Primitive Archer
Main Discussion Area => Bows => Topic started by: Gaust on February 21, 2014, 09:20:04 am
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"If one limb of your bow stave has more natural deflex than the other, and if the limbs are of equal length, make the limb with the greater deflex the bottom limb. Failure to do this could cause the lower limb - which is under greater stress - to bend too much once the bow is broken in. This problem is more pronounced with wide-limbed bows." - Paul Comstock
After reading this in TBB II, I was wondering about the recommendation that you tiller approximately 1/8" - 1/4" positive measurement on the upper limb, when the bow is to be shot split fingered. Would Paul's statement contradict this? I mean would you ignore this rule when you have a limb with more natural deflex than the other?
George
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I ignore most of the "rules". I haven't noticed much difference when a limb has a little deflex.
If one limb has reflex and the other deflex, I try to get them to match or make them both straight with heat. I have a hard time tillering a bow with two limbs bending opposite directions.
Patrick
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Good catch! If you have the lower limb slightly deflexed or with less reflex than the upper, that is serving the same purpose as the positive tiller. You want to use one or the other. Using both is like doubling down and will cause problems. When I heat in reflex, I always heat in 1/2" more reflex in the upper limb. This will compensate for the strain difference, maintain limb timing and give a nice symmetrical appearance at brace and fulldraw. The positive tiller does most of that with the obvious exception of the symmetrical brace. Josh
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These days I tiller the limbs even and preferably with the bottom limb slightly stronger, at full draw.
I check in front of a mirror, window at night or preferably a digi pic.
I generally prefer to put the stronger limbs, limbs with problems, etc on the top.
Jawge
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I think Paul's statement is rubbish. On even length limbs I will always use the stronger/more reflexed limb on the bottom. Never the top....ever.
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I think Paul's statement is rubbish. On even length limbs I will always use the stronger/more reflexed limb on the bottom. Never the top....ever.
I always use a deflexed limb as the lower. ;)
The goal no matter what the limbs are doing along the way is to have equal strain on both limbs at full draw. This means making the lower a little lower stronger due to the forces you place on the limbs during the draw not being equal. A bow is a little like a see-saw with different lengths eitherside. You need to have a heavier weight on the shorter side.
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Funny how that works eh' Mike?...:)
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I think Paul's statement is rubbish. On even length limbs I will always use the stronger/more reflexed limb on the bottom. Never the top....ever.
Interesting . With one limb reflexed more than the other, which limb has to bend further to reach brace? The higher reflexed limb....correct? So...if its bending further to equal the strain of the less reflexed limb, which one is stronger? ;) Josh
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My guess is the more reflexed limb.....:) I always thought we wanted to put the stronger limb on the bottom? Something is fishy around here.......
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Umm....it must be something to do with the angle of dangle....or magnetic fields....or something ;)
At the end of the day as long as you don't overstrain the wood and listen to/watch what it tells you....it'll all be good ;)
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Nope. The reflexed limb is storing more energy, but it has to travel further to equal the bend resistance of the less reflexed limb. This means the less reflexed limb is the stronger. Think of it like this. If you have to bows that are nearly identical. One is drawing 50#@26" the other is drawing 50#@28". The bow drawing 28" is storing more energy at 50# than the other. However, if you draw the other bow out to 28" it will be pulling more weight(stronger). See the difference between energy storage and strength? Josh
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Don't most people even out the limbs with heat/steam before they start? Wouldn't this solve the problem of the pre-deflexed limb ?
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Nope. The reflexed limb is storing more energy, but it has to travel further to equal the bend resistance of the less reflexed limb. This means the less reflexed limb is the stronger. Think of it like this. If you have to bows that are nearly identical. One is drawing 50#@26" the other is drawing 50#@28". The bow drawing 28" is storing more energy at 50# than the other. However, if you draw the other bow out to 28" it will be pulling more weight(stronger). See the difference between energy storage and strength? Josh
I agree Josh because I have just recently noticed this myself on a bow I was working on. I generally try not to use that much brain power though. :o
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For split-fingered shooters, the bottom limb should be the stronger of the two. To balance the strain on the limbs, that's a given, right? But I can see the argument that a naturally deflexed limb would be stronger because it is less strained at full draw, meaning it doesn't have to work as much as one that is more reflexed. Example: If you were stronger than I am to begin with, you wouldn't have to work as hard at the same task. But on a bow, if you were able to pull each limb separately, the more reflexed limb would be the stronger one.
George
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Got way too deep for my pea brain! Ill just keep doing what I do for whatever reasons I do it!
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The goal no matter what the limbs are doing along the way is to have equal strain on both limbs at full draw.
This is my goal. I try to keep it as simple as that. It feels easy to trick my self into other conclusions while I'm making the bow so I have to keep reminding myself this as I go along.
