Primitive Archer
Main Discussion Area => Bows => Topic started by: Badger on July 02, 2016, 08:27:15 pm
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I finally found a theory that the only one who agrees with me is me. This relates to tilering the bow. I know they shoot fine and without problems the way most of us tiller because for most of my life I used the same methods that are still popular today.
But, from a standpoint of pure physics it would seem to me that none of the forces that are present during the draw have any relation to the forces present during the shot. I would think that the best method for a pure clean shot would be to draw the bow back supported directly in line with the arrow rest and pulled at the point on the string exactly where the arrow knock will be placed. I say it should be tillered to draw straight back from here. My logic is that the bow hand is no longer relevant and the point on the string where we draw the bow is not relevant. The only thing relevant is how the mass of the arrow relates to the limbs through the string.
Hopefully one of our engineers can come on and either straighten me out or confirm what I am implying. I am only hard headed when I firmly believe I am right LOL>
I will concede that balance of the bow when drawing is important for proper shot execution and for this reason I still always tiller where my index finer lies on the string. But speaking just for arrow flight purposes what method would make more sense?
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I'm certainly not a engineer but I find your question interesting. If it was only about the arrow I think you might be right, but I think one of the biggest reasons we tiller bows like we do is for the survivability and longevity of our bows. Posiblly we could do both but I believe the bow probably takes priority. But I could be wrong lol
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Does a D loop like on a compound accomplish a more even draw? The drawing force is at small point above and below the nock.
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Bubbles, I am ignoring the draw all together and concentrating on the shot after the string has been released.
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If I have learned nothing else as I began building bows, I have learned this... The "simple bow" involves some pretty complicated "physics". It is a combination of a levers and springs. Lots of forces acting on the bow before draw and after release. Oh...I am not an engineer but I would think that hand placement on the bow relative to hand placement on the string have an impact on the forces after the release.
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Sounds like you need some good slo motion film of the release?
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If I have learned nothing else as I began building bows, I have learned this... The "simple bow" involves some pretty complicated "physics". It is a combination of a levers and springs. Lots of forces acting on the bow before draw and after release. Oh...I am not an engineer but I would think that hand placement on the bow relative to hand placement on the string have an impact on the forces after the release.
I think they do have some impact but I don't think near as much as we tend to think. The string has to get rid of the slack on release which I am sure it does very quickly, from that point on it is just the arrow and the bow, even the hand holding the bow has little influence.
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I can easily come up with several good reasons for tillering a bow to the way it is held such as more balanced in the hand and more stable to shoot, Less stress on the limbs, possibly quieter etc, but better arrow flight is not one of them.
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Two points are always in line...
Del
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Badger - try a thumbring :) them Eastern fellas knew a thing or two!
I don't see what you are saying about the position or bow hand/pulling point on the string not being relevant?
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Badger - try a thumbring :) them Eastern fellas knew a thing or two!
I don't see what you are saying about the position or bow hand/pulling point on the string not being relevant?
You and a few others are missing the point. Its all about tillering. I say it is not relevant to tillering because most of us let go of the string when we shoot the bow.
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I think we tiller bows the way we do to be able to store enough energy without damaging the bow.
What I mean is this: if bows were tillered as you said (supported directly on the arrow rest point, and drawn exactly on the nock point), you should draw them like that in real life as well, to get the maximum energy of your bow. But in real life points don't exist, only surfaces. The thing is, that you're in some extent "obliged" to draw a bow with your hands, which means that you can't draw it the way you'd tiller it and you have to take this fact into account as you tiller a bow.
To sum up, we DON'T tiller bows the way you mentionned, cause in this case the shape (tiller) of the bow as you draw it (with your hands) would be hinged or at least uneven and less energy would be stored in the bow. Of course once the string is released, only the force applied by the string (via the limbs) matters, but this force is directly linked to the energy stored in the bow wich is determined by the way you tillered and then drew the string. ;)
I hope it's clear enough ;D
BenBen
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What I wanted to show actually is that this quote
"it would seem to me that none of the forces that are present during the draw have any relation to the forces present during the shot"
appears to be flawed ;)
BenBen
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Badger, I have to admit that I read your post several times and could not follow it.
