Primitive Archer
Main Discussion Area => Bows => Topic started by: sleek on March 05, 2016, 09:48:40 am
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How do some of you guys get those beautiful sharp 90 degree hooks at the end of a bow? I need to make 5 inches bend 90 degree on osage. Every time i try it cracks on me with dry heat and steam.
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Boil it Kevin. Dry heat works but boiling is pretty much fool proof.
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If your bow is already braced and pulling around 20" the tip will be pretty thin. Boil them and they'll turn to noodles. With Osage it'll help if your last 5-6" is one ring
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How long do you boil them for?
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For yew I boil about 25-30 min, not enough experience with recurving Osage but I hear of guys doing it 30-40 min
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Yep, boiling is the only way to get the tightest bends. Leave the tips full width. Having the belly to one growth ring is essential. Round the edges over very well too. You can also notch the width if you want to concentrate the bend in one particular spot. Using a form with a strap of steel is pretty much obligatory too. Having a long pipe clamp or similar will allow you to keep tightening it, little by little, without removing it from the heat. Do not try and get all the bend at once.
If you use all these bits of advice you should be able to get 90 degrees. Then welcome to the world of proper recurves! ;)
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Yep. I put em in the pot cold, bring the heat up, and boil them a good long time. How long depends on 5hickness, of course, but too long is better than not long enough.
Also, get that wood as thin as you can first. And be willing to put belly overlays on or whatever, too.
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Just to add to the fun. I never strap mine and I only steam them, with great success. I make the entire bend in one shot as well. So there, that is exactly 100% opposite of what they told you as a method.
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I have the mental image of you throwing wrenches in gears and loving it.
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No sir. I throw experience at gears to help them rotate and mesh more freely.
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I like your style.
But what do i know right? ;)
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9 year old did this with dry heat, no strap and first time doing it, hell sleek if he can do that with dry ya got to be able to get a 90 deg bend boiling it, i double dawg dare ya 😈😈(http://i623.photobucket.com/albums/tt320/bubncheryl/kid%20bow/IMG_2499_zps7b7emhyz.jpg) (http://s623.photobucket.com/user/bubncheryl/media/kid%20bow/IMG_2499_zps7b7emhyz.jpg.html)
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All that with dry heat? Better man than I. Kudos.
I was able to get boiling to work. It bent right over limp as could be. No splinter or tear out.
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Experience counts, but everyone's does. Sometimes what works for us is what we prefer, or what we have the best tools for.
I have done lots, many even, sharp curves with steam and both dry heat, no straps. But I have done even more, and with better success, by boiling. My boiling set-up is definitely a better tool for the job than any of my steaming set-ups have been.
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With all due respect, Mr. Buck, pics, or it didn't happen. I want to see all these bows you talk about, I'm serious and curious. Id love to see just a few, or even snippits of recurves, handles, tip overlays, leather grips, whatever. Im not being my usual smarta** self either. It makes the words take on their proper meaning, at least for me.
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I quit posting bows about 12 years ago when I added the third job. I don't often get bows done, pictures taken, emailed off my phone, uploaded, and then here. I'm almost always on mobile at the hospital between patients when I post, or I wouldn't have time. I have a kid in a wheelchair, a wife and oldest daughter with severe anxiety and depressions, and another daughter who is autistic. My last two week paycheck had 118 hours on it, 38 of which are overnight call. I also worked 36 more hours on my tree service, so I am simply not making as many bows as I did the first 10-12 years. Sorry I couldn't fit my bowmaking and picture posting into your time-frame. I like helping new guys, so I show up to do that.
I have to admit that I do ruin a lot of bows, because I tend to mess and mess with them until I break them, or push them to the limits, and I don't mind when it happens. Owning a stack of bows isn't my motivation. But, I was there back on the Leatherwall, when Badger and a few other guys on here started making bows, many years ago. Just because I'm "new" to you........
I don't hear or feel your "due respect", despite my agreeing with you and having supported your opinions far more often than not. Part of your self-assessment is pretty accurate, but while you might be curious, that's not your primary motivation. However, I've got several bows in the works that I just might finish in the next little while, in several different representative styles it happens. So, your subtle cyber-bullying just might pay off.
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Just to add to the fun. I never strap mine and I only steam them, with great success. I make the entire bend in one shot as well. So there, that is exactly 100% opposite of what they told you as a method.
Good luck to you matey. You carry on doing what you are doing.
What I actually said was 'to get the sharpest hooks'......we all know that anybody can bend a recurve without straps boiling etc but to get the very tightest curves steam alone will not get you there. If you never try something (straps/boiling) how can you know what you are talking about....but of course I will bow down to your clearly superior knowledge on the subject.
Photos or it never happened is playground talk and for you to raise that point is imo disrespectful and childish.
Springbuck - Well said.
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Thanks you for the knowledge compliment Mike, it means nothing coming from you.
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What is this, a GOP debate?
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YAAAARGH! I likes to boil me hooks💀
(http://i1346.photobucket.com/albums/p696/Bryce_Ott/32CE83EA-E819-42DD-A9B3-5BECD48FD0B1_zpsvzjuxf2z.jpg) (http://s1346.photobucket.com/user/Bryce_Ott/media/32CE83EA-E819-42DD-A9B3-5BECD48FD0B1_zpsvzjuxf2z.jpg.html)
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Hey mike, are you still up for that personal bow trade? I couldnt reach you when you closed your last user name out. If not thats ok im fine just let me know.
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Crap bryce, thats over 90 degrees!
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Sweet books on that one Bryce. 😎 Loving it
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50# at 26" for a 45" bow with a max 35" working section. Good luck with that. While you're at it, buy some lottery tickets too. Seems to me you're more likely to pull the latter of.
In principle, this is possible. Heck, look at horn bows. but these bows have strains of 4-5% for a 3 cm wide working limb that's 2 cm thick. To reduce strain in osage to 1.1% you'd need a limb not thicker than (I'm guesstimating) 7 mm for a 26" draw, and to get your draw weight you'd need limbs that are >10 cm or so wide. Which is not what you have in store I guess.
But I'd like you to prove me wrong!
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This is around 70 degrees just steaming BL.No strapping/No boiling it either/No splicing or kerfing.Enough for me and the limbs too.....lol.
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ooops.
(http://i920.photobucket.com/albums/ad41/Beadman1/DSCN0951_zpstgnexs57.jpg) (http://s920.photobucket.com/user/Beadman1/media/DSCN0951_zpstgnexs57.jpg.html)
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Steam and nothing else. Had to actually open it up a bit and it curled up again past what this picture shows.
(http://i399.photobucket.com/albums/pp78/pat_05/IMG_0171_zpsrhftaii0.jpg)
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Pending on bow length and draw length you may have to cut some length off of those hooks........the main thing is having the string lift off the limb at about one or two inches from full draw..... anything else is wasted weight/mass.
DBar
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Pending on bow length and draw length you may have to cut some length off of those hooks........the main thing is having the string lift off the limb at about one or two inches from full draw..... anything else is wasted weight/mass.
DBar
Has this ever been proven?
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YAAAARGH! I likes to boil me hooks💀
If you put a barb on that you could catch fish ;D
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Pending on bow length and draw length you may have to cut some length off of those hooks........the main thing is having the string lift off the limb at about one or two inches from full draw..... anything else is wasted weight/mass.
DBar
Has this ever been proven?
I usually never get into forum debates ...but In my mind, there's no difference if the string lifts off at the nock or two inches down the limb from the nock, therefore more mass....what is your point? Why do you add tight recurves?
DBar
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Because they've been proven to work. The debate is whether they don't work until the string actually lifts off. They are dead weight either way.
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Because they've been proven to work. The debate is whether they don't work until the string actually lifts off. They are dead weight either way.
That's why I don't debate.. just listen........my point is they don't work as intended if the string doesn't lift off the limb.....maybe it's just adding "more" dead weight.
DBar
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So just speculating then. ;) A good test would be to build a bow that has sharp hooks and lifts off two inches from full draw and then increase the curves a few degrees so that it doesn't lift off and test it again.
