Primitive Archer
Main Discussion Area => Bows => Topic started by: huisme on January 10, 2015, 11:15:51 pm
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I've done bend tests on several woods and come to the same conclusion as everyone else, but I'm wondering how many people have tried this method.
The wood database was brought up on /r/bowyer, the normal talk about numbers happened, the normal suggestion that we need not worry about it was there, but I like knowing things to know things.
I suggest a/several 1/8"x1/2"x3' pieces of several woods be clamped to a bench, a button set to contact the wood precisely two inches below the resting point of the wood, holding the wood down, ensuring that when the wood is pulled down six inches, held for three seconds, and released the wood will strike the button and the time between release and collision can be tested.
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That would be an interesting test. I am not sure how much the actual weight of the wood might affect the test, usually on a test like this we are trying to isolate histerias. If it effectively did that it would be good in rating wood.
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Perhaps for a second/complimentary test a weight can be established one of the lighter woods and any heavier woods can be carefully reduced (don't give one piece a taper while the others are square) to match.
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So has anybody done this? I only have a tonne of locust, some vine maple and Oregon ash, and not enough osage at my disposal for now.
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marc
I have tested wood from staves I find local. what are you wanting to test for specifically? send a pm if you want to swap some black locust.
willie
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Because of the way an optimized black locust flatbow snaps back to brace compared to the same from osage I want to perform these tests, or see results is anyone has done it themselves, to see if these numbers might be what's missing from all the mathematical approaches to bowyery.
It really all started when someone brought up the article on the wood database where the author assumed a low modulus of elasticity was essential to good bow wood and therefore a wood like black locust is mediocre at best.
And I simply can not be told not to look into it because we already know enough about bowyery, ancestors knew best, good wood is good wood, etc. It's something we could know that could tell us why good wood is good wood and I will not be kept ignorant.
[end rant]
Are you looking to get locust? What for exactly?
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Several years ago Tim Baker and I ran some tests on 1/8" X 2" by about 18" long. We would pull it down to a certain depth that was in a locked position and then slide our finger off. We measued how far it would spring back past center. Black locust and ipe measured the best out of those we tested, I believe cherry was up there also. There was not a huge difference in any of them. Bamboo was one of the lower ones.
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The test you suggest would give acceleration but I am not sure if vellocity could be accurately calculated, I think it could. If you knew the amount of mass it was moving and the work you were applying downward you could come up with an efficiency figure. Usually n this type of test you are looking for hysterias. Not sure how accurately you could in it down. You would easily be able to record losses occuring as the wood became overstrained. This would be of good value I think.
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the author assumed a low modulus of elasticity was essential to good bow wood and therefore a wood like black locust is mediocre at best.
I am not sure that this statement is true. MOE (modulus of elasticity), is not really a description of elasticity as a bowyer would think of it. it is really a measure of stiffness. Yew is known for its bendability, as is Osage, but yew has a low moe and osage a high one, as one would expect, since osage is relativity dense and yew is much lighter. One the other side of the coin there are stiff woods, both light and heavy that don't bend much before they break- think of spruce- strong for its weight, but not a very good choice for something that is going to be highly stressed. It might break without warning. good bow woods must be evaluated in ways that most wood is not, as most wood is used well below its breaking point, and unfortunately, these tests are not commonly done for most woods by those that pursue such matters. As boyers we stress wood near and beyond its proportional limit. and yes black locust is a good bow wood, otherwise I would not be asking you if you had some to trade:)
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Marc, we were discussing this on /r/Bowyer earlier but now I realize what you're saying. It seems a test like this would produce values to test a wood's performance rather than design requirements. The problem I see is that wood varies so much from tree to tree it would be hard to get consistent results. For example, doing bend tests on thin osage splits from 2 different logs cut here, one bent into a U shape while another (thinner ringed) snapped. I can see some value though if you had the equipment.
As to getting wood for the testing, contact a custom lam grinder for FG bows (not 3rivers or binghams) get .125" lams (tapered?) Of several species. You can request quartersawn wood only at the two supplyers here in MO.
