Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on March 30, 2019, 09:22:46 am
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I have run across statements like this many times
Most older bows with wood or wood/glass limbs are not designed to take the performance strings such as Fast Flight, BCY 450, etc and Dacron is the preferred choice for these older or lightly constructed recurve bows.
What do they mean by"designed to take"? I've always(except for the first) used Fast Flight without a second thought. Didn't like the stretch of B50. What can go wrong using "modern strings"?
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When I first got started futzing with these primitive bows, this was on par with the holiest of sacred texts. You just couldn't use this material with wood bows at all, blah blah blah.
Yeah, can't make good bows from hickory, too. Or boards. Kiln dried wood explodes. Yew explodes if shot below 32 degrees F, or in a dry climate. So many things that are just so wrong.
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there might be more than this to it, but a wood string nock can split easier with a smaller diameter string that comes home harder. serve loops appropriately
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Been using almost nothing but FF since the 90s. I was told it would break a self bow. Being one who has to pee on the electric fence, I used FF on the first bow I ever made. 25 years later it's still shooting....with a FF string. Someone said it was so, and it got repeated often enough that it was accepted as fact. Kinda like JW's examples. All proven to be not so. Except for the belief that Osage is The King Of All Woods. That has been borne out as absolute.
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I have never had a problem with using FF plus or D97 with wood bows but I have freyed a few loops with glass & carbon bows due to hidden edges but I alwas pad loops with B50 I know guys that use artificial sinew for padding some glass manufacturers dont recomend FF but mostly HH type bows !
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I have seen older bow tips fail becasue of the using FF and such. I have an abundance of B-50 and will stick with it. Switched to B-50 on my FG longbow in the hopes of reducing draw weight. It seems to help the bow is measured accurately at 45#. So I'm thinking the B-50 will bring it down a couple notches. The stretch does not seem to bother me. On the safe side I use 14 strands. At the end of the day all I'm concerned about is Accuracy and I think this is what most of us are aiming for for. No pun... (lol)
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Slimbob. I watched somebody else pee on the electric fence.lol. I also watched guys liking FF and I gave it a try. I like it.
Bjrogg
A lot better than peeing on the electric fence
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I use FF all the time only damage I've seen is on a high poundage crossbow prod shooting light bolts at about 240 fps. It split down the limb. Decent reinforced nocks prevented it on the next attempt, so I figure it was
the my poor design rather than the materia ::).
Del
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I think the small diameter can be harsh,,,overlay or padding loops can resolve that,..I shoot both
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Yeah, I pad the loops since most of my strings are 8 strands. I used to make them 12, but only because the diameter of the string felt better. On the softer woods I use overlays, but with Osage, no problem with self knocks, so long as you fatten up the loop.
BJ...the need to pee on that metaphorical electric fence is a curse and a blessing. My 13 year old son suffers from the malady. It’s painful to watch sometimes😫. But it comes with its benefits.
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Any time I see a manufacturer advertise a bow as FF compatible I always assumed the the lack of stretch in the FF compared to the dacron was a factor in that. In terms of self bows it seems to me that if you tiller a bow out to 28" with a dacron string, and then later switch to FF it's stressing the wood in much the same way as a slight overdraw. Since the FF string won't stretch like the dacron, the limbs are going to have to move a bit more to reach the same draw length.
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I’m not sure that is the real problem. If you have ever watched the videos of bows being Dry Fired, it’s brutal the amount of vibration in the limbs. With some stretch, I would figure that at the moment of impact, the stretch acts as a shock absorber. The absence of stretch, like hitting a concrete wall and all of that energy is absorbed by the bow. With an arrow knocked, much of that energy is spent propelling the arrow. This is just my thoughts on the matter.
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Yeah I assume any difference in the stretch is actually of minimal impact, but as an engineer I can see why manufacturers recommend one or the other. Say they develop and test a particular model of bow with dacron, that's what they're going to recommend. The bow may work just fine with FF, but they didn't test it with FF, so they won't list it as FF compatible.
As for selfbows I think you're safe with either or, especially if you tiller the bow with the same string material you plan to shoot it with.
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Always used the non strech strings and never a problem .i do think the super thin strings should be padded at the nocks.
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I guess I wasn't thinking about the thinness of the strings. I can see that as being a problem now. As I said I've always used FF but I originallyused 10 strands. When I dropped to 8 strands I started padding the loops. I usually use overlays unless it's a very hard wood. I guess I may have just dodged the bullet by good luck more than good management
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Since the FF string won't stretch like the dacron, the limbs are going to have to move a bit more to reach the same draw length.
