Primitive Archer
Main Discussion Area => Bows => Topic started by: Badger on December 04, 2013, 02:38:19 pm
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Here in the modern world we have access to bow woods from all parts of the country and the world for that matter. Back in the primitive days a bow maker would likley only have access to a few woods. He would pick the ones that best suited his style or learn the styles that best fit the various woods he worked with depending on the job that he needed to get done. This is where I believe a lot of the problems come in when working with white woods. I don't believe for the most part we have perfected the styles around the woods we work with.
We often compare fiber glass bows to primitive all wood bows. On the average a fiberglass bow will have about a 15% advanatage in power. The best wood bows will however shoot at comparable speeds to high end modern bows. This is good evidence that we are loosing out primarily because of design. Design means a lot more than just recurve or r/d or hill style. Design really implies on how we intend to use the wood to best accomodate the style bow we plan to build. Wood bows can be comparable to modern bows in mass weight and can even edge out modern bows in the mass dept so we can't claim thats where we loose the power. The power is lost through hysterisis which is simply internal friction, it is also lost through poor tillering and poor design.
The old school of thought was that about 10% of our losses were due to hytrisis and that was just an unavoidable loss we had to deal with if we wanted to work with wood. As evidenced by the standout bows that can compete with modern bows hystrisis is more controllable than we have possibly thought it was. I did some tests a few years back that strongly indicated hystrisis really didn't play a part in the losses until the wood started breaking down. Thats where I came up with the no set tillering tecnique of monitoring the condition of the wood throughout the tillering process. The mass theory was also a product of this same series of tests.
When it came time to write the chapter I really felt I was a few years away from really having as much information as I needed to be as difinitive as I would have liked to have been. I did feel it was useful none the less and went ahead and wrote the chapter being fully aware I still had considerable work to do. I tend to have an aversion to attention even though I do love talking bows and arrows, the undo attention I got form the chapter sent me crawing back in my cave and I slowed way down on my bow building and my testing came to a standstill. A couple of years ago I retired form work and decided to continue where I left off with my passion for bow building returning.
I really didn't know exactly where to start, some of my equipment for testing had been dismantled and trashed or had become inoperative for one reason or another. I just started building bows, one after another every style I could think of from every wood I could get my hands on. I really didn't have a clear direction as much as I was just trying to stimulate questions and puzzels that I felt needed to be answered. I was no longer building bows to a specific weight or draw length as much as I was just building them to see what I could get out of them stopping just at the point where they started to breakdown. Just going by feel I knew most of them were going to be between about 50 and 60#. When I hit that point I would simply set the bow aside and start on another one with a slightly altered approach, never writing anything down of course. After a couple of hundred bows and a year or so went by I was starting to see patterns emerge. Regardless of design most of my bows were just starting to break down at around 23 to 24", and this is if I did my job and kept the tiller in ballance from the start, if I didn't they would start to breakdown sooner. I could still bring them all the way out to 28" with very respectable losses but they weren't perfect' they did have losses.
After dunking my head in a bucket of ice water and holding it here till I almost drowned when I came up for air my head was clear and I suddenly knew the answer, we all know the answer but tend to deny it for whatever reason. I sat back and thought about all the successful bows I have seen in my life, the ones that really shine and stay shiny for a long long time. I thought about the little Tim Baker red oak bows that he would make week after week at the Pasadena meets that would shoot about 170 fps. A tad faster than his famous mojam bow that by todays standards would not garner any attention. These bows were 1 1/2 wide about 45 to 50# 68" long and slight bend through the handle. He had perfected that particular design with that particular wood. They were taking about 3/4 set just unstrung. I thought about the few r/d bows I had made that had approached 190 fps and seemed to maintain that level as long as they didn't get overdrawn. I thought about the Mark St Louis bows with high consitent performance even under high stressed difficult designs. They all had one thing in common in that they were wide flat limbs where they needed to be wide. All of a sudden now I feel like I have a new direction to take and something I can actually start to narrow down.