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Perhaps using a high speed camera and counting the number of frames between letting go of the strip and its impact on a stop?
Better yet use a chronograph and use a long enough strip to activate both sensors
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I was thinking you could just twang the piece between the chronograph sensors.
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Perhaps using a high speed camera and counting the number of frames between letting go of the strip and its impact on a stop?
Better yet use a chronograph and use a long enough strip to activate both sensors
This would be a good method, I think. You could get acceleration and velocity and just about any instance with this. To get a sensor to do a similar thing could be quite expensive.
Maybe an accelerometer mounted to the wood, but that would vary drastically depending on where you put it on the wood.
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I like the high speed camera and chrono idea, I have friends with both ;)
Do you think a dozen of those lams David mentioned would be a decent sample for each wood I can get, or does everyone think like I do that I need to start making trades with this in mind? I can't make the lams consistent enough with my tools so it'd be a bit to ask of anyone (five sources?) to make a dozen identical lams of what they consider average osage and another dozen of some of their best (good luck making that happen, right?).
Willie, from the article:
In terms of looking at the raw mechanical data of woods, the best bow woods tend to be those that have a low MOE and a high MOR. (Stated another way, the best bow woods tend to be those that will bend easily, and not break.) It’s of little advantage if a given wood scores well in one area, and poorly in another (i.e., a very low MOE or a very high MOR). What is most important, regardless of how low the MOE may be, or how high the MOR may be, is the ratio of the MOE to the MOR; it must be easy to bend AND hard to break.
Locust is pretty hard to break; I've had one explosion because I'd cut right through a large pin knot and just hoped it'd be okay. Locust will, in my experience, fold over before it snaps if the back is perfect; it's MOR is 5.2 MPa higher than osage (estimated based on dry osage of course, but still), but it is significantly stiffer than any of the article's listed best bow woods.
This is why bowyers should be running these tests ;D O:)
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I don't think milled lams are the way to go. Unless they are perfectly straight grained a lot of the structural integrity will be missing.
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If all the lams are the same dimensional size wouldn't the different wood densities scew the results? Wouldn't a lighter piece return faster,or vice versa? To me they'd all have to weigh about the same mass wise,and also have the same bending weight(like draw weight). ???
Someone correct me if I'm wrong as I'm not the brightest crayon in the box ::)
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That's why I was thinking I'd need to many lams and didn't want to bend them especially far, just enough that they're taught through the whole process, and then use averages from dozens of tests noting the first, second, third, etc use of each lam.
Can you think of an alternative way to get dozens of dimensionally uniform pieces of a few woods? I know I can't get completely identical pieces out of locust, and this is fairly consistent wood.
Blackhawk, that's what I was thinking I'd need a good planer for, to reduce some of the denser woods to the same weight as standard thickness maple or whatnot. I figured leaving them taperless was the most reliable way to avoid better/lesser tiller interfering with results.
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Measuring the return speed of a sample doesn't require very sophisticated equipment. You can firmly clamp one end of a sample, pull back the free end and let it go. The samples with a faster return rate will vibrate at a faster frequency/higher pitch. The samples that the vibration dies out quicker have a higher degree of hysteresis. You can rank a pretty large number of samples from best to worse if you have a bit of a musical ear. There are apps for phones and pc's that can take it to the next level of sophistication if you want.
Alan
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If you are concerned about mass and density you could certainly correct for that. Weigh each sample and find the volume of it and you have the density for that piece-you don't even have to use the general published average values. If you then find the [(return rate)/(density)] for each sample you should have comparable results.
SOM
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If you are concerned about mass and density you could certainly correct for that. Weigh each sample and find the volume of it and you have the density for that piece-you don't even have to use the general published average values. If you then find the [(return rate)/(density)] for each sample you should have comparable results.
SOM
+1
I guess the most accurate way would be to grind your own and make them the same weight but then you would need a drum sander :p
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I would try making them all the same length and thickness then adjust the width so they all had the same pull down load.
