Primitive Archer
Main Discussion Area => Bows => Topic started by: Kidder on June 23, 2021, 03:05:26 pm
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A lot of very experienced bowyers refer to tiller shape matching the front profile. In another post I started I was referred back to TBB for this info. I’ve since gone through all four volumes, reading all the chapters on bow performance, tillering, etc. There is definitely reference to it, but for the life of me I cannot find a definitive statement on what proper tiller shape for various front profiles are, and importantly why they are that way. Can someone please explain this to me? Thanks in advance.
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A lot of very experienced bowyers refer to tiller shape matching the front profile. In another post I started I was referred back to TBB for this info. I’ve since gone through all four volumes, reading all the chapters on bow performance, tillering, etc. There is definitely reference to it, but for the life of me I cannot find a definitive statement on what proper tiller shape for various front profiles are, and importantly why they are that way. Can someone please explain this to me? Thanks in advance.
Try vol 4, page 95. I've read it so many times I knew the image i was looking for :fp
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I'm only a beginner, but as far as I understood the width of the bow all over the limb corresponds the amount of bend and as a result in drawlength gained from that same spot. e.g. if you have a pyramid limb you gain most of your draw length from the inners, steadily decreasing towards the outers. jmy2c
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A lot of very experienced bowyers refer to tiller shape matching the front profile. In another post I started I was referred back to TBB for this info. I’ve since gone through all four volumes, reading all the chapters on bow performance, tillering, etc. There is definitely reference to it, but for the life of me I cannot find a definitive statement on what proper tiller shape for various front profiles are, and importantly why they are that way. Can someone please explain this to me? Thanks in advance.
Try vol 4, page 95. I've read it so many times I knew the image i was looking for :fp
That’s the one! I read that last night and again today. I guess the problem is I just don’t understand it in relation to the shape of the side profile. Goes to show that knowing and understanding are two separate things.
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Kidder....You might be over tihnking this.I think it has to do with whether you have parallel width or tapered width limbs.Tillering is all about your thickness taper.Your thickness taper will be more aggresive with parallel limbs than with tapered width limbs.
You can do combos' too.Parallel width a ways to say mid limb.Then tapered width a ways on the same limb with less aggressive thickness taper.Each has it's own degree of aggressivenss of thickness taper.
A person needs to keep in mind the amount of work a limb has on it's length and where that is.Page 117 in the TBB 4 book.The outer limbs don't work as hard as the inner limbs.It's for a D bow but still the analogy corresponds to stiff handled bows too.
A nice smooth ever increasing reflex of any degree from just outside the fades to the tip.
That's why reflex is held better on the outer limbs more so than on the inner limbs and there's no reason to over stress the inner limbs with reflex because it has to do more work which will create stress and set and lose the resilience of your wood there.
The old mantra of 0 to minute set on the inner limbs with enough width to handle the load.A little set midlimb,and paractically 0 to no set on the outer limbs.
Sounds confusing but it really is'nt.Once a person establishes a thickness taper on making different types of bows enough times it is'nt quite so confusing.
Example.
http://www.primitivearcher.com/smf/index.php/topic,67543.0.html
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Two given physics principles of bows
1. a limb has to taper either in thickness or width or some of both.
2. any given thickness of any wood has a bend radius, that if exceded, creates set.
Consider the pyramid back profile with a width taper:
For a limb to have equal strain along it's length, it needs to be about the same thickness throughout it's length, and since the thickness remains even, it will result in a consistent bend radius, or a circular bend.
Since a straight limbed bow tapers in thickness, it should bend more as it gets thinner if the outer is to work as hard or be strained as evenly as the inner, yeilding a more eliptically shaped bend from the side view.
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I agree with Ed completely, but I will add a few thoughts. Parallel limbs, as Ed mentioned, get thicker as you move from mid limb to fade. Thick wood can’t bend as far as thin wood without taking set or breaking right? So the tiller shape ideally on that bow should be, less bend near the handle, and gradually more as you move mid limb. A pyramid bow gains little in thickness as you move toward the handle, therefore, being the same thickness along the limb, it can and should bend more circular than its parallel counterpart. That is the long and short of it. But this is all based on a perfect stave in a perfect world. Many are the times that I have ignored the whole thing. I made a bow some years ago, 2013 or so, that remains my favorite bow. Knotty Boy, if you care to look it up. It is a 66 inch Osage, bendy handle, covered with knots. I made it parallel from mid limb to handle. 1.5” wide. I kept the tiller circular because It was high crowned and I could not go much wider with it than 1.5” and I needed to compensate for the knots. All things equal, it violates the rule, but it shoots beautifully and has held up over time.
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The way I see it the reason for this is two fold. One, to make sure the limb is utilizing the mass where it needs to for low set. And two, for efficient movement of mass along the limb. For simplicity sake, a limb parallel it’s whole length should be highly elliptical and a perfect pyramid should be circular (slightly more inner limb bend) with variability between those extremes.
Areas of lower mass (width) should bend less than areas with more mass. This is because you need a certain amount of wood to do the work being asked of it. Narrower areas will need to be thicker to store the same energy but can’t bend to the same radius as wider thinner limbs.
As you get further out on the limb the mass has further to move during the power stroke. The more elliptical the bend the more efficient that movement of mass for any given profile. But that elliptical shape would have to be in balance with where the work needs to be done for low set.
Examples.
A pyramid bow with an elliptical tiller is more likely to take outer limb set though the movement of mass in the limb is quite efficient.
An American longbow (parallel width taper) with a straight thickness taper would bend a lot in the inner limbs with excessive mid and outer limb mass for low efficiency. It would also take set unless made wide to take the bend.
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I agree with that Ryan. Mass placement and movement is part of the equation for sure.
I will differ with you on one thing…and it is just my opinion, but the outer, more narrow limbs are under less stress, and can therefore bend in a circular manner, without the need for them being thicker to carry the load, as they are carrying less than the inner limbs.
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I agree with that Ryan. Mass placement and movement is part of the equation for sure.
I will differ with you on one thing…and it is just my opinion, but the outer, more narrow limbs are under less stress, and can therefore bend in a circular manner, without the need for them being thicker to carry the load, as they are carrying less than the inner limbs.
Not sure what you’re referencing with regard to the outer limbs from my comment.
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May be my interpretation of what you said is wrong, but paraphrasing, “areas of lower mass (width) need to bend less than areas with more mass…”
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May be my interpretation of what you said is wrong, but paraphrasing, “areas of lower mass (width) need to bend less than areas with more mass…”
That was a gross overstatement on my part. It’s definitely more complex than that. It’s difficult to describe the dynamics for a whole limb with each piece relative to each other.
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I meant to say and agree with what slimbob said about more extreme character bows.My thickness tapering descriptions were described for darn near perfect wood.Character bows with knots,pins,and whooptee doos, and wiggles can take longer to tiller.Before it's through you'll be using your eyes watching the bend and your finger tips feeling for irregularities to get to the final draw length.Unbracing checking for set along the way many times.
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I think, at least in theory, a pyramid bow can have a near perfect circular tiller and be right. The more narrow mid limb bending in the same circular ark as the wider inner limbs, precisely because as you move outward (toward the tip) the limb is under less strain, and can therefore be more narrow and yet carry enough mass to handle the strain. Again, on a perfect stave in a perfect world. From a more practical stand point, adjustments are made to compensate for all kinds of irregularities that throw the theory a curve ball.
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Agreed, nothing more to add other than this principle is absolutely key to making good bows :)
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IMO.
All good in theory, but for the average bloke making a bow the difference in those front profiles and tiller shapes is all but negligible. (And at a casual glance it's hard to spot the difference)
Especially if you start to factor in something like deliberately favouring stiff tips.
I've just spent ages helping a guy on an FB forum who was making 20# bows with a hinge in each limb. Finally got him to make one over 40# with no hinges... the front profile was 100% irrelevant.
Del
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Your student thickness tapered too quickly or unevenly in areas to have hinges.Hard to spot with pictures and not actually being there.Some students take longer to get the hang of this tapering than others.
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I pay little attention to the backs profile , I just try and spread the wealth over the whole limb, starting in the mid 2/3 then closer to the finish toward the fads and out toward the tips, I usually leave the last 6 inches or so stiff, to much bend to start off at the fads usually causes me problems because that is where it wants to bend anyway and if I get the tip moving to much to early I will get a whip tiller, either one not good. I am usually using wood with some knots or in prefections so what yall call the prefect tiller is not always achieved but works for me. :)
Pappy
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IMO.
All good in theory, but for the average bloke making a bow the difference in those front profiles and tiller shapes is all but negligible. (And at a casual glance it's hard to spot the difference)
Especially if you start to factor in something like deliberately favouring stiff tips.
I've just spent ages helping a guy on an FB forum who was making 20# bows with a hinge in each limb. Finally got him to make one over 40# with no hinges... the front profile was 100% irrelevant.
Del
Agreed.
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IMO.
All good in theory, but for the average bloke making a bow the difference in those front profiles and tiller shapes is all but negligible. (And at a casual glance it's hard to spot the difference)
Especially if you start to factor in something like deliberately favouring stiff tips.
I've just spent ages helping a guy on an FB forum who was making 20# bows with a hinge in each limb. Finally got him to make one over 40# with no hinges... the front profile was 100% irrelevant.
Del
No Del it is also very good in practise!
If you don't practise it you will get excessive set and over/under strained wood :)
Every piece of wood can bend a cewrtain distance before taking set.
Make it thinner it can bend further.
Thicker it can bend less before damage.
That is 'tiller logic' in a nutshell.
straight thickness taper eg. a pyramid, minimal thickness taper = no (or minimal!) change in bend radius.
parallel width limbs tave to taper in thickness = elliptical tiller. As you progress along the limb.....it gets thinner....right???? Therefore the limb that is getting progressively thinner must also progressively bend further as it gets thinner.
Stiff tips etc don't alter the fact that wood takes set at a certain bend radius :)
Maybe the difference is subtle but that doesn't matter the difference is there :)
Just like the difference between a balanced car wheel. Take a couple of those weights off and see how well it works :)
Front profile dictates tiller because of the above!
Front profile by definition cannot be irrelavent to tiller shape - the two are interrelated.
The wood doesn't think front view is 100% irrelavent.
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Most guys can't even detect an even curve so going beyond that and trying to see an involute type of curve is a step too far.
Looking for a "nice even curve" is a good goal.
I still agree with Del.
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Maybe somebody can give good examples of the different curves on bows so new guys can see the images side by side. That would certainly help everyone.
Maybe a thread with "here is the front profile" and "Here is the tiller shape" and why is it right or wrong.
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Most guys can't even detect an even curve so going beyond that and trying to see an involute type of curve is a step too far.
Looking for a "nice even curve" is a good goal.
I still agree with Del.
To each their own :)
But to play devils advocate.....how do you judge your nice even curve???
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Maybe somebody can give good examples of the different curves on bows so new guys can see the images side by side. That would certainly help everyone.
Maybe a thread with "here is the front profile" and "Here is the tiller shape" and why is it right or wrong.
That is a good idea.
I'm tillering a few elbs at the moment. They are a great example of elliptical/circular tiller. If you tiller an elb to have an arc of a circle 'even' curve it will be handshocky. However if you tiller one with the correct, quite prononced elliptical tiller you will get less set and a totally shockfree bow. I'll try and take some photos for an example of elliptical tiller.
The differences may be subtle but they matter.
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Maybe somebody can give good examples of the different curves on bows so new guys can see the images side by side. That would certainly help everyone.
Maybe a thread with "here is the front profile" and "Here is the tiller shape" and why is it right or wrong.
Here you are just to clarify ;)
Top pic is a 110# Yew character warbow tillered "arc of a circle" but with some character. Natural deflex in the lower/left limb, and a big knot and dip just right of the grip.
bottom pic is a 75# Yew ELB which at a casual glance looks to have elliptical tiller... but does it really? It just has a slightly stiff grip section where the billets are spliced. Or is each individual limb is "arc of a circle" ?
The front profile of both is roughly parallel for about 3/4 of each limb, then a smooth curve to a point at the tip with horn nocks.
Anyone is welcomed to try and critique the tiller, but it is far more a response to the actual wood than it is to the front profile!
