Skinny fast flight strings W/padded loops on non fast flight bows?

[Bjorn]

Like Chad said...............the strings get the blame. Personally I have had 5 bows break over the years: 3 old bows with B 50 strings and 2 new bows rated for HMPE with 12 strand D97 strings.

[wingnut]

I conviced Rob to reopen this thread because I though that real world experience would come forward to give the new guys some guidance.

So I ask: Joe new Guy buys a Kodiak magnum at his local pawn shop.  No string so he goes too the archery shop and the kid behind the counter figures what length string he needs and asks FF or Dacron? The guy goes whats the diff?  The kid says FF is faster so he buys it.

Are you going to tell him here that it's ok to shoot it or to go back and get the dacron string?

That's my final post on this thread.

Mike

[Andy Cooper]

There goes Rob talking about those hemp strings again.  :cool:  

Geez, Bjorn, how do you release without flinching? I've had one bow break and it still kinda freaks me out. If it had happened 5 times, I'd have some sort of psychologic disorder...other than the one(s) I already have!  :D

[Rob DiStefano]

i reopened the thread, so c'mon guys, tell me your good (or bad) experiences with hmpe and old bows.  don't be shy, if yer using that stuff with yer old bow, let us know so we can steer clear of you on the shooting line.  

but do show us why you think it's ok, why it's a safe enough for you.

i'll tell ya where it's got me - i see a guy with an old bear or howatt or hoyt or whatever and i'll go outta my way to ask about the bowstring he's using and if i hear "fastflight" i stay far away from him when he's pulling that string.

as they say, ymmv.

[tecum-tha]

The effects can only been modeled in a dynamic Hydrocode software. This software is usually run by people in the automotive industry who do crash tests or other vibration induced design.
What would be real interesting is the failure mode of the failed bows, which was blamed on the low stretch string.
One failure mode was the "cutting" along the string groove into the limbs and splitting them.
This was clearly induced by less string area on less string groove bow material area resulting in higher pressures beeing induced locally into the bow. This led to cutting and grinding because of the abrasive nature of the material. By padding the loop, the traditional contact area size can be reinstated, preventing the described failure mode.
The effect of the lower stretch must be simulated in a hydrocode to investigate potential failure modes modeling the fiberglas,the gluelines and the wood. Especially important is the used glue type in the bows.
Epoxy does not equal epoxy. So there may be timeline when certain glue compositions where discontinued and others added. These glue compositions will influence the dynamic behavior of the sandwich profile. And not to forget: bow glass is already a composite system by itself, beeing influenced by the glasfiber and the glue matrix....

[smoke1953]

I just don't know enough about strings to enter in on this discussion but would like to learn. All the letter and number terminology has confused me the last few years(easier to do nowadays). I have a modern longbow(Northern Mist), a relatively older glass longbow may be 20 years old or so(Massie), and a wood composite, Ipe and elm(Newwwood). Where should I go to inform myself at my options or I'd take suggestions unless this is hijacking the thread then please excuse me.

[Rob DiStefano]

Originally posted by tecum-tha:
The effects can only been modeled in a dynamic Hydrocode software. This software is usually run by people in the automotive industry who do crash tests or other vibration induced design.
What would be real interesting is the failure mode of the failed bows, which was blamed on the low stretch string.
One failure mode was the "cutting" along the string groove into the limbs and splitting them.
This was clearly induced by less string area on less string groove bow material area resulting in higher pressures beeing induced locally into the bow. This led to cutting and grinding because of the abrasive nature of the material. By padding the loop, the traditional contact area size can be reinstated, preventing the described failure mode.
The effect of the lower stretch must be simulated in a hydrocode to investigate potential failure modes modeling the fiberglas,the gluelines and the wood. Especially important is the used glue type in the bows.
Epoxy does not equal epoxy. So there may be timeline when certain glue compositions where discontinued and others added. These glue compositions will influence the dynamic behavior of the sandwich profile. And not to forget: bow glass is already a composite system by itself, beeing influenced by the glasfiber and the glue matrix....

all well and good ONLY if someone steps up to the plate and does the proper testing, whatever that may be.  

until then, the reports of blown bows should be cause enuf to think twice about combining hmpe and old wood/glass bows.

