoother feel of longer static recurve bows, though...

Could incense cedar sapwood or heartwood, sinew backed, be elastic enough to handle a 32" draw with a 50"ntn static recurve? (Korean design). Oh, and with something like 12" of resting reflex.
Sinew backed bamboo - yes, I saw one... but it's a bit strange since bamboo is so much stiffer in compression than sinew is in tension? Or is it? While horn seems to have similar stiffness in compression than sinew in tension.

Look at this crazy thing. It bends so much. Wonder how much hysterisis it has.
Code: [Select]
https://www.youtube.com/watch?v=mjd5gQx5uQU#t=1m9s
Would something that has a stiffness similar to sinew not be able to bend more, if sinew backed, than something stiffer?... .. Wouldn't materials with different stiffness, laminated, result in more shear force? So could incense cedar or juniper be better than bamboo sinew backed? (unless bamboo is less stiff in compression than I think)

Loon, not to be weird about it, but horn is a natural material. You could alternatively use bone. Possibly from a cow leg or giraffe or something with long legs and enough bone (you can easily find these bones online). Traditionally whale rib was used by some Arctic tribes to my knowledge. Horn has 8X the compressive ability of most wood. It isn't so much that cedar or juniper could or couldn't bend as far as horn ( I doubt it would, but who knows), it goes back to the graph listed above. At some point, even if the wood is still bending, it is going to deform and start taking a lot of set. Sinew offsets this, but that is sort of also missing the point. The woods ability to perform at maximum capacity before taking set and losing strength is what you are after. A lot of the really short incense cedar or juniper bows aren't ever pulled much past 22-24''.  This is stressing the wood just to the point you are getting the most out of it while at the same time utilising the sinew as much as possible by stretching it as far as possible. If you are trying at a full 30-32'' korean draw, horn or bone is really the best option. Bamboo has been used as both a core and belly material for these bows, but my understanding is that it is heavily heat treated to the point of blackening to increase its compression and help it resist set. Bamboo after all takes more set than any wood will, so this is important. If you are looking to make a bow out of something rather than horn, try heat-treated bamboo. You could even add a mulberry or maple core like the Koreans do to give it additional stiffness. It would be lighter than a hornbook since horn is quite heavy. It would be a cool project and I don't doubt you'd learn a lot, but I think horn is still far more durable and practical. 

Offline PatM

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Re: Compression Woods?
« Reply #36 on: February 22, 2017, 08:16:53 am »
Bone? Bone doesn't actually take a lot of bend.  Korean bows have been made with bamboo bellies. Bamboo doesn't really take more set than wood. It wouldn't make a fishing rod if it took set.

 

Offline PEARL DRUMS

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Re: Compression Woods?
« Reply #37 on: February 22, 2017, 08:49:38 am »
Do you think this would make a mighty fine, ligntning-hunting bow? I'm trying to make something real, real evil that I can hunt lightning with.

Good luck with your toe nail covered lightning hunting bow. I'm sure these guys will get to the bottom of it for you. Broad head design is MOST important for killing lighting.
Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize we cannot eat money.

Offline joachimM

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Re: Compression Woods?
« Reply #38 on: February 22, 2017, 04:44:44 pm »
Bone? Bone doesn't actually take a lot of bend.  Korean bows have been made with bamboo bellies. Bamboo doesn't really take more set than wood. It wouldn't make a fishing rod if it took set.

If I take data on the elastic modulus for bone, plus ultimate tension and compression strengths (from this 1974 paper http://dx.doi.org/10.1016/0021-9290(74)90018-9), it indicates that bone fails in tension at an elongation of c. 0.8% (which is less than most bow woods), and fails in compression (beyond the yield point) at a compression of nearly 1.2%, which is better than any wood. but it's darn heavy (SG c. 2.0). For its mass, it stores about the same amount of energy (in compression) as good bow woods. Overall, I'd say it's not that good that you should consider it as a belly material, unless you have no wood to work with, like inuit people did.

I see no reason why you'd use bone if horn or even wood is an option.