IMO. The real case which disproves the "front profile" theory is a Mollegabet, from the front, you can see the outer limbs are narrowed... but they can be either stiff levers or working limbs, or somewhere in-between!
NOTE:- I'm not saying front profile is irrelevant, just that it's relevance is often heavily masked or outweighed by other factors when using staves.
Del
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Most guys can't even detect an even curve so going beyond that and trying to see an involute type of curve is a step too far.
Looking for a "nice even curve" is a good goal.
I still agree with Del.
To each their own :)
But to play devils advocate.....how do you judge your nice even curve???
The typical circle held against a bent limb orc a gizmo will do that.
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I agree Meare Heath bows with parallel limbs should be tillered elliptically. Pyramid bows should be tillered with a circular tiller where a good part of the bending occurs near the handle where most of the wood is.
But there are exceptions. I prefer the Meare Heath style but if the limbs get too thin I begin to narrow them to bring the tiller home
Jawge
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That is a good idea.
I'm tillering a few elbs at the moment. They are a great example of elliptical/circular tiller. If you tiller an elb to have an arc of a circle 'even' curve it will be handshocky. However if you tiller one with the correct, quite prononced elliptical tiller you will get less set and a totally shockfree bow. I'll try and take some photos for an example of elliptical tiller.
The differences may be subtle but they matter.
Looking foreward to the pics. :)
IMO. The real case which disproves the "front profile" theory is a Mollegabet, from the front, you can see the outer limbs are narrowed... but they can be either stiff levers or working limbs, or somewhere in-between!
Del
As a basic principle of tillering a simple bow, the bowyer strives to strain the wood equally. this results in a bend appropiate for the thickness taper.
presuming the bowyer is doing a good job and the bow has enough nock to nock length to be drawn to its desired drawlength, then a longer stave can yeild a design with more features. For instance, a nonworking handle or stiffer tips or levers.
I am not sure a bow with additional features that incorporated lesser strained tips or handles would "disprove" basic tillering principle, it's just a matter of applying the basics to the parts of the limb that work.
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It’s not possible to tiller every bow the same way and get low set. Different shapes need to be tillered differently just because of that. How much of a difference that makes or how it needs to be done is up for debate but low set and then speed will tell the truth.
I do agree for the average bowyer that this might not matter but many of us strive for an ideal which can be part of the fun.
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"I am not sure a bow with additional features that incorporated lesser strained tips or handles would "disprove" basic tillering principle, it's just a matter of applying the basics to the parts of the limb that work."
A principle that is applied selectively and only when it suits is hardly a principle is it?
Del
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So I frankly agree with nearly every position put forward here. By that, I think it is sensible to build bows with “principle” in mind, and I think it is just common sense that informs me on this. It is in no way a must, only a way to marginally increase the efficiency of these bows we make, in certain circumstances. Del and I have been arguing this for 10 years I think.
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Even the term elliptical is a bit odd considering it would really mean a rather whip tillered bow.
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It is reasonable to "match" the front profile with the proper thickness tillering. But how are we going to accomplish such a "match"?
"The Mantra: Make inner limbs wide or long enough for virtually no set.
Make midlimbs wide enough for little set. Make outer-limbs and tips narrow
enough for lowest possible mass." (TBB4 p.150)
Can this mantra be applied to all kinds of front profile? At least for all wood self-bows?
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I think in a general sense, yes. It can, or should, be applied without exception. Don’t take set on the inner limbs…we know the consequences if we do. Keep the tips light…no question, this is preferable to heaven tips. You are simply left with the center, and since set is unavoidable, that is where it must happen. We should balance the mid-limb somewhere between too heavy and too light.
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If you're straining equally and set has to happen, it should take place everywhere the bow is bending then.
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That is a really good point that makes you stop and think. The inner limbs can carry more mass because we aren’t moving that mass much at all near the handle. We can afford the extra mass that minimizes any set without much I’ll effect on cast. So the inner limbs would necessarily be under marginally, less strain…I would argue.
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If you're straining equally and set has to happen, it should take place everywhere the bow is bending then.
I'm not trying to strain the wood evenly i'm trying to strain it optimally for a bow! Two different things :)
Pat - 'The typical circle held against a bent limb orc a gizmo will do that.' isn't an answer. What's a typical circle?
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I´m always trying to find find the right amount of bend for the inner limbs. They should bend as much as necessary in order to take the strain from the midlimb areas but not more. If they bend too much, the bow will be shocky. That´s why I start monitoring hand shock at half draw. If there is to much handshock, I´m removing some wood at the midlimb and outer areas. This ensures a better efficiency of the bow. But there´s also the other way around: I remove some wood from the inner limbs if feel that there´s too much strain in the midlimb areas. Usually it isn´t necessary to remove a lot of wood there because of the good leverage of the inner limbs.
But there is not much oppertunity to play with the tiller, if the bow is very short and narrow for its draw length. In this case, the strain of the wood must be distributed as evenly as possible over the entire length of the bow.
lonbow
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"What's a typical circle"? (quote from Bownarra)
Arc of a circle tiller has only 2 variables.
1. The radius of the circle.
2. What proportion of the circle does it include (e.g 1/3 of a circle or a semicircle)
If you try to define an arc of an ellipse there are a lot more variables, and I've yet to hear or read any actual definition that quantifies how elliptical is elliptical.
Maybe arc of a circle is a bit lazy, but it is vastly easier to interpret.
Del
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If you're straining equally and set has to happen, it should take place everywhere the bow is bending then.
+1. It has never made sense to me that people think the limbs are strained/stressed evenly along their whole length. To me this means the fibers are all doing the same amount of stretching in tension and compression which would result in the same amount of set everywhere. If not then this would mean thicker vs thinner limbs take different amounts of set under the same strain for some reason. I can’t wrap my head around that.
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I hear you Ryan.I do know bending it in 1 area too much causes set there if not compensated for with extra wood there.Making a bow according to the amount of power you need and getting most of that from an area on the limb that needs to be compensated for with extra wood there.Leaving less wood in areas on the limbs that take less strain like the outer limbs.
Then it's the discussion of what type of weight arrows are best suited for what type of bows.Whip tillered can shoot lighter arrows faster.Bows working from mid and inner limbs shoot heavier arrows faster.
Exception being short horn bows where their shorter limbs reduce mass considerably because of the composite materials in them.
I might be changing the subject here a bit.Bow making and it's use is such an individual thing there is no 1 size fits all.
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I think the fact that a limb needs to taper from fade to tip is easy to comprehend. I think once you start to study, learn and experience you get that to much stress causes set, and set is not your friend. But there has to be a better way to explain the correlation between profile and tiller and how to get to an efficient (or more efficient) bow. Even if that means creating categories like hunting, target, general, it's for heavy arrows, for light arrows, etc. We seem to interprete speed with efficiency, and speed can be gaged with each situation. So how do I constantly make my heavy hunting arrows go faster? What exact profile do I need to start with and expand from. I think the mass theory started down that road, but never got to completion. But there is probably more to it as well. Sorry for the ramble, but I am really trying to wrap my head around this.
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If you're straining equally and set has to happen, it should take place everywhere the bow is bending then.
I'm not trying to strain the wood evenly i'm trying to strain it optimally for a bow! Two different things :)
Pat - 'The typical circle held against a bent limb orc a gizmo will do that.' isn't an answer. What's a typical circle?
It's round. A typical circle is round.
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I think it’s helpful to think of these topics in terms of examples and thought experiments. Say you have a pyramid bow and a typical parallel limb taper (American longbow) bow and both have a circular tiller with the same amount of set. Which one would shoot faster and why? (Same poundage/draw length, length, etc. ;) )
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We seem to interprete speed with efficiency, and speed can be gaged with each situation. So how do I constantly make my heavy hunting arrows go faster? What exact profile do I need to start with and expand from.
Interesting question. With heavy arrows, a bow becomes more efficient, so efficiency gains are harder to tease out of designs. So maybe just a heavier draw weight? BTW, for me, a bow that is at my upper draw weight limit "feels" better if it is longer.
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We seem to interprete speed with efficiency, and speed can be gaged with each situation. So how do I constantly make my heavy hunting arrows go faster? What exact profile do I need to start with and expand from.
Interesting question. With heavy arrows, a bow becomes more efficient, so efficiency gains are harder to tease out of designs. So maybe just a heavier draw weight? BTW, for me, a bow that is at my upper draw weight limit "feels" better if it is longer.
Everything is a trade off. It's written over and over in TBB. Obviously a short bow is more convenient for hunting, but I agree a longer bow seems more comfortable to shoot. I don't typically sit in tree stands, and don't use commercial blinds much, so I need to get past the need for a shorter bow I think. I'm not even sure where that desire came from.
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I'm not trying to strain the wood evenly i'm trying to strain it optimally for a bow! Two different things :)
Not necessarily. By straining all the wood equally you are getting the most work/energy storage possible without overloading any particular part of the limb. That sounds pretty optimal to me.
+1. It has never made sense to me that people think the limbs are strained/stressed evenly along their whole length.
They certainly can be and this would be the optimal way to store energy in the limbs. A pyramid profile with a true circular arc tiller will see equal strain along the whole limb. Why do you think that isn't possible?
It's round. A typical circle is round.
Answer of the week! A better definition might be that circular tiller has a constant bending radius. Elliptical tiller has a larger radius at the base of the limb with the bend getting progressively tighter towards the tip.
I think it’s helpful to think of these topics in terms of examples and thought experiments. Say you have a pyramid bow and a typical parallel limb taper (American longbow) bow and both have a circular tiller with the same amount of set. Which one would shoot faster and why? (Same poundage/draw length, length, etc. ;) )
Probably the pyramid bow because the outer limbs are lighter, but that is a SWAG at best.
Mark
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I'm not trying to strain the wood evenly i'm trying to strain it optimally for a bow! Two different things :)
Not necessarily. By straining all the wood equally you are getting the most work/energy storage possible without overloading any particular part of the limb. That sounds pretty optimal to me.
+1. It has never made sense to me that people think the limbs are strained/stressed evenly along their whole length.
They certainly can be and this would be the optimal way to store energy in the limbs. A pyramid profile with a true circular arc tiller will see equal strain along the whole limb. Why do you think that isn't possible?
.... .... ....
Mark
Semantics. Bow limbs are not, and should not be, strained evenly. The total stress should reflect the relative position of the measurement. It's much more stressed near the fades and much less near the tips. But if we consider the amount of "wood" in each positions, each units of "wood" are, or should be, strained "equally".
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I agree it is semantics, but for a different reason. When we say “equal strain” along the limb, I think we some how conflate “equal force”, “equal strain” and “mass placement”. The force applied along the limb is equal. The mass placement along the limb is what determines the tiller. Having thought about this after Pats question, clearly, a bow limb is not ,”strained” equally along the length, depending on your interpretation of exactly what that means. A narrow, thick, working handle should not “feel” the strain that the working limb feels. At least in my opinion. The inner limb should not feel the same strain as the mid limb, and the outer limb should not feel the same strain as the mid limb. Mass placement determines how much stress is felt along the entire length of, I suppose, any bow. And that mass placement seems to me to be, the very essence of what we do. We strive for proper mass placement, not equal strain.
Edit. Mass placement will determine our tiller shape, elliptical, circular, or some variant between the two. This brings us full circle back to, what is the proper tiller shape for a given front profile? But we can at least dispense with the “equal strain” tangent.
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This is why a thread with examples and "here's what right and here's what's wrong would help. Some of the discrepancies is interpretation.
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Some of the discrepancies is interpretation.
agreed. Looking up the word strain in the dictionary gives many definitions. When strain is used in engineering, it is a percentage length measurement.
a bow back surface segment that measures 10" when the bow is unbraced, and is stretched out to 10.1" at full draw is said to be strained 1%.
Also, as defined in the engineering world, stress is a pressure measurement. For example, if the above bows back is sinew, then the stress/pressure at the sinew back surface is not very much compared to an otherwise similar back, bent just as far, but made from much from a stiffer materiel such as hickory.
For folks coming from a non-engineering background, different definitions of the same words are frequently in use.
Our language is like that. Are there definitions from TBB that differ?
