Wood bow logic and common sense and words of wisdom

[gfugal]

If you read it carefully it is worded just as it should be worded. If it is confusing you need to keep thinking about it until it is no longer confusing because it is one of the most basic and important fundamentals of bow making. For any given thickness there is only one minimum radius that the limb can bend to at that particular spot without damaging the wood. Any time a bow takes set in a particular place it is because the width was too narrow for the particular thickness or the thickness. Once this concept is understood it will always drive your designs. If a bow has parallel limbs and even thickness it will bend next to the handle and the wood will be more stressed there. If you start tapering the sides of the limbs it will start to bend more ( Pyramid) and your even thickness will be right. If you choose to leave the limbs parallel then you will have to start tapering the thickness so that the limbs bend more as they go away from the handle, this will even out the stress on the wood.

    I get the relationship, it is definitely more confusing than what I was making out to be, but that doesn't change the fact that that quote is hard to understand. What determines whether a wood fiber is damaged is the stress it undergoes. This is solely related to the thickness (where that fiber is in relation to the neutral plane) and the bend radius. Width has nothing to do with whether that fiber gets set. It may do so indirectly because if it's wider it takes more energy to get those multiple fibers to bend that same radius, therefore by it resisting bending they don't bend as far and thus don't get stressed as much (hence how you can tiller by adjusting the width in pyramid bows and such). However, if you took two flat pieces of wood of uniform thickness and width but one is just twice as wide (this is to eliminate different resistances to bending that cause tiller. Imagine the bend test Tim baker does). If you bent both pieces of wood the same radius theoretically all fibers would be under the same stress whether they are in the narrow piece of wood or the wider piece of wood. If the narrow pice gets 1/2 inch of set so would the wider piece (as long as they are the same wood, with not varying defects). The only difference would be that the wider one would take much more force to get it to bend to that same radius.

So yes I understand the width will determine tiller too, but that's not because it makes it so the fibers can stand more bend, just that they require more force to get that same bend. Thus by manipulating the width, you manipulate the forces required to bend the wood and thus get the tiller you desire. Same can be done with thickness but that's another relationship entirely.

[Badger]

   If you have control of your bow it will be just as stated, if you don't have control all that will go right out the window.

[pnwarcher]

gfugal, I hear you, that saying confused me for a long time too, still does sometimes. At the very real risk of making it more confusing for somebody, I'll offer my current take on it.

If more words were used to make it more specific (albeit less pithy), I think the saying would be:
Thickness determines the minimum radius to which the wood can be bent without taking set or breaking; for a given thickness, width determines how far the wood will bend when subjected to a given draw force on the string.
If I have a segment of limb of a certain thickness, I can bend that segment to a very specific minimum bend radius without damaging the wood.
If I have a segment of limb of a given width, it will bend when the string is pulled. If I make that same limb segment narrower and pull on the string with the same force, the limb will bend farther.

The practical implications being, among others: for a given bow length and draw length, the best bow is one that is everywhere thinned only as much as it needs to be to allow the necessary bend, while also being only as wide as it needs to be to achieve the desired draw weight. Which of course is the basis of the mass principle, etc. etc.

[gfugal]

   If you have control of your bow it will be just as stated, if you don't have control all that will go right out the window.

   I think we are saying the same thing. In my above example of two identical uniform pieces of wood, if you place a 5 lb weight on the end, the narrower one will bend more than the wider one. So you say "thickness controls how far it can bend and width controls how far it will bend" I think I get what you're saying now. Thickness determines how far it can bend safely without getting set, damaged, or breaking. Width, however, determines how far it will bend under a certain force. A wider bow will bend less than a narrower bow. This is essentially the same thing I was saying that thickness controls how far it can bend, and width determines how strong it is at that bend. The reason I think the original quote is confusing is because it makes it sound like width affects the ability of the wood bend further the smae way thickness does, when that's not the case.

[Badger]

   If you have control of your bow it will be just as stated, if you don't have control all that will go right out the window.

   I think we are saying the same thing. In my above example of two identical uniform pieces of wood, if you place a 5 lb weight on the end, the thinner one will bend more than the thicker one. So you say "thickness controls how far it can bend and width controls how far it will bend" I think I get what you're saying now. Thickness determines how far it can bend safely without getting set, damaged, or breaking. Width, however, determines how far it will bend under a certain force. A wider bow will bend less than a narrower bow. This is essentially the same thing I was saying that thickness controls how far it can bend, and width determines how strong it is at that bend. The reason I think the original quote is confusing is because it makes it sound like width affects the ability of the wood bend further the smae way thickness does, when that's not the case.

   I like to leave it a little vague on purpose, it forces us to take a little closer look at it.

