Author Topic: Modern strings  (Read 7184 times)

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Offline DC

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Re: Modern strings
« Reply #30 on: March 31, 2019, 05:00:34 pm »
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.

Offline avcase

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Re: Modern strings
« Reply #31 on: March 31, 2019, 05:15:50 pm »
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.

Offline IrishJay

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Re: Modern strings
« Reply #32 on: March 31, 2019, 05:40:30 pm »
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.

"The best camouflage pattern is called, 'Sit down and be quiet!' Your grandpa hunted deer in a red plaid coat, think about that for a second." - Fred Bear

Offline DC

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Re: Modern strings
« Reply #33 on: March 31, 2019, 05:57:30 pm »
Now you have something to think about tonight, weird huh ;D ;D

Offline IrishJay

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Re: Modern strings
« Reply #34 on: March 31, 2019, 06:03:06 pm »
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
"The best camouflage pattern is called, 'Sit down and be quiet!' Your grandpa hunted deer in a red plaid coat, think about that for a second." - Fred Bear

Offline IrishJay

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Re: Modern strings
« Reply #35 on: March 31, 2019, 06:15:59 pm »
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.
"The best camouflage pattern is called, 'Sit down and be quiet!' Your grandpa hunted deer in a red plaid coat, think about that for a second." - Fred Bear

Offline osage outlaw

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Re: Modern strings
« Reply #36 on: March 31, 2019, 07:08:44 pm »
The brace tension is only 5 lbs?  Can you string the bow without flexing the limbs?  ???
I started out with nothin' and I still got most of it left

Offline IrishJay

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Re: Modern strings
« Reply #37 on: March 31, 2019, 07:34:57 pm »
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.
"The best camouflage pattern is called, 'Sit down and be quiet!' Your grandpa hunted deer in a red plaid coat, think about that for a second." - Fred Bear

Offline IrishJay

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Re: Modern strings
« Reply #38 on: March 31, 2019, 08:23:21 pm »
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
"The best camouflage pattern is called, 'Sit down and be quiet!' Your grandpa hunted deer in a red plaid coat, think about that for a second." - Fred Bear

Offline bradsmith2010

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Re: Modern strings
« Reply #39 on: March 31, 2019, 08:30:26 pm »
I always learn something ;)

Offline avcase

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Re: Modern strings
« Reply #40 on: April 01, 2019, 11:49:24 am »
I have run across statements like this many times
Quote
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


Offline willie

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Re: Modern strings
« Reply #41 on: April 01, 2019, 12:52:37 pm »
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.