Offline gfugal

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Re: Compression Woods?
« Reply #39 on: February 22, 2017, 09:15:48 pm »
Chinaberry isn't really a compression wood of any notice...in fact it is hardly a bow wood of any notice despite have a good value on the bow wood index. I've worked with it several times and was never able to get a bow out of it. I think it may be a better wood in different growing conditions than what I deal with here.
That's helpful info. It's odd how some woods would appear to be good but end up being just crummy. Like I mentioned earlier there is no real data for yield points in compression or even tension out there. all there is, is failure points and stiffness. It's possible Chinaberry has excellent compression & tension strengths (meaning it takes a lot of bending to break them), but its yield points may be pathetically low. This would mean its elastic region would be small. If that's the case then once it does pass those yield points it becomes a mushy mess. A strong mushy mess, but a mushy mess nonetheless. Either that or it's an inconsistent wood. Rather than having low yield points, the wood is actually week with low failure points depending on growing conditions. Where under the right conditions it could be a good bow wood like when it was measured for the wood database, and in other conditions its not.
Oh, and Rosewood is an excellent compression wood, but good luck affording a piece of it. I made a black ebony bow some time back and it also made a nice bow, but I was never able to afford to try stressing the design to find out if it is weak in either tension or compression due to the cost of the wood. Like I said before also, Acacia is a great belly wood for compression.
Yeah, I was hesitent to included some of the exotic woods I did list; like Wenge, Olive, Lemonwood, Indian Rosewood, Chinaberry, Muninga, and maybe even turkey oak. I chose to include them because they were still somewhat obtainable, although maybe expensive, and because they were fairly well known woods. I know Indian Rosewood is supposed to be easier to get than Brazilian Rosewood, or Madagascar Rosewood. Madagascar Rosewood would be very very expensive, if you could find it at all. It currently has a restriction on it keeping it from being cut down anymore. I'm sorry I forgot to put acacia on the list. I'll go back and modify it.
You can try lots of different woods but I suggest using one good wood and trying different designs . That's what I am doing. All wood is different even in the same tree. Placement of mass is what makes a good bow. Light on the ends ,width, thickness, length.  Using one wood will get you there faster in my opinion.  O:) but I am asking questions on here just like you.  ;D Osage does both well. For me it's selfbows not backed bows at this time. Good luck with you adventure. Arvin
There is some wisdom in that. That way you can eliminate bow wood as a variable when you're trying to hone your skills and figure out where you went wrong. Unfortunately, some of us live in locations that make it hard to come across yew or Osage, unless we bought it and had it shipped. I live in Utah, and the only good bow woods I know of that grow natural in the wild is Utah Juniper and Mountain Mahogany. Both of which I haven't been able to find any data on. I originally posted this to determine what woods were good so if I happen to run into an assortment of woods when collecting from arborists, landscapers, the city, neighbors, or what have you that I would know beforehand what I would be working with. Even if did end up liking juniper or mountain mahogany I don't know if I could keep to using it alone. I'm a fickle person when it comes to preferences, and I enjoy making things different ways and from different material, even unusual material. But that's just me. Osage and Yew are usually right at the top of the lists for either compression or tension. They work, and everybody knows they do. No sense changing if you don't wan't/need to. 
Greg,
No risk, no gain. Expand the mold and try new things.

Offline gfugal

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Re: Compression Woods?
« Reply #40 on: February 22, 2017, 10:11:49 pm »
Since I practice Korean archery, I'd like to know that it's doable to make a bow that does something similar to the synthetic Korean bows without using horn, but [still] with natural materials. I definitely like the much smoother feel of longer static recurve bows, though...

Could incense cedar sapwood or heartwood, sinew backed, be elastic enough to handle a 32" draw with a 50"ntn static recurve? (Korean design). Oh, and with something like 12" of resting reflex.
Sinew backed bamboo - yes, I saw one... but it's a bit strange since bamboo is so much stiffer in compression than sinew is in tension? Or is it? While horn seems to have similar stiffness in compression than sinew in tension.

Look at this crazy thing. It bends so much. Wonder how much hysterisis it has.
Code: [Select]
https://www.youtube.com/watch?v=mjd5gQx5uQU#t=1m9s
Would something that has a stiffness similar to sinew not be able to bend more, if sinew backed, than something stiffer?... .. Wouldn't materials with different stiffness, laminated, result in more shear force? So could incense cedar or juniper be better than bamboo sinew backed? (unless bamboo is less stiff in compression than I think)
I'm not going to say it's not possible. As it's clearly been done. What's not clear in that video is whether the wood was damaged at all in compression. It may have passed its yield point but the sinew may be keeping it from manifesting any set. If that's the case most of the poundage of the bow is coming from the sinew, with the belly serving simply as a shpae holder.

One thing you have to understand with stiffness is that it doesn't determine how far a limb will bend. That's determined by the ratio of its yield-point/stiffness. Unfortunately, we don't have data for yield points so we have to make due with faiulure-point/stiffness. If a wood's yield point is low, It doesn't matter if a material is really stiff or not. All that means is that it will be easier to break once it bends beyond a certain point. Lets look at two bow woods for example: Yew and Black Ironwood. Ironwood is more than twice as stiff as yew, yet has a breaking point just barely more than yew. what this means is that the yew will be able to bend almost twice as far as the ironwood. However, the ironwood would be almost twice as heavy a draw than the yew for the same amount of material. But even then, I still don't think too much importance should be given to stiffness. In the example of the yew and Ironwood, you could easily make yew just as heavy of a draw  by simply adding more material. That way it's just as strong as a bow, and it can bend further if you needed it too. This is way yew bows tend to be thicker depth wise than say something like osage.