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but then you would need a drum sander
Eeeeexactly :o
Badger might be on to something, maybe I need to be looking for the width/thickness at which a sample bends to the desired six inches under equal weight. I do have a belt sander and access to a planer, but it's going to be a pain in the butt either way... But I will be doing this with weighed samples.
Avcase, I hadn't thought of that at all! I'm a drummer, so the rest of the band would say I'm no good for this but the fact is I just so happen to hear all the times the other instruments are out of tune ;) >:D
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I think this is a neat experiment, but density differences from one piece of wood to another will make it challenging to isolate the quality you want.
For instance, you might make your slats a standard length and thickness and vary width so that their masses are identical. This way you've factored out mass, and can measure return speed without that confounding variable. This would yield useful information.
But by keeping mass constant by varying width, you would be ignoring the fact that skilled bowyers commonly vary width to get different levels of performance from wood. So you might also try using slats of a standard length and width but varying thickness to hold mass constant. This would also yield useful information, but it would yield subtly different information than the above test.
And, of course, you could hold length, width and thickness constant and vary the mass of the slat. This would also provide useful information, but again the information would be subtly different from what you learn by the two above tests.
Because wood varies so much from tree to tree and even within a single tree in terms of its physical properties, you can't test a slat from a single species and generalize the data you gather to that species. You've made a single observation, and you have no idea where that single observation falls on the bell curve that represents the totality of possible values from that species. If you tested several samples from several trees of that species, you'll get a better sense both for the average value and how variable the values are among different wood samples. Of course the better you want to understand average performance and the variability around that average, the more samples you need to test and the more time and resources you'll need to invest in testing.
Finally, I'll second the idea that milled slats might not be the best option for this test. Sure, they're easy to get in quantity. But they don't represent wood that we use for bows, at least those of us who make self bows and try to use an uncompromised ring for the back of our bow. Using slats with uncompromised wood fibers adds more complexity to your experiments in the sense that you need to source vary particular slats, but in the long run I think it makes the results more applicable to bow making.
My two cents...
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Allens suggestion I think would give you the most useful information. I didn;t see his post till just now.
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I just don't se this having any practical value. People are still going to just select a piece of wood and judge how that piece will react to being made into a certain design.
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you would be ignoring the fact that skilled bowyers commonly vary width to get different levels of performance from wood.
I actually do intend to ignore that. I'm looking for what the wood does, not what we can do with the wood. It seems like as long as the wood is shaped consistently, probably edge instead of broad face reduction, results should be relevant.
I was thinking thirty samples from various trees in various locations for most woods and separate stacks representing average and exemplary ratios in ring porous woods like osage and locust. Furthermore, each piece would be tested five times to note degradation.
I can think of no replacement for milled slats though. This is already going to take me a long time to prepare and execute; add splitting, ring chasing, and sanding to bend uniformly and you're talking possibly two generations worth of work just to get the material in the testing jig. I'm open to suggestions if anyone knows how to get clean-backed slats, but otherwise the ~8" of bend over several feet doesn't seem like it's going to completely ruin the samples.
I just don't se this having any practical value. People are still going to just select a piece of wood and judge how that piece will react to being made into a certain design.
We will not have refrained from learning because it's easier to do so. We will know more about what makes a bow wood, and more about ourselves when we use or disregard information.
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I do think it is difficult to apply things like this, I am constantly trying. I do believe every variety of wood has an optimum thickness for a given radius. Finding it is the challenge.
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I'm with PatM. I'm not sure what you will come away "knowing" that you don't already know.
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I will know how quickly a slat of given wood at a uniform length and thickness reduced in width to bend eight inches under uniform weight will return to two inches of bend, after which I can compare woods. I will know which wood, on average, degrades faster from said testing as well. I will, in effect, know if some woods are faster as bows, and I won't be persuaded to be ignorant.
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The point is that you will figure all this out and then go out and cut down a fresh tree and be right back to making an educated guess when you start building the next bow.
Wood will just never be a strip of s-glass or carbon.
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Wood will just never be a strip of s-glass or carbon.
True.
