Primitive Archer
Main Discussion Area => Bows => Topic started by: jaxenro on September 21, 2016, 02:23:15 pm
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My understanding is on a flat bow the limbs remain parallel before tapering to the tips and on a pyramid the taper begins near the handle.
All things being equal which one is easier to tiller, and why? Or are they about the same?
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The pyramid fans will tout the fact that thickness taper remains constant from handle to tip on a pyramid profile, where on a parallel profile, the thickness tapers the length of the limb. Therefore less guess work on a pyramid. On tree stave bows specifically, I'm not sure it works like the theory suggests. You still have to scrape the flat spots and get the tiller correct either way. Roughing one out may be easier on a pyramid, but finishing them requires the same amount of skill and effort, so far as I am concerned.
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+1 You still have to get it to bend evenly.
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Kind of what I suspected - six of one a half dozen of the other :)
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The pyramid fans will tout the fact that thickness taper remains constant from handle to tip on a pyramid profile...
This hasn't been my experience, and I've made several pyramid bows. There's always a little thickness taper, though perhaps not as much as with more willowleaf-shaped limb designs.
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Attempted two times to build pyramid bow, both failed because of my poor choice of wood (good type of bow wood, but rotten which I didn't realize at beginning). In both cases while I did constant thickness throughout the limbs, on tiller it needed much scraping and when they broke, measuring made obvious that both bows had thickness taper. So in practice its different than theory of constant limb thickness.
I think constant thickness would probably be easily applied to the board pyramid bow.
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With a pyramid you start with a even thickness taper and as you tiller you end up with a slight taper
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might be in part because it doesn't end with 0 width at the tips?
are pyramid bows faster or less handshocky?
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Loon, you are exactly right. It can be laid out to aim for the point, then go parallel the rest of the way. Then, the tips will be stiff for the last 6 inches or so and the rest should bend pretty evenly.
But I usually do it as Bubby describes.
Jim
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When did we stop considering pyramid bows to be flatbows too?
Limbs with parallel limbs are harder to tiller maybe and the tiller should be elliptical.
Pyramid bows should be more rounded and almost circular in tiller shape. That is the near handle wood, which is wider should be doing its share of the bending. The tendency is to let the tips bend too much resulting in more set.
Yes, I've build some pyramids and probably tillered them not so well. I should have known better.
That's my story and I'm sticking to it. :)
Jawge
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yea im with George. I always thought of a Pyramid bow as a type of Flatbow.
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i think the difficulty in tiller these two styles is mostly subjective. I find it easier to tiller pyramid limbs because i can see the circular tiller better than elliptical tiller. I have trouble seeing how elliptical a tiller needs to be. Some might find it easier to tiller elliptical.
Eric
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I think we are talking pyramid vs alb
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probably depends on which one you make the most, that will be the easy one, they both shoot well,,
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what is the reasoning behind making the straight limbed bows more eliptical?
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what is the reasoning behind making the straight limbed bows more eliptical?
thinner wood can bend more without taking set
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Loon,
any portion of any bow limb should be thin enough to prevent set, but I guess what I am asking is why should I want the outer limbs of a flat bow to be thin enough to make them bend more than the inner?
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What bubby said is what I have found to be true on stave bows, not sure on board bows, never built one of them. ;)
Pappy
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Loon,
any portion of any bow limb should be thin enough to prevent set, but I guess what I am asking is why should I want the outer limbs of a flat bow to be thin enough to make them bend more than the inner?
Loon thats a good question, the reason falls into what I call tiller logic. If the outer mid limb is just as wide as the inner limb (parallel) it would need to bend a little more to be under the same stress.
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Steve's right. When you bend a board that has the same cross sectional dimensions (let's say a 1 x 4) across it's entire length, more bend will be focused at the board's center (or the fulcrum over which it's being bent). To compensate for this, you need to tiller segments of the board that are further from the fulcrum of you want them to bend more -- and be strained equally to -- wood nearer the fulcrum. For bows, the fulcrum over which the bow is being bent is your hand holding the handle, so outer limbs need to be tillered, either along their width or thickness, to make them bend more and handle more strain.
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agreed that the further out on the limb, the thinner or narrower it needs to be, but this does not necessitate that the bend radius should increase to keep the strain consistent. On a pyramid bow, the width narrows, and with a more parallel width limb, the thickness tapers.
I guess I just cannot see how the common advice to prefer circular or more elliptical is helpful. Strain is dictated by thickness, and an equally strained crossection will bend more if it is narrower, and less if it is wider.
I have found that closely monitoring where along the limb, that the set begins to show, is much more telling than aiming for a particular shape of bend.
Nothing wrong with the circular tiller of the pyramid, and it seems the same shape (without the non-working handle section) is also commonly advised for the more parallel width ELB type.
Is there something about energy transfer or arrow speed that makes one tiller shape more preferable over another?