Anyway, I tiller from the center initially and then either in front of a mirror or through digi pics make the bottom limb a bit stronger (1/4") or even at full draw.
Jawge
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If I understand correctly, I think an effective way of discovering if we're tillering our bows for optimum effect on the arrow would be to take high speed video of a huge sample of bows being shot. We could see tiller at full draw but also how the limbs behave through the shot. Are they traveling equally in terms of unbending and in terms of speed, where is vibration directed after the shot, or is there limb deformity during the shot that may indicate a tiller shape that is not quite where it's needed. Differences and increases in symmetry could possibly indicate small losses in efficiency.
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What I wanted to show actually is that this quote
"it would seem to me that none of the forces that are present during the draw have any relation to the forces present during the shot"
appears to be flawed ;)
BenBen
I don't think it is flawed, the presure point on your bow hand disappears when you let go of the string, also the limbs are responding to the point on the string where you are pulling, the instant you let go of the string the limbs will start responding at the point of your arrow knock.
As I said earlier I don't have a problem with the split finger method of tillering, there are several good reasons to tiller that way. But when I hear that this method of tillering is how it should be done for proper limb timing or for proper arrow flight thats when I say hogwash. Tillering for how we hold the bow is just another example of many of the tradeoffs we have to use when building bows. Most of us tiller so when we take a photo at full draw it looks ballanced and perfect. But the fact is the instant we let go of the string it is no longer ballanced and perfect because the pressure points all change.
Kind of like carrying a bucket of nails up several flight of stairs and then dropping them off the balcony, it doesn't matter to that bucket how you got them up to the balcony, they are going straight down regardless.
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From an engineering perspective, there is one difference between the draw (tillering) and the release. Specifically, the tillering process is a function of work, force over a distance. This is essentially the storing of potential energy where time is not a factor (it can happen relatively slowly). Upon release, the system becomes dynamic and time is critically important. Now we are talking energy, work over time.
Now, when we tiller and because of two dominant factors: 1) strings can only be in tension 2) the system must be statically balanced (the tension and lever arm must be equal across the pivot point otherwise the system wants to rotate) we are, generally, constrained to making the limbs the same length or very close to it. This has the effect of defining the limb geometry given that we are attempting to store the most potential energy is the least amount of wood.
Though, thinking about the Japanese bows, the off-center balance point is compensated by there being a corresponding amount of material in the lower limb so that the lever-arm/energy storage equations would balance out. The lower limb must also dictate the geometry and the upper limb is lengthened but bends less. I can only speculate, but the arrow position on the string should follow a straight and level line from release to brace point.
I have probably generated more questions than I answered and I am not entirely sure I addressed the question you posed, but there is a difference between work (tillering) and energy (release) and that is time.
Ken
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Ken, the question is not addressing work and energy. Only the issue of ballance in the limbs that is not the same when drawn as it is during the shot.
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ok I get it,, but give me an example of how to tiller with your theory in mind,, makes since to me,, I just need a practical application,,,,I agree with you,, once you let go of the string the bow doesn't know how it was held,,,especially with a light grip,, ,, making a bow look right,, does not always translate into best tiller,, I have always felt that when the bow is shooting great and not taking set,, there is no need to "Look" at the tiller,, looking at the tiller was just part of getting the bow tillered,, :)
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Kind of like carrying a bucket of nails up several flight of stairs and then dropping them off the balcony, it doesn't matter to that bucket how you got them up to the balcony, they are going straight down regardless.
The bucket wouldn't fall straight if you put some sideways momentum into it as it was released. Wouldn't that be what the string would do to the arrow, just as it leaves the nock, if the bow is simultaneously rattling in your hand due to handshock from poorly timed limbs?
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From my perspective, the work-energy aspect is important and a part of the balance of limb-string question. The wood that the bow is made of can only transfer work at a certain rate (this may tie back to your hysteresis hypothosis) and under a dynamic situation, each moment in time will have an instantanious state where the system could be evaluated. At each state, we would idealy want the nock of the arrow and the arrow pass to always follow along the original straight line intended, regardless of where we held the bow and pulled the string from.