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Some people have no common sense ....................everything must be proven/tested to them...
I don't think you have ever build a bow......prove it/test it with a full draw pic....or am I speculating?
Good night I'm done,
DBar
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Just say you don't know then. ::)
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YAAAARGH! I likes to boil me hooks💀
If you put a barb on that you could catch fish ;D
Seconds as a gaff hook :D
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Proving that too sharp hooks don't work when they don't lift off: easy.
recurves that don't lift off add mass to the bow. Mass that's not working at any point during the draw or increasing leverage. So you might as well have a shorter recurve and add lead to them. The longer it takes for a recurve to lift off during the draw, the longer it's dead mass. Sure, it gives a fatter force-draw curve. That's expended energy. Large part of that fatness is needed during release to move the heavy tips instead of the arrow. Hence, you're losing efficiency.
See it in terms of leverage and tip mass. Recurves have high early draw weight because early in the draw they are functionally shorter bows. A 60" bow with 5" hooks is at brace a 50" bow with the mass of a 60" bow. The functionally shorter bow strains the wood more at each increment of draw, so you have higher early draw weight. Later during the draw, when the string lifts off, the extra leverage comes into play. The bow becomes functionally longer, with more leverage, so less draw weight gains per draw length increment. But only when the hooks are cantered 90° relative to their original position is the leverage fully realized. Before that, the bow is still functionally shorter than its initial 60". But at all times, it carries at its tips the mass of the 60" bow. So the trick is to find where this trade-off between extra mass and extra leverage is optimized.
Kooi & Bergman 1997 http://www.bio.vu.nl/thb/users/kooi/kobe97.pdf
showcase this very nicely. With the extreme Hickman working recurve (2/3 of recurve) as a good example to contrast to a normal working recurve and static turkish and persian recurves.
https://www.flickr.com/photos/farflinger/5177069236/in/album-72157625386947492/
This bow design was patented by Hickman as a revolutionary new bow design. String lifts off completely at about 21". That means that before that, it's functionally a shorter bow, but with the extra mass of a longer bow, concentrated at the tips. The reason we aren't all shooting this high-energy storage bow is that it's not efficient at all. The fat force draw curve deceives the eye but not the arrow. And neither the mathematic model by Kooi & Bergman. In fact it isn't faster than a well designed straight stave bow with a flat force draw curve. Anything above the straight line in the force-draw curve of that bow is energy wasted in moving a returning limb with a portion of dead mass that becomes larger during the return of the limb. With cartilage-unfriendly hand shock.
If you don't buy this explanation: experience for yourself. Make a recurve with 90° hooks that don't lift off. And make them looooong. 10". And make a recurve with shorter hooks, that lift off early during the draw. See which shoots best. If you don't want to waste good bow wood for this, make these example bows out of PVC. Will take you 1 h in total.
it's just a matter of dead mass caused by bow parts that cannot store nor impart energy to the arrow by either working or adding leverage during the entire draw.
There's a reason why the fastest @10gpp wood-only bow built so far is a long straight stave bow without sharp recurves...
Joachim
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Sleek, i'm fairly new to the whole flippin tips thing. Here's my 2 pennies. I tried dry heat and lifted splinters twice. Steamed 4 different bows worth of tips, zero problems. I just let the bow sit for a few days after steaming. I vote steaming. But the choice is yours . Good luck either way.
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Still a lot of speculation there, Joachim. The static portion doesn't do any work whether it lifts off or not, right?
We are talking about static recurves, not working here.
Until that long straight bow outshoots the short flight bows with 90 degree hooks then there must be more going on.
Using your example of two different bows proves nothing, you need to use the same bow and only change the degree of the hooks. Apples to Apples.
It would take you half an hour with a piece of PVC.
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Proving that too sharp hooks don't work when they don't lift off: easy.
recurves that don't lift off add mass to the bow. Mass that's not working at any point during the draw or increasing leverage. So you might as well have a shorter recurve and add lead to them. The longer it takes for a recurve to lift off during the draw, the longer it's dead mass. Sure, it gives a fatter force-draw curve. That's expended energy. Large part of that fatness is needed during release to move the heavy tips instead of the arrow. Hence, you're losing efficiency.
See it in terms of leverage and tip mass. Recurves have high early draw weight because early in the draw they are functionally shorter bows. A 60" bow with 5" hooks is at brace a 50" bow with the mass of a 60" bow. The functionally shorter bow strains the wood more at each increment of draw, so you have higher early draw weight. Later during the draw, when the string lifts off, the extra leverage comes into play. The bow becomes functionally longer, with more leverage, so less draw weight gains per draw length increment. But only when the hooks are cantered 90° relative to their original position is the leverage fully realized. Before that, the bow is still functionally shorter than its initial 60". But at all times, it carries at its tips the mass of the 60" bow. So the trick is to find where this trade-off between extra mass and extra leverage is optimized.
Kooi & Bergman 1997 http://www.bio.vu.nl/thb/users/kooi/kobe97.pdf
showcase this very nicely. With the extreme Hickman working recurve (2/3 of recurve) as a good example to contrast to a normal working recurve and static turkish and persian recurves.
https://www.flickr.com/photos/farflinger/5177069236/in/album-72157625386947492/
This bow design was patented by Hickman as a revolutionary new bow design. String lifts off completely at about 21". That means that before that, it's functionally a shorter bow, but with the extra mass of a longer bow, concentrated at the tips. The reason we aren't all shooting this high-energy storage bow is that it's not efficient at all. The fat force draw curve deceives the eye but not the arrow. And neither the mathematic model by Kooi & Bergman. In fact it isn't faster than a well designed straight stave bow with a flat force draw curve. Anything above the straight line in the force-draw curve of that bow is energy wasted in moving a returning limb with a portion of dead mass that becomes larger during the return of the limb. With cartilage-unfriendly hand shock.
If you don't buy this explanation: experience for yourself. Make a recurve with 90° hooks that don't lift off. And make them looooong. 10". And make a recurve with shorter hooks, that lift off early during the draw. See which shoots best. If you don't want to waste good bow wood for this, make these example bows out of PVC. Will take you 1 h in total.
it's just a matter of dead mass caused by bow parts that cannot store nor impart energy to the arrow by either working or adding leverage during the entire draw.
There's a reason why the fastest @10gpp wood-only bow built so far is a long straight stave bow without sharp recurves...
Joachim
I sure would like to know where you got that statistic because it is quite contrary to my observations and to my experiences
I have made a lot of recurves both with short and long hooks and my chronograph experience has shown that in relation to speed it doesn't matter, flightbows might benefit a bit though. The real difference that I have found is that long recurves are much more sensitive to string tracking and the slightest imbalance will exacerbate limb twist, not so with short hooks. Quite frankly there's just too many variables at work here for accurate predictions
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I could care less if a static is faster or slower,or what the optimum length and angle is with them,or at what point its best for the string to lift off in the draw......i just like the sweet smooth draw of them ;) and how nasty sweet ~90° hooks look >:D and yeah besides good looks on a bow they do spit an arra to my liking :D
Btw...i use steam alone,no straps,n bend it all at once with good results that usually makes a nice clean non torn or splintered wood...such as this :)
(http://i1181.photobucket.com/albums/x436/blackhawk28/Mobile%20Uploads/100_2833.jpg) (http://s1181.photobucket.com/user/blackhawk28/media/Mobile%20Uploads/100_2833.jpg.html)
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On my tillering tree I can see when the string lifts off the static.
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There's a reason why the fastest @10gpp wood-only bow built so far is a long straight stave bow without sharp recurves...
I sure would like to know where you got that statistic because it is quite contrary to my observations and to my experiences
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Don't take it too literally. Rather, one of the fastest. I'm referring to one of Tim Baker's pecan bows shooting (if y remember right?) 192 fps at 10gpp and 28" draw. There may be or have been bows of similar performance (see your HHB bow on p66 of TBB4), but I'd be surprised if any of they had long 90° hooks.