The first thing I decided was that a pyramid design wouldn't allow me the lattitude I needed in thickness adjustment so I opted for a modified version of the american flatbow. I make the bow wide and keep the limbs parallel till about 12" from the tip as I near final draw length I start increasing my taper further up the limb as needed. The pleaseant surprise with these wide flat designs is that you really don't gain any mass to speak of as long as the wood is not breaking down. I was pleaseantly surprised as to how thin I could actually make the bows, My mass weight was staying about the same but the bows were much snappier and performed better. This strategy really pays off when working with very dry wood. I have always slightly rounded by bellies just because it makes the tools easier to use and didn't seem to hurt performance. Well from now on I will be making them as flat as I can maybe rounded by a 1/32" of an inch or so just to give my scraper something to bite into. The rate of taper I have been using is very similar to that of the English Longbows. It starts off almost imperceptable and gradually grows steeper as it nears the tip. Not a straight line like you might see on a pyramid.
Be back in a bit I got interupted.
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Hello Badger, how do you know when a bow is breaking down when you are tillering it? I am not trying to start a fight just wanted to know so that I can learn. Can you post a couple of detail pics of your bows and as you have far more experience as I do, do you have a favorite wood? Thank you for your thoughts
Peter
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Interesting so far. I'm looking forward to where you are going with this. I've got a roughed out HHB stave that I'm about to start work on, but I think I'll hold off until you've finished.
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Peter, its ok to disagree or even argue I enjoy good discussions. As far as how to tell when wood is breaking down. If you are trying to catch it real early in the process you can use your scale and your tiller tree. It might be a little harder for those that use the tree early on but it will still work. Once you have your bow floor tillered go ahead and put it on the tree, try to make it as perfect as possible before you bend it very far, in other words correct any flaws in the tiller as soon as you detect them instead of pulling a few more inches just to see what it look like.
Ok, suppose you have your bow on the long string and you haven't pulled it past about 6" yet but you feel it is close to bracing and you want to go a little further as it looks about perfect. Lets say your string is hanging loose at about the 6" mark. Pull the bow to 8" and write down the weight. If it looks good at 8" go to 10", now go back to 8" and see if the weight has changed. Lets say you now have the bow braced Pull it maybe to 10" and write down the weight, that will be your benchmark, now pull it to 11, go back and check the weight at 10 now pull it to twelve go back and check it at 10" again. If you need to remove some wood recheck the weight at the furthest point you had pulled it so far and start the process over. Each time you pull it to a new draw length pull it several times before rechecking your weight at the last benchmark. If you find it starts to drop a little weight you need to try and find out where it is breaking down before proceeding. If it is breaking down evenly all over you need to lower your expectations for draw weight. If it is starting to break down in one spot only then look for a place on the limb that you cna get bending more. I like to leave it stiff out of the fades a few inches and as I need that wood for more bend I can go back to it to increase my draw length.
If you have a straight limbed bow its easy, you unbrace the bow and set a straight edge on it looking for places where the straight edge starts to rock just slightly. Curvy d/r bows are not always as easy, I suppose you could trace the starting profile and then set the bow down against the pattern or just examine it real close looking for slight places that have taken set.
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Interesting so far. I'm looking forward to where you are going with this. I've got a roughed out HHB stave that I'm about to start work on, but I think I'll hold off until you've finished.
I am hoping Mark wades in here, he is really the expert at pulling off these designs with no damage to the wood. I think he just does it from experience but maybe he will share that with us.
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Than you Badger, think I will have to rethink how I make a bow. I never thought about the wood breaking down at such low draw lengths. Interesting please carry on with your post.
Peter
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I don't know if it matters but is the breaking down on the compression side or the tension side?
Thanks
Don
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Great article Badger. Entertaining reading.
A few years ago I was almost exclusively making bamboo backed bows from a select few of our Australian woods, mostly Ironbark and Spotted gum. I found these woods were sometimes tension weak, which is to say they could be described as brittle. However their set-taking properties were pretty good, and the stiffness was off the charts. I mean, it would leave Hickory for dead.
So the way to overcome the tension weakness is of course to put something more tension strong on the back.