Since you asked for an engineering answer, the tools generally used are to break the problem down into discrete instances in time. The things that must "add up" at each instance are, 1) the geometry must balance i.e. tension in string and effective lever arms must be equal around the pivot point 2) energy state must balance i.e. change in limb energy must equal change in arrow energy.
The differences between tillering and shooting the bow is time and possibly gripping the bow (conteracting torque intentionally or not).
To get a better idea of the release when tillering, making the tiller tree so that the saddle is on a pivot may be useful. (Like a flange bearing with a saddle mounted on a shaft) Then tillering can be done so that both even bending and no rotation occurs during the draw. Set the bow and draw point where ever you want, just tiller for both rotation and even bending. You would have to make sure the bow statically balances on the saddle in the first place by changing limb geometry on either side of the saddle or having tension on the string while holding the bow level, before letting go.
Ken
PS - one of the reasons I stopped approaching bow making from the engineering perspective is because you wind up having to deal with all the engineering required and very lttle of it it can be broken out independantly without ignoring something significant. This quickly leads to dealing with tensors or finite element analysis or both and takes a lot of fun out of it.
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Brad, I think tillering for split finger is about the best compromise. I think tillering for 3 under is pushing it too much. The main issue I have is some of the explanations that go behind the logic for tillering, I think it makes newcomers believe it is more complicated than it is. Bottom line is we should always tune the bow to the arrow and adjust nock height accordingly. As I said earlier it is some of the reasons given for tillering bows to the way we hold them that bug me more than the act of actually tillering them that way. There are plenty of good possible reasons to tiller a bow to how it is held so we don't need to make up some extra ones just to make it sound absolute. There is a little bit of a range in the middle we have to work with that will still allow us to properly tune our bow. It is not all that precise.
If presicion were needed I would choose supporting the bow at the arrow rest and pulling it down from the arrow nocking point.
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Kind of like carrying a bucket of nails up several flight of stairs and then dropping them off the balcony, it doesn't matter to that bucket how you got them up to the balcony, they are going straight down regardless.
The bucket wouldn't fall straight if you put some sideways momentum into it as it was released. Wouldn't that be what the string would do to the arrow, just as it leaves the nock, if the bow is simultaneously rattling in your hand due to handshock from poorly timed limbs?
One thing all springs have in common is that they build energy as they compress, if one is stronger or weaker it will instantly ballance with the other limb because of the string keeping them together. The handshock happens after the arrow leaves and you have a moment of slack in the string. As far as torquing goes that goes along with shooting tecnique and doesn't relate to the post.
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My logic is that the bow hand is no longer relevant and the point on the string where we draw the bow is not relevant.
I'm no engineer but I'm not sure I agree with this. If you imagine a full drawn bow and arrow, it is being held in position by your bow hand and your arrow hand. Now if you could let go with both hands simultaneously, the arrow nock would go forward and the bow grip would come backward as the bow straightens. The mass of each part would control how much. Since the grip is trying to come back it is putting a force on your hand which makes your hand relevant.
Don
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I think this is one of those nachos and beer topics, going to be a fun read😉
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My logic is that the bow hand is no longer relevant and the point on the string where we draw the bow is not relevant.
I'm no engineer but I'm not sure I agree with this. If you imagine a full drawn bow and arrow, it is being held in position by your bow hand and your arrow hand. Now if you could let go with both hands simultaneously, the arrow nock would go forward and the bow grip would come backward as the bow straightens. The mass of each part would control how much. Since the grip is trying to come back it is putting a force on your hand which makes your hand relevant.
Don
There is some small forces on the bow hand but the bow is still free to rock and bend where it wants. A one ounce arrow under accelration suddenly weighs about 1 1/2 pounds so has significant influence on the bow limbs at this point.