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One of my biggest issues with TBB when I first started was it's lack of definitions. I spent a lot of time internet searching words. Even then, if you don't put it in the correct context, it becomes unclear, and it's hard to know the context, until you "know the context". TBB is one of those books you need to read, build a few bows, read again, build a few more, read again, rinse and repeat. I don't know how many times before you've soaked it all in. I'm not close yet.
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I would agree with that completely. I read TBB 1 as I built my first bow. Then the others as I built the next few. Over the next 25 years I have reread them countless times. Not front to back, just chapters relevant to what I was working on. I’m a reader to begin with, so I have enjoyed them all, but there is only so much that can be conveyed in a book. Building them teaches you things that contradicts some of what was written, and some things were absent from the books entirely. Still, they are a very good resource.
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I agree they are a "must have" resource.
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Mark, it’s not that I think it isn’t possible but that it isn’t optimal for bows to be strained equally along their whole length. This is what Tim Baker’s Mantra suggests and that seems to make sense to me depending on the bow. I would say that it’s not terribly common for that to be the case in the real world anyways given that bows rarely show the same amount of set along the whole limb. Certainly the last 6-8” of a bow limb doesn’t take set in almost all bows unless quite whip-tillered.
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If we divide the bow limbs into many sections, the total stress for each section should be quite different. It should be much higher in the fade section than in the tip section, etc. That's the mantra.
But if we look at the unit stress of each section, by dividing the total stress in each section with the mass units in the section, it should be same for all sections. All "wood" in the limb should be evenly and equally strained. This is the underlying principle for the mantra and no set tillering.
Just my SWAG, scientific wild-ass guess.
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If we divide the bow limbs into many sections, the total stress for each section should be quite different. It should be much higher in the fade section than in the tip section, etc. That's the mantra.
But if we look at the unit stress of each section, by dividing the total stress in each section with the mass units in the section, it should be same for all sections. All "wood" in the limb should be evenly and equally strained. This is the underlying principle for the mantra and no set tillering.
Just my SWAG, scientific wild-ass guess.
Doesn’t really make sense that it would be stressed the same if there are areas of more mass to do less work. That’s actually not the mantra. If we define stress/strain as how close the wood is to deformation (set) then the inner limbs and tips should be less stressed so they don’t take set and the mid limb takes the brunt of it.
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I think the fact that a limb needs to taper from fade to tip is easy to comprehend. I think once you start to study, learn and experience you get that to much stress causes set, and set is not your friend. But there has to be a better way to explain the correlation between profile and tiller and how to get to an efficient (or more efficient) bow. Even if that means creating categories like hunting, target, general, it's for heavy arrows, for light arrows, etc. We seem to interprete speed with efficiency, and speed can be gaged with each situation. So how do I constantly make my heavy hunting arrows go faster? What exact profile do I need to start with and expand from. I think the mass theory started down that road, but never got to completion. But there is probably more to it as well. Sorry for the ramble, but I am really trying to wrap my head around this.
Don...For heavy hunting arrows your power needs to come from your inner limbs.
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I think the fact that a limb needs to taper from fade to tip is easy to comprehend. I think once you start to study, learn and experience you get that to much stress causes set, and set is not your friend. But there has to be a better way to explain the correlation between profile and tiller and how to get to an efficient (or more efficient) bow. Even if that means creating categories like hunting, target, general, it's for heavy arrows, for light arrows, etc. We seem to interprete speed with efficiency, and speed can be gaged with each situation. So how do I constantly make my heavy hunting arrows go faster? What exact profile do I need to start with and expand from. I think the mass theory started down that road, but never got to completion. But there is probably more to it as well. Sorry for the ramble, but I am really trying to wrap my head around this.
Don...For heavy hunting arrows your power needs to come from your inner limbs.
Which means what? How do you make the power come from the inner limbs?
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It means to get the bow to work close to into the fades but not take much set.
http://www.primitivearcher.com/smf/index.php/topic,67543.0.html
PS....A mid section working bow makes a good hunting bow too.
You pull a heavier bow than me nowadays and should be able to get a 550 grain to 650 grain arrow to go plenty fast enough for any big game kill.
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Semantics. Bow limbs are not, and should not be, strained evenly.
It is not at all semantics. A bow limb is simply a cantilevered beam in bending. The equations defining the strain, stress and deflection of that situation have been well defined and known for a century at least.
If we divide the bow limbs into many sections, the total stress for each section should be quite different. It should be much higher in the fade section than in the tip section, etc. That's the mantra.
But if we look at the unit stress of each section, by dividing the total stress in each section with the mass units in the section, it should be same for all sections. All "wood" in the limb should be evenly and equally strained. This is the underlying principle for the mantra and no set tillering.
You seem to misunderstand stress, strain and load/force. Stress and strain are related by the Young's Modulus (also known as the elastic modulus) and if the strain is constant as you say, then the stress is also constant. I have no idea what you mean with 'total stress' and 'unit stress'. Stress itself is a unit measurement, defined as a force per unit area.
Mark, it’s not that I think it isn’t possible but that it isn’t optimal for bows to be strained equally along their whole length.
I would agree with that, considering stiff tips and the like. I think it would be more precise to say the strain should be equal for the working portion of the limb which is what I was thinking of when I said the whole limb.
Mark
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It appears people are getting confused about what "even"stress or strain means now. Bow limbs are stressed unevenly depending on the location of measurement.
"Where Energy is Stored in a Bow Limb
Engineer David Dewey computed the numbers for several dissimilar bow
designs. .... Here’s the breakdown for a uniform-stress D-longbow:
Inches from center - energy
0 — 7”....................30%
7 – 14”.....................27%
14 – 21”.....................22%
21 – 28”.....................15%
28 – 35”.......................6%"
(TBB4)
Each sections should be stressed differently according to the location. What should be "even" is not the total stress on each sections, but the unit stress of each mass units in each sections.
The easiest way to see this is to look at a pyramid front profile bow. If the thickness stays same for the whole limb, each sections should have the relative widths as expected in the chart. The fade section should be 5 times wider than the tip section. That makes the unit stress "even" for whole limb. That's what we call an "evenly" stressed or well tillered bow.
This is what the mantra is trying to express. It can be an adjustment of width, thickness or both. "Uniform stress" does not mean each sections are stressed the same amount. They should be stressed in proportion to it position. This is why all wooden bow limbs should be tapered in one way or another, unless the material is so strong like fiberglass as to make the tapering almost irrelevant, but not quite.
I am talking about something that's almost too obvious to most people to make them incapable of bothering to see anything. But I see one person who is interested.
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scp.....The guideline you've shown is something I've always kept in mind while making bows and has proven to be sound information.While making more and more bows it has become second nature.It has worked for me.
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It appears people are getting confused about what "even"stress or strain means now. Bow limbs are stressed unevenly depending on the location of measurement.
"Where Energy is Stored in a Bow Limb
Engineer David Dewey computed the numbers for several dissimilar bow
designs. .... Here’s the breakdown for a uniform-stress D-longbow:
Inches from center - energy
0 — 7”....................30%
7 – 14”.....................27%
14 – 21”.....................22%
21 – 28”.....................15%
28 – 35”.......................6%"
(TBB4)
Each sections should be stressed differently according to the location. What should be "even" is not the total stress on each sections, but the unit stress of each mass units in each sections.
The easiest way to see this is to look at a pyramid front profile bow. If the thickness stays same for the whole limb, each sections should have the relative widths as expected in the chart. The fade section should be 5 times wider than the tip section. That makes the unit stress "even" for whole limb. That's what we call an "evenly" stressed or well tillered bow.
This is what the mantra is trying to express. It can be an adjustment of width, thickness or both. "Uniform stress" does not mean each sections are stressed the same amount. They should be stressed in proportion to it position. This is why all wooden bow limbs should be tapered in one way or another, unless the material is so strong like fiberglass as to make the tapering almost irrelevant, but not quite.
I am talking about something that's almost too obvious to most people to make them incapable of bothering to see anything. But I see one person who is interested.
Seems like you’re misinterpreting the data. A true pyramid bow from fade to a point at the tip will form an approximate arc of circle tiller regardless of width at the fade. The force will change though. If you make a theoretical bow that is 5” wide at the fade and 1” wide at the tip it will certainly be stiffer toward the tip. The difference in energy storage is more likely related to changes in leverage as you get further from the tip. That is my interpretation. You state that it was for differing bow designs so a pyramid bow would just be one of them.
You’re using the terms energy storage and stress a lot and energy storage doesn’t have to correlate with stress. If you have two bows of the same tiller shape and same set, they will store the same energy even if differing width profiles. The stresses in the bow limb will be different due to where the mass is along the limb.
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Ryan, you wrote "If you make a theoretical bow that is 5” wide at the fade and 1” wide at the tip it will certainly be stiffer toward the tip. "
That doesn't make any sense to me. Can you explain what you mean?
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Don, I’m just going off of what scp said about that energy storage in the limb correlating to width in a pyramid bow. But for the theoretical bow, if a true pyramid, tapering to a point, would produce a circular arc, then if the tips are wider than a point there will be excess mass along the whole limb stiffening the outer limbs progressively more toward the tip. This is assuming there is no thickness taper.
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Post from Woodbear Sep 6, 2006
“Some clarification of stress and strain is needed here.
Tom has correctly defined strain, it is a measure of the geometric deformation (stretch or compression) of the back & belly wood of the bow arm. I find it easiest to think of it in terms of percentage. That is a strain of 1% means the wood is 1% different in length compared to the original length of the wood without any applied force. 1% compression means the belly is only 99% as long as it is when no force is applied. 1% tension means that the back is 101% as long as without applied force.
Think about a short section of the bow arm say 100mm long, 20mm thick, and bending with a radius of 1000mm. Assuming that the cross section is rectangular, the length of the wood on the back is 101mm, and the length of the wood on the belly is 99mm long. The surface strain is 1% in both tension, and compression.
The relationship between stress and strain is stress equals strain multiplied by the elastic modulus (stress = strain * MOE). Strain is a unitless ratio, and stress has the same units as elastic modulus (MOE), and is measured in force per unit area (i.e. g/mm^2).
In the 100mm section of bow arm for example, let the wood be Yew with MOE of about 800,000g/mm^2, and the stress will be 8,000g/mm^2, or 1% of the MOE. Since the MOE is the same through out the wood (ignoring knots & defects etc.) equal stress and equal strain must both happen at the same time.
A bow with a perfectly circular tiller, and a thickness taper, can not have uniform stress or strain. Stress and strain will be highest where the wood is thickest. To obtain uniform strain and stress, the radius of curvature of the drawn bow must be proportional to the thickness of the bow arms through out the bow. A pyramid bow with circular tiller, and uniform arm thickness has uniform strain. An ELB with a thickness taper, can have uniform stress and strain if the tiller is elliptical, with the bend radius proportional to the thickness of the arms.
What Tim was talking about as stress, should properly be called bending moment, or bending force in the bow arm. The bending moment at any point on the bow arm can be found by measuring the distance from the location on the bow arm, to the string (at full draw for the maximum value experienced by the bow.), and multiplying by the string tension. The distance must be measured at right angles from the string to the bow arm location. It is clear that the distance from the string to the nock is zero right at the nock. The maximum distance from a point on the bow to the string will be from the center of the handle to the string. Half way down the arm from the center to the nock, there will be only about the distance between the string and bow arm, and consequently only half the bending moment. This is not exact since the bow arm is not straight but bent in an arc. A convenient way to see this is to take a photo of the bow on the tiller stick at full draw, and then measure the distance from the bow arm to the string all along the bow. The bending moment is proportional to the distance from the string, since the string tension is the same every where in the string.
Dave”
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Post from woodbear Sept 6, 2006
“
The question has been asked a number of times as to where the energy is stored in the drawn bow. Being curious about the answer, I adapted a bow design spread sheet to compute theoretical energy stored along the length of the bow arms.
The bow arm is divided up into 5 sections from the center to the tip. The first 20% I called handle. This includes the fades too as they are usually not fully bending when present. From 20% to 40% is inner bow arm. From 40% 60% is mid arm. From 60% to 80% is outer arm. Finally the tip area is from 80% to 100% of the bow arm length. There is a mirror image bow arm on the other side of the center of the bow. The computed bows are symmetric.