So anyway after a few bows I settled on two designs. A longbow about 68-70" ntn, from which I could get 1.5 lb per mm of width at the handle. The other was a flatbow about 66-68" long, and increasingly the handle riser got thinner and thinner so that every ounce of wood was doing some work.
Funny thing is the limb width taper on these were very similar to each other, and quite similar to yours: for just over 3/4 of limb length they were almost parallel, tapering possibly to 4/5 of original width over that length. After that it would taper in convex bulges to narrow tips, that got narrower as more bows got made.
These bows got to be very fast. I didn't have a chrono at that point, but as you said above, they were performing similarly to a glass bow a friend would bring over to shoot of similar length/draw specs.
Lately I'm making Red Oak bows, and am finding a slightly modified pyramid design to be working really well. Mainly for economy of time, but the performance aint too bad either. Not modified much, just a little. I recently made one that drew 37lb @ 26", which shot 13gpp 139fps. Not mind blowing, but for the slightly shortened draw and heavier arrow, I think that's nothing to be ashamed of.
Keep it coming Badger, I'm eager to learn more.
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If you work with the same woods and a similar desing all the time it usually isn't really an issue, you get good at that partiuclar design. But when you start playing around with different white woods or designs that involve a lot more reflex for instance it's good to know how to monitor your progress. I have mostly stayed away from recurves and stuck with a lot of D/R designs. Recently I started playing with some recurves with several inches set back and quickly found out I needed to make them wider and keep them wider further down the limb. I was really surprised how thin I could get the limbs if they had no compression damage.
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Careful Steve you may end up with what i been saying for years now ! :laugh: :laugh:
I need to go home and do some measuring, cause I don't , but I know some of my bows are not even 3/8 " thick at the 2/3s point of the working limb were I start tapering the width !
And save the riser section to make up what you lose in something else, like a knot !
Have fun
We await your findings !!
Guy
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I didn't plan it or anything, but my best bows came out of their staves like this. Wide and very flat bellied out until ten-twelve inches when it was roughed out, but I ended up fading the taper up the limb relatively evenly. Kept the inner limbs a little stiffer, made my recurves pull their own weight, forgot about draw weight to focus on tiller, toasted the BL strategically, eventually got the handles working juuust slightly, and finally decided I couldn't do more to the wood without hurting it. It hurt to see each one go as I've been lucky to pull such bows out of staves after only a little more than one year, but luck and a little pain are great teachers.
Of course, I just now put two and two together when I read your stuff ::)
Keep writing and I'll keep reading ;D
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buckeye, thats the funny thing, It aint nothing new at all. Just speaking for myself for some reason I just don't always go as wide as I need to go even though I know better.
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I still think this is a modern innovation for when we are trying to break speed records. I don't believe it had any basis in historical technique.
Many old school books mention breaking a bow in and finding the balance between broken in and broken down has likely always been the best compromise.
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I just had one of those AHA!! moments. It has been driving me up a wall that these extra wide bows are comming in at significantly less than my own mass formula suggests. We always think of width as mass when we talk wood bows. I did a little bit of math a few minutes ago, as much as a high school drop out can do that is. It does appear that mathematicaly it works out that at a certain point extra width can and often does become more economical with mass.
Maybe some of you math geeks can help me out on this. oz.
wide bow 58" long, 50#@26", 10" handle and fades, static recurves 4" behind handle, 13" total working limb, limbs mostly parallel with slight but progressive taper. Mass weight 18.5 oz. Limb cross section .340X 1.562=.531sq unches
Narrow bow, 19.5 oz " .420X 1.375=.577 sq inches
Smaller overall area in the cross section of the wider bow. Mainly because of slight almost invisible wood damage.
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The elasticity of the wood is what will determine how well a design will perform. With an elastic wood you can modify any design to be more compact and this can translate into more performance and/or more durability. Round belly, flat belly. For me this depends a lot on the wood, the design and what I want from the bow. My experience is that if you have an elastic wood you can keep the limbs narrow and have a slightly rounded belly for improved performance at the expense of durability. It really all depends on what you want. There are very few wood species that are reliable in what they will give you, HHB is one. It doesn't matter too much where you cut HHB you can expect a given return from the wood, as long as it's a healthy tree. Others, Elm, Ash, Maple, are variable, Elm being the worse of these. From what I have seen of Osage and BL they also are variable.