[gfugal]

gfugal, I hear you, that saying confused me for a long time too, still does sometimes. At the very real risk of making it more confusing for somebody, I'll offer my current take on it.

If more words were used to make it more specific (albeit less pithy), I think the saying would be:
Thickness determines the minimum radius to which the wood can be bent without taking set or breaking; for a given thickness, width determines how far the wood will bend when subjected to a given draw force on the string.
If I have a segment of limb of a certain thickness, I can bend that segment to a very specific minimum bend radius without damaging the wood.
If I have a segment of limb of a given width, it will bend when the string is pulled. If I make that same limb segment narrower and pull on the string with the same force, the limb will bend farther.

The practical implications being, among others: for a given bow length and draw length, the best bow is one that is everywhere thinned only as much as it needs to be to allow the necessary bend, while also being only as wide as it needs to be to achieve the desired draw weight. Which of course is the basis of the mass principle, etc. etc.

+1 yes this is how I understand it now. But I was just offering a take on the quote that may or may not make that more clear. As was phrased it was not clear for the longest time, and just got me to get hung up on the difference between the words can and will. If anything, if you insist on using that quote I think you should elaborate further like pnwarcher did or else it will not be "common sense" so to say for a new bowyer.

[Badger]

  I like to reduce as much as possible to one liners and then if questioned can explain. Or if it goes into some kind of glossary of terms the explanation would be there. Anyone can ask for an explanation.

[gfugal]

 

I think we are saying the same thing. In my above example of two identical uniform pieces of wood, if you place a 5 lb weight on the end, the thinner one will bend more than the thicker one...

I realize I made a typo. I meant to say "In my above example of two identical uniform pieces of wood, if you place a 5 lb weight on the end, the narrower one will bend more than the wider one."

I like to leave it a little vague on purpose, it forces us to take a little closer look at it.

I'm going to be honest. I don't get that mentality. If your goal is to help a new bowyer, you would want your advice to be as clear as possible.  Einstien said "If you can't explain it simply, you don't understand it well enough". I'm not saying you don't understand it, or that you can't explain it simply. You can, but just choose not to.

...I wanted to start a thread that should be helpful to any bowyer new or experienced that we can use on the bow bench when building a bow. I have to admit that I have learned more while helping others learn because I was forced to explain something that I had been doing by habit for many years. More often than not when I started to break it down so I could better explain it I would find a small hole in my logic and something new would be revealed to me.

   ...Feel free to challenge and debate, I promise to stay open minded. The goal is to come up with several little jewels that can be passed along within our community. Logic and common sense are things that could apply to any weight bow of any style or length. I suspect a lot of it will be a just finding a better more understandable way of saying something.

From your own statements, I don't know why you wouldn't want to simplify things more yourself, instead of remaining vague. It seems maybe this quote is one of those instances where being open-minded on how it's phrased (not the meaning) could prove beneficial.

[Del the cat]

Listen to the little voice that says... "that doesn't seem right" and step away.
Spend longer looking and thinking than actually removing wood.
Take off half as much as you think, you can always take more off later.
There is no such thing as working on one limb!!! What you do to one limb will automatically effect the other.
Del

[simk]

I find this a very useful thread - thanks Badger for collecting and condensing the 20 (?) golden rules.

I have many further but start with 2:

1. Be cautios with electric tools - they sometimes work faster than your brain.

2. Before any tillering and bending starts create a perfect workpiece: fix and shape your limbs and fades on +/-perfect dimensions regarding taper in thickness & width (Edit: But let the tips a bit wider to correct stringposition finally).

Cheers

[willie]

I don't get that mentality.

Greg, it's an invitation to buy the first round at the bowmakers bar.

[Badger]

  Greg, it got your attention because it was vague. If it was all spelled out you would have likely just skimmed over it . I find this when I am teaching someone. I want to create a discussion and I want them to initiate it. For some reason it seems to stick better.

[gfugal]

  Greg, it got your attention because it was vague. If it was all spelled out you would have likely just skimmed over it . I find this when I am teaching someone. I want to create a discussion and I want them to initiate it. For some reason it seems to stick better.

fair enough. We did discuss it after all.

[Jim Davis]

Gfugal, I'm with you and it's my approach that the clearer and shorter the telling of an idea, the better it is remembered.

1.Thickness determines safe radius.

2. Width determines draw weight.

That's all. It has worked every time for me over the last 20+ years.

[Selfbowman]

Steve I am not sure I understand all of what you said. I can say this though. I have been moving mass around in limbs for a couple years now. Trial and error. I recently built a pyramid bow that took hardly any set. Way over built in width. 2-1/2 inch at fades. Heavy on mass. 68" ntn. I did this because I had built several bows from the same tree and all took excessive set compared to my other previous bows. So I am not sure how this applies except the extra width did not take set. Arvin