Primitive Archer
Main Discussion Area => Bows => Topic started by: NorthHeart on March 04, 2018, 11:53:50 am
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All things equal(which they never are)...
Does a bow with more reflex at brace require more effort to string than one without, i think that most of us will agree so. Must not the limbs move a greater distance from their original position, and thus start building energy(poundage) sooner? Will a given bow (reflexed or not) shoot an arrow with more speed and power over a bow requiring less effort to brace? If you answer "yes", then isn't getting poundage at brace an important factor in bow building and one we should strive for to build faster and more powerful bows?
Onward....
Set is bad and robs bows of power, as well as puts more stress on the limbs, correct me if this is wrong. I've been reading a lot of posts regarding "no set tillering" and not pulling your bow past the final intended draw weight throughout the entire process. Here has been my experience so far. I use a long string and tiller the bow to approximately where it would be at brace, sometimes ill even go a bit over. Lets say i draw it to a max of 50# and it requires 40# to brace. I remove the long string and brace it up with the short string, knowing that it took 40# to get there. But when i put the scale back on it it starts back at zero pounds, not taking into account the 40# it took to get it to brace. I tiller the bow to my draw length, lets say for this example this one ends up 55# @ 24". I never pulled it past 55# on the scale, but in reality have i not put 95# of stress on the wood?
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All that is fine except there is only a limited amount of movement you can get from a wooden limb, so if you use that movement to brace the bow you can't also use it as draw length.
So with 2" of reflex you may get a 26" draw before it starts to take set or pull out the reflex, but without the reflex you'd get 28"
To answer your question:-
You can't just add up the weights... well I s'pose you can, but your target draw weight was for the braced bow, so that is how you must measure it.
As an illustration of the argument by reductio ad absurdum (reducing to the absurd... I think Harry Potter uses this technique ;) ):-
I expect any bow could take over 500# if it was clamped at one end pulled at the other in line with it's length.
Of course this is irrelevant, but it shows how there is only one important weight.
As long as you can hit target weight and draw without taking set, you can add as much reflex as you like >:D
Del
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The weight your pulling is more dependent on the leverage you have at the particular point you are pulling. When you have a bow on the long string and it is pulling 50# at 24" it will still be pulling 50# @24" if you brace it. Your string moves more than the limbs do so you have leverage. Stress is only relative to the radius of the bend and the thickness. If you have a lot of reflex it needs to be thinner in thickness because it is bending more and then wider to get the weight you need, no design should be under any more or less stress than any other design if we do our jobs. Wood only handles so much and we need to stay below that number.
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If I can try to distill some of what Del said (I agree with him), if you have a bow that has 2" of reflex and you pull it to 24" beyond brace height, you have moved the limb tip 2"+6" for brace height, + 24". So the tip has moved 32" from its rest position. You stipulated 40# to get it to brace height and 55# at 24".
That means that it took 55# to move the limbs 32". You don't add any part of the force at some distance to the total at 24". The 40 and 55 numbers are pretty unlikely anyway. It might be more like 25 and 55.
My curiosity runs more to how much more speed is given to the arrow by a reflexed bow than by a bow of the same weight that is not reflexed?
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But when i put the scale back on it it starts back at zero pounds, not taking into account the 40# it took to get it to brace.
Yes, about half the energy put into the limbs is unused in the powerstroke (full draw back to brace)
any ideas? utilizing some of this energy will take a very creative mind
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When you have a bow on the long string and it is pulling 50# at 24" it will still be pulling 50# @24" if you brace it.
The zeroing out when you brace causes me to scratch my head with 240m3srt. Maybe once you draw it to 24" it might equal the weight on tge long string at 24" but that's at the later draw lengths for string travel, but the limbs aren't moving the same distances between those two examples. I've experienced where the bow pulls 40# when the limbs move brace distance (lets say that's 18 inches on the long string hypothetically) but after I brace it and pull it to 8 inches the limbs are moving more than the 18 inches on the long string, but the weight is far below the 40# you had before. You would think it would be 40+ lbs since the limbs are moving further, but that's not the case. You have to pull it to around 18 inches after brace to get similar poundage but that is much further limb movement.
So my question is if bracing zeros out that poundage from previous limb movement, how does reflex add additional weight? Whether the pre-brace limb movement is 6 inches or 8 inches what does it matter, if it is only going to be zeroed out anyway? I know there's something I'm not getting (probably something to do with leverage and string angle) since reflex does increase performance, but I can't wrap my head around what's going on.
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If I can try to distill some of what Del said (I agree with him), if you have a bow that has 2" of reflex and you pull it to 24" beyond brace height, you have moved the limb tip 2"+6" for brace height, + 24". So the tip has moved 32" from its rest position. You stipulated 40# to get it to brace height and 55# at 24".
That means that it took 55# to move the limbs 32". You don't add any part of the force at some distance to the total at 24". The 40 and 55 numbers are pretty unlikely anyway. It might be more like 25 and 55.
My curiosity runs more to how much more speed is given to the arrow by a reflexed bow than by a bow of the same weight that is not reflexed?
Jim, it just depends how much reflex 15 fps diff is not unusual. A well made straight bow will usually hit around 165 or so and a well made slightly reflexed bow ( 1" ) will usually hit around 172or so. Some straight bows do go over 170. I think the only way to tell is test a bow straight and then reflex it and lower the weight back down to the same or just test it at 10 grains a pound at its new weight.
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When you have a bow on the long string and it is pulling 50# at 24" it will still be pulling 50# @24" if you brace it.
The zeroing out when you brace, causes me to scratch my head with 240m3srt. Maybe once you draw it to 24" it might equal the long string at 24" bit that's at the later draw lengths for string travel, but the limbs aren't moving the same distances between those two examples. I've experienced where the bow pulls 40# when ththe limbs move brace distance (lets say that's 18 inches on the long string hypothetically) but after I brace it and pull it to 8 inches the limbs are moving more than the 18 inches on long string, but the weight is far below the 40# you had before, when you would think it would be 40+ lbs since the limbs are moving further.
So my question is if bracing zeros out that poundage from that early limb movement how does reflex add additional weight, if what it adds is only zeroed out. I know there's something I'm not getting since reflex does increase performance, but I can't wrap my head around what's going on.
Simple it doesn't zero out, as soon as you start pulling it starts at a higher number. All the stress is going a different direction toward the limb tips until you start pulling it back toward the shooter.
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The whole key is to not brace a bow that is more than 20# heavier (10-15# is better) than potent draw weight.
Some bowyers can do it at floor tiller. They are more talented than I am.
I use the long string.
For a straight limbed bow, I long string tiller out to ten inches looking for good limb movement and target weight or a little over. Then I string it. This puts the bow at 10# over target. Plenty for me to tiller it.
If the limbs are reflexed 2 inches then I long string tiller out to 12".
Never mind increasing set, which you will of the bow is too heavy a t bracing, I broke some bows at the first stringing before I mended my ways. :)
Jawge
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When you have a bow on the long string and it is pulling 50# at 24" it will still be pulling 50# @24" if you brace it.
The zeroing out when you brace, causes me to scratch my head with 240m3srt. Maybe once you draw it to 24" it might equal the long string at 24" bit that's at the later draw lengths for string travel, but the limbs aren't moving the same distances between those two examples. I've experienced where the bow pulls 40# when ththe limbs move brace distance (lets say that's 18 inches on the long string hypothetically) but after I brace it and pull it to 8 inches the limbs are moving more than the 18 inches on long string, but the weight is far below the 40# you had before, when you would think it would be 40+ lbs since the limbs are moving further.
So my question is if bracing zeros out that poundage from that early limb movement how does reflex add additional weight, if what it adds is only zeroed out. I know there's something I'm not getting since reflex does increase performance, but I can't wrap my head around what's going on.
Simple it doesn't zero out, as soon as you start pulling it starts at a higher number. All the stress is going a different direction toward the limb tips until you start pulling it back toward the shooter.
In my experience it does not register the higher number. When braced, i pull it one inch the scale registers 3# for example, not 43#.
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Simple it doesn't zero out, as soon as you start pulling it starts at a higher number. All the stress is going a different direction toward the limb tips until you start pulling it back toward the shooter.