It is interesting to note that for an ELB like bow, the location of maximum energy storage is dead center in the bow handle. This even for an elliptically tillered bow. It makes sense, equal stress, and more wood equals more stored energy.
The comparison Indian style paddle bow is also working handle, but not fully stressed in the handle. I reduced the handle stress by about 10%. The handle is also significantly narrowed, both of which make for less bend in the handle. Even so, a substantial part of the energy of the draw is stored in the handle.
It seems that even though the bend is of long radius, and the movement of material is small, a very large part of the propulsion of arrow comes from energy stored in the handle of the bow. I have not computed the numbers for a stiff handle bow (yet), but I suspect that even on what we think of as a non-working handle bow, the handle is contributing as much energy as the tip portion of the bow.
Wood elastic modulus for Yew used for both bows. Energy is in Ft-Lb. for one arm, total the five energies, and multiply by 2 for the other arm, and you have the total draw energy.
70# @ 28", Long bow, uniform stress design with tapering thickness and width. (i.e. elliptical tiller)
% of arm from center - description - energy
0-20% - handle area - 9.58Ft-Lb 30%
20-40% - inner arm - 8.55Ft-Lb 27%
40-60% - mid arm - 6.97Ft-Lb 22%
60-80% - outer arm - 4.76Ft-Lb 15%
80-100% - tip area - 1.80Ft-Lb 6%
50# @ 25", Indian style paddle bow uniform stress except with narrowed handle at 90% of working arm stress (i.e. very elliptical tiller, 90% working handle)
% of arm from center - description - energy
0-20% - handle area - 4.44Ft-Lb 24%
20-40% - inner arm - 5.74Ft-Lb 30%
40-60% - mid arm - 4.68Ft-Lb 25%
60-80% - outer arm - 2.96Ft-Lb 16%
80-100% - tip area - 1.02Ft-Lb 5%
I hope this is what you eanted in the way of discussion of bow stress & energy storage.
Graphs of the bow designs with the stored energy overlaid on the back profile drawing.
Dave”
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I think the fact that a limb needs to taper from fade to tip is easy to comprehend. I think once you start to study, learn and experience you get that to much stress causes set, and set is not your friend. But there has to be a better way to explain the correlation between profile and tiller and how to get to an efficient (or more efficient) bow. Even if that means creating categories like hunting, target, general, it's for heavy arrows, for light arrows, etc. We seem to interprete speed with efficiency, and speed can be gaged with each situation. So how do I constantly make my heavy hunting arrows go faster? What exact profile do I need to start with and expand from. I think the mass theory started down that road, but never got to completion. But there is probably more to it as well. Sorry for the ramble, but I am really trying to wrap my head around this.
Don...For heavy hunting arrows your power needs to come from your inner limbs.
I take this as meaning a bend through the handle bow is more efficient for heavier arrows.
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I guess we need to break down the whole analysis into simpler and much smaller pieces. First thing first. Can we all agree that WOODEN self-bow limbs need to be tapered to be efficient? If so, why?
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The easiest way to see this is to look at a pyramid front profile bow. If the thickness stays same for the whole limb, each sections should have the relative widths as expected in the chart. The fade section should be 5 times wider than the tip section. That makes the unit stress "even" for whole limb. That's what we call an "evenly" stressed or well tillered bow.
A pyramid bow with a circular tiller will have the same bending stress (not 'unit stress') along the whole limb. You are misunderstanding what stress is defined as.
Thanks to RyanY for posting those quotes from David Dewey.
Mark
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I don't care for studying the engineering or physics terms at my age. I use ordinary language for everything, even for esoteric philosophical arguments. That said, I am not going to argue against any ordinary language words interpretation by engineers. But I would ignore nitpicking about the terms used here, when the usage should be reasonably comprehensible to any sympathetic reader.
The main issue is why we need to taper wooden bow limbs, especially when the cheap fiberglass bow limbs are just simple slats of same width and thickness all the way from fade to tip. We need to stop thinking that we understand when we have not defined the question clearly enough.
Why do we even need to bother tillering bow limbs? Even one piece bamboo slat bow needs to be tapered. Why? In ordinary language terms, if at all possible, please. Just as in the mantra. We are here trying to make our "primitive" mind acquire enough practical skill or wisdom to make efficient self-bows. Why do we need to taper the wooden bow limbs in a certain way? Do we know?
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We have to be nit picky about terms or there’s no point in having discussions like these if we all mean different things.
In the simplest terms for our meat processors, if we don’t tiller and taper a bow limb it’ll break. (lol) )P(
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The easiest way to see this is to look at a pyramid front profile bow. If the thickness stays same for the whole limb, each sections should have the relative widths as expected in the chart. The fade section should be 5 times wider than the tip section. That makes the unit stress "even" for whole limb. That's what we call an "evenly" stressed or well tillered bow.
A pyramid bow with a circular tiller will have the same bending stress (not 'unit stress') along the whole limb. You are misunderstanding what stress is defined as.
Thanks to RyanY for posting those quotes from David Dewey.
Mark
With "total stress", I am talking about the stress potential of each section. The question is why the wooden bow limbs need to be tapered in a certain way to avoid set.
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We have to be nit picky about terms or there’s no point in having discussions like these if we all mean different things.
In the simplest terms for our meat processors, if we don’t tiller and taper a bow limb it’ll break. (lol) )P(
We are not trying to write an engineering dissertation here. We are trying to learn practical skills to make bows with as little set as possible. How well do I understand the internal combustion engine is almost irrelevant for me to learn the skill to drive a car as energy efficiently as possible. Is it more energy efficient to use the break as little as possible? Does it even matter?
Are you sure we understand and agree with the "primitive" mantra we are talking about here?
BTW If we keep on correcting each other in our use of ordinary language terms, we will never agree on anything. If an engineer is still trying to correct Tim Baker in his use of terms, we will never learn anything from that very experienced bow maker.
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If it creates confusion then it matters and clearly there’s a lack of understanding between posters in this discussion. As far as the mantra, if you’re referring to Tim Baker’s mantra then there’s not really any room for interpretation since it’s written down.
The Mantra:Make inner limbs wide or long enough for virtually no set. Make midlbs wide enough for little set. Make outer-limbs and tips narrow enough for lowest possible mass.
If set is directly correlated with stress/strain then the mantra suggests different levels of stress/strain between the approximate portions of the limb.
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I don't care for studying the engineering or physics terms at my age. I use ordinary language for everything, even for esoteric philosophical arguments.
Math is not esoteric nor philosophical. If you cannot be precise with the terms and understand how they are defined then you will never be able to discuss this accurately.
Bow limbs are tapered because the load changes along the length of the limb and you need less and less material to carry it as you move towards the tips. It is more structurally efficient to width taper than thickness taper and it results in lighter limb tips, which gives higher performance.
Mark
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I don't care for studying the engineering or physics terms at my age. I use ordinary language for everything, even for esoteric philosophical arguments.
Math is not esoteric nor philosophical. If you cannot be precise with the terms and understand how they are defined then you will never be able to discuss this accurately.
Bow limbs are tapered because the load changes along the length of the limb and you need less and less material to carry it as you move towards the tips. It is more structurally efficient to width taper than thickness taper and it results in lighter limb tips, which gives higher performance.
Mark
Maybe so, but no one has yet defined how we can calculate, define or measure the correct degree of ellipicalness (if that's a word?). Despite my repeatedly asking!
Del
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In fairness though Del, that is like asking “How thick should it be?” Who knows, just thick enough.
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Del, I think it can be as simple as measuring set and controlling where we want it based on factors known to impact efficiency. If you want a more complete answer it would look something like David Dewey’s bow spreadsheet where you use measures of wood characteristics to determine a specific bend radius for a given width profile or vice versa. We need that type of expertise here for clarification. But it seems like some people want to keep the discussion to a certain level of simplicity.
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I don't care for studying the engineering or physics terms at my age. I use ordinary language for everything, even for esoteric philosophical arguments.
Math is not esoteric nor philosophical. If you cannot be precise with the terms and understand how they are defined then you will never be able to discuss this accurately.
Bow limbs are tapered because the load changes along the length of the limb and you need less and less material to carry it as you move towards the tips. It is more structurally efficient to width taper than thickness taper and it results in lighter limb tips, which gives higher performance.
Mark
That's the general idea of the mantra. But there is nothing exact or precise about it. Way too many variables to pinpoint the mathematical formula applicable to all types of wooden bows.
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Maybe so, but no one has yet defined how we can calculate, define or measure the correct degree of ellipicalness (if that's a word?). Despite my repeatedly asking!
Del
Del, For warbows, I posted a formula for ellipses based on an empirical study of the Mary Rose collection. Granted, it averages the dimensions of many of the artifacts and creates a single "Mary Rose" model. The formula was derived from a graphical solution of curve fitting, good only for that particular "model". With cantilevers, if you know the taper, the ellipse can be derived. EDIT: Ryan posted while I was composing. Woodbears spreadsheet was how I fit the curve for the Mary Rose model, and may be your tool of choice for any particular taper.
If it creates confusion then it matters
I agree.
The Mantra:Make inner limbs wide or long enough for virtually no set. Make midlbs wide enough for little set. Make outer-limbs and tips narrow enough for lowest possible mass.
By straining all the wood equally you are getting the most work/energy storage possible without overloading any particular part of the limb. That sounds pretty optimal to me.
I agree with both Tim's mantra and Marks analysis. Mark seems to be addressing efficiency of energy storage, while the mantra may include some good advice to prevent handshock and increase kinetic energy delivered to the arrow.
It is more structurally efficient to width taper than thickness taper and it results in lighter limb tips, which gives higher performance.
Mark, Do you have any insights as to why width tapering may trump thickness tapering?
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Scp, what type of precision do you expect? If you sampled every piece of wood for density, MOE, MOR and put it into David’s spreadsheet, you could almost cut out your bows with very little tillering. He has done this with many of his bows. Unfortunately most of us lack the physics, engineering, and maths knowledge to do this ourselves. Doesn’t mean it can’t be done.
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Here’s an example of the type of discussion that we want but aren’t knowledgable enough to have. (lol)
https://www.tapatalk.com/groups/paleoplanet69529/using-woodbears-spreadsheet-for-wood-testing-bow-2-t61290.html
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At the risk of seeming to place little value on the mathematical side of this, which is not the case, most of this work, for me anyway, is intuitive, Edisonian. It’s not that these precise mathematical formulas hold no interest for me, it’s just that most of building a bow for me, is done by feel. Granted, I have a wealth of experiences that inform me, and I stand on the shoulders of lots of other bow makers, at the end of the day, what length do I need for this particular bow? What width? How much can I reflex, safely? Straight taper or parallel? Tiller shape? How much less should it bend at this knot? All of these questions are more about how I feel about the stave in front of me. I enjoy the more technical discussions, as I think it helps to inform the intuitive It enhances it. But it can’t replace it. I believe, for me, that comes first, and everything else follows.
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At the risk of seeming to place little value on the mathematical side of this, which is not the case, most of this work, for me anyway, is intuitive, Edisonian. It’s not that these precise mathematical formulas hold no interest for me, it’s just that most of building a bow for me, is done by feel. Granted, I have a wealth of experiences that inform me, and I stand on the shoulders of lots of other bow makers, at the end of the day, what length do I need for this particular bow? What width? How much can I reflex, safely? Straight taper or parallel? Tiller shape? How much less should it bend at this knot? All of these questions are more about how I feel about the stave in front of me. I enjoy the more technical discussions, as I think it helps to inform the intuitive It enhances it. But it can’t replace it. I believe, for me, that comes first, and everything else follows.
I feel the same way. While it probably can be done with math and getting data from wood samples, I think we’ve gained enough knowledge through experience to get extremely close to anything that would be optimized by knowing the math. Without actually taking measurements, wood is heterogeneous enough that it wouldn’t be very predictable anyways. Experience can be just as good a teacher if you keep trying to optimize and are willing to experiment trying new things.
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Scp, what type of precision do you expect? If you sampled every piece of wood for density, MOE, MOR and put it into David’s spreadsheet, you could almost cut out your bows with very little tillering. He has done this with many of his bows. Unfortunately most of us lack the physics, engineering, and maths knowledge to do this ourselves. Doesn’t mean it can’t be done.
What makes you think I am looking for any type of precision per se? I am simply against the perception of understanding when all we got is an approximation. I make bows for physical exercise. Even the maximum arrow speed is not my goal. The real goal is to advance my physical and mental health while doing what I like to do.
I don't care if I cannot understand the math and physics involved. There are way more important things than them for me like philosophy and ethics that I am not quite good at yet. What concerns me is the tendency for heuristic advises to turn into dogmas.
Therefore, I do try to understand such mantras using my own understanding of ordinary language words. Mere allusion to math and physics does not impress me. If they have real understanding of the matter, they should be easily able to converse with me at my "primitive" level. Hence, I have my own suspicion of their own incomplete understanding.
So far, I have not seen any apparent misunderstanding, using technical terms or otherwise. What I have seen is a kind of intolerance that betrays their own lack of mastery of the issue at hand. I am always happy when someone say "I don't know" in any forum or conversation. I am not seeking precision, but am looking for my own deeper understanding.
When people say I am confused, turning my ordinary language terms into misused jargons, I think they probably do not understand what I am trying to say. Otherwise they would have used my own words to express what they actually understand. People just love to say what they think they know without actually trying to understand what other people are trying to say in their own awkward way.
Have you ever made a perfect bow? How about an universally perfect bow? Most people settle for a bow that is a little better than the last one. As for me, I keep on going for the simplest bow I can imagine with certain minimum specs I want. I also expect to understand my life a little better in the process.
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You did say whatever mantra you’re talking about isn’t precise.
Seems like you want people to explain a complex concept simply enough and in a way that you believe it. These concepts are very complex and any distillation will be incomplete to some degree. If you want to understand something then it’s worth at least learning to use the language that is actually relevant in these discussions instead or asking others to try and understand your version of them.
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Do you have any insights as to why width tapering may trump thickness tapering?
I was just referring to efficiency on a tip weight basis. You could make a constant width limb and use nothing but thickness taper to get it bending nicely but the tips would be heavier than thicker, narrow tips.
Your comment on the energy storage is correct. I only mention constant strain in the context of maximum energy storage in the working portion of the limb. There may be other reasons to alter that, such as stiff tips or weight distribution in the limb.
If you sampled every piece of wood for density, MOE, MOR and put it into David’s spreadsheet, you could almost cut out your bows with very little tillering.
You certainly can. It's how I did my last bow and that worked out as well as it is ever going to with a rookie doing the work. The hardest part is being precise with the limb cross sections along the length.
At the risk of seeming to place little value on the mathematical side of this, which is not the case, most of this work, for me anyway, is intuitive, Edisonian.
Nothing wrong with that. It's a perfectly legitimate way to do things and I understand how therapeutic working like this is. I use the math to get around my inexperience and let me make better bows than if I was just hacking around without guidance. I will never live long enough to make the many hundreds (or thousands) of bows some here have made to gain the experience in that fashion.
So far, I have not seen any apparent misunderstanding, using technical terms or otherwise. What I have seen is a kind of intolerance that betrays their own lack of mastery of the issue at hand.
scp, I am not being intolerant. But the terms must be precisely used or they are meaningless in this discussion. You refer to 'unit stress' and 'total stress'. What I think you mean with 'unit stress' is the stress at any particular point on the limb and what I think you mean by the 'total stress' is actually the strain energy stored in a particular section of the limb. Does that sound correct?
Mark
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So far, I have not seen any apparent misunderstanding, using technical terms or otherwise. What I have seen is a kind of intolerance that betrays their own lack of mastery of the issue at hand.
scp, I am not being intolerant. But the terms must be precisely used or they are meaningless in this discussion. You refer to 'unit stress' and 'total stress'. What I think you mean with 'unit stress' is the stress at any particular point on the limb and what I think you mean by the 'total stress' is actually the strain energy stored in a particular section of the limb. Does that sound correct?
Mark
Correct about "total stress". But my "unit stress" is simply the total stress divided by the mass unit in the section. This is a kind of pretentiously named "mass principle" applied to the bow limb tillering. In a well tillered bow, all "wood" mass units are doing their share of work.
Scientific terms are not as precise or exact you appear to believe. I did study some philosophy of science decades ago. At that time, paradigm shift was in vogue. Doing physics in ordinary language is not as useless or inefficient as you seem to think. Most politicians are doing their science in ordinary language and they dictate which way the science goes. Money matters even in science.
I think your statements concerning a well tillered bow is better than the strangely specific mantra, but possibly less useful unfortunately. All generalizations are never as precise or exact as you tend to believe, even with good grounding in physics.
I think it might be quite unexpected, but I am using the bow making conversations here as a window into how people from diverse backgrounds interact to accomplish shared understanding of complex issues. So far, not that great.
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I think it’s helpful to think of these topics in terms of examples and thought experiments. Say you have a pyramid bow and a typical parallel limb taper (American longbow) bow and both have a circular tiller with the same amount of set. Which one would shoot faster and why? (Same poundage/draw length, length, etc. ;) )
Since this is getting off topic and only Mark bit on this, I’ll give my thoughts on this scenario.
Starting with the pyramid bow because it seems easier to understand. 2” at the fade Straight taper to the tips very mild thickness taper in a real world scenario, let’s say 1” of set where the set is uniform along the whole limb (hypothetically), circular tiller. Now let’s design the parallel limb bow to try and take the same set with the same tiller shape.
We will say the second bow has limbs that are parallel in width to mid limb and then taper towards the tips. For the parallel width, if we start at 2” wide, the rest of the limb will have more width in terms of total back surface area. Keeping it 2” wide it would mean the inner limb would take the same set as on the pyramid bow. Given that the rest of the limb is wider than the pyramid bow it’ll have to be thinner to bend to the same degree. Being thinner, the back and belly are closer together and will stretch less resulting in less set in the rest of the limb. Remember the goal here is to make the bows have the same amount of set. We WANT the parallel limb bow to take a bit more set in this scenario so we will make it narrower, say 1.75”. Now that the inner limb is narrower but bending to the same radius as the pyramid bow, it’ll have to be slightly thicker for the same amount of force to bend it to that degree. Being thicker, the back and belly stretch a bit more resulting in more set getting us to that 1” mark. The bow is narrower than the pyramid bow in the inner limb but then becomes wider at the point where the pyramid bow narrows under 1.75”. The rest of the limb, again, being wider, will need to be thinner to bend to the same degree as the pyramid bow. The wider thinner cross section of the mid/outer limb is more massive than the narrower/thicker cross section of the pyramid bow. This moving mass robs the parallel limb bow of efficiency and thus it’ll shoot slower given that the set is the same and both bows store the same amount of energy with the same tiller profile.
Now, how would we make the parallel limb bow more efficient with the same amount of set? The parallel limb bow having more width and therefore mass in the mid/outer limb can afford to have that area bend more to both store energy and the shape of the bend results in less mass movement compared to the pyramid bow. F Where the bow takes set would move from the inner limb to more mid limb after making the inner limb thicker to resist the bend, take less set, and allow the mid/outer limb to bend more. This bow would be narrower than the previous one as we are less concerned about inner limb set and thus overall mass for the design is reduced. The energy storage will lower slightly as a result of a more elliptical tiller shape but the minor difference in this for same length bows with these profiles will be overcome by optimizing mass movement. This is why it seems most conservatively designed bows of differing styles shoot about the same speed if optimized.
To me, it’s pretty easy to understand why it’s helpful for bows to be tillered differently based on their width profile. Understanding exactly how to do this for every bow is a challenge given so many factors involved but low set with skinny outer limbs is a good start? It’s also possible that this one dimension of gaining efficiency isn’t the end all be all for arrow speed for other reasons (limb vibration comes to mind).
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Scp. I think the conversation has gone, about as I would have expected, which is, not so bad. I have seen this for years on here. Somewhat “newish” folks asking well intentioned questions, that would be far more relevant and well received, if asked in a college classroom. No offense meant to those in pursuit of higher education, but this is not an exact science. Every type of wood comes with its own peculiarities. Within a given species, the properties of one stave can differ pretty dramatically from its neighbor stave. To add to that, we are not building furniture, where somewhat exact dimensions can be plugged and played. We are asking a piece of wood to let us bend it, until it is near broken, and then do that again 5000 times. Without coming apart, all at once or a little at a time. That it is a moving target, and all the math in the world CANT tell you what kind of lead you need to take. Only lots of repetitive practice, until intuitively, without thinking, you can hit the center. Its not the answers that you may misinterpret, but the questions themselves.
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You did say whatever mantra you’re talking about isn’t precise.
Seems like you want people to explain a complex concept simply enough and in a way that you believe it. These concepts are very complex and any distillation will be incomplete to some degree. If you want to understand something then it’s worth at least learning to use the language that is actually relevant in these discussions instead or asking others to try and understand your version of them.
Frankly I don't remember why I would have said the mantra is not precise, when it is not meant to be precise but just peculiarly specific. I must have been thinking that it lacks the depth of explanatory power.
This is a little better in that aspect:
"Bow limbs are tapered because the load changes along the length of the limb and you need less and less material to carry it as you move towards the tips. It is more structurally efficient to width taper than thickness taper and it results in lighter limb tips, which gives higher performance. ~Mark"
Or the "mass principle". These "principles" have some structural and functional information with more explanatory power.
But as Willie noted, those two probably conflict each other, because using thickness tapering of narrow limbs will usually make the bow lighter than using the width tapering on wide limbs.
Now we need a deeper understanding.
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All generalizations are never as precise or exact as you tend to believe, even with good grounding in physics.
Some seemingly simple formulas in physics are actually empirical observations correct in 99% of cases, and are accepted as "generally" valid, at least until applied to the outliers. Other formulas are by definition, derived from mathematical units. sorting them out is probally beyond the scope of this thread, as I haven't seen Kidder for a while. BTW, soil mechanics, or geophyiscal engineering makes use of a total stress vs unit stress concept, but it is the only field that I know of that does.
I think it might be quite unexpected, but I am using the bow making conversations here as a window into how people from diverse backgrounds interact to accomplish shared understanding of complex issues. So far, not that great.
After studying engineering long ago, I must confess I find the the study of the human condition to be much more of a challenge. I actually think we are doing quite well at finding a shared understanding. I was much impressed by the balance in Slim's reply #84
(and the fact that he still identifies as deplorable after 5 years, makes me chuckle every time he posts)
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"I think it might be quite unexpected, but I am using the bow making conversations here as a window into how people from diverse backgrounds interact to accomplish shared understanding of complex issues. So far, not that great."
That has to be the understatement of the post.
I think a lot of use just want to know what direction to go in to make more efficient bows. I think Ryan and I are on the same path. (Although my path is a bit longer). I tend to immerse myself in a subject to try to keep my mind sharp. I'm self taught through two careers. I just want to learn what technique will get my progression to better, more efficient bows without actually building hundreds of them. So far all guidance has been vague and wide open to interpretation. I have always learned by doing, but typically one can find an example that can be precisely followed. O (-_)k, maybe with a precise example of a wood bow it will not come out precisely on the numbers, but it should get you to a working bow with working knowledge of how and why you got there.
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"I think it might be quite unexpected, but I am using the bow making conversations here as a window into how people from diverse backgrounds interact to accomplish shared understanding of complex issues. So far, not that great."
I think that's a bit disingenuous.
You can't really expect people to follow the thread when it gets into lengthy maths/physics/spreadsheets/formulate etc, when it is expressed in brief sound bite style posts. (And I'm not into reading any referenced scientific papers).
Speaking for myself, I'm unlikely to ever be making bows by numbers or formulae (Although I have made bows from some basic Mary Rose figures).
To me tillering is only ever really be done by eye and feel, which is why I keep banging on about how and arc of a circle can at least be seen and judged as a start point... ok you can make it a tad more elliptical that that... BUT (IMO) you can't actually quantify or measure it in any meaningful way (other than going by the "no set" principle*)... if only for the simple fact that there is virtually no decent baseline or frame of reference from which to take measurements.
The esoteric technical points probably have some value if one was to make a bow using a CNC machine!
Del
* Using the "no set" principle is not going for "elliptical tiller" or "Tiller based on front profile" ... it is simply tillering for no set!
PS. I shall try very hard not to comment further on this thread ;)
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I think with stave bows, the best you will glean is a general approach as opposed to hard and fast rules. I’ve learned a lot reading through just these posts here, and am so appreciative that many of you delve into the technical aspect of this stuff, because the discussions that you have opens my mind to understanding things that I did not previously.
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"I think it might be quite unexpected, but I am using the bow making conversations here as a window into how people from diverse backgrounds interact to accomplish shared understanding of complex issues. So far, not that great."
I think that's a bit disingenuous.
+1. Anytime someone takes this type of stance in a discussion it's always a last-ditch effort to stay on the high horse.
BUT (IMO) you can't actually quantify or measure it in any meaningful way (other than going by the "no set" principle*)... if only for the simple fact that there is virtually no decent baseline or frame of reference from which to take measurements.
You absolutely could do this but it would require measuring each piece of wood for it's individual properties and then making all your calculations based on that. 99.999% of bowyers don't have the knowledge or interest in doing this.
* Using the "no set" principle is not going for "elliptical tiller" or "Tiller based on front profile" ... it is simply tillering for no set!
PS. I shall try very hard not to comment further on this thread ;)
The problem with only basing this on no set is that you can get overbuilt bows. This is why most average osage bows are probably overbuilt dogs. They take no set but have 1/2-5/8" wide tips with most of the bend in the inner 3rd of the limb resulting in a ton of moving mass. This is why it's helpful to compare bows such as in my example. The front view profile absolutely matters for reasons other than no set.
I demand a response.
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The problem with only basing this on no set is that you can get overbuilt bows.
Ryan, are you referring to just building a bow with no set, or Badgers "No Set" tillering method?
With the latter method, you are actually detecting early indications of compression damage before set becomes apparent in the side profile. It does not indicate where the damage is about to occur if you do not reduce your weight goal though, so one should have a good idea beforehand which side profile is ideal for your chosen taper.
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@RyanY
"...
I demand a response."
My response:-
<shrugs>
Del ;)
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The problem with only basing this on no set is that you can get overbuilt bows.
Ryan, are you referring to just building a bow with no set, or Badgers "No Set" tillering method?
With the latter method, you are actually detecting early indications of compression damage before set becomes apparent in the side profile. It does not indicate where the damage is about to occur if you do not reduce your weight goal though, so one should have a good idea beforehand which side profile is ideal for your chosen taper.
Not referring to that and that’s my understanding as well. If we use set as the only indicator for tiller shape then we can still get inefficient bows. Mass distribution and movement need to be accounted for as well like you are saying should be thought of beforehand. Maybe I misinterpreted Del’s last point.
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How do you tiller a heavily scalloped bow?
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You absolutely could do this but it would require measuring each piece of wood for it's individual properties and then making all your calculations based on that.
It does. It isn't too much work to measure MOE of your material, which is by far the most important number to have. I now do a bend test sample for every bow I make to get MOE and go from there. I use more general limits for set based on larger samples from the same type of wood. David Dewey compiled a fair amount of sample data as has Alan Case.
In my case it is more time efficient to do this than to just hammer through making bows until I get enough experience to have it down. One thing I will say to all beginners is that it is completely worthwhile to tiller a few bows from scratch before trying to be more scientific as it helps develop your eye for how a bow should bend on the tree. I had one small tweak to make on my last bow that I made using David Dewey's spreadsheet and I never would have noticed it if I hadn't hacked at a couple from scratch before moving onto the more science based approach.
Another thing to realize is all my number crunching and design work only gets me maybe 95% of the way home. The inconsistencies in wood and the less than perfect nature of woodworking will always leave me needing to do a bit of tillering to finalize a bow. So science can replace a lot of the art, but not all of it, which is fine with me. There should always be a bit of magic mixed in there somewhere.
Mark
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"I think it might be quite unexpected, but I am using the bow making conversations here as a window into how people from diverse backgrounds interact to accomplish shared understanding of complex issues. So far, not that great."
I think that's a bit disingenuous.
+1. Anytime someone takes this type of stance in a discussion it's always a last-ditch effort to stay on the high horse.
Exactly. That's what philosophers do. They try to make people realize they don't actually know as much as they believe. And they are hated for that. Especially by those who need certainty in life.
No amount of math will solve all the problems of bow making with natural materials in any near future. We are not even at the stage of fully categorizing all the relevant factors involved, I guess. People love to pretend to know better than others. Philosophers love to pretend to know nothing when there are so many things we already know well enough.
Humility brings knowledge. Knowledge brings hubris. Saying things like these is just another desperate attempt to pretend to know more than we actually do. Nature laughs at our certitude. Who would have thought million of people would die so easily and unnecessarily in this age of science and technology?
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There should always be a bit of magic mixed in there somewhere.
Mark
Love this.
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Yep you can put all the figures and dimensions to a bow you want but when it comes to bending and tillering it that goes out the window for final dimensions when tillered.Then it's by eye and feel and there is always a bit of majic to it then.
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How do you tiller a heavily scalloped bow?
This is a great question. I think there’s two ways I would go about it.
The simple version would be approximating the bow based off of the narrow sections of the limb to avoid set or breakage in those areas and tiller to a shape based off of that.
The more complex version would split the bow up based on a couple approximations. The limitations of the inner limb are the narrow parts of the scallop given that moving mass doesn’t matter as much here. The opposite is true in the outer limb where the wide portions of the scallop are more detrimental to efficiency due to excessive mass. Even though the wider portions of the inner limb could bend to a tighter radius with low set by being thinner, this would increase the movement of the outer limb robbing efficiency. The narrow portions of the outer limb are more similar to an average bow and as a result can bend to a fair degree. To make outer limb mass movement more efficient it might be possible to squeeze more bend out of the wider outer limb sections to result in a more elliptical shape assuming relatively parallel or mildly tapered limbs similar to existing scalloped bows.
I don’t know what a “Heavily scalloped bow” is to you but I think in general these ideas could guide the tillering thought process. No doubt any tillering of specific sections of the limb would be technically extremely difficult due to the small margins of thickness and varying tapers along the limb. Given that there’s not a perceivable performance advantage that I can tell due to the nature of having areas of excessive and nearly unusable width, I’d always go for the first method.
Speaking of unusable width, mollegabet bows with sharp transitions from a wide working limb to a narrow stiff outer limb likely have inefficient use of the wood in that area for either low set or mass movement.
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I'm not into quessing.I'm into testing.
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I'm not into quessing.I'm into testing.
I look forward to seeing your multiple tests of PatM’s heavily scalloped bow. Does an n=10 seem reasonable? (lol)
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Willie - I’m still here. Just mentally processing these things. I started out in engineering and made it about 3 weeks until my calc professor told the class to “forget everything we’ve covered so far - it was supposed to be for a different class.” It was that point that I went in a different direction that led me to the law. So needless to say, I don’t have the background that makes studying these things easy. For me it is about art - from seeing the bend, to shaping, inlays, overlays etc. But that doesn’t mean that I don’t want to understand it on a mechanical level, just that that aspect doesn’t come as natural. I’ve also learned a ton from this thread. I’m not looking to “build bows by number”, just looking for any way to enhance what I find an incredibly enjoyable craft and “craft” bows that are more durable, faster, lighter or whatever the goal is. Having that knowledge will help me utilize understand the path to the goal. So thanks to all for contributing, even if a good portion is at the edge of my comprehension, and frankly disputed. As a side note, I find it interesting that there are those who can function on such an advanced mathematical level and still be drawn to wooden bows opposed to glass. We are an interesting group for sure...
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This is amusing to read, going down all sorts of rabbit holes.......these threads show the problems with not talking face to face.....
The 'answer' to all this is really very simple. Follow the set mantra and listen to the wood. It will always show you whats going on - it can't do anything else!
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Willie - I’m still here. :OK
I went in a different direction that led me to the law. :OK
I find it interesting that there are those who can function on such an advanced mathematical level and still be drawn to wooden bows opposed to glass.
I find natures composites more intriguing than glass or metal. What makes it fun for myself is it is not often one gets to design something right to the limit of breaking, with no harm done if it blows.
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Speaking of unusable width, mollegabet bows with sharp transitions from a wide working limb to a narrow stiff outer limb likely have inefficient use of the wood in that area for either low set or mass movement.
I also find that transition interesting. It's rather appealing to senses, but problematic in execution. The width narrows rather sharply when the thickness increases gradually. Way too complex for me to begin to understand how those curves would look in mathematical formulas. For that matter, I even have no idea how to describe mathematically the simple but graceful bend of bow limbs in full draw. Either forgotten or more likely never learned.
It would be much simpler if the width can be narrowed gradually as the thickness increases gradually, according to the need. But the change in thickness matters much more than the change in width.
See, https://www.primitivearcher.com/smf/index.php?topic=65396.0
Intuitively, I see the efficiency of the Eiffel tower transition, not inefficiency.
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Last night I decided to join Clay Haye's patriot site. I'll just cut my beer intake in half to cover it.
So how is this relevant? He has a new video on using calipers to help tiller. He calls it "micro tillering". As with most of his stuff, he doesn't have great detail.
I started college in a civil engineering track, and took classes on truss design, so I don't necessarily agree that wood is to unpredictable to formulate or calculate a predictable design given some assumptions. I barely made it through those classes, I could always (well, maybe not always) come up with the answers but could never show how, and the professors didn't like that. Along with really not being experienced enough making bows, I am not sure where to start, but I really think some old school commenters are really missing an opportunity to help further the craft. There is nothing wrong (imo anyhow) with bringing modern ideas into and old craft. One can choose to use them or not, just like we choose modern broad heads or stone.
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... but I really think some old school commenters are really missing an opportunity to help further the craft...
I really think you are making assumptions about how some old school commentators practice their craft! ::)
Del (an old school commentator who does know the value of a cube root and can use a set of vernier calipers!)
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... but I really think some old school commenters are really missing an opportunity to help further the craft...
I really think you are making assumptions about how some old school commentators practice their craft! ::)
Del (an old school commentator who does know the value of a cube root and can use a set of vernier calipers!)
It wasn't a comment on how they practice their craft ( see the comment on "One can choose to use them or not") it was a comment on how they advance said craft. It's ok to want to stick to the old ways. There really real really is nothing wrong with that. The problem arises when they insist that everyone do the same.
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The work of Hickman et al covered a lot of this decades ago in Archery The Technical side.
In fact when Torges and Baker started sniping at each other the comment was made by Torges that Baker was lucky that the copyright had expired or he could have been caught with plagiarizing.
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... but I really think some old school commenters are really missing an opportunity to help further the craft...
I really think you are making assumptions about how some old school commentators practice their craft! ::)
Del (an old school commentator who does know the value of a cube root and can use a set of vernier calipers!)
It wasn't a comment on how they practice their craft ( see the comment on "One can choose to use them or not") it was a comment on how they advance said craft. It's ok to want to stick to the old ways. There really real really is nothing wrong with that. The problem arises when they insist that everyone do the same.
Actually it's the other way around. Most people here, including old timers, are rather well acquainted with mechanics, basically using ordinary language terms. Things get murky when some people tries to use higher math and physics to answer questions that are basically about skills, craftsmanship, or at most mechanics.
In my view, their math and physics are not quite mature enough to answer questions in bow making with natural materials. Otherwise we would have robots making character bows. But the money is not there. There are much more effective ways to kill people than using wooden self-bows.
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@ DonW
No one (AFIK) is insisting that everyone do the same.
A lot of us others spend a lot of time trying to not only help newbies advance their craft, but also advancing their own.
I'm always careful to point out that how I do things is NOT the only way, and I'm only too happy to learn from others.
I do however try to keep it simple and based on practical demonstrable theory and experiment.
Del
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The work of Hickman et al covered a lot of this decades ago in Archery The Technical side.
In fact when Torges and Baker started sniping at each other the comment was made by Torges that Baker was lucky that the copyright had expired or he could have been caught with plagiarizing.
No need to worry about that. Tim Baker is basically using ordinary language words to explain some technical stuff in his own way.
But as his bow making skill is improved, it's the scientists who need to explain what he is doing correctly in technical terms, preferably after producing bows of his caliber first. If the ordinary language terms work for him, most bow makers simply need to learn that language, no matter how vague or ambiguous it might be. There is no need for them to translate the language into scientific terms that might be still too immature to work on natural materials used in artistic ways.