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Got way too deep for my pea brain! Ill just keep doing what I do for whatever reasons I do it!
If it ain't broke, don't fix it ..right? Lol! Once again, I think I contributed more confusion than clarity. Sorry bout that. Josh
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So why do we add reflex to bows if it slows them down and draws power away?
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Because it stores more energy. Josh
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Now Im confused..............for real....
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I get back on this in an hr or so. Josh
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Im unsure how the stronger limb can have less energy. Seems contradictive to me. Energy=strength in my mind.
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Comstock's smarter than I am but I am more stubborn...stubborn Greek. Been called that more than a few times.
Reflex on the bottom.:)
Funny how you can ask a simple question from a group of experienced bowyers and get several different answers.
I think of it this way...
My bottoms limbs take a little more set but 1/4 to 1/2" so whyso that little bit of reflex compensates for that.
Jawge
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I should mention that starting with even limbs bottom takes more set in my bows.
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I get the gun out and make them both the same >:D
Saves on brain time.
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I never really gave it any thought, when it comes time to choose top or bottom limb I just choose based on whatever I am looking at that moment.
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The key is the length of the power stroke. The limbs don't know if they're reflexed, flat or deflexed. They only know how far you bend them. With 4" of reflex and a 28" draw, your limbs are under the same strain as flat limbs being drawn to 32". What that means is your storing the energy of 32" draw bow. Longer power stroke. You do however lose a little bit of that energy by the actual shorter stroke on the reflexed bow. Meaning a flat profiled 50#@32" bow is transferring more energy to the arrow than the 4" reflexed50#@28" bow. Likewise, the 4" reflexed 50#@28" is storing and transferring more energy to the arrow than a 50#@28" flat profiled bow. But there's even more to it than that. To get the reflexed bow tillered to 50#@28", you will have to remove more wood than you would from a flat profiled 50#@28" bow. Resulting in less mass. Strength is only one factor in the energy storage equation. Strength and energy storage are not synonymous. Josh
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I go with what works for me ( seems most of the wood I have is way to twisty and wavy , the big reason I'm chasing good osage wood this year , took off today to go after another good tree).
I have all four volumes of TBB and when you read them things change from the first to the last as more bowyers tried different styles .
I don't have enough bows under my belt to contribute to this but a lot of good reading and lessons here , thanks.
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I, too, have enjoyed reading the comments. Soaking it all in. Thanks.
Makes me not want to cut in an arrow shelf, however.
George
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The key is the length of the power stroke. The limbs don't know if they're reflexed, flat or deflexed. They only know how far you bend them. With 4" of reflex and a 28" draw, your limbs are under the same strain as flat limbs being drawn to 32". What that means is your storing the energy of 32" draw bow. Longer power stroke. You do however lose a little bit of that energy by the actual shorter stroke on the reflexed bow. Meaning a flat profiled 50#@32" bow is transferring more energy to the arrow than the 4" reflexed50#@28" bow. Likewise, the 4" reflexed 50#@28" is storing and transferring more energy to the arrow than a 50#@28" flat profiled bow. But there's even more to it than that. To get the reflexed bow tillered to 50#@28", you will have to remove more wood than you would from a flat profiled 50#@28" bow. Resulting in less mass. Strength is only one factor in the energy storage equation. Strength and energy storage are not synonymous. Josh
But when now adding reflex one should design the bow wider and add more surface area to the wood to take the strain and still have healthy wood...which adds mass,and in most cases if done correctly it'll actually have more mass than the straight limbed bow,and not less as you stated it would....
I've always put stronger limb on bottom,and that's worked well for me after many bows,but what doni know?
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Good point Chris! I stand corrected on the mass. Josh
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This is a fun topic. Got my brain working in a good way. Making valid points. I too don't have enough bows under my belt to contribute but what Josh is saying makes sense.
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Ya know, I used to think I knew what the heck I was doing, but I disagree with other bowyers so often, I'm beginning to wonder :o
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The key is the length of the power stroke. The limbs don't know if they're reflexed, flat or deflexed. They only know how far you bend them. With 4" of reflex and a 28" draw, your limbs are under the same strain as flat limbs being drawn to 32". What that means is your storing the energy of 32" draw bow. Longer power stroke. You do however lose a little bit of that energy by the actual shorter stroke on the reflexed bow. Meaning a flat profiled 50#@32" bow is transferring more energy to the arrow than the 4" reflexed50#@28" bow. Likewise, the 4" reflexed 50#@28" is storing and transferring more energy to the arrow than a 50#@28" flat profiled bow. But there's even more to it than that. To get the reflexed bow tillered to 50#@28", you will have to remove more wood than you would from a flat profiled 50#@28" bow. Resulting in less mass. Strength is only one factor in the energy storage equation. Strength and energy storage are not synonymous. Josh
..... But any bow of regardless of design /weight/ length will draw 0 # at 0 " of draw. If then draw to the same draw length and weight, do they not have the same powerstroke? ...