[Rob DiStefano]

Originally posted by smoke1953:
I just don't know enough about strings to enter in on this discussion but would like to learn. All the letter and number terminology has confused me the last few years(easier to do nowadays). I have a modern longbow(Northern Mist), a relatively older glass longbow may be 20 years old or so(Massie), and a wood composite, Ipe and elm(Newwwood). Where should I go to inform myself at my options or I'd take suggestions unless this is hijacking the thread then please excuse me.

if you're unsure, and if at all possible, go back to the source (bowyer) and ask.  if that's not possible, and i were you, i'd stick with a dacron bowstring.

[Shawn Leonard]

But as Chad said, all these blown bows, were they gonna blow regardles of string material. I have seen a several bows blow up over the years and at least 3 of them were older bows using B-50 or a linen string. I also have seen a couple blow that were overlaid and set-up to shoot FF and they blew up too, ask Curt(Guru) about his bow that blew. It was of very modern design and he was shooting FF. Again I have to say if you pad the loops and di everything possible to prevent the string from cutting into the limb, add wool or moleskin or velcro in the string grooves and you want to attempt it, that is up to the person. Just use a thread like this to make an informed decision and listen to whatever makes ya feel safe. Shawn

[LBR]

Spot-on Shawn.  Bows break.  Anyone with any amount of "real world experience" knows this.  

To completely avoid the risk of having one break on you, the only 100% "safe" thing to do is never draw back a bow.  After that, avoid old bows and self bows, since they have the highest failure rate (regardless of the string used).  Then find out which bowyers have ever had a bow fail and avoid all of those.  Ooops....right back to step one, because anyone who's made any number of bows has had a failure.

What I'd like to do is find out if the string actually caused the failure, and why.  If we could pin that down, then we could possibly modify a string to avoid this.  

I don't have the means, equipment, or brains for such a test, but I'd sure be interested in the results if anyone were to do it.

Until then, I will continue to recommend (as I ALWAYS have) to stick with dacron on older bows.  As I've ALWAYS said on this topic, better safe than sorry.

However, until I see actual, verifiable proof, I cannot honestly say that I know a "FF" type string is detrimental to old bows.  I can just say that, in my opinion, it's not something I would do.  Too many great bows on the market to worry about what string I can use on a select few.

[Rob DiStefano]

almost all new stick bows (within the last 10 to 15 years or so, at the very least) are built to handle modern hmpe (High Modulous PolyEthylene) bowstring fiber.  hmpe is at least twice as strong (in terms of tensile strength), if not 3x as strong, as a comparable diameter strand of dacron (polyester) fiber.  i don't know what the precise measured difference of elasticity is between known diameters of hmpe and polyester, but it is significant.  12 strands of hmpe will have a tensile strength of at least 1200#, while 12 strands of polyester will have at best 600#.  but, and more importantly, hmpe will have far far less stretch than dacron.

"old bow" means a glass/wood composite bow that was built, for the most part, somewhere between the late 1940's and perhaps on to the late 1980's and early 1990's.  the type of fiberglass and resin epoxies used in those old bows, coupled with limb tips that have little or no substantial physical enhancing, were meant to be used with the best bowstring fiber available at those times - dacron (polyester).  

if you are unsure if a stick bow was built to handle hmpe bowstring fiber, and the bowyer/company is unavailable, you will be at a safety risk by using an hmpe bowstring.  why?  because people have witnessed these bows self destruct when used with hmpe bowstrings.  hearsay?  yes.  fact?  none documented on video that i know of.  