The opposite is actually true. The tension in the string at full draw is less than for the braced bow. As the tension on a string is reduced, it contracts or shortens. More tension on the string, it stretches or lengthens. For a “stretchy” material like Dacron, change in string tension has a bigger effect on the string length than a material like FF. So what happens when the bow is at full draw and the tension on the string is less than at full draw? The string contracts or shortens at full draw, but it contracts more for the Dacron string than it does for the FF string. If the Dacron string contracts more at full draw, then this requires the limbs with a Dacron string to bend a little farther than to make up for it compared to a FF string.
Alan
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I've heard the idea that string tension is less at full draw before, but I can't see how that would work from a physics standpoint. In physics a general rule of thumb for everything from springs, to fluids in a pipe to electricity is everything moves from high to low. Ergo at full draw the limbs are at a higher potential than at brace. When we remove outside influence (your string hand holding the system at the higher potential) the system will move back toward the lower potential, in this case brace. Because brace has the lowest mechanical potential energy possible in the system, tension at this point would also have to be the lowest at this point.
Another more practical way to look at this is, brace a bow, put it on your tillering rig. There is a certain amount of tension in the string to hold the limbs at brace. Now with your scale hooked up, slowly pull until the limb tips start moving (the string will move some before the tips due to stretch in the string). Once you find the force at which the tips just start to move, you've found, approximately, your brace tension. And this will of course be considerably less than full draw weight.
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+1 :D ....! Ununderstandabl how can something i pull, lose the tension :D
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I am so confused,, )P(
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It has to do with the mechanical advantage of the bow and string. There is a name for it, something to do with beams. At low brace the bow has the advantage over the string. A forty pound bow can put up to 60-70# tension on the string, I've measured it. As you draw the bow the string loses its MA and string tension drops. I put a scale in the string and as you draw it the tension goes down.
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Pope mentioned this in his book.
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If you had a low enough string to limb angle at brace it could happen. The example numbers I crunched were a 45 degree string limb angle at brace (mechanical advantage to the limb) verses a 90 angle ( string in line with direction of limb movement at draw, no mechanical advantage) limb tension at brace would have to be 70.7% of full draw tension for tension to stay constant. So for a 50lb bow, to have 50lbs string tension at brace, the limbs would have to already have 35.35lbs of tension in them.
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We discussed this here
https://www.primitivearcher.com/smf/index.php/topic,64869.30.html
My 40# bow actually has around 100# of string tension at brace. Remember we are talking string tension, not bow weight.
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DC I'm not doubting that you measured more then draw weight at brace, I'm just saying that the tension will go up at full draw. String tension at draw is always going to be higher than draw weight. The only way draw weight will equal string tension is if you are pulling directly along the length of the string. Of course even at full draw there is some angle between the string and the direction you're pulling on it. Tension will be draw weight divided by the sin of that angle.
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I can't remember what the string tension was at full draw. I do remember that it dropped dramatically. You don't forget when things go so opposite to what you expected ;D ;D
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Did a quick test. I'm not sure what the draw weight was doing during any of this because my only scale was hooked up inline with the string. But at brace string tension was 5.32lbs at about 26" draw it was just over 31lbs.
(http://i61.photobucket.com/albums/h66/jayres83/bow%20pics%202/Screenshot_20190331-184857_Gallery_zpss3r3k4rn.jpg) (http://s61.photobucket.com/user/jayres83/media/bow%20pics%202/Screenshot_20190331-184857_Gallery_zpss3r3k4rn.jpg.html)
(http://i61.photobucket.com/albums/h66/jayres83/bow%20pics%202/20190331_184748_zpsutoyaxpz.jpg) (http://s61.photobucket.com/user/jayres83/media/bow%20pics%202/20190331_184748_zpsutoyaxpz.jpg.html)
(http://i61.photobucket.com/albums/h66/jayres83/bow%20pics%202/Screenshot_20190331-184844_Gallery_zpsmur3lgih.jpg) (http://s61.photobucket.com/user/jayres83/media/bow%20pics%202/Screenshot_20190331-184844_Gallery_zpsmur3lgih.jpg.html)
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What is the draw weight normally?
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34# at 28" but the test string with the scale tied into isn't the same length as the normal string for this bow.
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I don't know. Unless your bow has an awful lot of set. Can we see it unbraced? I'm not the only one that has done this test. Yours is the first one I've seen with that low a reading at brace.
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That now does have alot of string follow, I'll try it on another bow at some point, probably won't be until later tonight though.
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Here's my grandsons bow. It's about 7# at 15". It has quite a bit of set and it still has about 7# string tension at brace. It drops about a half pound when you first pull it. And a picture of full draw on the tree with two scales.