Now mention of the tillering tree makes me want to put my 2 cents in. I know they are safe but if you want to get the most out of your bow then pull it by hand during the tillering process. Feeling what your bow does as it's being drawn back is important. Also keeping the bow at full draw on the tree, or by hand, or with a T stick for more than 5 seconds is a waste especially when you have finished tillering your bow. You don't shoot that way so why subject the bow to this?
We all have our own methods of laying out and tillering a bow out. Some think it out, I think Steve falls into this category. Personally I make bows more by feel. There's not much point in my trying to explain how I do what I do since much of it is done by instinct. There are certain things that are immutable, elasticity of a wood being of prime importance is one such thing. Like many I like to keep the limb width of my bows close to the same from fades to about mid limb. Intuitively I know that the extra mass I get from the wider limbs at that location won't make much difference in performance, if any, but will make a difference in how much set the bow will take. Also wide limbs at those points will make very little difference in air resistance.
Balancing the width of the limbs to the elasticity of the wood is where the fun begins
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I just had one of those AHA!! moments. It has been driving me up a wall that these extra wide bows are comming in at significantly less than my own mass formula suggests. We always think of width as mass when we talk wood bows. I did a little bit of math a few minutes ago, as much as a high school drop out can do that is. It does appear that mathematicaly it works out that at a certain point extra width can and often does become more economical with mass.
Maybe some of you math geeks can help me out on this. oz.
wide bow 58" long, 50#@26", 10" handle and fades, static recurves 4" behind handle, 13" total working limb, limbs mostly parallel with slight but progressive taper. Mass weight 18.5 oz. Limb cross section .340X 1.562=.531sq unches
Narrow bow, 19.5 oz " .420X 1.375=.577 sq inches
Smaller overall area in the cross section of the wider bow. Mainly because of slight almost invisible wood damage.
Steve
It shouldn't work that way. If wood is 8 times stronger in thickness and only 2 times in width then logically to get a same draw weight you would have more mass with the wider bow. I'm sure there are other factors that come into play though, the one that comes to mind is that wider limbs will more likely keep their spring (less crushed cells) better than narrow limbs which would therefore boost their ability to store energy. Sheesh, this is just too complex.
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Now mention of the tillering tree makes me want to put my 2 cents in. I know they are safe but if you want to get the most out of your bow then pull it by hand during the tillering process. Feeling what your bow does as it's being drawn back is important. Also keeping the bow at full draw on the tree, or by hand, or with a T stick for more than 5 seconds is a waste especially when you have finished tillering your bow. You don't shoot that way so why subject the bow to this?
I second this to oblivion and back. I use a mirror to tiller all my bows. It is long enough I can step on the string and draw the bow horizontally. The only time they ever sit on a static wooden tiller tree (or anything like one) is when I make a bow too long or heavy for me to string, and I need to pull it on the longstring to string it, so I will pull the longstring and slip the string on one of the tiller tree notches in order to string it. Doing it this way, I will never string a bow with a hinge, because it is so apparent. And I will not string a bow with unbalanced limbs most of the time, for the same reason. For the most part I will not string a bow that does not have an already good tiller, but some may argue I longstring tiller too far.
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Not much I can add to this discussion, but I would like to see some kind of standard where by we can judge each others bow's performance. For example, once I get my bow to length and weight, I simply weight the first 3". If the bow is braced at 5 1/2" I draw it down to 8 1/2" and record it's weight. I'm looking for at least 12# or over at this point. I know from experience that it'll drop 1# once the honeymoon effect is over. Several variables of course, like reflexed/recurved bows, but at least it's a method of determining what I've got.
Anybody want to share their numbers........Art
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I use the same methods myself. I have the bow 90% tillered before I ever bend it more than a few inches. But for the sake of expalining it I use the tiller tree and a scale.
As for the width making it lighter. It can only happen if the narrower bow is killing off some wood cells. If your wood is pristine narrower is always lower mass. If a bow needs to be a bit wider to keep the wood in pristine condition it also becomes more efficient with the use of the wood.
