Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on August 30, 2020, 02:36:03 pm
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Every so often I wonder about different wood I could use for the belly so I go off to the Wood Database. To my way of thinking "Crushing Strength" would be the criteria for compression but in looking at the numbers they don't seem to follow common use for bows. For example Black Locust shows a higher CS than Osage. Crushing strength is, I imagine, crushing to yield and we want crushing to just shy of yield and the ability to recover from that. Is there another number that I could use in combination with Crushing strength. Yew is 8100 so I imagine I want 8000 or better but I'm not sure. Ipe is 13,600. Anything you can add?
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Don’t know about that DC but I depend on density and use that for compression. The more dense the better the compression. I could be all wrong. The more dense the more weight unfortunately. No scientific proof just what I have observed. Also it has been said here the best bow will come from a good balance of tension and compression. Also that changes with design. And the can of worms gets bigger and bigger . Arvin
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It's the elasticity in compression that matters more. Many great bow woods are not particularly compression strong.
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Pat, I think you're using the term, elasticity, the way I would. It's the "springiness" we talked about a while back. The "Modulus of Elasticity" that the Wood Database uses seems to be something else. They refer to it as an indicator of strength or stiffness. I guess I was hoping for something that doesn't exist, a chart of springiness or hysteresis.
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I'm curious about black locust. I've heard some say that it is high in compression but some other factor makes it prone to chrysals, perhaps the elasticity or lack there of.
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I'm curious about black locust. I've heard some say that it is high in compression but some other factor makes it prone to chrysals, perhaps the elasticity or lack there of.
That caught my eye. If the "Crushing Strength" is until failure you'd think that a chrysal would be a failure and Osage should score better than BL. I wouldn't think that elasticity would enter into their test. I'm thinking that must be a typo.
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Ok I’m watching. Keep going guys. Arvin
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You need to look at the tests done by bending, not the direct crushing or pulling apart tests.
Young's modulus and work to maximum load etc. Look at known good bow woods and isolate key features. Then you can find numbers of woods not typically used and compare. I will say that almost every feasible bow wood has been tested at some point it seems.
A guy on Paleoplanet did a collection of wood data and charted it several years ago. Good bow woods made a pretty scattered bunch of dots on his chart though. The one with the best numbers seemed to be some type of Rosewood not used for bows generally.
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To be honest I would forget the numbers and just use a simple bend test.
Modulus of elasticity is no good for a bent limb and its ability to spring back.....moe is simply can the object have a load applied directly to it and return to normal shape once the load is removed. It is not bending data! Unless you want to drive your car over your bow it is of little use :)
Also was it straight grained, nicely dried wood they used in the first place.....NO!
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Pat, I think you're using the term, elasticity, the way I would. It's the "springiness" we talked about a while back. The "Modulus of Elasticity" that the Wood Database uses seems to be something else. They refer to it as an indicator of strength or stiffness. I guess I was hoping for something that doesn't exist, a chart of springiness or hysteresis.
you are correct Don. springiness or elascity is not related to MOE or stiffness.
yew and spruce are both woods of similar stiffness, except yew will bend twice as far (roughly) than spruce without taking set or breaking. ipe and osage are both stiff woods, osage of course being much better for being able to bend further.
we can make a similar width of the same poundage bow with both spruce or yew. the yew in that designs thickness will be "overbuilt", because we have not asked it to do all that it is capable of. Building the yew bow as a thicker bow would be more in line with yews potential. the thicker bow would be narrower of course, when built to the same draw weight. if only yew were as stiff as ipe.....
https://www.tapatalk.com/groups/paleoplanet69529/picking-a-wood-for-a-bow-t28706.html (https://www.tapatalk.com/groups/paleoplanet69529/picking-a-wood-for-a-bow-t28706.html)
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DC, here's a pic that visualize a fatal compression failure. See the frets and finally a clean cut of fibres on the belly...
Willie: You are right. I did the same bow with yew/ash and (compression)spruce/ash. For the same drawweight the spruce bow clearly needed more thickness and more mass (weight). Regarding commonly used bowwoods Osage, yew and ipe seem to be unbeatable in compression.
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DC: my understanding of the crushing strength test is that they use a hydraulic ram to push a half round ball bearing a given depth into a piece of wood. The numbers relate to the force required to reach said given depth. So useful in telling us how much abuse in the woods our bows could take, but probably not much else. This cold also explain why locust has better numbers in this regard than osage, despite it's tendency to chrysal when under a longitudinal compressive load.
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Pat, I think you're using the term, elasticity, the way I would. It's the "springiness" we talked about a while back. The "Modulus of Elasticity" that the Wood Database uses seems to be something else. They refer to it as an indicator of strength or stiffness. I guess I was hoping for something that doesn't exist, a chart of springiness or hysteresis.
The published numbers for MOE is the reverse of what you need when making bows, that is to say the lower the number in relation to the wood density is better.
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DC: my understanding of the crushing strength test is that they use a hydraulic ram to push a half round ball bearing a given depth into a piece of wood. The numbers relate to the force required to reach said given depth. So useful in telling us how much abuse in the woods our bows could take, but probably not much else. This cold also explain why locust has better numbers in this regard than osage, despite it's tendency to chrysal when under a longitudinal compressive load.
That's the "Hardness Test" isn't it? Yes, it is, I just looked.
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A guy on Paleoplanet did a collection of wood data and charted it several years ago. Good bow woods made a pretty scattered bunch of dots on his chart though. The one with the best numbers seemed to be some type of Rosewood not used for bows generally.
I guess archers that actually know what the numbers mean have combed through these charts. I'm wasting my time doing it again when I don't know what I'm looking at ;D
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I'm wasting my time doing it again when I don't know what I'm looking at ;D
OK, fair enough
Every so often I wonder about different wood I could use for the belly......
combined with what wood for the back?
and what is the bow going to be used for?
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Bamboo. I tried Hard Maple and it was fine but I was always concerned about the grain. Also all I could get was kiln dried. Don't know if that's an issue or not. And out here in the west it's pricey. I don't know if I've even seen Hickory. All the tool handles seem to be Ash or some mystery wood from the South or East. So I've settled on Boo although it seems to have almost doubled in price in the last 2-3 years. Politics I think.
This was not a question about a particular bow. I've run out of Yew and was just exploring possibilities. I was curious whether or not any native woods may have decent compression. None that I can find info on do, except Yew.
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The published numbers for MOE is the reverse of what you need when making bows, that is to say the lower the number in relation to the wood density is better.
Not necessarily stiff, but dense? I can see this as being an advantage if used with a properly sized an optimum stiffness backing.
which woods come to mind?
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We’re talking about compression wood here. That means a backing can be used to demonstrate the best compression woods. Crushing strength should not come inti plat at all here. That is for core woods in composites. Black locust is not a contender. Osage is, but the best compression woods can handle the most amount of bend without taking set. So lighter woods good in compression are best. Yew is great, but I would argue the best are much lighter. Woods with very low sg around 30-40 with a true backing to take all the compression. Specifically I think incense cedar and juniper are the best compression woods.
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You can compare Osage to Bubinga, I know Bubinga is low in elasticity and will chrysal easily or to Black Locust which has similar density to Osage but a higher MOE, most know that Locust is a bit low in elasticity
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Snakewood was very highly regarded in the past. You can still get it but you'll pay dearly for it.
Tulipwood (the rosewood variety)seems to have good properties as well but it's also hard to get in bow lengths.
Lilac may be one to look for too.