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You don’t need a scale, just pluck the string while it is being drawn and listen to the pitch lower as the bow is drawn. Lower pitch = Lower string tension.
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I just redid the test with a 45# FG recurve. To my surprise it started at 67# at brace (test string matched shooting string length this time.) and it did decrease to 43# as I drew it close to string lift off. After string lift off it started coming back up, but the scale kept spinning away from me so I wasn't able to see the full draw reading. I'll have to check the full draw reading when I have an extra pair of hands to help out.
(http://i61.photobucket.com/albums/h66/jayres83/bow%20pics%202/20190331_194516_zpsaqcnzym6.jpg) (http://s61.photobucket.com/user/jayres83/media/bow%20pics%202/20190331_194516_zpsaqcnzym6.jpg.html)
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Now you have something to think about tonight, weird huh ;D ;D
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Ok, my final test on the recurve showed 67# at brace, dropped to it lowest at 43# just before lift off, came back up to 45# at 28." Bow is manufacturer labeled at 45# @ 28", but it's old so I draw tested it and got 42# @ 28", so I stand humbled gents, there is enough mechanical advantage to make string tension go down as draw length goes up. The exact relationship probably varies based on bow design, hence why I got such different results for the string follow bow
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On another note, two great things about this forum,
1) Always educational
2) Things like this stay a friendly discussion and dont devolve into name calling and stone throwing. It says alot about the quality of the folks that hangout here.
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The brace tension is only 5 lbs? Can you string the bow without flexing the limbs? ???
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When I got the 5lb reading the string/scale setup was the wrong length, so the bow wasn't braced properly. I just redid the test with the right length string and the results showed a decrease in string tension with draw.
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Since real world testing has proven you guys right and me wrong, here's a link to a physics paper on how a bow stores energy that proves me wrong with math.
https://www.google.com/url?sa=t&source=web&rct=j&url=https://arxiv.org/pdf/1511.02250&ved=2ahUKEwjthpzd8K3hAhUE5awKHbMKC6kQFjAPegQICRAB&usg=AOvVaw3476uJQUSaeN8sZyfTfVoX
I guess it's a good thing I'm an electrical engineer, not a mechanical, because I was way off on all counts on this one. (R
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I always learn something ;)
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I have run across statements like this many times
Most older bows with wood or wood/glass limbs are not designed to take the performance strings such as Fast Flight, BCY 450, etc and Dacron is the preferred choice for these older or lightly constructed recurve bows.
What do they mean by"designed to take"? I've always(except for the first) used Fast Flight without a second thought. Didn't like the stretch of B50. What can go wrong using "modern strings"?
Going back to the original question, the bow builders will build their bows to be good enough to handle whatever string material they are accustomed to using. Dacron is pretty forgiving and allows the bow builder to get away with things that they may not have considered if they had developed their bows using using the latest grade of SK99 Dyneema. For example, use of weak paper micarta tip overlays, designs using thin wide tips with abrupt side notches cut into the limb, leaving excessive limb mass in the outer limb, use of large string loops that tend to split a tip rather than hold it together, or use of thin string loops, or bonding methods, etc.
I have some bows built prior to the advent of Dacron and these have many characteristics that should allow them to work just fine with the more modern FF-type materials. Linen was the high performance string material at that time, which is much less elastic than the synthetic Dacron/polyester materials that eventually replaced them.
It is also interesting to see the influence string materials have on historical bow designs too. For example, many horn bow designs use very large string loops with a relatively narrow and weak nock in the bow limb. The strings used with these bows were typically made of silk, which has very elastic properties similar Dacron. When manufacturers started building modern versions of these bows, they had all kinds of issues with the durability of the nock with modern string materials, but they figured out how to address this without adding any significant mass or having a major impact on the appearance of the bow. One method is to add thin overlays of woven glass or linen micarta to either side of the siyah nock to prevent splitting. Another way is to add an insert of glass or micarta into a slot cut into the middle of the tip to prevent splitting. These methods are similar to the methods used to prevent arrow nocks from splitting.
When I started building very heavy flight bows using the latest ultra-stiff string materials and shooting sub-1ggp arrows, it was common to blow a tip overlay off after only a couple shots. But I have learned to adjust to this without adding performance-robbing bulk to the limbs and now i rarely experience this failure.
Bottom line is wood self bows are more than capable of handling the latest string materials. The bow builder will figure out how to make their design work with whatever string material they intend to use.
Alan
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Thanks Alan,
it's nice to be able to understand the experience of others, even if it is what many would consider a minor point about strings.