String material for flight archery

There is a greater mass at the ends of Turkish bows than modern target or flight bows. The greater inertia plus the different materials probably contribute to the fragility of tips. Adam will no doubt have a more precise explanation.

You can increase the thickness of the loops of the strings. Weight at the end of the string is not as critical in the effect of string mass as it is in the centre of the string.

There are two mechanisms that contribute to the breaking effect of strings. One is the diameter of the string at the loop and the other is the resilience of the string itself. The first can be changed by using separate loops of thicker material or putting extra strands into the ends of a conventional endless loop string. The other can be helped by using a string with the minimum number of strands for a safe string.

Most other changes like putting more twist in the string or using a heavier projectile aren't much use in flight shooting. Be careful to test your strings before the contest. I had a linen string explode on me while shooting one of Adam's bows in Utah. It is truly a scary incident.

Can't help but note that the same has been said for modern recurves made before mid-90's (I think it was), in that the tips then were not capable of handling the behaviour of fastflight strings - much as if releasing without arrow.

I am not sure if the breakage of strings has anything to do with the mass of tips. I think the breakage comes from the great tensile stresses in the strings when the brace position is approached on release. In selfbows, the stresses are less to begin with (selfbows are longer) and the bending parts of limbs are long enough to absorb the stress by buckling or vibrating. In the composites the bending sections are very short, so there is not enough limb to buckle and the stress is directed to the tips. The more efficient the bow, the chance of string breakage is greater.

It is true the strings break mainly at the loops/nocks. This is no doubt the reason why the loops were made much thicker than the string proper. I found loops made of natural materials and of the same thickness as the string break rather soon in use. I recently had a 137lb war bow break when tested with a linen string. It is indeed an unpleasant experience, even though the bow was mounted in the machine. I used however linen strings in sub-60lb bow without problems - the string broke after some use, but at the arrow nocking place where it flexes the most. Linen is much more brittle than Dacron or silk.

The bows break at the nocks when used with FF-type strings. The stress has to go somewhere and these materials act as a stiff wire or a steel cable. There is no use making loops of a softer material, such as Dacron, and the rest of the string with FF. The FF string will cleanly cut Dacron at the junction point (at the knot).

I found the use of horn overlays or inserts does not protect the bow nocks in those heavy weight bows from the stiff strings. Maybe a some kind of protection could be made with metal.

I undestand the Grozer bow is a modern laminate. It is best in this case to consult the bowyer about the strings.

Adam

Adam, according to your experience on hornbows, is Dacron the best string material in terms of longlife and endurance?

Use any string other than the type supplied with Grozer bows and the warranty is void.

Alas Orda, my warranty was void from the start, as the supplied string was broken somehow in the shop (rather dodgey now I think of it). I've used only dacron strings which give roughly the correct brace height (about 8" if I'm right) made by myself since. The bow is much older than a year in any case.
I've had a string break due to poor serving and negligence before, I can only say this was unpleasant, fortunately the bow survived.

Having considered your advice Adam, I think I can only use a lighter dacron string, and shall forego using the newer materials. It's too great a risk to be had when the bow is currently irreplacable. I should hate to be in your position where you test the bows literally to destruction. Did the ears shear off, or did the string cut the nock and above off? If, as you say it is due to the small size of the bending limb, I find it unlikely that reenforcing the tip would be of use, the damage would probably just be exhibited at another vulnerable spot.

I use a 14 strand dacron string currently, for a 55lb bow (at 28"). Would a 10 strand string be a safe bet? I'm worried that as only 5 strands will be present at the nocks, the string may break. Is a laid in type string effective here? I do a special version in which there is no give, but 10 strands would be present along the entire length.

My string breaking experiences are limited. However, I remember a discussion of the use of FastFlight and other high tech materials in the Traditional Boyer's Bible which proposed that the reason for strings breaking bow nocks was the use of the same number of strands for a FF string as for the equivalent Dacron string.

Their answer was to conform to the recommendations for the number of strands for the individual material. I have not tried this myself. It does sound plausible.

What I do know from personal experience is that too big a string for the arrow nock will contribute to a bad release which is the bane of flight shooting. While original Turkish nocks clipped onto the string, they were loose and could move up and down easily. That is to say the hollow at the base of the slot of the nock was bigger than the diameter of the string.