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I look at it this way...on a pyramid bow, more of the bending has to take place closer to the handle where it is thickest to minimize set. If a pyramid bow is tillered elliptically there will be more set towards the tips.
Jawge
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I sometimes wonder if people's advocacy of circular vs elliptical tiller gets muddled by semantics. When I see a bow with a rigid handle and non-bending tips the overall tiller looks elliptical. I posted pics and a description of a pyramid bow (http://www.primitivearcher.com/smf/index.php/topic,57979.0.html) not too long ago and would call my tiller of that bow elliptical, not circular.
For bows that bend through the handle, I tend to tiller them so that although the handle does bend, it doesn't bend as much as the limbs do. This, combined again with non-bending tips, means the tiller again ends up elliptical, not circular.
I can't say that I've ever seen a bow that was tillered so its bend pattern is actually circular. Maybe someone can link to one?
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I think Steves point is an interesting one, and I dont disagree with it, but I will add this, if a bow with parallel limbs to midlimb, has a bend radius that is the same from handle to midlimb, then it's thickness will be greatest near the handle. Thicker limbs will not bend as far as thinner limbs without taking set. Widen the limb near the handle and it will be thinner and can bend at the same radius without taking set. Do that and you have a pyramid.
Also, I agree with Eric. Circular is rarely right as a tiller shape in my opinion.
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Another way to think of it. Thickness determines how far something can bend and width determines how far it will bend.
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I sometimes wonder if people's advocacy of circular vs elliptical tiller gets muddled by semantics.........and would call my tiller of that bow elliptical, not circular.
could well be the case. so to qualify my questions a little better, I take "elliptical tiller" to mean a limb that is stiffer in the inner working portions and comes around into a tighter radius the further out you go, (or a limb that bends more near the handle and less towards the tips). Whether or not these limbs are separated by a non-working handle is not being considered. So on the other hand, a bow with two circle of arcs, separated by a non-working handle, being similar in appearance to an ellipse, I would still consider to have a circular tilller.
In other words, has a progressively bent limb been shown to be better for certain applications, whether it is a bend thru the handle bow with a stiffer center, (or a holmie type with stiffer outers), or is it all in how well you tiller the curve you choose without damaging the wood?
Maybe someone can link to one?
please see http://www.primitivearcher.com/smf/index.php/topic,58175.msg805298.html#msg805298
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Willie, I will take a stab at your question as I have considered the question myself. If you tiller to a circular shape, then a bow will take set evenly along it's length. Set on the inner limbs is costly to performance. Keeping them slightly elliptical (less bend inner limb) remedies that issue.
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Slim
thanks for taking a stab.It made me go back a read Baker's "Mantra" for avoiding set on the inner limbs. I suppose the penalty to performance comes from loss of early draw weight that comes with string follow.
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agreed that the further out on the limb, the thinner or narrower it needs to be, but this does not necessitate that the bend radius should increase to keep the strain consistent. On a pyramid bow, the width narrows, and with a more parallel width limb, the thickness tapers.
I guess I just cannot see how the common advice to prefer circular or more elliptical is helpful. Strain is dictated by thickness, and an equally strained crossection will bend more if it is narrower, and less if it is wider.
I have found that closely monitoring where along the limb, that the set begins to show, is much more telling than aiming for a particular shape of bend.
Nothing wrong with the circular tiller of the pyramid, and it seems the same shape (without the non-working handle section) is also commonly advised for the more parallel width ELB type.
Is there something about energy transfer or arrow speed that makes one tiller shape more preferable over another?
To figure all this out you simply need to watch the set. The wood will most certainly try to tell you that a parallel width bow needs to get thinner as you move out to the tips and vice versas with a pyramid.
Make some simple test bows to prove it.
A pyramid is strained more evenly and scientifically is the better bow. The real World can be different but the theory is correct.
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See P 32-33 TBB 2 for a good discussion of pyramid vs parallel tiller by Tim Baker. Jawge
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The definitive science on bow design was done back in the 1930s by Paul Klosteg and Clarence Hickman. It's all in "Archery, the Technical Side." It's kind of overwhelming math and physics at times, for me at least. But we're just reinventing the bow when we try to sort it out from scratch.
Klopsteg was a brilliant engineer who did secret and very technically advanced work for the U.S. during WWII. He was also an avid archer and bowhunter. He did lots of experimenting with arrows, bows, accuracy and related issues.
Get the book if you can.
Jim Davis
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the TBB2 reference George cited, is indeed a good explanation of the tiller profiles obtained with pyramid or parallel limbs. Of course the tillers presume straight tapers combined with a constant thickness (or width as the case may be)
Jax started this thread asking which was the easiest to tiller, and I apologize to Jax for morphing the question to
"which tiller is better for what?"
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I think that a pyramid is easier to tiller jmho
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I think so too but only of they are tillered properly which is more rounded than elliptically tillered. Otherwise you'll just get more set. :)
Jawge