String Stretch

Trenton G. · May 19, 2017, 10:19:00 PM

Hey guys. I've recently started making my own Flemish twist strings, but I've run into an issue with stretching. When I make a string, I usually make it just a bit short because I know that it will stretch. What I've found though after shooting a string and getting it to the desired brace height is that if I unstring the bow, then string it up in a few days, the string has shrunk back to the original length and the stretching process repeats itself. This is really frustrating since I can't get any consistency. Is there something that I'm doing wrong to cause this? Any help would be appreciated.

Mo_coon-catcher · May 20, 2017, 08:55:00 AM

Are you prestretchjng the string after twisting it up? I make mine out of 8 strands D97 and 2 strands B50 and I get about 1" of stretch Initially then it stays put. I stretch mine by putting a hickory dowel through each loop. I'll put one dowel under my feet and depending on the string length, I'll barace my hands on either my shoulders or head. And use my legs to push and stretch the string before I put it in the now for the first time. Probably putting a couple hundred points of force on the string.

Kyle

frank bullitt · May 20, 2017, 09:36:00 AM

Dacron, I'm guessing?

Leave the bow strung for a time, after shooting, if possible. Then check brace. Keep record. Check, adjust, if needed, shoot more. Until settles!

frank bullitt · May 20, 2017, 09:37:00 AM

Dacron, I'm guessing?

Leave the bow strung for a time, after shooting, if possible. Then check brace. Keep record. Check, adjust, if needed, shoot more. Until settles!

kevsuperg · May 20, 2017, 10:24:00 AM

I leave my shooting bows , 1 is B50, 1 is D97, strung all the time.
Once my brace is set ( adjust a couple times with B50) they never really change.
No reason to string and unstring your glass bow. Leave it strung
Also I make my B50 Flemish about 1/2 shorter than the usual 3-4 depending on bow to accommodate the stretch.
I also don't really prestretch my strings, just give a good pull to straighten everything out then string and adjust as needed.

LBR · May 20, 2017, 11:43:00 AM

That is the nature of polyester (dacron), and to a lesser degree other materials. I can put a dacron string on my stretcher and literally watch it contract once the load is removed (around 250#).

Easy solution, unless it's a self bow, is leave the bow strung. If it's a self bow, allow time for the bow to be strung a while and/or put several shots through it to let the string stretch back out.

DarrinG · May 20, 2017, 03:21:00 PM

I see the same thing a lot on the bow I have that I shoot B-50 on. I can shoot awhile, set the brace, shoot awhile and when finished, unstring. Several days later when I restring the bow, the brace is high again and it takes a few arrows through it to stretch back out to the correct brace height for the bow. I'm one of the guys who does not like to leave a bow strung when not shooting it every day. Just one of the downsides of B-50, but boy does it ever shoot quiet and smooth on my Martin/Howatt!

Trenton G. · May 20, 2017, 11:27:00 PM

Thanks for the input guys. I am not sure what the string material is. It was given to me by a guy who builds self bows that I met while on a camping trip. There isn't a label on the spools and I never thought to ask. I will try pre stretching them to see if that works. I don't really like leaving my bows strung either, mainly for storage purposes, but if that's what it takes, that's what I'll do.

LBR · May 21, 2017, 12:39:00 PM

For a selfbow guy, most likely it was Dacron (B-55 or B-50).

How many strands are in the string and what draw weight? More strands may help a little. Low strand count 100% HMPE strings (Dynaflight, 8125, 8190, etc.) will stretch/contract more, as will Dacron.

Trenton G. · May 21, 2017, 01:33:00 PM

I found it online and it's B50. The bow that I'm currently having issues with is a 62 pound longbow and the string has 14 strands.

David Mitchell · May 21, 2017, 04:06:00 PM

On my bows with Dacron strings, I just press down on the limb tips after I string up and get the little bit of stretch out. I can actually feel it.

LostNation_Larry · May 21, 2017, 09:50:00 PM

I've seen it happen. I like David Mitchell's suggestion.

frank bullitt · May 27, 2017, 10:01:00 AM

After reading these posts over, possible this might be a spool of artificial sinew, nylon?

I never understood all these "Stretchy" statements, in reference to dacron/polyester strings.

Trenton G. · May 27, 2017, 12:24:00 PM

QuoteOriginally posted by frank bullitt:
After reading these posts over, possible this might be a spool of artificial sinew, nylon?

I never understood all these "Stretchy" statements, in reference to dacron/polyester strings.

I figured out that it's B50.
I don't know if it's the string that stretches or the fact that I'm still new to making strings and possibly not doing it quite right.

LBR · May 27, 2017, 12:42:00 PM

It's the material. Polyester ("Dacron") stretches, and contracts. It stretches/creeps more in hot weather.

That was one of the main reasons for the invention of "Fast Flight". Less stretch/creep = better consistency and stability.

two4hooking · May 30, 2017, 08:52:00 AM

I shoot B50 and make my own strings. After reading Sagittarius and hearing about how Swinehart heated his bowstrings in the oven I got myself a little potpourri crock pot and melted my beeswax in it. When I make a new string I soak it in the hot beeswax for several minutes and then take it out of the wax and string up my bow hot. After rubbing excess wax away and after it cools I get very little / no stretch. Been doing it this way for several years now on quite a few strings. The wax really gets into the string and helps it last also.

ber643 · May 30, 2017, 09:38:00 AM

Makes sense to me. I've always folded a small piece of leather and really burnished the heck out of my Flemish Twist strings (back when my hand cramps didn't preclude me from making them). Seems like your method of heating the wax in might well be easier on the hands, and less work.

LBR · May 30, 2017, 11:51:00 AM

Pure bee's wax is as hard as a rock when it cools. Bow string material comes pre-waxed. The materials go through heat when the color is cooked on. Too much heat will damage the material.

May 30, 2017, 12:21:00 PM

Chad, how much is too much heat? Is there any data / documented experience available on bowstring failure using this method? I'll admit it's new to me but I have not tested nor read / heard anything contrary. I have not read the reference from where this experience was obtained either.

Perhaps, back then they may have experienced some painful failures, eh?

Rob DiStefano · May 30, 2017, 12:25:00 PM

I've been building bowstrings since the mid 1950's in both Flemish twist and endless styles, using linen initially before moving on to B36 and eventually on up to kevlar (bad stuff!!) and with today's HMPE.

"B50" is "Dacron". Both are trade names for "polyester" (i.e. - "polyET" or polyethylene terephthalate). Polyester and excessive heat are not things that go together well, and will change the properties of polyET. Saturating any bowstring material with any manner of "wax", be it natural (bees) or petro-chemical (oil resin) will do nothing to keep it from stretching under tension, which is the only way to get the material to take a "set".