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The bow is also trying to accelerate but in the opposite direction so it's effect is also increasing. This is when we need an engineer. The bow out weighs the arrow by a factor of 15-20 so the arrow is going to move much more. I'm thinking that subtle changes in grip are going to come into play here. Although, decent archers seem to agree that this bow is a sweet shooter and that one is a POS so there is definitely something inherent in the bow that makes it sweet. That's all I got :) :) :)
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I'm not an engineer, but this is my take on it. There is a LOT of energy stored in the limbs at full draw. When we drop the string, they expend that energy, most of it into the movement of the arrow. It is their energy that controls the arrow, not the other way around. If relative limb strength isn't balanced, the arrow nock doesn't come straight back relative to the shelf/handle during the draw, and then upon release, the opposite, or nearly so, happens and some of that energy, proportional to the degree of unbalance, is 'misdirected' and sends the arrow's nock end in a direction other than perfectly straight ahead.
If, as you contend Steve, the weight of the arrow balanced the energy of the limbs the split second the string was free, arrow flight would always be perfect, no one limb could ever be too strong, and handshock would never be increased because of it.
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Arvin, I mostly agree with what you are saying. I do agree we need to be ballanced, my only contention is that tillering for the way we hold the bow durring the draw is not ballanced for the way it will shoot. Obviously it is close enough as great bows are made every day using this method, including myself. I said both limbs will always have identical pressure on them but that doesn't mean they will travel on the right path. This is why we tune our bows and adjust arrow nock height to make up for subtle differences we might experience and it works fine. I don't even suggest anybody change anything, I just suggest when someone is explaining how it works not to say a perfect full draw tiller shot is needed to ballance the limb timing because limb timing is different when the string is released.
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https://www.youtube.com/watch?v=ir5GKAQG14g
At about 1:20 min in this video Mike is shooting the longbow. Right after he released you can see the nock end of the arrow drop a bit. At the same time the bow rotates counter clockwise(top come back) a bit. Is this what we are talking about?
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https://www.youtube.com/watch?v=ir5GKAQG14g
At about 1:20 min in this video Mike is shooting the longbow. Right after he released you can see the nock end of the arrow drop a bit. At the same time the bow rotates counter clockwise(top come back) a bit. Is this what we are talking about?
Yep, thats exactly what I am talking about, you can see the yumi bow does not do that.
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Agreed.
The best tiller for the bow is not always the picture perfect, photo op tiller.
For example, knots should appear slightly flatter than the rest of the limb.
Yes, the bow needs to be balanced at full draw and on release (limb timing) all of which includes the nock point and where the arrow pass is located..
Disagree.
You are holding the bow and need to account for that in your tillering. Heeling vs high wrist should be different tillers.
Why would you discount that ?
Jawge
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I agree Jawge. Bow hand position was always known to be critical on wheelie bows with over draws and short lite arrows. It's never mattered as much for me on wood bows but I always just figured it was because the dynamics are so much less mechanical, and so less critical, but still of some importance. Still may not address Steve's overall point though.
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Agreed.
The best tiller for the bow is not always the picture perfect, photo op tiller.
For example, knots should appear slightly flatter than the rest of the limb.
Yes, the bow needs to be balanced at full draw and on release (limb timing) all of which includes the nock point and where the arrow pass is located..
Disagree.
You are holding the bow and need to account for that in your tillering. Heeling vs high wrist should be different tillers.
Why would you discount that ?
Jawge
Jawge, are you suggesting that the bow returns in the same path it was drawn?
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I don't see how a bow can remember what happened on the draw and return in the reverse and mirror the same movements.
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A bow can't "remember" what happened on the draw. However, force will always follow the path of least resistance and arguably (very arguably) the relatively slow (static) path of the draw is equivalent to the fast (dynamic) path of the release. When I say path, I mean both the physical movement as well as the force flow.
Ken
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Badger, no, just saying how you hold it affects how you tiller it... or should.
I guess I don't understand your point.
Jawge
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Badger, I will say you are very creative,, to come up with such a fresh topic or something new to "discuss" creativity is indeed infinite,, :) :),,,
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Badger, I will say you are very creative,, to come up with such a fresh topic or something new to "discuss" creativity is indeed infinite,, :) :),,,
LOL, I think you nailed it Brad!!
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I would think that if you built a machine that held the handle in a free swivel and pulled the string in a straight line that the release path would mirror the draw path. The swivelling handle would let the bow line itself up with the draw point. There would be no pulling up or down.
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Jawge, I think a lot of folks are not understanding. I will try to make it simple. If you expect the arrow to travel in a level straight line through the shelf during the shot then you would need to tiller the bow using your hook placed right whee the arrow nock would be and the bow supported right at the arrow rest. When you drew the bow it would show slightly out of tiller but once you dropped the string it would go back to perfect tiller. Obviously this is not important for a good shooting bow but when people get to explaining the reasons for tillering for the way they hold and draw the bow I believe they are misrepresenting how the arrow returns.
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LOL, why didn't you say that. Several people on here tiller that way.
Badger, if you tillered it like that why would it appear out of tiller ever on the draw or on the release?
If you remember, last night on a post I mentioned that I finish tiller while drawing (digi pic) to sharpen up the tiller. Nothing approximates the way you hold the bow.
I'm probably still not understanding. :)
Jawge
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I believe I know what you mean Steve although I don't really know the answer. I would think that the arrow could tell you whether or not it is being shot properly in relation to how the bow is tillered by how it behaves during the shot
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I believe I know what you mean Steve although I don't really know the answer. I would think that the arrow could tell you whether or not it is being shot properly in relation to how the bow is tillered by how it behaves during the shot
Mark, I think the point is that it is not all that critical as some would have us believe, that's why we adjust our nocking point. I think on my flight bows I am going to start tillering them from the arrow rest to the nocking point. Bows will always need a good tiller but their is a range of places in the middle that will work fine.
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Badger, in order to get the arrow to travel perfectly straight past the arrow rest (no porpoising up or down) you don't need to tiller the bow supporting it at the arrow rest, while pulling the string from where the arrow nock will be. In fact, that would ensure that it DIDN'T fly as well as it could have, had you tillered it while mimicking your own holds on both the bow and string.
If we do mimic our shooting idioms while balancing relative limb strength, we won't ever have to move the nock point to make up for limb strength imbalance. I set my nock point where I decided it would be before I even started the bow, and arrows fly perfect from shot #1.
You're right, bows don't have to be tillered perfectly to shoot 'ok', and sometimes folks have to adjust nock height to adjust limb balance, and they can make ammends. But the farther we stray from optimum, the harder bows are to tune, and the more harsh they are to the shooter and arrow flight. Conversely, the closer they are to optimum, the more inherently tuned they are, the softer they shoot, the quieter they are, the better the tiller holds, etc. You know, all the good qualities bowyers claim to strive for ;)
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Steve
What I meant by during the shot is the time between when the string is released and when the arrow leaves the bow. Observing the arrow in that time period might tell you something. If you want to tiller from rest to nocking point you'll first have to determine a nocking point
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I believe I know what you mean Steve although I don't really know the answer. I would think that the arrow could tell you whether or not it is being shot properly in relation to how the bow is tillered by how it behaves during the shot
Mark, I think the point is that it is not all that critical as some would have us believe, that's why we adjust our nocking point. I think on my flight bows I am going to start tillering them from the arrow rest to the nocking point. Bows will always need a good tiller but their is a range of places in the middle that will work fine.
The easiest way to tiller would be to make the center of the bow your holding point and keep bother limbs equal in length and stiffness. We should probably keep the arrow shelf as close as possible to the center holding point and tune the bow by adjusting the nocking point. That means during tillering we can just use the center of the string to pull on the bow. Keep it simple and do not overthink it too much. We will always have the adjustable nocking point to tune the bow properly.
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The reason I mentioned the thumb ring Badger is that it takes out (most) of the problems of have three fingers on the string (making a flat) that has to be straightened out at release before the arrow gets a proper push. If you only have one 'fingersworth' of drawing area on the string you reduce this factor and therefore the differences during draw versus during release....thus (helping to) negate this problem that you raise.
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Steve
What I meant by during the shot is the time between when the string is released and when the arrow leaves the bow. Observing the arrow in that time period might tell you something. If you want to tiller from rest to nocking point you'll first have to determine a nocking point
I never really thought about that before Mark. I will give that some thought. I usually just get the limbs bending even and then select the point on the string I want to use. The reason I mentioned the thumb ring Badger is that it takes out (most) of the problems of have three fingers on the string (making a flat) that has to be straightened out at release before the arrow gets a proper push. If you only have one 'fingersworth' of drawing area on the string you reduce this factor and therefore the differences during draw versus during release....thus (helping to) negate this problem that you raise.