Typicaly I usually either heat shape or glue up bows with from 3 1/2 to 4" reflex. I often finish after shooting in with 1 1/2" reflex and I am fine with that. If I can take that same bow and maintain all but maybe 1" of the reflex I put in it will perform much better even if I have to go a bit wider to do that. If I go wide enough to avoid any set I have all my wood cells working instead of sleeping and it takes less.
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Thats exactly right Art, I figure about 2# loss for honeymoon and about 1/2" of set.
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Wow I'm really surprise with myself, I'm beginning to understand all of this. The light came on for me about 3 bows ago. And this conversation is fine tuning my thoughts. this is great keep it going. you guys have got to have more great stuff in your heads.
Thanks,
DBar
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I'm only drawing 24-25" on my best days Steve. So that would explain that 1# difference in the honeymoon effect.......Art
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Dan, we used to have conversations like this all the time. The bows kept getting better and better because folks became more aware of proper demensions. There is less room for improvement now that there was 10 years ago. Very little need to really know anything more than what you can pick up at these web sites. For some of you who are interested in going to other levels I am kind of presenting this as potentially a new frontier worthy of looking at. I guess you would call it recognizing, identifying and countering losses of power.
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Art, good point, I have most of my losses starting about 23", I seldom tiller past 28".
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Chapter? where can i read it? Mass principal? seen the term alot, but where i can i read up on it? man there are some great conversations and great thinkers over here on PA. lovin it.
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...I have most of my losses starting about 23", I seldom tiller past 28".
Badger, when you note that you have most of your losses starting at about 23 inches, what is the total length of these bows? This is me hearkening back to a post I started a month or two back pondering relationships between performance and the ratio between the draw length and total length of a bow...
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Eric, the losses can be relatively minor but shorter bows more so than longer bows but to some extent all bows that I think I have designed to draw 28".
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this is a good read so far for the poses the question is the hope of a new book on the back burner???
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Damnit Steve, Thought you said we were not saying anything for another couple yrs.......now here comes more bow pics!! ;D
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Very interesting discussion. This is pretty cool timing as I have been shooting a bow similar to what you are describing and although I haven't done any real "testing" with it, it would seem there are some noticeable advantages to it over a skinnier design. The bow was made by Brad Smith and he sent it to me to shoot for a few weeks. It is an Osage bendy handle 61ntn. It is about 1 3/4" wide until the last 11-12". I would say it averages about 3/8" thick. It has some character and Brad done a great job tillering it. I think this bow was around 67@28. This was the first time I shot a bow of this design. I was skeptical but was surprised at how well it performed. I think the wider limbs also helped with the character parts and help reduce any set or string follow. This bow was kind of an eye opener for me as far as the wider style goes and this discussion is confirming this wasn't a fluke. I suppose I'm going to have to rethink the whole wide limb deal. Thanks for bringing this up Steve. Matt
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Hi Steve
I have a question that goes back to the last paragraph of your opening post.
The first thing I decided was that a pyramid design wouldn't allow me the lattitude I needed in thickness adjustment so I opted for a modified version of the american flatbow.
However, as I read what follows, it seems that you are referring to tillering by removing wood from the sides of the bow?
And....
The rate of taper I have been using is very similar to that of the English Longbows. It starts off almost imperceptable and gradually grows steeper as it nears the tip. Not a straight line like you might see on a pyramid.
Is this also referring to removing wood from the sides?
I hope you don't think I am trying to be picky about your writing, I am just trying to understand your methods of tillering better.
Thanks for sharing :)
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Akswift, yes I do side tiller once I establish how much mass I am needing in the bow.
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ive always said that the paddle bow was a sophisticated design:) wide and flat and pulls 22-24'' of draw :)
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Does it win speed and distance contests?
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draws to short ;)
(as if thats all that hold it back hahaha)
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Badger
Thanks for clearing that up about side tillering.