can anyone prove that hmpe is capable of blowing an old stick bow's limb(s)? no ... not unless it is tested using a shooting machine ... and even then, it may not blow immediately and may not blow for a thousand firings.  why?  i don't know.  it may have to do with bow design, the current state of the bow's materials, and other factors.

how could an hmpe string cause a perfectly good old bear bow in pristine condition to delam a limb tip?  these are some of the involved parameters - the condition and the materials used in the stick bow, the build and materials specific to the bow's limb tips, the diameter of the hmpe string loops, the weight of the arrow in regards to the bow's holding weight, the method of release.  

hmpe stretches very little as compared to polyester.  after release, as the bow attempts to return to brace height, the transmission (bowstring) delivers the stored limb energy to the vehicle (arrow).  if the arrow is too light, or if by other means it does not accept the transmitted energy, that energy is redirected via the transmission back to limbs - first at the tips - then to the riser.  high speed/slow motion videos show that in great detail.          

since there is much less elasticity with hmpe bowstrings, as the limbs return to brace height the abrupt stopping of the limbs terminates all the residual force to the bow's limb tips.  

my theory is that with dacron there is a fair amount of stretch and that allows the unused limb energy to flow back to the limbs, down to the riser and (perhaps) to the shooter's bow hand ... whereas with hmpe, it stops dead at the limb tips (because the non-elastic string will not allow the tips to significantly move forward) and the unused limb energy goes back into the string (ever notice the higher pitch that hmpe strings give on release?).  the pivot points for all this energy movement are the bow's limb tips.  they are the nodes that take the brunt of the released limb/string force.  they need to be significantly built up/beefed up for that task.

[robtattoo]

Well, I'm prepared to do some testing on this to put it to bed, once and for all.

If a bowyer, any bowyer, would be prepared to send me 2 identical, unused bows, NOT rated for HMPE strings, I will fit one with a B50 string & one with an HMPE string with padded loops & shoot identical arrows from each one.
I'll take one shot with each bow, continuously until either one of the bows gives out, or until I get sick of testing (say 100 arrows a day with each bow for 3 months)

Once I've done this I will return both bows to the bowyer.

If the HMPE strung bow survives the test, I'd call it fairly conclusive. If it dies, I'd also call it fairly conclusive.

How'd that be?

[Jeff Strubberg]

I don't have two identical bows, but I do have a bear recurve I'd dedicate to that kind of testing.

Rob D, I salute your caution.  I don't think anyone should be encouraged to make this kind of change without some serious testing on that particular bow platform.  Having said that, you have to throw out every one of the breaks you've see occur with kevlar.  You know that stuff was notorious both for cutting into bow limbs reinforced or not and for breaking under the string servings whenever the heck it felt like it.

[Rob DiStefano]

Originally posted by Jeff Strubberg:
....  Having said that, you have to throw out every one of the breaks you've see occur with kevlar.  You know that stuff was notorious both for cutting into bow limbs reinforced or not and for breaking under the string servings whenever the heck it felt like it.

right, kevlar bowstrings (if you could even find any today, and i hope no one can) have nothing to directly do with this topic.  my prior posted references to kevlar were strictly for the effect of a blown bow and nothing more.

[smoke1953]

Rob, you're helping my learning curve even if some may be theory.

[Shawn Leonard]

Robtattoo, I believe you may have to take other steps too, like wrap the string ends in biwhush or heavy wool yard, velcro in the string groove, as to proper steps to be taken I have no clue but agree with Chad as I stated earlier. Use at you and your bows own risk and know the possibility exist that a bow may expode. Look at Bob Lees older bows I am talking from 15 years ago, they were not rated for FF but man I shot a bunch of those bows with every kind of string there is and never had a problem. Same with a Schaffer I owned for a couple years. I will say if you are gonna try FF on a bow, know the risks and try to minimize them the best ya can if ya can for safties sake. Shawn

[tecum-tha]

Chad is spot on with saying there is no such thing as hard evidence the bowstring material was the culprit, why the bow failed.
In my post I described one known and evident failure mode of a bow using a very thin and highly abrasive string material.
Result: We should pad our loops to adequate strand counts to resemble the same diameter string than once before. Hemp string material is much less stretchy than dacron, but since its tensile strength was less than dacron, a thicker string was used spreading the forces out into a bigger local area at the bow nocks.
In soft yew wood english longbows, horn nocks where used, because of horns ability to withstand higher pressures and probably failures by splitting limbs from down the nocks.