Don't get me wrong either: I'm not saying (static) recurves are always bad and reduce efficiency. My point is that there is an important trade-off to take into consideration, which I tried to explain above. Just assuming that big hooks will boost performance of any bow is wrong.
Kooi & Bergman 1997 equally conclude that net efficiency of Turkish composites (with rather small static recurves) must be smaller than that of straight-stave bows:
"Notwithstanding this, the efficiency η of the ‘Persian’ bow, and certainly that of the ‘Turkish’ bow, is rather low. This implies that the initial velocity ν is not as large as one would expect on the basis of the static performance. This is caused by the relatively heavy ears. These considerations demonstrate why these bows can, inherently, be no better than long straight-end bows; a large part of the available energy remains in the vibrating limbs and string after the arrow
leaves the string"
This is confirmed in practice by tests of Adam Karpowicz (http://www.atarn.org/islamic/Performance/Performance_of_Turkish_bows.htm). None of his bows shoot faster at 10 gpp than 185 fps, which is less than the 190 fps of your own HHB or Tim Baker's pecan board bow. Note that with your HHB recurve there is a nearly immediate lift-off early in the draw, which is required to boost efficiency.
joachim
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I don't believe anyone said big hooks, they said sharp. Whatever length you need to make them sharp.
The bottom line is still what cast is achieved with each type and sharp hooks historically have done much better.
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I could care less if a static is faster or slower,or what the optimum length and angle is with them,or at what point its best for the string to lift off in the draw......i just like the sweet smooth draw of them ;) and how nasty sweet ~90° hooks look >:D and yeah besides good looks on a bow they do spit an arra to my liking :D
Btw...i use steam alone,no straps,n bend it all at once with good results that usually makes a nice clean non torn or splintered wood...such as this :)
(http://i1181.photobucket.com/albums/x436/blackhawk28/Mobile%20Uploads/100_2833.jpg) (http://s1181.photobucket.com/user/blackhawk28/media/Mobile%20Uploads/100_2833.jpg.html)
And blackhawk returns with the perfect response👍👍👍👍
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There's a reason why the fastest @10gpp wood-only bow built so far is a long straight stave bow without sharp recurves...
I sure would like to know where you got that statistic because it is quite contrary to my observations and to my experiences
Don't take it too literally. Rather, one of the fastest. I'm referring to one of Tim Baker's pecan bows shooting (if y remember right?) 192 fps at 10gpp and 28" draw. There may be or have been bows of similar performance (see your HHB bow on p66 of TBB4), but I'd be surprised if any of they had long 90° hooks.
Don't get me wrong either: I'm not saying (static) recurves are always bad and reduce efficiency. My point is that there is an important trade-off to take into consideration, which I tried to explain above. Just assuming that big hooks will boost performance of any bow is wrong.
Kooi & Bergman 1997 equally conclude that net efficiency of Turkish composites (with rather small static recurves) must be smaller than that of straight-stave bows:
"Notwithstanding this, the efficiency η of the ‘Persian’ bow, and certainly that of the ‘Turkish’ bow, is rather low. This implies that the initial velocity ν is not as large as one would expect on the basis of the static performance. This is caused by the relatively heavy ears. These considerations demonstrate why these bows can, inherently, be no better than long straight-end bows; a large part of the available energy remains in the vibrating limbs and string after the arrow
leaves the string"
This is confirmed in practice by tests of Adam Karpowicz (http://www.atarn.org/islamic/Performance/Performance_of_Turkish_bows.htm). None of his bows shoot faster at 10 gpp than 185 fps, which is less than the 190 fps of your own HHB or Tim Baker's pecan board bow. Note that with your HHB recurve there is a nearly immediate lift-off early in the draw, which is required to boost efficiency.
joachim
[/quote]
I was the one that tested that bow. At 28" and 10 grains per pound it tested at about 170 fps. At 31" it tested at about 58# and was shooting a 500 grain arrow. 170 is still very fast for a straight limbed bow but not the same as 192. The 192 was shot at 31" draw and closer to 8.6 grains per pound. So we have a big difference.
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I have a friend who was at MoJam when Tim shot that 192fps arrow. It seems like he had an unusual release of rearing his body back and jumping forward in conjunction with releasing the arrow.
I could be wrong as this was a long time ago but I remember hearing this from my friend.
It seems like he brought the pecan bow sealed in a container from an arid part of the country as well.
These memories might be the workings of a slightly senile old guy, myself, so don't put too much stock in them.
My friend had just made a tour of a the southwest before stopping at Mojam on his way home to Alabama. He shot in the same speed test with a sinew backed bow with a poundage in the mid 40s, it was as dry as a bone and got he something like 180fps out of it.
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I don't believe anyone said big hooks, they said sharp. Whatever length you need to make them sharp.
The bottom line is still what cast is achieved with each type and sharp hooks historically have done much better.
Sharp hooks will lift off later in the draw. Same story.
I don't hear anyone arguing against what 's written by Kooi & Bergman: in order of efficiency, working moderate recurve > straight bow > asiatic composite > extreme hickman working recurve
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No, I mean what happens if they DON'T lift off?
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Eric, at Mojam everyone shot the same 500 grain arrows regardless of bow weight. They used a different scoring system. Tims bow was 47# and shot at 164 fps. This bow scored higher than any other bow using the scoring system they had. The 192 bow was tested by me as I talked about in my post a few places up. I think the scoring system they used was 100 plus draw weight subtracted from the speed. Tim had a plus 17.
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No, I mean what happens if they DON'T lift off?
Then it's just like having a shorter straight bow with even heavier tips than a regular bow. A textbook example of unwanted dead mass if you ask me.
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So that two inches of lift off at the end of the draw is enough to make the bow pay for all that added mass?
Many others would say it's the increased string tension early on that is the beneficial part.
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The lift off helps in a couple of ways. It adds to the force draw curve by building weight slower as it becomes effectively a longer bow as it lifts off. It also help with the efficiency by giving leverage back to the arrow at the end of the power stroke making the bow more efficient.
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I'm not disputing that lift-off is ideal merely the much thrown out thought that without lift-off the bow is just a short bow with weighted ends.
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I am not sure how you could not have lift off? I can see not having optimum lift off but none is hard to visualize.
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you are all missing some important points...imho. recurves change the string angle whether they lift off or not....this adds leverage to the draw.....less string angle decreases stacking.... string angle determines the amount of leverage... this affects arrow speed because you are essentialy getting more weight for less effort, this is how levers of all types work....also recurves that dont lift off still add early draw weight making for a smoother draw,,,and makes the working section work harder, getting more work out of the limbs ( provided they can take it) . Also if the recurve opens up and " works" this makes a bow more effecient...as I see it anyway!!!....open to be proven wrong though, maybe I'm deluded?
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No lift off is achieved by increasing the recurve. The bow Bryce posted likely won't lift off unless really hauled back.
dragonman, I am aware of those factors, just trying to focus on this one factor and whether it actually is true or not.
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Without liftoff, it would be like tying the string below the whole recurved tips. In that case, they are just dead weights attached to a "shorter" bow.
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There it is again....
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Ok. I will chime in again. If at full draw there is a portion of the receive the string is still laying on, what is that portion doing? My impression, nothing. But I don't know if it affects string tension. Now that leads me to wonder what string angle at full draw is desired? If 90 degree is best should a recurve be cut down until the angle desired is reached and the rest is therefore unneeded weight? Of course you don't need to cut the recurve down, you could open it up some or make it work open at full draw. What are the performance differences?
All speculation but I would love to know for certain.
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So that two inches of lift off at the end of the draw is enough to make the bow pay for all that added mass?
Many others would say it's the increased string tension early on that is the beneficial part.
I'm sorry, I think you got me wrong or I expressed myself wrongly. Lift-off for the last two inches will not outweigh the added mass IMO. Lift-off should happen as soon as possible during the draw.
