Different woods different styles

[bowtarist]

Don't usually read this deep into the bows threads, but this is an interesting subject.  Way over my head, but will definitely take this info into consideration in an up coming bow I'm wanting to build.  Thanks!!! dpgratz

[RyanY]

What a distraction from studying.    Love the discussion so far. I think its pretty well understood that optimal design and strain will yield great bows. The way I've thought about it for a while now is that the bow should be wide enough for minimal set, this showing that the bow is not over built but not too under built. The question is, where is that optimal strain and maybe is it possible to get no set and know that the bow is not over built. I think experience holds the answer without getting extremely scientific. Using mass as a separate parameter is good because we don't necessarily require the bow to take any set to know it's near optimal strain. From the research that's been done on the mass principle, it has shown that all woods will follow it to some extent. I believe yew is (one of?) the exception. My understanding of this is that all wood stores an equal energy per mass. BUT because of wood's variability as a material I believe there may be more exceptions to this rule. Only further research will tell. Because of this I think there may be a best (fastest) wood but I don't think we have enough data. Until then design and building technique are the best factors that determine the quality of a bow. (IMHO)

[Badger]

 Ryoon, thats exactly right. Some woods tend to be more elastic and can be built at slightly ower mass maybe 10%. Yew falls into this category as well as osage. With osage I don't deduct the 10% because I really like the extra margin and a lot of the mass is in the handle and fades anyway. As I get to know different woods I start to get to know how far light or heavier I want to go with the mass. It is pretty conservative so I seldom go any heavier.

[Don Case]

Since every piece of wood is different(even within species) when you are in the throws of tillering, how do you decide when to narrow and when to thin? I like Del's technique of "go too far and then back up a step" but I've found it to be a great source of firewood
Don

[Bryce]

  Bryce, I used 12 on the recurve I was talking about more often 14 or r/d bows, and then I continue to increase the taper as I build depending on how it is going.

yep i got that part

[Wooden Spring]

OK, maybe this is a stupid question, but then, you all know how new I am to this... I keep seeing "wide and flat" as a description of the bow.
Do you mean that it is simply rectangular in cross section?
Or do we mean that it is consistent thickness / no taper?
Or something else?

Help those of us out who haven't earned their bowyer IQ yet... 

[blackhawk]

Now that sounded like a much smarter and wiser ryoon from a year ago...variablity is a big factor some times and can wreck or derail a properly designed,tillered,and mass principle bow

[Badger]

OK, maybe this is a stupid question, but then, you all know how new I am to this... I keep seeing "wide and flat" as a description of the bow.
Do you mean that it is simply rectangular in cross section?
Or do we mean that it is consistent thickness / no taper?
Or something else?

Help those of us out who haven't earned their bowyer IQ yet... 

Thats exactly the question that started me on the mass priniciple. 1st of all I am a backyard bow builder and not a geek by any stretch of the imagination. I do everything the hardway by actually building bows and then looking for patterns.

     The first thing I had to do was develop some very basic common sense" bow logic" taking into consideration a few givens. The most important is that wood only has 1 correct thickness and it will be different on every bow we build. The challenge is to find and be able to express working techniques that will allow us to ge close to this perfect number on every bow we build. Obviously we are not going to do bend tests and calculations that are way above my head anyway.

    The most common denominator I found that best predicts both the demensions and the proper tiller is mass. It is always good to think of thickness as how far a bow can bend and width as controlloing how far it will bend. If you have to reread that and think about it do so, it is an important basic piece of info that is good to drill into our heads.
 
   When we bend something we will always create a radius, the radius may not be the same for the entire length of the limb and certainly the radius wont always be the same for different bows. working with the most elastic woods we have the inside radius needs to be less than 1% smaller than the outside radius, most woods are about 25% less than that. This is just something to keep in mind when you see a narrower section of the bow that is thicker but bending more than a wider thinner part of the bow. You know it just aint right. You don't have to figure anything here just keep it in mind.

   Bow logic tells you that if you have paralell limbs it could only be for one reason and that is you want the outer limb to bend more than the inner limb giving you an eliptical tiller shape. Bow logic will alos tell you that if you have a tapered limb the bow should bend at least equally and the thickess should be about the same. Theoreticaly you could build a bow at one specific thickness and then tiller it completely from the sides for a nice round tiller.