Do you mean to say that before you tiller the sides, you bring the thickness down with the assistance of a weight scale?
ak
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Man! I wish I had a whole year to experiment on this! So far my favorite design as far as having a mindset of a hunter (priorities of speed aren't as high as others) I have realized a pretty straight taper from 1/4-3/4 of the limb then tapering a little bit faster, the bow smokes an arrow and is very quiet and accurate. I am excited because if your design theory is correct, I will have an absolutely amazing yew flatbow done in a month or so.
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very interesting!
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I came to the conclusion a few years ago that the less you have to pull a bow during tillering, the better the outcome. I start by making the thickness taper of each limb as perfect as I can by feel and floor tillering. When I'm satisfied that I've tapered the limbs as good as I can using that technique, the bow is usually ready for the short string. If there is a problem, it will be revealed by the braced bow - there is no need to pull it further. I'll make the brace as perfect as I can and then it is usually a simple matter of removing wood evenly from both limbs to achieve final weight using Steve's no set tiller technique. My tree is used sparingly in this process.
It's interesting that Steve has come to prefer a parallel limb design with most of the taper occurring in the last 12 inches of the limbs. I came to a similar conclusion as that was the design that I seemed to consistently get the best results from.
Good discussion Steve!
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Been doing the same Gordon, once you have a really good looking braced profile tillering becomes incredible simple. I came to it by making the parallel section of my VM bows longer and longer. At this point Iam measuring 14.5" from center line as the parallel section not counting the fades and handle. Which doesn't leave the last 12" tapered, but just over. I will try 12" from the nock point once I get gabes bow finished :)
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Steve you missed this fellows question I think !
Chapter? where can i read it? Mass principal? seen the term alot, but where i can i read up on it? man there are some great conversations and great thinkers over here on PA. lovin it.
Since it is your writing I will leave it to you to answer , I cant remember which volume it is anyway !
Guy
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I do miss the old forum too Steve. A lot of the guys on the forum today don't realize that a lot of what they know and practice today we hashed out and over years ago. Those were exciting and stimulating times. My hat's off to you for trying to revive some of those moments for this new crowd..........Art
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Very interesting subject.
I've only recently begon to Persued the Mass Principal.
I look forward to learning more.
-gus
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I do miss the old forum too Steve. A lot of the guys on the forum today don't realize that a lot of what they know and practice today we hashed out and over years ago. Those were exciting and stimulating times. My hat's off to you for trying to revive some of those moments for this new crowd..........Art
There's a heck of a lot of info in that old forum. I saved a lot of the threads pertinent to my posts but they're in a different format and are not compatible with this board. I'm sure somebody must know where it is. In fact I bet PA could make some money putting the contents of that old board on DVD and selling them. Maybe I'll suggest it to someone. It would be a shame to lose it completely
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Bryce, I used 12 on the recurve I was talking about more often 14 or r/d bows, and then I continue to increase the taper as I build depending on how it is going.
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Don't usually read this deep into the bows threads, but this is an interesting subject. Way over my head, but will definitely take this info into consideration in an up coming bow I'm wanting to build. Thanks!!! dpgratz
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What a distraction from studying. >:D Love the discussion so far. I think its pretty well understood that optimal design and strain will yield great bows. The way I've thought about it for a while now is that the bow should be wide enough for minimal set, this showing that the bow is not over built but not too under built. The question is, where is that optimal strain and maybe is it possible to get no set and know that the bow is not over built. I think experience holds the answer without getting extremely scientific. Using mass as a separate parameter is good because we don't necessarily require the bow to take any set to know it's near optimal strain. From the research that's been done on the mass principle, it has shown that all woods will follow it to some extent. I believe yew is (one of?) the exception. My understanding of this is that all wood stores an equal energy per mass. BUT because of wood's variability as a material I believe there may be more exceptions to this rule. Only further research will tell. Because of this I think there may be a best (fastest) wood but I don't think we have enough data. Until then design and building technique are the best factors that determine the quality of a bow. (IMHO)
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Ryoon, thats exactly right. Some woods tend to be more elastic and can be built at slightly ower mass maybe 10%. Yew falls into this category as well as osage. With osage I don't deduct the 10% because I really like the extra margin and a lot of the mass is in the handle and fades anyway. As I get to know different woods I start to get to know how far light or heavier I want to go with the mass. It is pretty conservative so I seldom go any heavier.