But I will know if there is a diference between sixty samples of osage, sixty samples of locust, thirty maple, thirty hickory, thirty ipe, etc, and which ones average higher or lower in this test. I'd love to get some greenheart too, that stuff sounds insane.
I know I'm coming across as defensive but I don't have time to consider how useless more data might be, and there's no way to avoid suggestions I do exactly that.
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Don't get me wrong huisme, the results from such a test will be interesting and I will be following to see the results if you pursue this. The point I am making doesn't change as a result of my admitted curiosity. Is this information new? Will it translate into building better bows? I am recovering from a long love/hate relationship with Black Cherry. Well, actually I was in love with the idea of loving Black Cherry. This infatuation was based on some of the engineering values associated with it, and some of the things Tim Baker had written about it. After multiple runs at building my "dream bow" from BC, and ending up with nothing remarkable at all, I realized that yes, I can build a bow from BC if I build it the way BC bows need to be built. The low hysteresis values were of little value in the real world, as you had to modify the design to compensate for its brittle nature. You compensate for it and end up with a bow that performs like all the other bows from all the other woods. Each having their own compensating factors. Some were dogs that just didn't perform, some were exceptional, and most were somewhere in the middle, regardless of any engineering value. A simple bend test on each piece of wood, for me anyway, tells me what I need to know about THAT piece of wood.
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I'm just not sure what you intend to do with the info in a bow building application.
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Post it in a few places, maybe write a new/more informed bow wood article for the wood database, maybe even contribute to the wood database itself, refer people to the information so they understand why I use some woods and not others, and otherwise enjoy the information.
Slim, that's pretty much what I intend to find out. It's not like anyone could look at this one test any more than any other number and know how every piece of everything tested is going to perform, but everyone who values information like that in the wood database already knows that and can function accordingly.
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But I will know if there is a diference between sixty samples of osage, sixty samples of locust, thirty maple, thirty hickory, thirty ipe, etc, and which ones average higher or lower in this test.
If you use slats created as described, then no you won't. You'll know if there is a difference between X samples of these woods that have unknown levels of wood fiber integrity. Which means, in the end, you won't know much of anything that's relevant to self-backed bows. You might choose to draw conclusions anyway, but those conclusions may and probably will be erroneous because you've decided to design your experiment to be easy to carry out rather than useful to carry out.
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How much variance do you think there will be? Is a board bow so much worse than a single ring backed bow?
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Well Jay Massey was of the opinion that lumberized Osage lost most of its good qualities.
What sort of slats were you thinking of?
Your test will also skip the effects of trapping and crowns etc.
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The crown issue was actually a concern at first as I like locust better with just a bit of crown, but since we're going for raw material properties rather than optimal anything (for this first test anyway, later on I could try shaping while keeping equal mass) it's okay that we don't shape anything to perform its best.
Which actually makes me think reducing thickness to match flex under x pounds would be better than width, then compression/tension doesn't come into play quite as much I think...
I don't know why it would when other woods can be used as backing strips. It has a decent MOR doesn't it? What's different? And how can I test it?
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What's the value of doing raw materials tests if the goal is to apply the data you generate to making bows? It seems like design is pretty integral to this experiment to me. Regarding the impact of fiber integrity, I think the variability it adds can be huge. Again though, it will depend on your wood choice. If you get perfectly straight grained boards that have been milled perfectly to follow that grain, then the difference between that and a shaped stave will not be so big. Especially with woods known to hold together well, like elm and hickory. But other woods are less tolerant of grain runoff (I'm thinking osage and black locust, among others), so for those woods fiber integrity will make a huge difference in how they perform in your test.
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I meant what type of bow will this cause you to make with the wood?
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I think a length of 18 inches or so has been mentioned for test slats??? At that length or longer, when you start narrowing them to have equal mass you are going to start getting a different air drag, which will affect your readings.
The Forest Products Laboratories tested hundreds of samples of each wood to come up with their averages for mechanical properties. Any smaller number of tests is going to render results that are accordingly less significant.