    Nearly all the woods we work with are going to fall into the specific gravity range of somehwhere between 50 and 100, the great majority of those will be between 60 and 80. The majority of the bow we build are going to be between about 45# and 65#. This is where I feel the mass principle is most accurate.

     The mass principle can be very valuable in determining how to execute a particular design for instance. You may want to build a hickory backed ipe english longbow. You want it 6ft long but you only want it to be 50#. You don't want the bow so narrow that it is uncomfortable to shoot just so you can make mass, so what you do is modify the tiller shape until it is the right mass at the width you feel will be comfortable. Lets say for instance you have roughed the bow out and got it bending. it feels like a 100# still but is bending. You weigh the bow and find out it is 6 oz too heavy to hit your target mass and you know only about 2 oz more wood will come off to make your weight. You go the the program and start adding length to the handle and fade number. If you add 4 then you will use just a slightly elyptical tiller, if you add 8 you will use a full elyptical tiller, if you add 12" it will be whip tillered. They should perform pretty well if built like this and not have handshock.

     Say you are working on an American longbow with parallel limbs most of the way down. You keep in mind the weight of the wood when you rough it out, for mid 60 bows for intance you might figure 1 3/8 for osage as a starting point 1/1/2 for locust and 2" for a lot of the white woods, + or minus depending on the density of the specimen. You simply rough out the bow, get it bending and then check the mass weight. Figure you have at least a couple more ounces comming off just to make weight so if you are within 2 or 3 ounces you just keep tillering the belly as you get closer you can adjust the width a little at a time or more to adjust for mass weight and fine tuning tiller.

    The secret is knowing how to do the input, modify the length of handle and fade input to accomadate your tiller shape. If you want circular limbs use the exact measurement of your handle and fades if you want elyptical then add 2 or more inches depending on how extreme you are going.

    If your tips are stiff say for six inches you may want to use a draw lenght figure 1 or 2 inches longer than you are actually going to draw it. If the tips are stiff for 10" you may want to use a figure 2 or 4" longer than your actual draw.

[Buckeye Guy]

Ryoon
How much does a Poplar bow weigh anyway !
Guy

[Badger]

Ryoon
How much does a Poplar bow weigh anyway !
Guy

 The same as any other bow

[Arrowind]

Now that sounded like a much smarter and wiser ryoon from a year ago...variablity is a big factor some times and can wreck or derail a properly designed,tillered,and mass principle bow

I've been learning that first hand.  Since most of my bows are Hickory. (MOST not ALL) I have come to realize that one piece of the exact same species can very from another....never would have thought that with out building bows...and I would not have known that had I not built so many from the same type of wood (or have read it on this forum or in one of the TBB books).  I don't think anyone can really have a true understanding of something without experience though. (in most cases).  So now I am convinced that you have to have several samples of the same species to draw general conclusions about that specific wood. 

[Bryce]

Ryoon
How much does a Poplar bow weigh anyway !
Guy

 The same as any other bow

BOOM!!! You've just been 'Mass Principle'd'
Lol

[bubbles]

BOOM!!! You've just been 'Mass Principle'd'
Lol

 

[mikekeswick]

Some interesting reading guys.
Tillering for me is becoming more and more about bending the wood less to get where i'm going.
I always trace the original profile onto my tillering board to have a definate reference as to the begining shape of the stave. After extending draw length, exercising the limbs etc unstring it and immediately put the bow back on the board to see how it compairs to the traced outline.
I too find set really starts around 20 - 22 inches and from here on out it about minimising losses.
I used to think deflex was a bad thing full stop but again over the last year or so i've been finding that it can also be a friend in that it allows the wood to stay a little fresher getting to full draw....it can definately be used to advantage.

[Aussie Yeoman]

I think what Badger meant to say is that the thickness of a piece of wood determines how far it will bend, and the width determines how much force is required to bend it that amount.

That's the key principle of the bowmaking spreadsheet I developed. It's a case of drawing a goal tiller shape, measuring the radii at various points to determine how thick a bow's limb needs to be, then figuring out just how wide it needs to be at those points to achieve the desired draw weight.

Badger, I think it's funny how sometimes things come full-circle. I'm pretty sure in TBB1 Tim talks about (I think) Comstock's 'modified Meare Heath' design, which is a wide flat limbed design but which tapers more abruptly that the original for the last 10 or 12 inches or so. That was superceded for a few years in favour of other designs, and here we seem to be coming back to a very similar design.