The increased string tension certainly is beneficial. But if you have a 60" stave with 5" 90° hooks at each side that don't lift off during any part of the draw, you might as well just make a straigth stave 50" bow (or cut off the hooks). it will have the same string tension at brace and have the same force-draw curve. But it will have lighter tips. Now, as Badger stated: any recurve will show at least partial lift-off, however; it's only the dead-mass part that doesn't lift off (or too late) that should be cut off.
The cost of the higher string tension at brace is the higher tip mass. the benefit of a recurve is first the higher string tension, because it's functionally a shorter bow at brace (the functional length defined by the length of the string between the contact points of the recurves). A short bow will stack earlier and heavier. When recurves lift off, they functionally lengthen the bow, compensating for the higher stack. Basically, recurves with complete lift-off let you start with a 50" bow, and let you end with a 60" bow. Stack is essentially a reduced leverage because the limbs' functional length shortens during the draw (the below fig should clarify this).
The later the lift-off, the less distance the limbs travel back during wich the recurves function as levers. In some sharp recurves (with late or even without complete liftoff), the advantage of higher string tension at brace doesn't outweigh the disadvantage of the added mass. This is the trade-off to watch out for., this is what makes the extreme Hickman recurve less efficient that it's fantastic FD-curve suggests.
The longer the limbs, the later the lift-off of sharp recurves, and the less net gain there is. Also, the longer the limbs, the less stack (percentage reduction in effective leverage length) there is, and the less need for compensation of stack.
There are more subtle ways to get higher string tension at brace, with less cost of added mass of sharp recurves. Deflex-reflex bows like Marc St-Louis' (http://www.primitivearcher.com/smf/index.php/topic,52801.0.html) or other low-stack designs
Anybody has a good picture of Karpowicz's low stack design? Basically a straight setback eiffeltower bow with an elevated handle. At brace the string lies nearly flat on the entire limb, with immediate lift-off during the draw. Drawn, the bow resembles angular bows.
And please, those who haven't done so, do an attempt to read (parts of) Kooi & Bergman's paper. http://www.bio.vu.nl/thb/users/kooi/kobe97.pdf
It will clarify a lot of things that are questioned over and over again here.
Joachim
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So that two inches of lift off at the end of the draw is enough to make the bow pay for all that added mass?
Many others would say it's the increased string tension early on that is the beneficial part.
I'm sorry, I think you got me wrong or I expressed myself wrongly. Lift-off for the last two inches will not outweigh the added mass IMO. Lift-off should happen as soon as possible during the draw.
The increased string tension certainly is beneficial. But if you have a 60" stave with 5" 90° hooks at each side that don't lift off during any part of the draw, you might as well just make a straigth stave 50" bow (or cut off the hooks). it will have the same string tension at brace and have the same force-draw curve. But it will have lighter tips. Now, as Badger stated: any recurve will show at least partial lift-off, however; it's only the dead-mass part that doesn't lift off (or too late) that should be cut off.
The cost of the higher string tension at brace is the higher tip mass. the benefit of a recurve is first the higher string tension, because it's functionally a shorter bow at brace (the functional length defined by the length of the string between the contact points of the recurves). A short bow will stack earlier and heavier. When recurves lift off, they functionally lengthen the bow, compensating for the higher stack. Basically, recurves with complete lift-off let you start with a 50" bow, and let you end with a 60" bow. Stack is essentially a reduced leverage because the limbs' functional length shortens during the draw (the below fig should clarify this).
The later the lift-off, the less distance the limbs travel back during wich the recurves function as levers. In some sharp recurves (with late or even without complete liftoff), the advantage of higher string tension at brace doesn't outweigh the disadvantage of the added mass. This is the trade-off to watch out for., this is what makes the extreme Hickman recurve less efficient that it's fantastic FD-curve suggests.
The longer the limbs, the later the lift-off of sharp recurves, and the less net gain there is. Also, the longer the limbs, the less stack (percentage reduction in effective leverage length) there is, and the less need for compensation of stack.
There are more subtle ways to get higher string tension at brace, with less cost of added mass of sharp recurves. Deflex-reflex bows like Marc St-Louis' (http://www.primitivearcher.com/smf/index.php/topic,52801.0.html) or other low-stack designs
Anybody has a good picture of Karpowicz's low stack design? Basically a straight setback eiffeltower bow with an elevated handle. At brace the string lies nearly flat on the entire limb, with immediate lift-off during the draw. Drawn, the bow resembles angular bows.
And please, those who haven't done so, do an attempt to read (parts of) Kooi & Bergman's paper. http://www.bio.vu.nl/thb/users/kooi/kobe97.pdf
It will clarify a lot of things that are questioned over and over again here.
Joachim
Will you grab a piece of PVC and confirm all of that?
It really does seem like something is being overlooked here if you examine those old records.
And without going all Pearlie on you, how many statics have you experimented with?
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Levers that dont lift off are simply not just dead weight, its silly to say so.
I appreciate that Pat, but I dont think the leverage principle can be seperated from what is being discussed,its part and parcel of how all types of recurves function...
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PatM, I appreciate we are staying civil here >:D
I might try to show it with PVC, if you promise to read Kooi & Bergman's paper :P
But I have the feeling I could come up with tons of data, scientific evidence supporting the point I've been making, and still some people won't believe it, because their gut feeling says otherwise.
To each his or her own.
I could as well return the argument and say "prove me wrong", and let you do the hard work. O:)
Sure I havent made a ton of bows, certainly not of static recurves. I bank on other people's experience (among which some peer-reviewed scientific papers), common sense and logic.
I don't see anyone taking the logical arguments to show that I made a critical mistake in some reasoning. All I read is "I don't think so" or some variants thereof.
I don't know what hard facts to present to you other than what I have shown already, about the Hickman recurve, about the efficiency of different kinds of bows (straight, recurves, asiatic composites, extreme recurve, ...), both theoretic and in practice, etcetera. There's been a ton of threads on this and other archery forums on the trade-offs of recurves. What I wrote about is not my work, my experience... I'm just tying different ends together.
My goal in life is not to convince you. I might build the PVC examples. You could still say "well, that only counts for PVC" or some other arguments.
If we agree to disagree that's fine with me.
Sorry Sleek for abusing your thread here. Hope it's been at least to some use.
Joachim
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You know I'm pretty sure it was me that originally steered you towards the papers of Kooi over on Paleoplanet ;)
I have read them.
Sometimes it's hard to tell if those guys actually built real bows though or just drew diagrams and did the math.
I do know that their names are absent on those old records.
I keep hearing about better ways to achieve performance and yet all of those better examples don't deliver at the salt flats.
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Some use..... Im out of popcorn. :D
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The only benefit I coud see to a recurve that didn't open up would be the amount of reflex it introduced. I would have to agree that if it didn't open up it wouldn't add any benefits of a recurve. Joquin, did you see my post above on the Tim Baker bow you mentioned? I have done a lot of testing on bows but I have never tested one that did not open up. Aside from that I have never seen a straight limbed bow anywhere near as fast as a good well made recurve. The Baker example given above was only par for a well made straight limbed bow.
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Oh jeez not this tired debate again.......
You can find this same subject, with at least 100 results in the search bar with the same arguments.
I say...MORE HOOKS!!!! Let's see em!
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Sounds like we need to see some force draw curves that correspond with where the string is on the recurve. I'd like to see if there's a moment of change when there's significant lift off of a recurve.
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I'm no mathematician, but I have built a fair amount of statics.
I went through a phase where I was FD charting every bow, about 9 or 10 bows, and all but one were recurves. Depending on length and degree of curves, I could always see on the graph where the string lifted off, but I will admit it was never as drastic or "wheelie bow-ish" as I would of hoped.
All my top performing bows have been shorter statics
I've never built a bow where the string did not lift off, and I don't think I've ever seen one, modern or artifact, but I would be curious to see those numbers as well
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Well folks,
since I came up with the freaking PVC, it's time I delivered...
So here 's a mini test bow out of electric PVC pipe. it's 1/2", thin walled and will probably pull 10-15 pounds at 24" or so. it's 45" with 6" hooks (a bit more than the intended bow this thread originally started with). It took me some time to make the recurves non-working...