I have read this whole thread. I see a danger of introducing too many variables. Density within a species, moisture content, grain orientation, ratio of spring wood to summer wood, and other factors would need to be held within very close tolerances to produce useful information.
The testing of non-homogenous materials just has too many variables to permit the extraction of some types of useful data. Average bending strength and work to maximum load are about the only useful predictors in my estimation.
Jim Davis
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Ash, that's why I've decided to return to just reducing thickness.
My results aren't going to be as thoroughly tested, but they will be results. If anyone intends to do hundreds of tests for each species I'll gladly sit by and watch, but so far I'm the only one who seems to be interested in justifying tests like this.
As for density, do you think reducing thickness over the whole slat would be better to control mass or bend under uniform weight? I intend to keep the slats in a controlled climate to help control moisture content and I'll take a reading as part of each test. I intend to use quarter-sawn samples that could have been used as self board bows; seems like if they'll throw an arrow they can be tested. Early/late wood ratios are certainly on my list of priorities.
Pat and Eric, it could cause me to make more from one species or less from another. If one material moves faster than another I look at that material and consider the other variables to decide if that's what I want after doing the same with other fast materials. Is this particularly fast wood available in large quantities in my area? Does is require ring chasing? Doe sit glue well? Is it suitable for laminates? Belly or back wood?
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I think Allens frequency checking test would be the most useful. If you are checking the speed of return for any accuracy you would need to know how much work it is doing returning. This would be very hard to figure out. All you are looking for in this test is histerias and frequency of vibrations would best reflect this.
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Hey Steve, here's another monkey wrench for me to brandish.
How about uniform slats bent to a particular distance and released, this time with a miniature microphone attached near the base and the output fed to an oscilloscope (or it's current equivalent) to read amplitude, frequency and duration of vibrations. It seems this would give a real comparative test of the resilience of each wood and the rate of loss of energy to histerisis.
What say you?
Jim
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Jim, I think that is similar to what Allen was proposing, I would agree with that as well.
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I don't know that this is useless information. How much it is likely to impact a bowyer's actual decision making I don't know...I would bet as Pat suggested that people will use the staves they have regardless. But looking at return rate with given mass slats will give some information about the energy storage, I don't know that it is necessary to invoke harmonics. The more energy stored the faster the slat will overcome momentum and return to rest.
Also, while wood is not a completely homogenous material, trends within a species may be clear even after a relatively small sample size. I would not be shocked to hear that a certain species had values that were all pretty close to each other whereas other species may be incredibly inconsistent. Which are which may be of some value, and of the inconsistent samples did the better cases have anything in common-like late/early wood ratio?
Are there a lot of variables that may impact the results? Sure. Does that mean that trends will not show up or that people cannot look at the slat dimensions and make some educated guesses about how or why the slats behaved the way they did? Not really. I am interested to see what comes of this.
Huisme, are you planning on testing hop hornbeam? I would be curious to know how that stacks up against some of these other woods.
SOM
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I agree that there is useful information to be gained by the proposed tests.
But I think there are so many variables that unless they are all addressed few, if any, valid conclusions can be gained.
I would greatly like to see testing done with the care of a master's or doctoral thesis but written in a textbook tone.
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Also I'd like to see 60 samples of each heat treated for varying lengths of time. That's 60 for each duration as well. >:D
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I agree that there is useful information to be gained by the proposed tests.
But I think there are so many variables that unless they are all addressed few, if any, valid conclusions can be gained.
That about sums it up.
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To address some concerns with the variability thing it may be useful to have control experiments built in. Instead of going for same dimension slats, or same mass slats, or same width slats do same dimensions as well as same mass as well as same width...try a sample of each to see which of these different things actually makes much of a difference. It may add to the total number of experiments one needs to run, but it should help isolate which of the variables you need to control for and which are actually impacting results and which of them make essentially negligible differences. The absolute value of the return times will change from one set of conditions to another, but the relative return times if you rank different woods may not change much. If that were the case it would suggest that this is a more worthwhile thing to do as the results then appear to be more general behavioral things as opposed to engineering tricks or special case scenarios from slat to slat.
SOM