Bow profiles: Obviously a multitude of risers failed over time, because they were cut to center or even past center. The bowyers did not think about a bow mechanically, but in matters of balance, beauty and mostly arrow clearance.
This can lead to additional forces in the riser cross section not accounted for by the bowyer. Reason: the shear center of the cross section  is no longer close enough to the centroid, inducing torsion strain additional to the bending stress.
Nice little graphical description:
 http://www.mcadcentral.com/proe/forum/forum_posts.asp?TID=38317

thread of bimbo666

Most bowyers are not engineers and do not calculate their bow designs. Even if one calculates a bow design, it is usually not done using dynamic hydrocode modeling. Way to expensive. The software alone is $15000 per year and you need a specially trained operator who knows what he does.

Old bow risers: A lot of old bow from the late 50ies to the late 60ies were using a very field bow like sight window. Long and slender and prone to torsional problems. But most bows during this time were of low to moderate weight, mostly probably in the 40-45# area. The heavier a bow gets, the more will the riser area get stressed. If you get higher in draw weight without reinforcing your riser, it will sooner or later break.
This is especially true for wooden risers, because wood is an inhomogenious (natural) material.
There is a reason why modern risers are made from metal, thin laminated and/or pressure-resin impregnated woods. The material is made more homogenious and thus is less prone to local failure.

For all the people who had failures:
Could you describe the failure mode of the bow, that failed? Especially the modern low stretch rated bows? But also older bows which failed no matter what the string material was?

[LBR]

Sounds like we are getting somewhere.

Just to be clear, I have no doubt there havs been old bows delam with HMPE strings.  My point is there's been a ton of old bows delam with dacron strings--I've got first-hand experience with this.  I have a brand-new bow in my shop (not one I sold, or even bought) that de-lamed the first time it was drawn to anchor.

What caused the failures?  As I said before, a FF type string has always been the scapegoat if that was the string on the bow.  If not, then it's "something else".  I've yet to see any proof of this, and being a string nut, this bothers me.  It wasn't that many years ago that several folks were proclaiming that FF strings would shorten the life of any bow.

The lack of stretch/creep may be a factor, BUT....there's at least one "primitive" string material that is similar to the HMPE materials for lack of stretch/creep.  Off the top of my head I can't remember which one it is....silk, I think?  Anyhow, I've never heard it blamed for breaking bows.

Erring to the side of caution is a good idea, IMO.  I won't recommend tiny strings for that reason--I've had too many reports of disasters due to them, but I won't berate someone for liking them.

I like the test ideas and volunteers, but if I had a choice I'd take it further.  If a particular string shortens the life of one bow, will it shorten the life of the rest?  Reason says it should.  If it will shorten the life of a bow, how much and why?  Is there anything that can be done to fix the problem?

I'm just a stickler for details, at least on this subject.  Seeing/hearing tons of erroneous statements over the years has made me a bit of a skeptic.

Now you guys have gone and made me nervous, so I made a Dacron to go on my Pete George that had a fast flight. I could see no nock damage on it yet. I have a Hill that does not have the end cap, just the wedge, that I have a padded fast flight.  It is 68" long and I draw it to 58@ a 26 plus draw.  Should I be concerned about that one too? The Pete George Yew fiberglass bow has no more hand shock with my B50 than it did with the FF, it may be a couple of FPS slower, but not enough that I can tell.

[Jeff Strubberg]

Seems like linen is very low stretch, but it's also very large as far as fibers go, and linen strings are usually of a huge diameter.