To answer your question about different stiffnesses of sinew and belly material, the answer is pretty much it doesn't matter that one is stiffer than the other. the stiffnesses of the two materials have no influence on each other unless you change the depth thickness to accommodate them. What strains the material is not the poundage of the bow but the amount of stretch or compression each outer section undergoes. This is solely determined by how far it is bent, and how far the material lies depthwise from the core of the bow. The further from the core the more it will be stretched or compressed. That's wy thicker bellies undergo more tension. Not because some magical property of the wood changes when there's more of it. It's just that the outer fibers are being asked to do so much more and they fight back that much stronger.

Lets say you had two bows of equal depth, both sinew backed, with the only difference being that one had a very stiff belly material like horn and the other didn't. Lets also say both bows were bent the same distance. Because their depths (limb thickness) were the same the stiffer bellied bow would have to be much stronger. You would think then that the sinew on the back of the stiffer bow would be under more stress. This isn't the case. The sinew on the back of both bows are both equal distances from the core, and are both being stretched just as much for that bend. The only difference is the belly material. The material on the belly of the stiffer bow does not like to be bent, so that extra poundage is coming from it alone as it fights to restore its self to an unstressed profile.

So don't worry about a stiffer belly material overstressing the sinew. In fact, it would stress it less, because the depth would decrease for the same poundage than it would be with a less stiff material. Plus the nice thing about sinew is its designed to take a beating as far as stretching is concerned.  It's the recoil in the achelies tendon that essentially propels an animal off the ground when it jumps. Could you imagine building a bow that could shoot an arrow as heavy as a half an  elk several feet off the ground? yet sinew in the achelies does that every time the animal jumps.
Greg,
No risk, no gain. Expand the mold and try new things.

Limbit

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Re: Compression Woods?
« Reply #41 on: February 23, 2017, 12:04:30 am »
Bone? Bone doesn't actually take a lot of bend.  Korean bows have been made with bamboo bellies. Bamboo doesn't really take more set than wood. It wouldn't make a fishing rod if it took set.

Bone would only be used with sinew similar to horn and it does take compression very well. It was recommended as a substitute for horn and horse ribs were what was suggested. I haven't used it, but others have with success. I am getting my information on bamboo set from the potential bow wood's list by Tim Baker who notes it takes more set per mass than any hard wood. I always have issues with it taking more set than wood as well when making un-heat treated all-bamboo bows, so I agree with the statement. Being there are over 1,500 species of bamboo, I am sure there is a lot of variation in there though and the bamboo used for fly-rod making is Tonkin bamboo which is an exceptional species.

Offline joachimM

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Re: Compression Woods?
« Reply #42 on: February 23, 2017, 04:12:40 am »
I see you focus quit a lot on this "bow wood index" of the wood database.
http://www.wood-database.com/wood-articles/bow-woods/
This index assumes that the best bows are made from woods with low modulus of elasticity (bending easily with little force) and high modulus of rupture (allow them to bend very far, in tension).

Basically, those are not the qualities I would look for in a bow. I want both high MOR and MOE: such bow would (for the same bow mass) require more force to be pulled (hence storing more energy per drawn inch) AND be allowed to be drawn far. And you want this not only in tension, but also in compression.

Unfortunately, there is this trade-off between the two: either you have high MOE and low MOR, or the opposite. That's what the regression line in both my earlier graphs show.

And you also need to take wood density into account: bow mass is critical to performance, hence Steve Gardner's mass principle. That's why I divide all MOE and MOR data by the specific gravity (SG), so as to standardize. Only then can you really compare wood qualities.

Now, when you take all available bow making materials and compare them on this scale, you can guess what comes out as the best bow-making stuff... We don't say its name on this forum, it belongs to the dark side of archery...  >:D >:D >:D


Offline Del the cat

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Re: Compression Woods?
« Reply #43 on: February 23, 2017, 04:19:24 am »
I haven't read through the whole thread, but just felt the need to explain why the reptile scale idea won't work.
Why do you think reptile and fish scales overlap?
It is to provide flexibility/mobility! Which is exactly what you don't want in a bow belly.
As the others have said a butt joint is fine as the joints just compress against eachother rather than sliding over eachother as would happen with scales.
Del
Health warning, these posts may contain traces of nut.