Jose: at this time Dacron or perhaps another polyester string is the only choice, other than the natural strings. It lasts well enough and I rarely use more starnds than 4x the draw weight equivalent.

As to the Mike's Grozer bow: I honestly do not know what to say. I have very limited experience with glass replicas (I made a few, but only as experiments, most broke). If the bow is 55lb, I would then use 55x4=220lb string. It about equals 220/35 = 6 strand of Dacron B50. So the 10 strand string should be OK. I would only make sure the bow nocks are well rounded and smooth.

Bede: I found the equivalent strength strings are not any safer for hornbows. The HDPE strings just do not stretch enough. It is frustrating to see those nice fps numbers for selfbows equipped with FF type strings, approaching good composites, and not being able to anything about it. I hope the problem of stiff strings will be solved by someone soon.

Adam

Adam,
I am glad you have tested this. Some of these ideas sound good and may work with lower poundage bows, but you are working in the high end where everything is working at maximum stress.

I am taking one of your bows to the Utah Flight shoot. I am hoping to have a pre stretched gut string ready for it by then. Last year it broke a linen string on the first shot.

Thanks Adam, I wasn't sure what the breaking stress of Darcon B50 was. 10 strands therefore looks ample. The bow nocks are smooth enough, but now I look, I can see the compression marks where my string sits. I'm beginning to think that the knotted string may be the best way to go for this bow. If only I could get it to work.

It would be possible to verify if nock breakage and working limb length were correlated with a theoretically simple enough experiment. A few bows (not necessarily horn bows) with graduated difference between their limb lengths, all using the same string. This would require a lot of consideration though, at many variables could be inadvertently changed at once.

Adam,
Do you have any pictures of a failed bow tip due to a fast flight string? I am not an experienced horn bow builder so I am not completely sure of how the bow nocks are constructed for a Turkish horn bow. For my all-wood flight bows, I always use a tip overlay glued in at an angle so that the string is cutting across the grain of the overlay at brace and this usually never fails. On the other hand, I'm not building 130+lb bows either! I'm curious if the nock of the traditional Turkish bow constructed in a way that the string pulls parallel to the grain and splits the tip?

I have spent quite a bit of time this past year testing a number of string materials (mostly linen) and found that the very best quality linen is several times stiffer for it's mass than B50 (also linen can be higher strength for it's mass) so I bet a high quality linen string might produce similar results with a Turkish bow as fast flight did.

What did the Turks use for their strings on their flight bows? Was it silk? Silk is very elastic like B50. It is interesting that the Turkish design can perform as well as it does with such an elastic string material as B50. I wonder how much the bow design is influenced by the choice or availability of string materials?

Bede,
I look forward to see you at the Salt Flats this year and am eager to see what you come out here with. As mentioned above, I have some high quality linen that you are welcome to. I hadn't had a chance to test gut string and am curious how it compares for strength to weight and stiffness to weight with the linen.
-Alan Case

Alan:

The bottom of the nock (marked black in the drawing) is sheared off. The wrapping of the tip with sinew below the nock (done usually in flight bows) does not help, but prevents splitting of wood down from the nock which happens without the wraps. Horn overlays, as well as the inserts of horn (as in the Crim-Tatar bows) do not offer any protection.

The violent reversal of the bow when the nock fails often leads to the breakage of the bow.

Old bows I have seen had silk for the strings. The end loops were made of twisted silk yarn, quite thick and impregnated with a combination of glue, rosin and wax. The strings were made of silk thread. What I found interesting, the thicknes of the silk strings was not greater than the equivalent B50 strings.

Adam

Adam,
For some reason, I was thinking of the nock breaking towards the belly side; you see so many old bows broken there. However, what you are illustrating is caused at the final part of the string's travel. It is much more obvious in the Oriental bow tip than when it occurs in a modern recurve.

Alan,
I will be bringing whatever bows are in shootable condition. Dr Grayson and I are thinking of some traditional string designs. He had a gut string on the Turkish bow that broke when I drew it. The string survived. I am testing some arrow speeds to find out whether it is better to use a majra and modern bows (Korean) or a siper and traditional bows (Turkish). Due to the arrow length rules, I can only effectively compete with the majra in the modern classes. I am tempted to make up darts of the length appropriate for the traditional rules and see how they perform. However the majra puts more stress on the string. Gut would help there.