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Because it stores more energy. Josh
Is it storing more energy or just transferring it more efficiently to the arrow by not allowing the limbs to vibrate as much as the arrow leaves the string?
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Ya know, I used to think I knew what the heck I was doing, but I disagree with other bowyers so often, I'm beginning to wonder :o
Offer your rebuttal, disagreement or whatever and lets see. I explain things as i understand them. If I'm wrong, I'm wrong. I don't have a problem with being corrected or challenged as long as the challenge is more substantial than "you're wrong!" . If you can explain where I'm wrong I'm all ears. Josh
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Lost arrow, even though the archer is not drawing the string, the energy from bracing the bow is still being stored in the limbs. Its just being held by the string at brace. The reflexed bow having had its limbs bent further to brace it, is storing more energy before the archer ever draws the bow. This is what people refer to as string tension. The higher the string tension at brace, the more energy there is stored in the limbs at full draw that is available to be transferred to the arrow. Just for instance, if a flat profiled bow draws 10# at the first inch of draw, the reflexed bow might have 15# at one inch. This means that your force draw curve starts at an advantage with the reflexed bow in the first instant the bow is drawn. I hope that makes some sense. Josh
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I'm not sure what evenly reflexed limbs have to do with putting a more reflexed limb on the bottom but ok.
I will offer this. When tillering reflexed bows they show high early draw weight so it is easy to under shoot weight.
Jawge
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Yeah Jawge, that did spin off course pretty bad. My apologies for my part in that. Josh
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That's ok, Gun Doc. Those spin offs can be enlightening. Jawge
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First before you ever bend the wood draw the profile of the back onto something. This is the reference. Any set the bow takes will be show as deviation from this outline.
If one limb is reflexed and one deflexed - simply aim to get to full draw with equal set and you have done your job. Then look at the finished bow and notice how the limbs still hold that difference in r/d, at brace, during the draw and at full draw.
The problems come when you forget that the goal ALWAYS is to have the forces in the bow balanced at full draw.
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Mike, maybe it's the goal but it seems to me that with wood bows, perfect balance would be difficult to achieve. Too many factors. So we're left with questions like - which limb should be on the bottom and why? For those of us who have a hard time achieving the perfect tiller, it's take what you can get and just go ahead shoot it.
George
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Gaust, most of us on here made bows before we knew or even questioned these types of things, and I would bet that many of those early "primitive" attempts are still shooting today. Still, knowledge can be a powerful thing. I honestly don't know who is right here, but I'm digging the debate. I will typically put the weaker limb on top, but I would not necessarily call the deflexed limb the weaker limb. I have looked back at mine and any I have with uneven handles, the deflexed limb ended up on the bottom, without much thought put into it really...
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First before you ever bend the wood draw the profile of the back onto something. This is the reference. Any set the bow takes will be show as deviation from this outline.
If one limb is reflexed and one deflexed - simply aim to get to full draw with equal set and you have done your job. Then look at the finished bow and notice how the limbs still hold that difference in r/d, at brace, during the draw and at full draw.
The problems come when you forget that the goal ALWAYS is to have the forces in the bow balanced at full draw.
Although I don't trace any shapes, that's the best description to low set/perfect tillering Ive heard. Basic and concise. Nice work Mike.
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Keep in mind that the extra energy stored in the bow to achieve high string tension at brace is not actually available to the arrow....
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SLIMBOB, Paul Comstock's statement confused me, to say the least. I always thought the stronger limb on the bottom, no matter if it has a natural deflex or not. He did not mention strength. I just did not know which one overrode the other. But, thanks, everyone for the discussion and your opinions. It was very interesting and informative.
George
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This is interesting but i have to admit i havent given it much thought before now. I always shoot a bow alot flipping it end for end and let the bow decide what it likes before shaping the handle..reflex/deflex be damned... Im not really sure that this is even relevent unless you are really pushin the limits of design such as flight bows.. only my opinion ofcourse tho... Brian
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Keep in mind that the extra energy stored in the bow to achieve high string tension at brace is not actually available to the arrow....
Then why bother?
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Because it allows the f/d curve to start at a higher number in the initial stages.
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I find myself reading Paul Comstock's quote again and again, and I'm trying to come to grips with his logic. I understand that the stress that the bottom limb endures is greater than the top limb. His recommendation to put the naturally deflexed limb (if you have one) at the bottom means it would be bending already to begin with, therefore it can take the stress better than say a straighter or more reflexed limb. If you put that naturally deflexed limb as the top limb, the straighter or more reflexed limb at the bottom would have to work more (bending stress). It is a matter of balance after all, and that's what he meant. Anyway, I think I see says the blind man.
George