The thumb ring does give beautiful flight, watching some of the slow motion videos showed them to be flawless.
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Badger, in order to get the arrow to travel perfectly straight past the arrow rest (no porpoising up or down) you don't need to tiller the bow supporting it at the arrow rest, while pulling the string from where the arrow nock will be. In fact, that would ensure that it DIDN'T fly as well as it could have, had you tillered it while mimicking your own holds on both the bow and string.
If we do mimic our shooting idioms while balancing relative limb strength, we won't ever have to move the nock point to make up for limb strength imbalance. I set my nock point where I decided it would be before I even started the bow, and arrows fly perfect from shot #1.
You're right, bows don't have to be tillered perfectly to shoot 'ok', and sometimes folks have to adjust nock height to adjust limb balance, and they can make ammends. But the farther we stray from optimum, the harder bows are to tune, and the more harsh they are to the shooter and arrow flight. Conversely, the closer they are to optimum, the more inherently tuned they are, the softer they shoot, the quieter they are, the better the tiller holds, etc. You know, all the good qualities bowyers claim to strive for ;)
Arvin, the quality of your bows speaks for itself. I plan to experiment with it a bit more. As I said earlier in the post. I can see a lot of good reasons to tiller from our holding points. I plan to try it out on a few flight bows shooting the ultra light arrows and see what happens. I know tillering the standard way I have to raise the arrow nock quite a bit to get clean flight.
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Steve, I'm not Arvin. I'm Jeff D.
Lol, here I thought you were ignoring me. Guess I should go back and look for where you may have addressed me as Arvin ;)
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I always thought you were Arvin LOL
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Mark I am in your camp on this I think. A tuned bow and arrow will get you your best flight regardless of the tiller. A good tiller will make the bow easier to tune and give you the best flight.the point here is to get the best flight possible. Knocking point will affect this as much as spine. If the limbs come to rest evenly they will deliver less shock and deliver more cast. Think of a Asian bow with a longer top limb. I have never built one so I am not sure of it their cast or shock. This is over kill in your theory . But possibly may shed some light on the question. The problem is our hands get in the way. I don't know what to do about that. Or did I miss the whole point here. Lol Arvin
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There are some benefits to designing and tillering bows so their tuning is optimum, predictable and inherent, as opposed to seeking it by moving the nock point up and down, or trying to adjust pressure points under the bow hand by how we grip it. Through design and tillering, we can keep the bow's static balance point, our bow and string hand fulcrums, and the dynamic balance point all within very close proximity to one another, sometimes all one and the same, which makes for a bow that draws without a shift between the static and dynamic balance points requiring navigation during thoughtful tillering and each draw afterwards. Those are my favorite bows to shoot, and I can tell if a bow has those qualities before I draw its string 3".
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Badgar, intresting topic, could you visualize your thought and compare it with what you consider the usual tiller in sketches ?
Think that would help me to understand:)
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Steve, I'm late getting here, but as somebody said, it's a creative concept.
Since we always must hold the bow against the force of the string. (UNTIL THE ARROW IS GONE), the bow hand is always going to exert a force that is part of the vector that is traced by the arrow nock.
Since we hold the bow below the arrow, on release, there will always be a force tending to rotate the bow's top limb toward the archer. (As someone noted about a video early in this thread).
This idea is similar to the issue of making the limbs equal length or making the bottom one shorter. (And whether to make a shorter lower limb stronger than the upper limb--I say that latter practice makes no sense, because a shorter limb of equal strength will return faster anyway).
Ultimately, I don't think any of these ideas matter a whole lot. As has been said, adjusting the nocking point nearly always can get rid of porpoising. Adjusting the nocking point amounts to balancing all the forces during the launch of the arrow.
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Mark I am in your camp on this I think. A tuned bow and arrow will get you your best flight regardless of the tiller. A good tiller will make the bow easier to tune and give you the best flight.the point here is to get the best flight possible. Knocking point will affect this as much as spine. If the limbs come to rest evenly they will deliver less shock and deliver more cast. Think of a Asian bow with a longer top limb. I have never built one so I am not sure of it their cast or shock. This is over kill in your theory . But possibly may shed some light on the question. The problem is our hands get in the way. I don't know what to do about that. Or did I miss the whole point here. Lol Arvin
Arvin, I was always getting you and Jeff mixed up by your handles for some reason. I 100% agree on the good tiller. I am a little skeptical on the importance of tillering from a specific spot as long as it is close.
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Jim, one of the gusy here psoted a slow motion vidio of the arrow being released split finger, the arrow traveled less than 1" before it dropped due to the slack comming out of the string. This is what I was reffereing to. Not sure of the optimum way to compensate for that. I have a feeling it is somewhere between the finger point and the arrow nocking point.
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Steve, yes, the forces on the string will not be exactly where they were in static equilibrium. So, the nocking point is going to react to the new angles of force.
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Man you guys are confusing me with all this , guess I will just go back to letting them fly to the target on their own just like always Haha
Good read anyway Steve
keep on searching!
thanks
Guy
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Man you guys are confusing me with all this , guess I will just go back to letting them fly to the target on their own just like always Haha
Good read anyway Steve
keep on searching!
thanks
Guy
Sometimes I get bored and like to stir the pot a bit. I am not adverse to poking some of my buddies here as well. I enjoyed the conversation.
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Hmmm? Recently I've been making more short bows center shot. At first it was because horn limbs were not the same length and I did not want to cut them. Then I liked how they shot better and started doing it with wood bows too. When I tiller a equal length limb bow I put the tiller stick in the center of the handle. When I tiller a center shot bow I put the stick on the top of the handle where the arrow passes(still in the center). Now you have me thinking maybe it's just that and if I try a equal limb bow tiller at the top of the handle it will also be a improvment. ??
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I don't know if I tiller correctly or not ? I tiller by pulling my bow string on scale 1/2" below knocking point and pulled by hand at throat of handle just below the shelf. I do however not cut my shelf till I get the bow close to weight desired in case I need to flip the bow to hit weight easier and correct tiller at same time. My bows usually bend pretty good though. Arvin
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This topic reminds me a lot of my research of asymmetrical bows:
https://redhawk55.wordpress.com/2010/08/22/asymmetrical-bow-designs-vol-1-what%C2%B4s-harmony/
I' ve to add a reply to a discussion about asymmetrical bows in the Paleoplanet- forum: http://paleoplanet69529.yuku.com/reply/224548/t/Re-old-designs-reloaded-asymmetrical-bows.html#.V3zNQ6Z76bg
The exact Golden Ratio is 1.618, but as a common sense a 2/3:1/3 ratio is usual. The question is, if this ratio is referred to the really working parts of the limbs or does it mean the location of the nocking point. I havenīt checked it yet.
Due to my knowledge the nocking point of a Yumi bow is located 1/3 apart from the bottom tip of the bow.
Itīs not at all true that short or asymmetrical bows are used only by mounted or kneeling archers, they take advantage from those bow- design, but there is enough evidence that short or asymmetrical bows were used by foot soldiers too. Think of the Parthians, what about the short West Coast-Indian bows................................?
Almost every excavated asymmetrical bow I had the oppurtunity to study measures 121- 140cm in length, the excavated arrows were measuring at least 54cm and at most 66cm in length and almost all of them were barreled. It is obvious that the "asymmetrical bowyers " have laid out the shorter lower limb 0.5-1cm wider than the longer upper limb. A lot of fitting bow- cases and quivers(Goritoi) had been excavated too.
For a first test I made 2 easy to do D- bows out of the same black locust-stave, with a length of about 120cm and about 20lbs drawweight. I shot the same arrow with these bows, almost no difference in speed. But the f/d-curve of the asymmetrical bow results in a higher energy- storage.
A typical f/d- curve for an asymmetrical bow increases steeply in its first third then it flattens a bit. My experience is that the an energy- storage of 85- 95% is usual for this design. The last asymmetrical bow Iīve done seems to store about 110%, cause this means such a high storage Iīll recheck it again.
