? for the skinny string experts

[Rob DiStefano]

while perhaps, maybe, there is some merit, on some bows, for using hmpe bowstrings, to me it's worse than playing russian roulette, and for me and my family's sake i don't wanna take a chance that i'm not feelin' lucky.

i'm just saying that there have been countless reports of old(er) bows failing with hmpe bpwstrings.  these aren't bad bows either, they were good, well functioning bows to begin with and the introduction of a dyneema string blew off limb tips.

so i'm saying this to all - be really care if you feel the urge to test out hmpe bowstrings on bows that are not at all rated for low stretch, low creep bowstrings.

i see a lotta mentioning here of bcy formula 8125 string fiber.  that's the same dyneema blend fiber as dynflight'97 and dyneema'02, only half the diameter.  why?  it was made specifically for use with recurves for a higher strand count to allow the string to be better 'rounded off'.  a strand of that f8125 is still gonna be around 50% stronger than b50 or b500 dacron.  btw, the median diameter of b50/b500 is the same as df'97 and d'02.

[George D. Stout]

JC,  I have a lot of respect for Rob, and many others here.  However, there has been no meaningful tests on older bows, so the point is moot until that happens.  We can opine all day, all week, all year, and it doesn't get past the opinion stage.  I've been at this going on 46 years and have opinions also....and they are just like everyone elses opinions.

That said, I'm doing my own tests, at my own direction, to prove one way or another that there is merit...or there isn't...as to the fragility of old bows versus new strings.  No one has shown by doing that there will be dire straits ahead.

Confusion is a product of the lack of legitimate information.  My old Shakespeare, for one, has only Wenge overlays on the tips, and has shoot over 2000 arrows with a 6 strand 450+ string.  What I'm finding...so far...is a mild mannered bow that is shooting better than ever...less vibration, quicker on the shot, and as quiet as any string material I ever used.

I have a 61' Bear Polar, that has three layer fiberglass tip overlays....it is shooting the same string material and is much quieter and better behaved than with a 12 strand dacron.  Enough of the guesstimates on old versus new...show me the numbers..show me the tests done to prove/disprove.

If I have issues with any of these bows, I will post such outcomes....my skin is pretty thick and I can admit failure if it comes.  As of this point, 1/15/2010, I'm not expecting the need to report failure.  Your mileage may vary of course, but at this point talk is only talk...we must have proper findings...that's what I'm doing.  And remember, I was a hard-headed, dacron-only, kind of guy for decades.  

And a final disclaimer for those who don't read complete posts/threads:  This is not a suggestion for you to start putting low stretch strings on your old bows....So don't do it unless you are satisfied you want to try it.  It's a personal decision to try something new; I don't have a lot invested in those old bows and feel it is worth the effort.

[Terry Green]

Originally posted by kybowman:
Wow.  
Now I'm really confused.            

Yes it can be. Unfortunately it is ever increasing the néed to separate the wheat from the chaff on Internet forums. You need to ask more specific questions and pay attention to decifer the Truly knowledgable and experienced from the keyboard cowboys with their bandwidth rodeos.

[artifaker1]

8125 is 92% SK75 and 8% SK65 for some reason. It is rated at nearly the same strength as D97 (latest I seen; 120lbs for 8125) and is noticeably smaller than D97.
And once again the stretch rates for SK75 off of the rope web sites show very small rates in my above posts. Virtually none. It is an anti stretch material for sure.

[JC]

George, I get where you are coming from. Actually, I'm really surprised to hear you trying it out...kudos to you for experimenting, always something to learn. First carbon arrows, now skinny strings...before you know it you'll have carbon/foam limbs and be wearing synthetic camo        

My point is, you can experiment all day, you can "prove" something up one side and down the other, and one instance of "anecdotal evidence" can totally disprove to an individual all your "proof". There is no way to accurately test to the point where you can be assured it will not hurt older bows...just as there is no way to prove it will hurt old bows. But it doesn't matter one bit either way if it's my bow that blows up because I took someone's advice and tried a string that at best, has had a substantial history of breaking other vintage bows. That's all I'm trying to prevent and I believe Rob's intention as well. 6 million guys shooting ff on vintage bows does not erase the two I lost. Knowing what I know now, the potential gain, in my opinion, was not worth the risk of me losing the bow. It's as simple as that for me but as you said, your mileage may vary.

The opposite side of the coin is skinny strings on modern bows. Ron LaClair and others have used them for quite some time with great longevity in bows. I switched some time ago when it first started to grow in popularity but only through my own testing and proof. So far, with no failures I'm very happy with the benefits, mainly reduced noise. The increased speed was a nice side benefit but not enough to really make a difference outside of a chronograph. But I changed only because the risk of permanent bow damage due to string failure is greatly reduced because it's a "modern bow." If I thought for one second it would hurt my beloved Morrison in any fashion, I'd go back to whatever string was historically "safe" simply because the proven (minimal) gain would not be worth risking the loss.

[Jeff Strubberg]

Originally posted by Rob DiStefano:
 

Originally posted by Jeff Strubberg:
 

Originally posted by bearbowman:
Those skinny D-97 will shoot on an old bow but padded loops or not you are gonna rattle those old bows apart. The real issue was the glues used back in the day. They were nothing like the glues today.
Sure if you pad the loops really well the tips should be fine but that is not the real issue with the low stretch string. Why do you think Bob Lee fought tooth and nail before they finally went to FF strings? Because the whole world was using them and they had to bite the bullet. 4 or 5 years ago Bob Lee would not warrant a bow that had FF on it.

Actually, making a bow more efficient (like lowering string weight)reduces vibration.  Less moving mass means less oscillating mass, which means less strain on the bow after the arrow has left. [/b]

i don't think vibration, or lack thereof, is the issue - imo, it's the fact that hmpe strings just don't stretch/give anywhere near the stretch factor of dacron.  if the limb tips on any bow can't absorb that shock, they'll blow off.  

i saw that back in the 70's with kevlar low stretch strings - oooo, that was nasty! [/b]

Agreed.  That wasn't the misconception I was trying to correct, though...

you are gonna rattle those old bows apart

Vibration isn't the problem with old bows using modern materials, because vibration is actually reduced with fast flight materials.  It's that really quick stop at the end that gets 'em!

I'd also submit that the way bow tips are cut and shaped is as much of a problem as what materials and glues are used.  I've seen self bows shoot fast flight with no problems when the string grooves and tip mass were cut to allow it.

[DCM]

http://www.answers.com/topic/rope-stretch    

I sincerely hope folks will invest the time it takes to at least entertain this argument.  It's not practical to test bows to failure, obviously, so the practical way is to at least test the argument that FastFlight can be used in a way that is indistinquishable from Dacron in terms of the strings working properties.  One must accept the premise that laws of physics apply the same in each case, which would be hard to argue against in my view.  I'm paraphrasing from the URL above for clarity.

The argument hinges upon this factor:

"Nylon stretches about 10 to 15 percent under a load equal to 30 percent its breaking strength..."

It stretchs as a constant factor (30%) of it's breaking strenght.

"Dacron... stretches only about 3.5 to 5 percent under the same conditions... Spectra stretch about 1 to 2 percent"

They all stretch 30% of breaking strenght.

   http://en.wikipedia.org/wiki/Bow_string    

So if Dacron has roughly 1/2 the strenght per strand of FastFlight then the strand count comparison would be about 10:5.  So a 10 strand B50 would stretch roughly the same as a 5 strand FF.  Honestly I don't trust Wiki here, I can only cite from memory but I think it's more like 40# for Dacron and 100# for FF.

I'm not suggesting these numbers can't be argued one way or the other.  Only that given this premise: both materials stretch as a constant factor (30%) of it's breaking strenght, comparable strings can be fashioned.

Now, if you compensate string mass difference by increasing arrow mass, and make the loops the same diameter, how is the bow going to know any different?

You may ask, why would you want this?  My answer is, it means I can shoot a heavier arrow with ZERO penalty.

Also, lower mass string on a bow is actually better for the bow than a heavier one, if no extra engery is left in the bow by compensating with arrow mass as described above.  What makes bow limbs flex at the bottom of the power stroke is the energy left in the bow, by ITS moving parts, both limbs and string.  When you have low mass limbs and string, you have less energy and so less stress on the bow as it has to vibrate off this energy.

I'm not trying to be butthead here.  I know I use provocative language.  But I think if folks would just stop and think this through some would see it differently.  I honestly don't care what kind of strings you use, I just think it's important to be faithful to the underlying science in ones advocacy, in all things.  And the burden generally is accepted to fall upon the declarer, in this case the supposition that "FF will break yer bow."  Absolutely it CAN, but not if applied to the task in an all else equal ratio.  And I also agree bow limb/string groove design is a factor.  But only in the sense some designs are stronger than others.  If you have a weak design (like an old Ben Pearon with no overlays at all), then apply a weaker (FastFlight) string, and compensate with much higher arrow mass.

[Rob DiStefano]

dcm, i know from whence you come, and i believe i understand where yer going.

the one common denominator in all cases is the string fiber and its associated empirical data.  them's the hard facts.  

the loose canon in all of this is the bow and the archer.  

i do believe there are instances where hmpe will work on bows that don't have the 'fast flight certificate of approval'.  the question then becomes, 'you feelin' lucky?'  umm, no thanx, not a chance i wanna take.  ymmv.

[onewhohasfun]

I will remain neutral in this discussion. But if you have ever removed the tips on an old bear as per Bowdocs Restoration 101 thread, You will be able to see that the lack of glue on these tips certainly does not help the situation. 20% of surface contact with glue is not uncommon. Bow doc recommends replacing tips even when using a  dacron string.

[DCM]

Rob I'd hoped we'd achieve just about what you spoke.  I reget only the part of that concept that includes from my pov an element of randomness or luck.  And admittedly in some cases the most practical choice is B50, absolutely.

[George D. Stout]

Most issues with the old Bear's you speak of are with the old micarta tips, not the fiberglass overlays more common after 1959.

As I said, everything we talk about here is just talk.  It's good fodder for getting the hair-covered computer going, but it's like running with paper scissors.....doesn't mean too much.

Rather than waste any more brain cells, and having to ingest more Omega 3's, I'm finding out myself.  That said, I still can't give you a definitive answer for another couple thousand shots, and that will take awhile 8^).  

As far as feelin' lucky Rob, I don't do well on lottery tickets; probably more like the little guy in Peanuts who has the cloud over him all the time 8^).  But I digress......on with the program...tune in for future information.  I will post photos of the limb tips imbedded in my navel or other body part if and when my old bows bite the dust.  Heck....maybe I am feelin' lucky.
No use doing something stupid if you don't let everyone in on it.    

[Rob DiStefano]

give 'em heck, george!  :D

[LittleBen]

Bringing this back from the grave against my better judgement. Since everyone ahs an opinion and no one wants to hear mine, I'll just give a status update on my situation.

I tried a 14 strand 8125 string on a ~1969 york tunderbolt that had walnut and hard maple overlays. The string began literally chewing and splintering the bottom limb tip overlays within 10 shots. The top limb tip remained fine. I believe the issue was a poorly cut string groove that created unnecessary pressure points; the string wasn't sitting in the groove well.

Those overlays got filed off and replaced with 2 layers of 1/16" phenolic, and string grooves cut in properly.

No problems for ~2-300 shots. I don't anticipate issues. Bow tuned to same arrows at a brace height of 7.5" instead of 8.5".

Thats all the data so I'll stop there.

[Rob DiStefano]

littleben, what style of string - flemish or endless?  ....

[LittleBen]

flemish, I lack an endless string jig.

Just to add to the fun, I have another nearly identical (49# vs 50#) 1973 york thunderbolt that is in the process of being refinished with phenolic overlays also, and will get a 6 or 8 strang 8125 string ... haven't decided yet.

Maybe if I get fiesty I will do the actual math on some of this string stretch guesswork and try to estimate the %elongation of each string type under normal shooting conditions.

[Rob DiStefano]

as i suspected.  adding to the gamble of hmpe on such an old bow, with its old glass, i suspect the  lack of dacron served loops did you in ... or rather, did your bow's limb in.  almost ALL commercial trad bows of those 50's 60's 70's and even 80's eras used endless bowstrings.  flemish strings weren't the norm at all, and scarce as hen's teeth.   :D

[LittleBen]

I got that feeling too Rob. Actually, I used to have a dacron flemish string on the later bow (the 1973) and had not problems. But as anyone who's used it knows, when HMPE is under alot of tension it gets ridiculously hard, like wire. I think it was that really hard lumpy surface of the flemish string which added to the problem of bad nock grooves and cause extreme pressure points ... I mean, what's the shear strength of hard maple? it's alot of force I can tell you that, and little pieces of grain were literally getting sheared off.

Anyone, I got some quick info on the modulus (stiffness) of dacron (polyethylene terepthalate) and dyneems (UHMWPE or HMPE).

The tensile modulus of Polyethylene terephthalate is roughly 2.8-3.1 GPa according to wikipedia.

The tensile modulus of HMPE is above 116GPa according to EuroFibers supply.

That means that for two strings of equal diameter, one dacron, and one HMPE, the HMPE string will only stretch 1/40th as much as the dacron string (we're not talking about creep but just the elastic stretching of the string)

So in order to have the same amount of stretch (i.e. % elongation) the HMPE string would have to be roughly 1/6th the diameter of the dacron string.

Lets do the same math assuming the stiffness of dacron is actually 5x the number given by wikipedia. In this case, the HMPE string of equal diameter stretches 1/8th as much as the dacron string, and a HMPE string would ahve to be slightly bigger than 1/3rd (~1/2.8) the diameter of the dacron string to equal the stretch at a given load.

Long story short, unless the numbers I've got for the dacron are way off, even a skinny string of HMPE is much stiffer than a dacron string.

Thats not to say there's no merit to the position that a skinny string is safer than a full diameter strign of HMPE, it's just the math. Take it for what it's worth.

[Bjorn]

Ben It is interesting that you bring up the change in brace height. Jay St. Charles told me to expect lowering the BH about an inch on one of his bows when switching to an FF type string.
I tested the braking strength of single strands several years ago and found it was about half of what the manufacturer was reporting in every case. More recently some manufacturers have stopped publishing those numbers altogether.  

[LittleBen]

Breaking strength is a risky game when it comes to threads. Since a single "strand" of bowstring is actually a single ply bundle of many many strands, alot of factors can influence the results. Not the least of which being test methods .. also twist, temperature, elongation rate, history of elongation of the material.

It is interesting to note that the published numbers may not be what you see in real life. I think I heard someone also say that the strength can be reduced by as much as 40% when the fibers are bent, or in any way loaded other than perfectly in tension.

[LittleBen]

Just calculated the diameter of 8125 and dacron and determined that according the the numbers I have for modulus, a 6 strand 8125 string is approximately 4.5x stiffer than a 12 strand B-50 string, meaning the dacron stretches by 4.5x as much.

So long story short, if skinny strings are safe on old bows, it's got to do with more than just the stiffness.

(dacron vs FF, dacron vs 8125, skinny strings on old bows, skinny strings on vintage bows, B50 vs 8125, stiffness of skinny string, stretch of skinny string)