Adam,
It does look as though the string forces are pulling parallel to the grain of the materials in the tip. Even a small leather pad in this area is not enough to keep it from splitting when shooting a very light arrow with a very stiff string. It would require an overlay with grain perpendicular to the string force but this might be a little odd looking because of the sharp angles of the siyah Vs. string. Did the horn bow makers ever use an insert of a perpendicular grain wood slat or horn set into a kerf in the bow tip similar to how it is done by the arrow makers? I don't know if what I'm describing makes sense.

I hope to get more hands-on experience with the construction of these sinew-wood-horn composites in the coming years.

Bede,
It should be a great time shooting at the Salt flats again. Dr. Grayson was exercising with his workout bow last time I visited and I'm up late at night again building arrows and working on bows to get ready for the shoot.
-Alan Case

I?ve almost never the problems you are talking about, but I haven?t done much bows with 100lbs plus.
I do a very carefully choice of wood for recurves and siyahs. No knots, no twists, the growthrings run along the back and belly!!. No possibility to split. Usually I steam- bend them.

Our ancestors didn?t have any dacron or fast- flight. Anyway they did strong and durable strings for bows with 130lbs plus.

In 2003 I had problems with my linen- strings, so I decided to have a closer look to the subject. I found a farmer who cultivated flax organically, the linen- yarn produced with his flax is of outstanding quality.
He told me that the flax of 2003 is really bad, cause it was a really hot summer in Europe. Flax don?t likes low temperatures and wet conditions. The best flax grows near the sea sides of Belgium, the Netherlands, Ireland, Northern Germany.
Flax is a living material, you?ve to know it well, when you?ll use it for such a stressed object like a bow- string.
The modern cultivation of flax wants to produce as much as possible, not the best quality. Environmental pollution is for sure another reason for the nowadays worther quality of flax and other naturally grown string materials.

I have done some strings with organically cultivated silk, hemp, ramie and nettle, same results.

Michael

Alan:

The Crim-Tatar horn insert I mentioned in my previous post is just such piece of horn you describe, similar to the arrow nock inserts. These inserts were used in the Tatar and Indo-Persian bows. As I said, not of much help.

Adam

Is not simple horn plates on sides enough?

From what it seems about the point of breakage, I don't think anything with a grain will be enough. Nor do I think it would wise to just put steel in the tip. The break would might just occur elsewhere.

Adam, Having though about it vaguely, and using the clue that Bede gives that the break must happen at the end of the shot, due to its nature. And using the fact that equally short (if not shorter) bows use Fastflight with less issue. It is likely then that the design of the bow is contributing to it's fail. I would suggest (timidly if anything) that as the string is released, it and the bow begin oscillating quite happily as the bow returns to brace height, but then, as the string lands on the string bridge, the string has changed. It is now effectively shorter, but it still wishes to continue vibrating, to the same degree. This it cannot do (also due to the steel-like quality you describe). The shortened nature of the string may lead to the bow's fail. This idea isn't really helpful, but if you wish to cure the ailment, it's nice to know why it's there.

I've not worked anything through on this yet, and shall see if I can make any sort up model up and out of it, though I doubt success (my modelling has never been brilliant). I'm not even confident about how the string does oscillate to begin with. Has Mr B.W.Kooi done any work on this?

Regards

Mike, what you say may be correct and more research has to be done. I do not recall if Kooi did any modelling of string vs limb stress etc, but he did find that the acceleration of the limbs was not smooth in the composites. The tension in the string is very high when the string "shortens" at brace, much higher than in the straight bows, even if the straight bows are short. Clearly, something has to give, either the string or the bow. By the way, the Turkish bows do not have bridges.

Adam

Ah, my mistake, by bridge I meant 'the place where the knot sits (or would sit) on the belly side of the bow'. My own replica has a shallow groove that is made from a block of wood. I was under the impression that 'string bridge' was synonymous to this.

Mike,
A "string bridge" is generally an applied leather, bone horn or wooden pieces that accepts the knot of the string on the belly of the bow. They have many different shapes, but rarely have any grooves.

Adam,
Have you had strings break at the loop except from abrasion?

Yes, I had several instances when the strings broke at the loop. One of them was a too thin loop made of silk. The other were linen and B50. The loops in old strings were very thick, at least as thick as the string itself - no doubt for durability.

Adam