I made it with big and sharp hooks so they won't open up completely at full draw. its 23:50h right here, so I wont be testing it anymore tonight.
And yes PatM, that's you who sent me the link to the papers! I nearly forgot about that. Thanks again, you see at least I'm trying to use them in a sensible way. This means you already did your part of the bargain I proposed, so I really need to do my part too O:)
So just to make sure we agree on the setup:
This particular test bow, I'll put on the tree and get a FD-curve. Next, I'll shoot it with arrows that fit 10 gpp as close as possible and chrono it. But the lightest carbon arrows I have lying around are 26" 210 grain so let's hope I get a bit higher draw weight. I'll try to take 20 measurements, in order to average out variation caused by differences in release (I'm not exactly a drawing machine). I will see to where the recurves open up and to what extent they seem useful to me, and I'll shorten them next. I'll shorten the string for the same brace height, and recalculate the FD-curve. If I'm correct, the FD-curve should be identical.
Next, I'll chrono it again with the same arrows 20 times. I do a standard t-test (a statistical test to find out if there is significant difference between two groups of observations) to test if the bow with shorter hooks shoots any faster, on average. If it does, it supports the argument that the rest of the hooks are dead mass not contributing to string tension and other performance.
Badger: yes I read about it. Thanks for correcting me there. It's not just a matter of opening up (partly or completely), its also to what extent they open up. When projected on the X-axis, how much net limb length does it give? If the angle is still sharp, the horizontal projection of the recurve will be less than its actual length (but with the same mass, of course).
But do you agree that the fastest 10gpp wood-only bows so far don't have extreme (90°) hooks and shoot about 190 fps?
cheers
Joachim
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And here it is strung. it's bending too much in the handle section and draws 10# at 22" but what do you expect from electric pipe...
So I'll really have to find even lighter arrows. Maybe I can check for my longest chop sticks and fletch them ;D
Joachim
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This officially belongs in around the campfire. We have PVC posted in the bow section, blasphemy. Sleek I do not have much experience in Statics but the few I've done boil or heavy steam and have your jig ready and bend them in one shot.
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It would be neat if you could get a variety of degrees of recurve from the same piece and also chop them off entirely and test it as a short bow strung across the points of string contact.
That might introduce too many variables with heating and getting the material tired though.
The hollow outer portions should be enough to compensate for the fact that we do still reduce tips as much as we can.
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This officially belongs in around the campfire. We have PVC posted in the bow section, blasphemy. Sleek I do not have much experience in Statics but the few I've done boil or heavy steam and have your jig ready and bend them in one shot.
This is just a mechanical theory test, not a material discussion.
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This officially belongs in around the campfire. We have PVC posted in the bow section, blasphemy. Sleek I do not have much experience in Statics but the few I've done boil or heavy steam and have your jig ready and bend them in one shot.
Paulsemp: please read the thread before these posts. It's basically a test to see when sharp hooks are useful on a bow and when not, upon request. I don't mind continuing this thread with this specific question somewhere else, but I just want you to read the background of the reason why this is showing up here.
thanks for taking the time to do so and judge afterwards. I specifically imitated a bow design resembling the one that Sleek is intending to build. Whether or not it's made out of PVC is pretty much irrelevant right here. It's meant as a proof of principle with regards to performance.
J
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Three things happened. As you tryed to flip your tips.
You heated the wood to HOT TO FAST and you did'nt use some sort of OIL GREESE, This helps by keeping the moisture in only if you go SLOW.
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The oil or grease is unnecessary
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Talking full curls here, not flips.
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Yeah i know, 6 pages worth, the post i responded to said flipped tips, plus ya don't need it with steam or boiling
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Yeah i know, 6 pages worth, the post i responded to said flipped tips, plus ya don't need it with steam or boiling
Sorry, I just meant regarding the first post in response to CA.
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Where would wood quality fit in importance? If I want tight recurves is primo, straight, knot and blemish free wood right on top of the list or can you get away with some?
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You always want the best wood possible
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Results on test shooting the PVC-bow. First with big hooks, then hooks shortened to smaller recurve (compare pics).
All shot with a custom-made reed arrow (163 grains; actually two broken arrows with the tip footed with chopsticks to the bottom part). Don't mind the plastic nock.
The amount of the hooks that was cut off was c. 5 cm, in total 14 grams (215 grains).
Force-draw curves were close to identical early in the draw. Late in the draw, the bow with the big hooks cleary gets the leverage, as the poundage levels off.
Average arrow speed (23 measurements) for the big hooks: 92.5 fps.
Average arrow speed (20 measurements) for the smaller recurves: 103.7 fps.
The difference was statistically highly significant, with the bow with smaller recurves shooting faster. As expected.
The draw pics show where each bow had lift-off, and how that affected string angle and the horizontal projection of the effective limb length (leverage).
Note that on the right one pic at 18" is positioned next to the one at 16", so shift that one mentally down one square...
String tension at brace didn't seem different (same tone!). The bow with the big hooks was more difficult to draw, as it sometimes wanted to shed its string. For that reason I deflexed it in the handle compared to the previous picture.
So PatM, I hope that satisfies you 8)
It completely follows the predictions I made with relation to excess mass and leverage.
Joachim
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You increased poundage by about 10% but the increse in kinetic energy went up almost 25%. Not sure if you could attribute all of that to the size of the hooks but it was the only thing you changed so worthy of looking at further.
You nver have addressed my question to you on the baker bow you mentioned, I have asked it 3 times now.
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I think that is a impressive contribution to the argument by Joachim..
Ignore my previous comments...( I think everyone did anyway )!!... i didnt read everything properly and misunderstood the discussion... i thought it was about recurves that wheren't sharp enough to lift off...not 'hooks' that where too sharp to lift off at full draw..
we all make mistakes... hahaha.....
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Higher draw weight would account for the increased arrow speed therefore there is no advantage one way or the other
Some wood species heat bend better than others
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There seems to be a misunderstanding of what we were mainly trying to test here. It wasn't about big hooks versus small hooks, it was about degree of hook of the same length of recurve.
Lift off versus no lift off.
Are you sure you didn't also draw the shorter bow further relative to length as well? It looks like it is being bent more.
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You increased poundage by about 10% but the increse in kinetic energy went up almost 25%. Not sure if you could attribute all of that to the size of the hooks but it was the only thing you changed so worthy of looking at further.
You nver have addressed my question to you on the baker bow you mentioned, I have asked it 3 times now.
Badger, I thought I did address it? But you asked multiple questions, so let's be sure we're talking about the same thing: was it whether or not I saw that I was wrong about that pecan bow (yes I acknowledged that), or was it how you could not see a recurve not lifting off during the draw. That question was answered a few comments ago.
I'm sorry if I'm still not answering your question. Not because I don't want to, just because I'm not sure to which question you are referring.
PatM: well, then I or someone else will just have to do another test with a different bow :P
Next weekend I guess.
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Do you understand what I mean though? Am I correct that you then drew the shorter version of the bow much farther relative to the new length?
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PatM
Yes you're absolutely right. The recurves of the second bow didn't only lift off completely earlier, the bow was also strained more. So two things changed at once, while I should have limited it to a single change. No way I can disentangle the effect of these two changes now. that's why I mentioned "So just to make sure we agree on the setup:"
Next week. And I'll start another thread for that so Sleek will be freed of my design comments O:)
Now, what I did show, is that it's a piece of caketo test this kind of questions: all you need is a heat gun, a chronograph or a smart phone with a chronograph app, and some PVC pipe. Oh, and a broad mind that acknowledges that PVC can be useful to primitive archery >:D
So please folks, be my guest.
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Hard to think of all the variables that can be changed, even accidentally. If you just use the same bow and back off the curves a little bit, brace height will then change unless the string is adjusted .
I was thinking that a few sets of slip fit wooden recurves of the required degrees would be a good idea but who wants to make multiple sets and make sure the weight is identical ???