Not entirely no, but there is a good amount of zeroing going on. The limb movement at 28" on the long string is not the same as if it is at 28" after brace. If you were to continue to pull the long string to where you get similar limb movement (maybe more then 34") you would have a much heavier draw than 40#. So where does that extra poundage go? It's lost somewhat in bracing, (hence why lower brace heights store more energy). This is why i think it has a zeroing effect of sorts. Although not all of it is zeroed since extra reflex does increase the stored energy, especially during early draw.
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So where does that extra poundage go
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Simple it doesn't zero out, as soon as you start pulling it starts at a higher number. All the stress is going a different direction toward the limb tips until you start pulling it back toward the shooter.
Not entirely no, but there is a good amount of zeroing going on. The limb movement at 28" on the long string is not the same as if it is at 28" after brace. If you were to continue to pull the long string to where you get similar limb movement (maybe more then 34") you would have a much heavier draw than 40#. So where does that extra poundage go? It's lost somewhat in bracing, (hence why lower brace heights store more energy). This is why i think it has a zeroing effect of sorts. Although not all of it is zeroed since extra reflex does increase the stored energy, especially during early draw.
You also have to recognize the different angle. Even a 100# bow only takes a little bit to move the string 1" from brace. There is a huge mechanical advantage to a deflecting a string or cable only a tiny bit from straight. At straight, a scale reads zero, at one inch maybe a pound, at two inches maybe three pounds, at four inches maybe 10 pounds. The first few inches do not produce a linear result in force required for deflection. After that the force line becomes straighter for a while, then turns upward when the bow begins to "stack."
Willie's useful chart above uses a constant weight at different angles. For bows, it's more useful to recognize the different "weights" of pull at each angle to produce particular forces at the bow tips.
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In my experience it does not register the higher number. When braced, i pull it one inch the scale registers 3# for example, not 43#.
this is what I think, may not be true. The first inch is important. A straight bow of 40# will pull roughly 2# in the first inch. A reflexed bow of the same weight will pull a little more, maybe 2 1/4# or so in the first inch. It's not much but it adds up to that 5-10 fps.
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Yes, about half the energy put into the limbs is unused in the powerstroke (full draw back to brace)
any ideas? utilizing some of this energy will take a very creative mind
I'm thinking this is what deflex does. The deflex/reflex bows I've been making lately are very easy to brace but don't seem to suffer for speed like you'd think they would. But there seems to be a limit.
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Simple it doesn't zero out, as soon as you start pulling it starts at a higher number. All the stress is going a different direction toward the limb tips until you start pulling it back toward the shooter.
Not entirely no, but there is a good amount of zeroing going on. The limb movement at 28" on the long string is not the same as if it is at 28" after brace. If you were to continue to pull the long string to where you get similar limb movement (maybe more then 34") you would have a much heavier draw than 40#. So where does that extra poundage go? It's lost somewhat in bracing, (hence why lower brace heights store more energy). This is why i think it has a zeroing effect of sorts. Although not all of it is zeroed since extra reflex does increase the stored energy, especially during early draw.
Limb movement has nothing to do with it. I do it all the time and I build about 2 bows a week. Ignore limb movement just read the scale at where it reads on your tree just like it was braced. I do it on all styles of bows short and long heavy and light and it always works, not dead accurate but very close within a couple of pounds.
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You really have to think about 2 things when you are thinking about early draw weight. Your bow limb is like any spring it builds as a rate of so much per inch. The vast majority of the weight you gain is due to lack of leverage as your string angle changes, not the loading of the limbs, they don't load all that much as they build.
The other thing you have to look at is how much of the lower limb is at a low string angle. So the unbraced profile has a lot to do with string tension. The longer the area of limb sitting at a low string angle the higher your weight will be.
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Your bow limb is like any spring it builds as a rate of so much per inch.
Springs are linear so where does the hump in the lower end of an FD curve come from?
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DC, you did not read my post, you read like one line it sounds like. read it again. String angles and leverage.
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No, I read the post a few times and I knew I was taking this a bit out of context. I thought it might make it easier to understand if I took it one section at a time. I've done a little experimenting with bamboo sticks standing in for limbs and I did notice that the leverage dropped as I pulled the thing. I attributed this to the lever getting shorter as the limb bends. This accounted for the draw getting heavier toward full draw but I couldn't figure out what made the early draw weight hump.
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You really can't take one item and isolate it because they are all interacting. A hump in the force draw usually will have something to do with a sudden change of string angle or changing string angle that is not linear.
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I think the majority of the extra poundage created by a re flexed starting point will remain unused and so provide some extra speed but not as much as you think.
That's OK if you want to get the most out of your bow but you could get more by increasing the draw weight and reduce some of the shock to the bow and more importantly the string when the release comes to that sudden halt at brace height!
If you are building heavier bows and using natural material strings these things take on a different perspective.
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The other thing you have to look at is how much of the lower limb is at a low string angle. So the unbraced profile has a lot to do with string tension. The longer the area of limb sitting at a low string angle the higher your weight will be.
Regarding this explanation were you referring to the lower limb of the bow, as opposed to the upper bow limb. Or by lower limb are you referring to the portion of a limb in relation to how far it is away from the handle? Its hard for me to even state what im asking i hope it makes sense. Things that would be simple when explaining and pointing to a bow in person are a bit harder for me to understand or explain online with just words.
Would you mind posting a pic or diagram of a "lower limb at a low string angle"?
Also, "string angle" and how it relates to the tips is a concept id like to understand better. I get how a pulley system helps to lift a heavy object but my mind cant seem to apply leverage to a bow.
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I think you guys are looking at tip movement and the effort it took to get it to brace. You don't have any leverage when bracing a bow but when you first strt to pull a bow you have a huge leverage advantage. Tip movement is kind of meaningless if you don't include the leverage at a given spot. At full draw you have given up most of your leverage and that is why it pulls harder, not because the limbs are loading up.
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" then isn't getting poundage at brace an important factor in bow building and one we should strive for to build faster and more powerful bows?" To me, yes. This is in some ways a primary goal. Top three for sure. One other being low set. I can't abide a mushy string.
Badger: ' When you have a bow on the long string and it is pulling 50# at 24" it will still be pulling 50# @24" if you brace it." I believe you, but his surprises me. In the TBB I, Baker did that experiment where a bow braced 3" out-shot (for speed) the same bow braced 6", despite landing at a lower full draw draw weight. It was pretty darn close, though.
"Simple it doesn't zero out,...." Yeah, long string is loose, while braced string is quite tight. The bow is stretching on that string. That first inch of draw while braced may register only a few pounds, but that's down to geometry.
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Certain principles that exist which make it hard to "cheat" the systems. Stuff exactly like how a bow with lots of reflex should shoot faster, but reflex CAN cause extra set, instability, higher limb mass, and are harder to tiller properly. Net gains may or may not be realized. Likewise, recurves easily store more energy, but often have issues with tip weight and stability, thus net gains may or may not be realized. As such, IMO, it comes down to how much you push the envelope, and whether your skills are up to the task.
I have sketched out some RIDICULOUS designs I will probably never get around to trying, hoping to "cheat" these principles. It would be great to achieve radical profiles that still manage to relieve strain on wood, increase early draw weight, counteract oscillation/vibration, dampen lateral wobbles, stiffen tips, create zero stack, etc... Stuff like hollow bows, Superlight limb tips, weightless recurves, two stage recurves, string bridges, inverted limbs (incredible F/D curve, but totally stupid in every other practical way), cable backs, string stoppers, bizarre limb and handle arrangements, etc..
What WORKS for me tends to be; enough mass in the right places, MODERATE reflex or recurve, skinny tips, heat treating, Perry reflex, good workmanship, and knowing how much is too much to ask of your materials.
To the original post: Baker covered a lot of this in the first TBB Design and Performance chapter, though sometimes he mentioned it in passing and didn't dwell on it. Less set or even reflex increase performance. Deflexed tips help bows survive to higher draw weights. How do thickness, width, and length affect stiffness, set, and mass? He stated that less or more of a limb's bending potential can be used up by high brace heights, short working sections, reflex or recurves, etc. So, yeah, any given limb can only bend so far, and if much of that potential is used up before we get a string on it, less is left to get it to full draw. It's a balancing act.
I don't know how you add up the numbers exactly, though. I don't think you can add one atop the other in a meaningful way. I think you have what you have once you start pulling the braced string, and high early draw weight is good. You just have to get there