Offline gfugal

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Re: Compression Woods?
« Reply #44 on: February 23, 2017, 01:27:16 pm »
I see you focus quit a lot on this "bow wood index" of the wood database.
http://www.wood-database.com/wood-articles/bow-woods/
This index assumes that the best bows are made from woods with low modulus of elasticity (bending easily with little force) and high modulus of rupture (allow them to bend very far, in tension).

Basically, those are not the qualities I would look for in a bow. I want both high MOR and MOE: such bow would (for the same bow mass) require more force to be pulled (hence storing more energy per drawn inch) AND be allowed to be drawn far. And you want this not only in tension, but also in compression.

Unfortunately, there is this trade-off between the two: either you have high MOE and low MOR, or the opposite. That's what the regression line in both my earlier graphs show.

And you also need to take wood density into account: bow mass is critical to performance, hence Steve Gardner's mass principle. That's why I divide all MOE and MOR data by the specific gravity (SG), so as to standardize. Only then can you really compare wood qualities.

Now, when you take all available bow making materials and compare them on this scale, you can guess what comes out as the best bow-making stuff... We don't say its name on this forum, it belongs to the dark side of archery...  >:D >:D >:D
I would prefer the ratio of Tension-Yield-Point/MOE-under-tension, but considering there is no data that I know of giving yield points, I rely on the Bow Index. For the woods I listed, the bow index was less of a factor, I considered the ratio of crushing-strength/MOE. Again I would prefer the ratio of Compression-yield-point/MOE-under-compression, but unfortunately, there is no data for that. I think we're saying similar things, it's just that we have different priorities we focus on. I agree with you that the best material would be in the upper right corner of your graphs. You, however, put more emphasis on the weight and stiffness of a wood. I look mostly at the flexibility (how far it can bend without breaking). Really it depends on your design in mind. The reason I think max flexibility is most important is because I have short backed bows in mind, like the one loon mentioned in his post. It doesn't matter if the material is lighter or stiffer in those situations if it ends up breaking or getting ridiculous amounts of set. However, if you have a long bow with a draw length that's less than 45% of its length then the wood won't be bending that far so you can look at other factors such as weight and relative stiffness compared to density and give less priority to its max flexibility, just as long as it's flexible enough. I really don't give much attention to the stiffness of the material, only the ratio of failure point and stiffness. In my mind, if one material is less stiff but more flexible you can remedy its lack of stiffness with more material.

You mentioned in your post that you updated the graph to include other materials like sinew, horn, and etc. Is there a way that you could send me that data by chance? I would love to look over your work and see what I could figure out from it. Maybe I'm not giving enough emphasis to wood density like you suggest. I have personally never read the mass theroy. Mybe someone could send me a photo copy of it from the book.
Bone? Bone doesn't actually take a lot of bend.  Korean bows have been made with bamboo bellies. Bamboo doesn't really take more set than wood. It wouldn't make a fishing rod if it took set.

Bone would only be used with sinew similar to horn and it does take compression very well. It was recommended as a substitute for horn and horse ribs were what was suggested. I haven't used it, but others have with success. I am getting my information on bamboo set from the potential bow wood's list by Tim Baker who notes it takes more set per mass than any hard wood. I always have issues with it taking more set than wood as well when making un-heat treated all-bamboo bows, so I agree with the statement. Being there are over 1,500 species of bamboo, I am sure there is a lot of variation in there though and the bamboo used for fly-rod making is Tonkin bamboo which is an exceptional species.
Bone may do compression very well since that's what its designed for. It isn't bendable at all, since it is brittle and will break in tension. I'm wondering if its elastic in compression though. It's very stiff in compression that's for sure, which is good for its purpose. However, I wouldn't think it has a very large elastic region of compression, but joachimM gave data saying that it can compress 1.2% which is more than most woods can compress before breaking. I'm not sure what the nonelastic region of bone is, I'm guessing its pretty small since I have a hard time imagining bone taking set. based off the data I would say it could be a good belly material if done right, but have never personally tried. If I were to do it, I would have it be thin enough that it's purely on the belly and doesn't cross over at all into the back where it would undergo tension. I would also make sure your bow is long enough. Jim Ham tried it once but he said that the bow stacked like crazy. Tim baker showed in the TBB that if a bow stakes its not because its near its breaking point but because of the string angle. So maybe thats why his stacked not because of the bone. Its also possible though that bone has a nonelastic region that is stiffer than the elastic region. This isn't the case with wood, but it would explain why Jim said it felt like it was going to explode. JoachimM do you know how bone behaves after it has passed its yeild point in compression? does it get stiffer or weaker like wood?
Greg,
No risk, no gain. Expand the mold and try new things.