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May as well keep it on here. It is what the thread has evolved to and its is related. My question was answered page one. I'm good.
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An invitation for broad minds to bring some pvc creations? sound intriguing.
And a whole week before show and tell?
I think sleek just put more popcorn on the shopping list..........
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If this devolves into a bunch of plastic bows it should be moved
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It's testing of mechanics! Nothing to do with the actual materials for bows. Remember Tim Baker's foam food tray mini bows? Same idea.
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Next week. And I'll start another thread for that so Sleek will be freed of my design comments O:)
What you did here is just wonderful, Thank you. Your contribution surely deserves its own thread. As for this thread, it is clear that Sleek got his answer early on. Time to sum up here, if I may.
The surest and easiest way to make "sharp hooks" is to boil the stave tips. But with enough skill, they can be made by steam and even dry heat, of course.
The issue of no liftoff is a read herring and moot, because nobody make such a bow or even saw one.
joachimM tried to show us that the "sharp hooks" need to be rather short to be effective. So far as I can tell, that is the opinion of most experts here anyway. We are not sure whether such a short recurve bow is no better than a straight bow or not.
Higher draw weight would account for the increased arrow speed therefore there is no advantage one way or the other
If we make the draw weight constant, not the draw length, the conclusion by joachimM might not be pertinent.
There seems to be a misunderstanding of what we were mainly trying to test here. It wasn't about big hooks versus small hooks, it was about degree of hook of the same length of recurve.
Lift off versus no lift off.
Are you sure you didn't also draw the shorter bow further relative to length as well? It looks like it is being bent more.
Nobody makes a recurve bow with no liftoff. The issue might be which is better: earlier liftoff or later liftoff. And that question was only partially answered by the experiment of joachimM, as pointed out by Marc above.
As the original issue is how to make "sharp hooks" safely, PatM's question is somewhat more pertinent in this thread. The question is what would be the most useful "sharp" angle of recurved tips. Less than 90 degrees or even more than 90 degrees or 90 degree is simply the best? IMHO it would depend on the length of the recurved tips.
As for using PVC models for experiment, it does not bother me but if it does bother some members here, I think we can use bamboo strips. Most importantly, we need to agree on exactly what is the question that needs to be answered by the suggested experiment. I eagerly wait for more experiments by joachimM in his own threads with his own issues. I sure hope he does an experiment to answer the question of PatM. Thanks in advance.
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I eagerly wait for more experiments by joachimM
So please folks, be my guest.
I thought all were invited to bring a model?, and I think your material of choice would be ok, Pat.
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Plastic models are fine with me. Why let our noses in the air to plastics over wood interrupt knowledge? If we so then we deserve to be uninformed. Let it happen here.
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scp, People have actually made no lift off recurves. Someone posted a yew recurve on here once that still had full contact at full draw.
The Scythian bows also arguably had full draw contact.
Maybe Bryce will chime in whether that bow he posted is in action yet. Seems like unless it was drawn ridiculously far it would also have contact.
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Plastic models are fine with me. Why let our noses in the air to plastics over wood interrupt knowledge? If we so then we deserve to be uninformed. Let it happen here.
There fine with me too sleek, just in around the campfire
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I'm going to draw a few diagrams of theoretical angles and curves to try to illustrate how things will change accordingly.
I will be using a piece of charcoal on Birch bark.
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Please.... do.
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I'm all outta bark and charcoal and I won't stoop to the level of using a 2B and a sheet of printer paper on a primitive site. ;)
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scp, People have actually made no lift off recurves. Someone posted a yew recurve on here once that still had full contact at full draw.
The Scythian bows also arguably had full draw contact.
Maybe Bryce will chime in whether that bow he posted is in action yet. Seems like unless it was drawn ridiculously far it would also have contact.
I guess it's a matter of semantics. For me, "no liftoff" means the string contact with the bow never changes. So long as there is a curve in the recurve, there would be a liftoff no matter how small it might be. If it means, as you seem to imply, any residual contact of sting with bow tips, you are correct. Used in that sense, I don't see any usefulness of such "no liftoff". Enlighten me, please. How does such a residual contact increase efficiency?
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I'm all outta bark and charcoal and I won't stoop to the level of using a 2B and a sheet of printer paper on a primitive site. ;)
Want me to carrier pidgon some to you or do you prefer fox?
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I'm not saying it does. I'm just questioning if anyone has ever proven that a bow that is too sharply curved to lift off might as well just be a bow that is the length of the string contact points.
Some of the bows I am mentioning miss total lift-off by a mile. if the string is in a groove it might just barely be getting out of the base of the groove at full draw.
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I'm all outta bark and charcoal and I won't stoop to the level of using a 2B and a sheet of printer paper on a primitive site. ;)
Want me to carrier pidgon some to you or do you prefer fox?
;D
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Hard to think of all the variables that can be changed, even accidentally. If you just use the same bow and back off the curves a little bit, brace height will then change unless the string is adjusted .
That's why we have mathematic models... But these don't seem to count here 😳
As for the liftoff in Scythian bows: see pic: total lift-off. And it should be drawn to 30" i guess, not 28".
I will make a new set of models asap, with equal final poundage but different fd-curve as a result of different angles of recurves, and different lift off during draw.
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True, but the real bows must still match the mathematical bows. ;)
That is no Scythian bow. I mean the actual historic bows.
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I dont care what it is thats beautiful.
I have to say i have never had brace change by recurving a bow.
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I have to say i have never had brace change by recurving a bow.
What do you mean by change?
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I want to see a static from you sleeky, I don't recall seeing one. I like 'em.
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Pearl, I just got into them. So to be clear and fair, all my recurve to recent have just been reflexed tip to point of almost contact with the string. Never had to adjust the string after that. Neither . Have I had to on the most recent with 90ish degree hooks.
Pearl, I just made one with static and a proper recurve. Its 45"ntn weighs 60@26. You seen the thread?
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http://www.primitivearcher.com/smf/index.php/topic,56318.0.html
This is it. First full around static I have made. Technically its the second but the first isn't finished yet and its 41inches ttt.
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I just looked. They look good, but I question how long those dragsters will race. You know me! Holding together for a picture and shooting 2000 arrows is another thing. Good challenge and learning experiment all the same.
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My goal is a reliable weapon. Experience is the reward of time and effort. I'm putting mine in now.
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I have to say i have never had brace change by recurving a bow.
What do you mean by change?
Well. Just that. Never had to adjust the string to drop brace because its always the same for me after recurring. Am I doing something wrong? Does everyone have to adjust the string after that?
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Keep up the work.
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That's why we have mathematic models... But these don't seem to count here 😳
They would count if I had an advanced education. But I don't. For some one like me(and probably others) if I see a page of formulae it might as well be written in Chinese(it does look like it). If I insisted that all my questions were written in Arabic, do you think I would get many answers? I'm 68, it's a little late to change me. Maybe mathematicians and physicists should learn to answer questions in English(or whatever language is being spoken at the time and place)
Sorry, rant mode off
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That's why we have mathematic models... But these don't seem to count here 😳
Maybe mathematicians and physicists should learn to answer questions in English(or whatever language is being spoken at the time and place)
DC, you have an important point here. Maybe it's a good idea to translate some of these papers into laymans' terms, make a kind of simplified resumé highlighting the main aspects. That's what I have tried to do piece by piece in my comments when referring to some papers. But apparently, not well enough.
Frankly, when I read such papers, I rarely go through the entire math section. It would take me days or sometimes even weeks to study these portions to figure out what they exactly or even approximately represent. I largely trust in the scientific peer-reviewing process to control that the math wasn't complete bollocks.
I read what I can understand, and draw my conclusions. Don't let the math scare you :)
Joachim
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I know it's a tough row to hoe trying to put this stuff in laymans terms. Models and pictures work wonders. We need more people like Isaac Asimov (sp?) I do try to wade through the math but when you put in a search like "simple bow mechanics" and the first three hits are full of sqiggly things. Maybe "basic" instead of "simple"? Nope, same stuff. Asimov could explain how the universe worked in simple terms, surely there is someone out there that can do the same for a bent stick. :D :D
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DC-
I was recently researching through some of those kind of papers, and like Joachim, I just try to glean what is pertinent to bow building from the simpler parts of the paper, and rarely look at the math.