Speed is comparatively low to the stored energy, efficiency is 53- 73%
Exact numbers will be posted soon.
Shooting an asymmetrical bow is at first a strange experience, cause you feel a kind of imbalance when drawing it. But soon this is compensated ,when the arrow is released and the upper limb moves a bit down. If you are used to the "loose grip" youīll soon enjoy such a designed bow.
This design is an additional option for every self- bowyer, have a look at asymmetrically grown woods.
2 pics of the first asymmetrical selfbow I did. It is made of Black locust. It measures in length in width, the upper limb measures 67cm in length, the lower limb measures42cm in length. It draws 22lbs at 22", speed with a 280grains arrow is about 110f/s.
Thinking back I' m still wondering why there is such a heavy loss of energy? I think that' s the point where Steve and my research are meeting?
Any ideas?
Michael
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Red hawk I am no engineer but I think speed is lost in the physical mass of the wood and its placement. The better we lighten the ends and keep the draw weight up the better cast we will get. Hitting the happy medium is our goal without breaking the bow. That been said. I believe we may be able to achieve this with as even limb length and center shot not only in respect to spine but but tip to tip may be the key. I had a friend build several bows that where right and left handed . The site window was in the middle.left handed your hand would be on one end right handed your hand would be on opposite end . These shot very well. I think a cross bow is the best example of total center shot bow. No hand placement to deal with. Am I way off track here guys if so tell me so. Arvin
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Michael, two of our biggest losses come from hysteresis and vibration. Vibration can be minimized by keeping the weight down in the outer limbs and also reducing the amount of working limb available to vibrate. I also believe that the tapers we use on a bow also effect this. I have noticed that in most cases bows with elliptical tillers tend to have less shock. The hysteresis is mostly a bi product of compression damage to the limbs so using an adequate design to handle the draw weight and length helps a lot here.
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A bow spends most of its time at FD with hands in the string right? The shot is a tiny speck of time in a shot sequence. I figured that's why you tiller so it looks good in the hand. Because most of a bows life it is being pulled and held with hands on the string.
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Can asymmetrical bows be better than symmetrical bows? I doubt it, but there is a video that says so.
With a high speed camera and two medieval bows, weapons experts compete to see which bow was the ultimate medieval weapon.
From: JAPANESE BOW: BUILT TO KILL
http://bit.ly/1rwOr2W
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A bow spends most of its time at FD with hands in the string right? The shot is a tiny speck of time in a shot sequence. I figured that's why you tiller so it looks good in the hand. Because most of a bows life it is being pulled and held with hands on the string.
Thats fair logic and one of the main reasons I feel is justified. The differnce between tillering for the released bow and the drawn bow are fairly small anyway and can be easily adjusted for.
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Can asymmetrical bows be better than symmetrical bows? I doubt it, but there is a video that says so.
With a high speed camera and two medieval bows, weapons experts compete to see which bow was the ultimate medieval weapon.
From: JAPANESE BOW: BUILT TO KILL
http://bit.ly/1rwOr2W
I don't think it makes a lick of difference if the bow is tillered right, the limbs could be 2 feet difference in length and still shoot fine.
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That video does not mention the draw length. I think it's just a case of longer draw length storing more energy. I wonder how they have missed such a simple fact.
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'Slightly' asymmetrical bows are better in some ways. The bow's longitudinal center, string hand fulcrum, and dynamic balance point can all very close to each other, in fact they can all be perfectly aligned, essentially one and the same, which makes for redeeming qualities that are impossible to obtain with symmetrical bows. I think I already covered that in a previous post.... or maybe it was the other thread.
Steve, I do think it matters.... degree of limb length discrepancies that is. Once the difference in length gets beyond a certain point, it becomes impossible to balance them just by making one stronger than the other. Study the unbraced profile of the Yumi and you'll soon pick up on some of the measures the bowyers take to achieve some semblance of balance.
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I have played around quite a bit with asymetrical bows using drasticaly different length limbs. It does get a little tick sometimes but once they are ballanced properly they shoot fine. As long as the arrow draws straight back and the limb mass is appropriately distributed there is no problem tuning them.