Tiller shape vs front profile

[RyanY]

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.

[mmattockx]

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

[Del the cat]

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

[SLIMBOB]

In fairness though Del, that is like asking “How thick should it be?”  Who knows, just thick enough.

[RyanY]

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.

[scp]

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.

[willie]

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?

[RyanY]

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.

[RyanY]

Here’s an example of the type of discussion that we want but aren’t knowledgable enough to have. 

https://www.tapatalk.com/groups/paleoplanet69529/using-woodbears-spreadsheet-for-wood-testing-bow-2-t61290.html

[SLIMBOB]

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.

[RyanY]

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.

[scp]

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.

[RyanY]

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.

[mmattockx]

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

[scp]

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.