In my searching, I often find well written explanations, often from first or second year college texts, but hesitate to post the links, as there are often comments in the threads, that make you feel as if a scientific or engineering oriented posting is out of place or at least pushing the limits, here at PA. If you have a specific interest. by all means do not hesitate to ask, and as for the Issac Asimov version for wood science, I can recommend Understanding Wood, by Bruce Hoadley , and I may even be able to find a pdf copy if anyone is interested.
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I did some more testing with PVC models, and got some interesting results. Nothing unexpected. Not to me, at least. ::)
see http://www.primitivearcher.com/smf/index.php/topic,56377.0.html
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O:) Sigh. The deflex is another variable. I am purely talking about ONE variable in the SAME bow.
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O:) Sigh. The deflex is another variable. I am purely talking about ONE variable in the SAME bow.
It will ware you out, wont it? :)
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No, I think I have access to a a piece of PVC so that I can illustrate what I meant.
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O:) Sigh. The deflex is another variable. I am purely talking about ONE variable in the SAME bow.
Com on PatM, you're wrong, IMHO. Not deflexing would have added a variable, namely it would have changed peak draw weight at the same draw length. Of course a bow with higher poundage will shoot faster. That's not the point here. Both bows weigh exactly the same. mass and draw weight at same draw length. Net reflex is identical.
You could level the playing field by changing the draw lenght on the less recurved bow, so as to have the same peak draw weight. One at 24", the other at 27" or so. But then the power stroke would be different, and you would object on that.
Look: peak draw weight is identical, but the energy stored in the strongly recurved bow is higher because it is still strained more, in spite of the deflex. What everybody regurgitates is then that this bow should shoot faster, because it stores more energy. Well, theory says it doesn't necessarily. People react by saying: "well that's just theory".
I showed it doesn't in practice. What else do you want??
It's easy to stand by and criticize. You're ignoring hard facts right now. Stored energy (the area beneath the FD-curve) is NOT equivocal to efficiency.
It's your turn now to show, empirically, that I'm wrong and you're right. I have shown hard facts 8). You have given your opinion :-\. Facts versus opinion.
I tend to value your opinion most of the time, but unless you come with equally hard facts, I say you have been trumped :P
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O:) Sigh. The deflex is another variable. I am purely talking about ONE variable in the SAME bow.
The variable is the change of angle. We are trying to keep the draw weight and draw length constant. What would be your way of keeping them constant, while just changing the angle of recurve only?
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No, you're missing the point. I was strictly talking about people making a bow that is a few degrees sharper than 90 and other people saying that the recurve should be eased off a few degrees in order for the recurve to work at all.
Would you actually leave the full mass on the recurves in the real world? Reduce both of your bows at the tips as much as you safely can and then test them again. That's what we actually do when we make bows ;)
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I was strictly talking about people making a bow that is a few degrees sharper than 90 and other people saying that the recurve should be eased off a few degrees in order for the recurve to work at all.
That's a very good question, but joachimM is not addressing it. Still we can extrapolated from his experiment that it would be better to make the hook less sharp. I hope he is willing to un-bend his sharp hook model slightly, say just 10 degrees, and test it and compared the result with the numbers before un-bending. We can even stipulate that any change in draw weight and length would be within the margin of error.
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No, you're missing the point. I was strictly talking about people making a bow that is a few degrees sharper than 90 and other people saying that the recurve should be eased off a few degrees in order for the recurve to work at all.
Would you actually leave the full mass on the recurves in the real world? Reduce both of your bows at the tips as much as you safely can and then test them again. That's what we actually do when we make bows ;)
PatM: and what will you compare then? Arrow speed of bows of different poundage?
Next the full mass: well I explained you cannot tiller PVC that way. Despite this, the highly recurved bow performed much worse.
The point I was trying to make is that a force-draw curve is not a good proxy of performance. Bows with fat hooks have fat FD-curves. But they are deceiving. They store more energy but do not necessarily impart more energy to the arrow. I have explained the mechanics of the reason for this.
Two bows with the same peak draw weight, one sharply recurved the other weakly: which one will shoot a 10 gpp arrow faster (or transfer its stored energy most efficiently)? Probably the bow whose FD-curve resembles a straight line the most.
I wasn't even talking about a few degrees above 90. The point is that whenever you have a recurve that's not lifting off during some part of the draw, that reduces efficiency of the bow. So how would you test this then?
Recurves, especially in highly strained designs like the various asiatic composites, make the bow unstable (flip-flop tendency) unless the entire lower limb is made very wide and the ears are made very stiff. One way to reduce this lateral unstability a bit is by allowing the ears to be set back a bit more than a contact ear at brace.
The hungarian composites lift off immediately (contact recurve with long ears), but the lower limbs are very wide, and the ears are stabilized laterally with bone, for its very high stiffness. The ears are rather heavy, but the lift-off is immediate.
Turkish composites have rather short and light ears, and are set back a tiny bit. This setback adds stability, and lift off is very early in the draw. So it concedes a tiny bit of efficiency for stability. Idem for the korean bow.
The Chinese Manchu composite has ears set back a high degree. They lift off only at about 22". But when drawn to 36 or even 40", this is even relatively speaking a fast lift-off. These bows weren't made for high efficiency, they were made very heavy to shoot war arrows the size of broomsticks. They didn't care about 10 gpp or high dry fire speed.
So how do you define "in order for the recurve to work at all", and how would you test this without comparing apples to pears? And mind you, it will show exactly the same as what I've shown if you can make a level playing field.
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Performance aside, which is smoother to draw[less stack] and shoot [stable]? That is what I mainly look for. ;) another can of worms. ;) :)
Pappy
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Pappy, very good question, but to a large degree a matter of personal preference. My shooting was more consistent with the longer bow. In general, long bows shoot more stably and have less stack. I admit that the lift-off of a good recurve at the end of the draw eases the archer (more leverage), but that's like saying "it feels good when the headache stops". The leverage was there all the time for the longer bow, not only at the end.
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And Pappy, your latest trade bow will lift off immediately in the draw, making this degree of tip flipping close to ideal for performance
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I'm not sure how much clearer I can make the fairly simple experiment.
You know I have routinely steered people down the more Hungarian bow tip profile because the lower angle recommended by Kooi seems to be the best compromise between stored and delivered energy. I make this type almost exclusively.
The question is about the oft repeated statement that nobody has bothered proving. You think that you did but you smothered your test with confirmation bias. Recommending that people make sure they make the hooks huge and clunky for example.
We already know that heavy tips smother cast but that's not the point of the test.
Remember I have never said that too sharp recurves work just fine, I asked if they had ever been proven to not work AT ALL.
I will say that sharp recurves must still hold some sort of advantage. Otherwise straight or even Hungarian type bows would shoot better than the sharp statics of the 30s and 40s that have never been approached in the modern era.
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Pat, you make continuous references that todays bows cannot approach the bows of the 30's and 40's and you are dead wrong. Bow performance is based on the speed of the bow where flight shooting is the distance. They got better distances using different rules. Our arrow speeds are right up there. They had some great flight shooters in that era but flightshooting does not gage a bow, A chrono tells the story of a bows speed. My fastest light arrow bows have short sharp statics but I achieve better distances from bows much slower due to arrow tuning issues.
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Steve, I have yet to see evidence of those different rules. They just shot wood and feathers apart from the very latter stages of that era.
You just said that flight shooting doesn't gauge a bow and then said your sharp statics are faster. Well then it seems that those bows shoot faster AND farther.
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Pat, I agree that the sharp hooks work very well for the speed, I am just saying flight shooting is not a good gage for a bow, only a chrono tels that story. When they strted hitting the big distnces is when they started using vanes and eleveated rests. I can get 50# bow speeds at 300 fps but much slower bows will outshoot this bow because of tuning problems. If you are talking strictly bows you cannot use flight shooting as a reference because it involves a lot more than just a bow.