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@ DonW
No one (AFIK) is insisting that everyone do the same.
A lot of us others spend a lot of time trying to not only help newbies advance their craft, but also advancing their own.
I'm always careful to point out that how I do things is NOT the only way, and I'm only too happy to learn from others.
I do however try to keep it simple and based on practical demonstrable theory and experiment.
Del
Sorry if I struck a nerve. I wasn't referring to you Del, and I agree you share a lot of information and you're youtube channel and post have helped myself and many other new bowyer wanna be's. I'd suggest you keep doing what you're doing other than going on the offensive. It's sometimes hard to judge written intent. Assume it's positive and you will help a lot more. It's hard to trust someone who doesn't trust themselves.
Remember, just because someone is new to bow design, doesn't mean they lack applicable knowledge.
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The work of Hickman et al covered a lot of this decades ago in Archery The Technical side.
In fact when Torges and Baker started sniping at each other the comment was made by Torges that Baker was lucky that the copyright had expired or he could have been caught with plagiarizing.
There is no plagiarizing in work that's meant to be shared. If it's not meant to be shared then it must be a monetary thing. IMO it's ok to profit, but not ok to stifle progress to further profit.
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As a side note, I find it interesting that there are those who can function on such an advanced mathematical level and still be drawn to wooden bows opposed to glass.
IMO, wood holds a magic to it that you don't get with modern composites. It just speaks to some people. Besides, no one here is interested in absolute performance or they would be shooting a compound bow. The path to the highest performance bow has already been shown and we choose to not go that route.
Things get murky when some people tries to use higher math and physics to answer questions that are basically about skills, craftsmanship, or at most mechanics.
I can design a bow to any desired level of strain on the limbs, calculate how wide and thick the limbs need to be to not exceed that strain level at my target draw weight and whatever width/thickness taper is required to make it bend how I want. There is more than one set of skills and this is how I choose to exercise my particular skills and craftsmanship.
Mark
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The work of Hickman et al covered a lot of this decades ago in Archery The Technical side.
In fact when Torges and Baker started sniping at each other the comment was made by Torges that Baker was lucky that the copyright had expired or he could have been caught with plagiarizing.
There is no plagiarizing in work that's meant to be shared. If it's not meant to be shared then it must be a monetary thing. IMO it's ok to profit, but not ok to stifle progress to further profit.
The issue is more about re-sharing as if it's your own. it's not always about money. People like to keep credit for themselves if they did the grunt work.
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The work of Hickman et al covered a lot of this decades ago in Archery The Technical side.
In fact when Torges and Baker started sniping at each other the comment was made by Torges that Baker was lucky that the copyright had expired or he could have been caught with plagiarizing.
There is no plagiarizing in work that's meant to be shared. If it's not meant to be shared then it must be a monetary thing. IMO it's ok to profit, but not ok to stifle progress to further profit.
The issue is more about re-sharing as if it's your own. it's not always about money. People like to keep credit for themselves if they did the grunt work.
Agreed. Credit needs to be given where credit is due.
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... but I really think some old school commenters are really missing an opportunity to help further the craft...
I really think you are making assumptions about how some old school commentators practice their craft! ::)
Del (an old school commentator who does know the value of a cube root and can use a set of vernier calipers!)
I don't qualify as an old school poster but if I ever have to learn what those words mean in order to make a proper bow I think I would quit.
I could be wrong on this, but t seems like there are really two main approaches in this thread, bowyers that prefer to approach the craft from a science/math/engineering standpoint and those that approach from an art/intuition/spiritual viewpoint. I don't think either approach is better than the other, just different ways of attacking a problem.
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I could be wrong on this, but t seems like there are really two main approaches in this thread, bowyers that prefer to approach the craft from a science/math/engineering standpoint and those that approach from an art/intuition/spiritual viewpoint. I don't think either approach is better than the other, just different ways of attacking a problem.
There is definitely overlap. Just like in hunting practices.
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Things get murky when some people tries to use higher math and physics to answer questions that are basically about skills, craftsmanship, or at most mechanics.
I can design a bow to any desired level of strain on the limbs, calculate how wide and thick the limbs need to be to not exceed that strain level at my target draw weight and whatever width/thickness taper is required to make it bend how I want. There is more than one set of skills and this is how I choose to exercise my particular skills and craftsmanship.
Mark
Feel free to let us know when you have a robot or a software that can turn a wooden stave into a world-class flight shooting bow. Good luck.
Do you have a simple flat bow design for Hickory boards that can shoot 170 FPS with 10 GPI arrows?
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Feel free to let us know when you have a robot or a software that can turn a wooden stave into a world-class flight shooting bow. Good luck.
Do you have a simple flat bow design for Hickory boards that can shoot 170 FPS with 10 GPI arrows?
It’s this kind of antagonistic close minded bull crap that turns these threads sour. Clearly you’re on the distasteful side of your so-called observation of social interactions in this community.
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I guess my musings were getting out of hand and becoming way too off-topic. To be fair to the original poster, it would be nice, as several people suggested, to have a nice example of good tillering "perfectly" matching the front profile.
It would be even better if that example is created using a modelling software for bow making. I sure can use a detailed description of the thickness tillering for a hickory board flat bow. But I am simply incapable of following the technical language used or mentioned by some people here. So I will stick to the ordinary language used by people like Tim or Badger.
What would be the best way to "match" the front profile with "perfect" no-set tillering? All I can think of so far are the so-called mantra and the mass principle applied to the tillering of each sections. My attempt to describe my meager understanding was a complete failure, mainly due to my unfortunate choice of common words that conflict with an established technical phrase.
I have seen a couple of promising starts, but they were not followed up, partly because of my distracting musings. I do believe we can have some useful principles with more explanatory power.
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It would be even better if that example is created using a modelling software for bow making. I sure can use a detailed description of the thickness tillering for a hickory board flat bow. But I am simply incapable of following the technical language used or mentioned by some people here. So I will stick to the ordinary language used by people like Tim or Badger.
What would be the best way to "match" the front profile with "perfect" no-set tillering? All I can think of so far are the so-called mantra and the mass principle applied to the tillering of each sections.
here is a modeling project that could give you the shapes given the tapers, or vice versa. It would not be necessary to input actual stiffness values obtained by testing, The default Moe is typical of many white woods.
you only need to provide the dimensions for your bow. Without specific test values, the resulting designs will be relative rather than actual. There is an output graph that shows stress, and the maximum stress is where one would first see set.
the shoulders on the mollie where you suspect to much wood? You could get a pretty good idea of how to do it better.
https://www.virtualbow.org/
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I have downloaded VirtualBow program, but never got around to make any bow using it. Has anyone made a hickory board flat bow using this program and achieved 170 FPS with a 10 GPI arrow? That's the maximum I expect from my intuitive tillering using just the graceful shape of bends. I expect dozens if not hundreds. Does anyone have the front profile and thickness tapering chart printout for such a bow?
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I have downloaded VirtualBow program, but never got around to make any bow using it. Has anyone made a hickory board flat bow using this program and achieved 170 FPS with a 10 GPI arrow? That's the maximum I expect from my intuitive tillering using just the graceful shape of bends. I expect dozens if not hundreds. Does anyone have the front profile and thickness tapering chart printout for such a bow?
Do you have any pictures of this bow? Or any bow for that matter?
Pretty sure this has been done by the people who developed some of these programs. At least one person as Steve (Badger) reported in this post from July 17, 2007.
As per my red Oak challenge. Our own Dave Woodbear sent in his bow, the only entry. I have a feeling he would have won if there would have been a hundred entries. he did a great job on this one. He sent the bow to me with instructions that it had not been drawn past 10" but should come out at 50# and 28" draw. Well, the bow hit 50# at about 24" so I halted any further testing until I got his permission to take it to 28". I did a force draw curve on it out to 28" and it read just shy of 60#. After excersizing on the tiller tree and shooting a couple dozen arrow through the bow she leveled out at 56#. The bow is 72" long and took less than 1/2 set. I used a 510 grain arrow for the testing, did several shots at 27" and then moved up to 28". A 3 shot series at 28" gave me a 179 fps, 180 fps and 181 fps, Bow came in at slightly over 18 oz, projected mass for this type of by via my own calculator would have been 20 oz. The unique traping method he used on the limbs effectively lowered the mass. At the fades the bow is about 1 1/2 wide on the belly side and 1" wide on the back side, very extreme trapping. Maybe Dave can tell us more about how he designed this bow. Steve
Are you asking this because you’re truly interested in if there’s a reliable method or for some other reason?
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Here’s the full thread about David Dewey’s (Woodbear) bow if anyone is interested.
https://www.tapatalk.com/groups/paleoplanet69529/woodbear-s-red-oak-entry-t13237.html
Turns out you can design and build fast bows using science and maths as long as you actually know what you’re doing. The question here has an answer. It’s just that we’re missing the smart people to actually give us plebeians a dumbed down explanation. To say it doesn’t matter or that it can’t be done is just ignorant.
Forgot to include the link. This is what I’m talking about. ::) :fp
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Hey Willie. Thanks for the very nice comment yesterday. I think you may have found this fella some answers with this. And btw, in the event that I might possibly be one of the “old timers” refereed to earlier, I will have you know sir, that I’m in my prime. I enjoy the technical side of this as much as anyone. That was what I most admired about the things that Tim Baker brought to the conversation. His research answered many questions as to WHY, certain things we were doing worked, and others didn’t. I found the discussion fascinating. I still do. I am no master that has built a thousand bows. Maybe a hundred at this point. I’m a journeyman, at best. But I wouldn’t trade the moments I have accumulated over the years, building bows, for much else. I didn’t discover myself, or commune with the elders, nor anything else metaphysical. I was never searching for those things. But by doing, I learned, and I enjoy passing it on, like lots of others on here. I’m still doing and still learning, and helping others when I can. Wouldn’t trade away any of it nor change the way I’ve done it.
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Do you have a simple flat bow design for Hickory boards that can shoot 170 FPS with 10 GPI arrows?
Not yet, but then I haven't tried, either. How long is the bow, what draw length and what weight?
Does anyone have the front profile and thickness tapering chart printout for such a bow?
It is more complicated than that. You need to match the dimensions to the characteristics of each piece of wood along with the bow length, draw length and draw weight. Not every piece of wood will give you that performance, either.
Mark
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Are you asking this because you’re truly interested in if there’s a reliable method or for some other reason?
I have built at least 50 bows. Most of them took me just several hours as I don't even bother to sand them. The earliest handful took me days if not weeks and they are still my better bows. If you want pictures as a proof, how are you going to verify that I did not take pictures of someone else's workshop? Many people seem to have lost all sense of honor, trust, and integrity somehow. I live and die on my words, at least in my mind. And I am also quite good at telling whether or not a person is lying or not, by just reading his posts. I simply ignore liars and cheats, unless I am interested in their pathology for whatever reason.
As for the Woodbear's bow, it is much better than my best bows, but you said it was actually tillered by a master bowyer called Badger! I have no verified 170 FPS bow, as my release through the chrono is so terrible. I shoot the purchased fiberglass recurves through it, and get around 160 FPS only. Most of my good bows shoot around 150 FPS on a good day.
I am not against math and physics as tools, other than that I think they are better at destruction than at creation of life forms. Therefore I don't trust them in the matter of the meaning of life. They will eventually be used to make robots that can replace all master craftsman, artists, and even doctors. But they should not be allowed to dictate the meaning of human life.
Here I am mostly interested in getting ordinary language "principles" to achieve perfect tillering. I want them to have some explanatory powers to help us understand how bow making with natural materials works. I find the mantra and the mass principle quite useful but not very satisfying. Not good enough at giving me the illusion of deeper comprehension, at least not anymore. ;)
Bow making is just a hobby for me. All I want is to be able to talk about bow making, using just ordinary language words but still intelligently enough to get better at it somehow, without the need to learn anything with a stiff learning curve.
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Do you have a simple flat bow design for Hickory boards that can shoot 170 FPS with 10 GPI arrows?
Not yet, but then I haven't tried, either. How long is the bow, what draw length and what weight?
Does anyone have the front profile and thickness tapering chart printout for such a bow?
It is more complicated than that. You need to match the dimensions to the characteristics of each piece of wood along with the bow length, draw length and draw weight. Not every piece of wood will give you that performance, either.
Mark
My current go-to design is a hickory stave bow that is 68 inch long, with 10 inch stiff handle, 1.75 " wide at fade, flat pyramid limbs, and 8" stiff and straight tips. Sadly my preferred draw weight is just 30 pounds now, at 28" draw length. Mildly heat treated belly with hopefully almost no set. Limbs are usually too thin to be trapped.
I usually get just 150 FPS. I like to get 170. If someone gives me a thickness chart for perfect tillering of this bow, I am willing to get the caliper out and actually use it. Thanks.
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Well....it took 10 pages but I believe these two link will get me closer to understanding. A great original question.
https://www.virtualbow.org/
https://www.tapatalk.com/groups/paleoplanet69529/woodbear-s-red-oak-entry-t13237.html
Thanks for those!
Now if someone can just help me remember how to shot like I did when I was 16!
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I have built at least 50 bows. Most of them took me just several hours as I don't even bother to sand them. The earliest handful took me days if not weeks and they are still my better bows. If you want pictures as a proof, how are you going to verify that I did not take pictures of someone else's workshop? Many people seem to have lost all sense of honor, trust, and integrity somehow. I live and die on my words, at least in my mind. And I am also quite good at telling whether or not a person is lying or not, by just reading his posts. I simply ignore liars and cheats, unless I am interested in their pathology for whatever reason.
As for the Woodbear's bow, it is much better than my best bows, but you said it was actually tillered by a master bowyer called Badger! I have no verified 170 FPS bow, as my release through the chrono is so terrible. I shoot the purchased fiberglass recurves through it, and get around 160 FPS only. Most of my good bows shoot around 150 FPS on a good day.
I am not against math and physics as tools, other than that I think they are better at destruction than at creation of life forms. Therefore I don't trust them in the matter of the meaning of life. They will eventually be used to make robots that can replace all master craftsman, artists, and even doctors. But they should not be allowed to dictate the meaning of human life.
Here I am mostly interested in getting ordinary language "principles" to achieve perfect tillering. I want them to have some explanatory powers to help us understand how bow making with natural materials works. I find the mantra and the mass principle quite useful but not very satisfying. Not good enough at giving me the illusion of deeper comprehension, at least not anymore. ;)
Bow making is just a hobby for me. All I want is to be able to talk about bow making, using just ordinary language words but still intelligently enough to get better at it somehow, without the need to learn anything with a stiff learning curve.
Turns out if you actually read the quote, all Steve did was pull the bow further than the intended draw weight. How can you possibly judge people as liars on the internet if you missed a point like that? Glad you finally came out about your bias against math and physics tools. Your excuse for not sharing your own work further adds to your bizarre character. You have no credibility that I can discern. Your last statement about not wanting to take on anything with a steep learning curve speaks volumes.
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I would not buy a six digit price tag farm tractor to tend my tiny 4x8 raised vegetable garden. But I would definitely buy the best hand tools I can afford. For most hobbyists here, even TBB1 is not particularly recommended. Just get Jim Hamm's 84 page booklet and a sharp hatchet, and go for it.
As for "matching" the working limb thickness profile with the front width profile, just look for a graceful line of bent limbs, as bow makers have done for thousands of years. If you like to look are shapely girls or boys, you will have no problem there. Just make sure you are looking at a person mature and powerful enough to handle you.
Now I am looking for a way to appreciate the limb thickness changes of an unstringed bow and figure out how beautiful they will be when the bow is braced and drawn. Any ordinary language heuristics would be more than welcome. Thanks.
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As for the Woodbear's bow, it is much better than my best bows, but you said it was actually tillered by a master bowyer called Badger!
David Dewey made that bow based on his spreadsheet design, never bent it to more than ~10" draw length and then sent it to Badger for testing. Badger then exercised it on the tree while working the draw length out to 28". He never touched the bow aside from drawing it. It was that thread that convinced me a bow can be designed mathematically and work well. Learning to use David Dewey's spreadsheet is a bit of a struggle but it has given me accurate results to date.
They will eventually be used to make robots that can replace all master craftsman, artists, and even doctors. But they should not be allowed to dictate the meaning of human life.
That's an interesting take on it, but is well OT for this thread.
My current go-to design is a hickory stave bow that is 68 inch long, with 10 inch stiff handle, 1.75 " wide at fade, flat pyramid limbs, and 8" stiff and straight tips. Sadly my preferred draw weight is just 30 pounds now, at 28" draw length. Mildly heat treated belly with hopefully almost no set. Limbs are usually too thin to be trapped.
I usually get just 150 FPS. I like to get 170. If someone gives me a thickness chart for perfect tillering of this bow, I am willing to get the caliper out and actually use it. Thanks.
For that design you will want no thickness taper at all. Maybe run the limbs parallel for ~2" out of the fades and then taper straight to narrow knocks (how wide are your nocks?). You may not get 8" of stiff tips that way, but certainly the last 5-6" will not bend much. The short parallel section gives you a bit more leeway when trying to get a smooth bend into the fades. I have found it is easy to get a bit of a hinge going right at the fades when you start the width taper immediately out of them. Somewhere Badger suggested the short parallel bit and it worked well on my last bow.
I have seen comments about it being hard to get light bows very fast based on the 10gpp formula, perhaps that is some of your issue with getting as fast as you want. If you want more speed I would suggest making the bow narrower at the fades to get more thickness to the limbs (higher strain levels are more efficient until you get set) and heat treating a bit of reflex in for more early draw weight. Even moving the tips 1" forward of the handle makes a very noticeable difference in early weight and is not very hard on the limbs.
Mark
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To Mark: Thanks for the useful observations.
I guess exercising a bow properly is a part of tillering.
For my flat pyramid bows, most tillering is done on the band-saw. Working limbs are basically all same thickness for the full length. After that I just scrape from the fade to the beginning of stiff tips in long even strokes, until I get to the desired poundage.
I do make the handle and fades longish, often over 12 inches in total, but sometime I forget and make the fades too short and cause a hinge there. Starting at 2" from the fade sounds very reasonable for that issue.
I do reflex the working limbs about 2 inches while heat-treating the belly. Usually about 1 inch is left after shooting it several dozen times.
All these are very nice, but too specific and without much explanatory power. I would love a more generalized mantra that incorporates the mass principle into each sections of bow. You started on that route but got distract by the effect of thickness and width taper on the total mass.
How about a new thread for this newer mantra? I do not start one because I cannot promise to follow through to its natural conclusion. Thanks.
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I have seen comments about it being hard to get light bows very fast based on the 10gpp formula, perhaps that is some of your issue with getting as fast as you want. If you want more speed I would suggest making the bow narrower at the fades to get more thickness to the limbs (higher strain levels are more efficient until you get set) and heat treating a bit of reflex in for more early draw weight. Even moving the tips 1" forward of the handle makes a very noticeable difference in early weight and is not very hard on the limbs.
Mark
I agree.
I do reflex the working limbs about 2 inches while heat-treating the belly. Usually about 1 inch is left after shooting it several dozen times.
perhaps your reflex loss has more to do with your heat treating method and not necessarily indicative of the limb being stress hard enough to create set.
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All these are very nice, but too specific and without much explanatory power. I would love a more generalized mantra that incorporates the mass principle into each sections of bow.
Ah, I understand now. Arvin (Selfbowman) and I discussed that some and he is also looking for an optimum distribution of mass along the limb for his flight bows. I have nothing to offer there yet as I don't have enough bows made using analytical design to be able to cross reference the final performance with the design parameters.
Maybe one day I will get there but I have lots of other hobbies and things that fill my days, leaving me with minimal time for building bows in quantity. Currently work is busy and we are in the middle of building a new house out in the country. Once that gets put to bed I should be able to dedicate more time in the wood shop to some lam bow experiments I started on over winter. The first try was a failure due to glue related issues, but attempts will continue until a conclusion is reached.
Mark
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he is also looking for an optimum distribution of mass along the limb for his flight bows.
is this another way of asking how much a "stiff" tip can bend, and still be effective as a lever?
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I do reflex the working limbs about 2 inches while heat-treating the belly. Usually about 1 inch is left after shooting it several dozen times.
perhaps your reflex loss has more to do with your heat treating method and not necessarily indicative of the limb being stress hard enough to create set.
Quite possibly. In this kind of situation, I am not actually trying to reflex the limbs for sure, hence "mild" heat treating. I am mostly making sure that the hickory limbs are dry enough to prevent set. One could say the "reverse set" was not taken properly. Anyhow it does prevent any string follow, as I started with a straight stave. If I want I can easily heat treat the bow again, this time properly to brown color, and that reflex, usually just 2 inches again, stays put. After "exploding" several bows over the years, I play safe, until the day I decide to push it for some kind of personal record, like 170 FPS. The day will come when I reassemble my shooting machine, a glorified draw board, with proper parts this time, one of these days. ;)
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I do reflex the working limbs about 2 inches while heat-treating the belly. Usually about 1 inch is left after shooting it several dozen times.
perhaps your reflex loss has more to do with your heat treating method and not necessarily indicative of the limb being stress hard enough to create set.
I can easily heat treat the bow again, this time properly to brown color, and that reflex, usually just 2 inches again, stays put.
If you notice gain in draw weight you might consider side tillering to get it back down.
also, piking makes a bow effectively thicker. Another way to get the width, length, thickness ratios more in line at your 30# draw.
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I do reflex the working limbs about 2 inches while heat-treating the belly. Usually about 1 inch is left after shooting it several dozen times.
perhaps your reflex loss has more to do with your heat treating method and not necessarily indicative of the limb being stress hard enough to create set.
I can easily heat treat the bow again, this time properly to brown color, and that reflex, usually just 2 inches again, stays put.
If you notice gain in draw weight you might consider side tillering to get it back down.
also, piking makes a bow effectively thicker. Another way to get the width, length, thickness ratios more in line at your 30# draw.
Thanks. All good ideas.
For now I leave them alone as I don't mind them to be overbuilt, too strong, or whatever, so long as they shoot acceptably. I will start tuning them for testing later. I just keep on shooting them occasionally as they are, noting what I can do with them if necessary. It's high time for me to start writing these options down. BTW I do pull up to 45 lbs. if the bow came out that way.
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he is also looking for an optimum distribution of mass along the limb for his flight bows.
is this another way of asking how much a "stiff" tip can bend, and still be effective as a lever?
I don't think so. Arvin was making almost exclusively pyramid profile bows but he was searching for an optimization of how much weight to have in the inner/mid/outer limbs. He had put a lot of effort into it (to the point of cutting up successful bows to weigh the parts up and keep records on it all) but I was not really useful for that as it involves some limb dynamics that the software we have isn't capable of analyzing.
On the stiff tips question, I can say it is more than I would have guessed. Badger has told me that his super narrow lever style flight bows used a lever that was only ~30% thicker than the working portion of the limb, which leaves quite a bit of flex possible with the length and width of the levers involved. Can't argue with the results, though.
Mark
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Mark, if I have correctly observed Arvin's flight bow, while it has a pyramid width profile, the tiller shape was not an arc of circle tiller with less bend in the inner limbs and with stiff tips, is that correct?
My interpretation of his winning bow was that the wide inner limbs were overbuilt to take absolutely zero set, the mid limb just wide enough to not take set or take very little set, and stiff mildly reflexed outer limbs for low mass and high energy storage. I assume the low amount of working limb also contributes to low limb vibration. Narrowing of any portion of the bow would make it more efficient for mass movement but at risk of increasing set. I have no idea how to optimize what he already made but those are my thoughts. It would almost be a different bow with too many changes.
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Ryan,
Arvin would have to speak to the finer points of those designs himself. I believe you are correct on his efforts to avoid set. Both him and badger are obsessive about avoiding set at all costs and Arvin certainly was concerned about minimizing vibration in the limb as well. I think the vibration reduction was a main point of his quest for the optimum weight distribution along the limb.
Mark
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This is one of the main reasons molles are super nice to shoot. Same with hornbows in general) very little room for limb vibration. If it ain't losing energy to vibration then it is free to go into the arrow. Very important point that.
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Exactly...That's been my experience.It's just a fine patient tuning to tillering.