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Since every piece of wood is different(even within species) when you are in the throws of tillering, how do you decide when to narrow and when to thin? I like Del's technique of "go too far and then back up a step" but I've found it to be a great source of firewood :D
Don
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Bryce, I used 12 on the recurve I was talking about more often 14 or r/d bows, and then I continue to increase the taper as I build depending on how it is going.
yep i got that part :)
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OK, maybe this is a stupid question, but then, you all know how new I am to this... I keep seeing "wide and flat" as a description of the bow.
Do you mean that it is simply rectangular in cross section?
Or do we mean that it is consistent thickness / no taper?
Or something else?
Help those of us out who haven't earned their bowyer IQ yet... ::)
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Now that sounded like a much smarter and wiser ryoon from a year ago...variablity is a big factor some times and can wreck or derail a properly designed,tillered,and mass principle bow ;)
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OK, maybe this is a stupid question, but then, you all know how new I am to this... I keep seeing "wide and flat" as a description of the bow.
Do you mean that it is simply rectangular in cross section?
Or do we mean that it is consistent thickness / no taper?
Or something else?
Help those of us out who haven't earned their bowyer IQ yet... ::)
Thats exactly the question that started me on the mass priniciple. 1st of all I am a backyard bow builder and not a geek by any stretch of the imagination. I do everything the hardway by actually building bows and then looking for patterns.
The first thing I had to do was develop some very basic common sense" bow logic" taking into consideration a few givens. The most important is that wood only has 1 correct thickness and it will be different on every bow we build. The challenge is to find and be able to express working techniques that will allow us to ge close to this perfect number on every bow we build. Obviously we are not going to do bend tests and calculations that are way above my head anyway.
The most common denominator I found that best predicts both the demensions and the proper tiller is mass. It is always good to think of thickness as how far a bow can bend and width as controlloing how far it will bend. If you have to reread that and think about it do so, it is an important basic piece of info that is good to drill into our heads.
When we bend something we will always create a radius, the radius may not be the same for the entire length of the limb and certainly the radius wont always be the same for different bows. working with the most elastic woods we have the inside radius needs to be less than 1% smaller than the outside radius, most woods are about 25% less than that. This is just something to keep in mind when you see a narrower section of the bow that is thicker but bending more than a wider thinner part of the bow. You know it just aint right. You don't have to figure anything here just keep it in mind.
Bow logic tells you that if you have paralell limbs it could only be for one reason and that is you want the outer limb to bend more than the inner limb giving you an eliptical tiller shape. Bow logic will alos tell you that if you have a tapered limb the bow should bend at least equally and the thickess should be about the same. Theoreticaly you could build a bow at one specific thickness and then tiller it completely from the sides for a nice round tiller.
Nearly all the woods we work with are going to fall into the specific gravity range of somehwhere between 50 and 100, the great majority of those will be between 60 and 80. The majority of the bow we build are going to be between about 45# and 65#. This is where I feel the mass principle is most accurate.
The mass principle can be very valuable in determining how to execute a particular design for instance. You may want to build a hickory backed ipe english longbow. You want it 6ft long but you only want it to be 50#. You don't want the bow so narrow that it is uncomfortable to shoot just so you can make mass, so what you do is modify the tiller shape until it is the right mass at the width you feel will be comfortable. Lets say for instance you have roughed the bow out and got it bending. it feels like a 100# still but is bending. You weigh the bow and find out it is 6 oz too heavy to hit your target mass and you know only about 2 oz more wood will come off to make your weight. You go the the program and start adding length to the handle and fade number. If you add 4 then you will use just a slightly elyptical tiller, if you add 8 you will use a full elyptical tiller, if you add 12" it will be whip tillered. They should perform pretty well if built like this and not have handshock.
Say you are working on an American longbow with parallel limbs most of the way down. You keep in mind the weight of the wood when you rough it out, for mid 60 bows for intance you might figure 1 3/8 for osage as a starting point 1/1/2 for locust and 2" for a lot of the white woods, + or minus depending on the density of the specimen. You simply rough out the bow, get it bending and then check the mass weight. Figure you have at least a couple more ounces comming off just to make weight so if you are within 2 or 3 ounces you just keep tillering the belly as you get closer you can adjust the width a little at a time or more to adjust for mass weight and fine tuning tiller.
The secret is knowing how to do the input, modify the length of handle and fade input to accomadate your tiller shape. If you want circular limbs use the exact measurement of your handle and fades if you want elyptical then add 2 or more inches depending on how extreme you are going.
If your tips are stiff say for six inches you may want to use a draw lenght figure 1 or 2 inches longer than you are actually going to draw it. If the tips are stiff for 10" you may want to use a figure 2 or 4" longer than your actual draw.
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Ryoon
How much does a Poplar bow weigh anyway !
Guy
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Ryoon
How much does a Poplar bow weigh anyway !
Guy
The same as any other bow
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Now that sounded like a much smarter and wiser ryoon from a year ago...variablity is a big factor some times and can wreck or derail a properly designed,tillered,and mass principle bow ;)
I've been learning that first hand. Since most of my bows are Hickory. (MOST not ALL) I have come to realize that one piece of the exact same species can very from another....never would have thought that with out building bows...and I would not have known that had I not built so many from the same type of wood (or have read it on this forum or in one of the TBB books). I don't think anyone can really have a true understanding of something without experience though. (in most cases). So now I am convinced that you have to have several samples of the same species to draw general conclusions about that specific wood.
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Ryoon
How much does a Poplar bow weigh anyway !
Guy
The same as any other bow
BOOM!!! You've just been 'Mass Principle'd'
Lol
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BOOM!!! You've just been 'Mass Principle'd'
Lol
;D ;D ;D ;D ;D
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Some interesting reading guys.
Tillering for me is becoming more and more about bending the wood less to get where i'm going.
I always trace the original profile onto my tillering board to have a definate reference as to the begining shape of the stave. After extending draw length, exercising the limbs etc unstring it and immediately put the bow back on the board to see how it compairs to the traced outline.
I too find set really starts around 20 - 22 inches and from here on out it about minimising losses.
I used to think deflex was a bad thing full stop but again over the last year or so i've been finding that it can also be a friend in that it allows the wood to stay a little fresher getting to full draw....it can definately be used to advantage.
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I think what Badger meant to say is that the thickness of a piece of wood determines how far it will bend, and the width determines how much force is required to bend it that amount.
That's the key principle of the bowmaking spreadsheet I developed. It's a case of drawing a goal tiller shape, measuring the radii at various points to determine how thick a bow's limb needs to be, then figuring out just how wide it needs to be at those points to achieve the desired draw weight.
Badger, I think it's funny how sometimes things come full-circle. I'm pretty sure in TBB1 Tim talks about (I think) Comstock's 'modified Meare Heath' design, which is a wide flat limbed design but which tapers more abruptly that the original for the last 10 or 12 inches or so. That was superceded for a few years in favour of other designs, and here we seem to be coming back to a very similar design.
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Ryoon
How much does a Poplar bow weigh anyway !
Guy
The same as any other bow
Steve I get the idea , even if I don't use it .
But since Ryoon is most likely the only one with a working Poplar bow, and with poplar being a bit of an extreme to the light weight side wood , I wondered if he had checked it, and would he give us his input !
Just a thought even if its not a good one !
Who knows maybe Osage really is not the king !
I will let you folks that are way smarter than I carry on now !
Thanks for all you do to further the great addiction !
Guy
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Guy, I have made a bunch of polar bows, some of them have been real shooters but usually give out after not too many shots. I know a guy who had a sinew backed poplar that he used year after year on his 3-d shooting that shot like a demond, it was a great bow. I did a video of breaking one several years ago, I had pulled it back to about 38" and the string final came off the nocks and it didn't break inspite of having about 5 or 6" set.
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Guy, made it home today for a break from studying and measured the bow. Turned out to be 19.5oz in mass. With the wide tips and bulky handle there's definitely a little excess mass in there. Stringing it up and drawing it a few times, it feels pretty stout and stiff. But that could be me getting flabby. ;)