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I still consider a shot for distance a very good compromise when not owning a chrono.
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You may consider it such but years of experience will teach you otherwise. If you are shooting heaver arrows it can be a pretty good guage but flight arrows won't even give you a clue.
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Any arrow is not going to go far if it's not going fast initially. A really slow bow won't shoot far no matter what arrow you use.
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Your perception of far is what needs work Pat. A bow shooting 230 feet per second can reach 400 yards yet they usually will go just over 300 yards. A shot of about 500 yards with a 50# bow you could feel assured you had a fast bow and everything is right. With a shot of 400 yards or 300 yards or even 250 yards you may still have just as fast or even a faster bow but you simply got poor flight for whatever reason. Heavier bows shooting heavier arrows don't suffer with this near as much, once you get over 300 grains or so flight starts becomming more consistent.
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Pat, you make continuous references that todays bows cannot approach the bows of the 30's and 40's and you are dead wrong. Bow performance is based on the speed of the bow where flight shooting is the distance.
Badger, thanks for clarifying what seemed to be a babylonic speech confusion.
Yes I'm talking about efficiency, not raw speed. Efficiency is the kinetic energy of the arrow divided by how much energy you put in the draw (area below the FD curve). 10 gpp seems to be a good proxy for that. And if not, it's at least what we typically shoot when hunting.
By the way, the Kooi & Bergman paper suggests that the most efficient bow design is a deflex-reflex bow with a gentle working recurve (basically aking to the duoflex design), very closely followed by a straight bow (Table 1 in that paper).
The straight bow will not shoot as fast as the contact recurve, but it will be nearly as efficient. Mark the difference.
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Your perception of far is what needs work Pat. A bow shooting 230 feet per second can reach 400 yards yet they usually will go just over 300 yards. A shot of about 500 yards with a 50# bow you could feel assured you had a fast bow and everything is right. With a shot of 400 yards or 300 yards or even 250 yards you may still have just as fast or even a faster bow but you simply got poor flight for whatever reason. Heavier bows shooting heavier arrows don't suffer with this near as much, once you get over 300 grains or so flight starts becomming more consistent.
Where did I say what I perceived to be far? You do toss around those theoretical distance possibilities quite a bit though. ;)
I am fully aware of what efficient means but there are no prizes for efficiency.
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I'm not sure how much clearer I can make the fairly simple experiment.
You know I have routinely steered people down the more Hungarian bow tip profile because the lower angle recommended by Kooi seems to be the best compromise between stored and delivered energy. I make this type almost exclusively.
Good, I'm glad you're still a sensible man >:D
Remember I have never said that too sharp recurves work just fine, I asked if they had ever been proven to not work AT ALL.
I've never claimed they don't work at all. The world is not black or white. My point is that the trade-off between added mass and added strain is less than optimal for efficiency in sharp recurves.
They won't work at all if they don't lift off during any part of the draw. As Badger pointed out earlier in this thread, they always lift off at some part of the draw. My point is that this doesn't weigh up to the drawbacks of the added mass.
If that's clear, it seems we are starting to agree :P
We already agree that contact recurves/hungarian types of statics are the most efficient.
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But people WERE making black and white statements and I just asked if that fact had been physically proven.
I am aware of the discrepancy between stored versus delivered energy and I always bring that up when people claim that a f/d curve tells the story of how a bow performs.
The point of sharp recurves is purely for increased performance even when the relative inefficiency is considered.
That's why they are reduced to absolute minimal dimensions in an effort to harness at least SOME of the increased stored energy.
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I don't think I'll ever make another static again. Too much conversation about charts and plastic. Starting to sound a lot like work to me
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Pat the distances are not really theoretical, these are approx distances expected from glass bows shooting carbon arrows and plastic vanes out of well tuned bows with elevated rests and such.
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I don't think I'll ever make another static again. Too much conversation about charts and plastic. Starting to sound a lot like work to me
There is a LOT more discussion about performance of other bows relative to a discussion of static angles.
Four books in fact. You probably have them.
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But people WERE making black and white statements and I just asked if that fact had been physically proven.
I am aware of the discrepancy between stored versus delivered energy and I always bring that up when people claim that a f/d curve tells the story of how a bow performs.
The point of sharp recurves is purely for increased performance even when the relative inefficiency is considered.
That's why they are reduced to absolute minimal dimensions in an effort to harness at least SOME of the increased stored energy.
But then my question is: what defines "performance"? See my latest results. I removed the deflex you commented upon in the sharply recurved bow, and shot it. Despite higher peak draw weight and a lot more stored energy, it still didn't outshoot the other bow with a straightish FD-curve. When I then also drew the other bow further (to strain it evenly to the same peak draw weight, thus with a 1" longer power stroke), it clearly outshot the sharp recurve, again.
So my suggestion now: you come up with a design of two bows to compare. You define the rules a priori, how they should look (clear drawings please), how to test them and what defines better or worse performance. If possible, I make the bows (PVC models) and test them. This way there's no more "well that's not what I meant" or "you're doing it wrong".
Deal?
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joachimM, I'm sure most people here appreciate what you are doing, a lot. Many people are simply making suggestions to make your experiment more relevant to them. You don't have to grant their wishes.
But I sure, as PatM, would like to see what happens if you "un-bend" the sharp hook a little. You already have everything set up. Kindly just heat the tips of the sharp hook bow and make the angle slightly less, say 75 degrees, and test its speed, for us, please.
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I am just talking about the same bow with a slightly altered curve. If you want to call that an entirely different bow I guess you can.
But if you want to be realistic with the recurve at least make the effort to either reduce the weight of the tips or make them a sensible size relative to what's moving them. It's about finding a way to get SOME of that increased energy out of the bow and into the arrow.
Do you think that is impossible?
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The big problem with PVC is that you cannot tiller it by removing material. Sideways you rely on the rigidity of the sides. if you remove that, you have floppy tips. If you cut out a V in the center and then push the rest together with heat, you still need glue (and mass) to hold it together.
What I can do, however, is add wooden static recurves to the ends (just shove it in) of different angles/sizes. It's a lot more work than just taking a heat gun and adding a bend, though, but that way it's possible to reduce mass at the tips as needed.
But tell me how sharp (degrees) and how long the recurves need to be (percentage of bow length). "Slightly altered curve" is rather susceptible to interpretation differences.
Also if testing different designs, it's often easiest to exaggerate so as to have enough statistical power to find differences with a limited number of observations. Hence my maybe exaggerated differences. I don't think that for a proof of principle this is bad.
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I know the potential drawbacks of using it as a working model.
Wooden tips are probably a more sensible but labor intensive solution.
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After 9 pages ....common since seams to be much more economical ..... :) ;)
DBar
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You also don't get into debates. lol.
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You also don't get into debates. lol.
Maybe just smarter than the average "bar" .....:)
DBar
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Maybe. Or maybe not.
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Your right ....I don't have any PVC...........
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Neither do I.
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But I sure, as PatM, would like to see what happens if you "un-bend" the sharp hook a little. You already have everything set up. Kindly just heat the tips of the sharp hook bow and make the angle slightly less, say 75 degrees, and test its speed, for us, please.
Will do.
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All I can say is THANKS for keeping it nice guys. That says a lot for this bunch. But ha sharp hooks are cool looking so that should stand for something. ;) ;D ;D ;D
Pappy
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wow... The original post was something about how to get sharp hooks - steam or boiling/ straps or not.... Here's my contribution. It depends on if I can chase a belly ring or not. If I can reduce the belly to one ring in the area I am bending, then steam alone and going strapless works good for me. If the stave has issues, drying checks/knots/pins, or I can't reduce the belly to one ring, then boiling and straps are my choice.
Some of the posts in this topic reminded me of a line from my favorite movie, Lonesome Dove. Woodrow Call said "I swear Gus, you'd argue with a possum". :laugh: