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Message started by jlasud on Feb 9th, 2013 at 3:00am

Title: Crossbow string
Post by jlasud on Feb 9th, 2013 at 3:00am
Can't seem to find much info on how many strings of Dacron one needs for a 170 lb crossbow with a steel prod.
I found two references,one mentioning 48,the other 50 strands,both mentioned by some guys on a forum.
Can anyone here,help me answer this question? Are these info's i found correct?

Title: Re: Crossbow string
Post by David Morningstar on Feb 9th, 2013 at 6:12am

http://paleoplanet69529.yuku.com/topic/6208#.URYuD6U03wg

Title: Re: Crossbow string
Post by jlasud on Feb 9th, 2013 at 9:28am
Thanks! Quite a wide range of numbers used for the same bow strength.
"my" bowyer made me a 20 strand string,which lasted a surprising ~10 shots before it broke,even though more like 50 strands would have been needed.
This shows that Dacron can take some punishment before breaking.
Even to my unexperienced eye the string was skinny,but i said to myself,the bowyer must know his job.
Luckily he said,that hes going to make me a 50 strand string,without additional payment.
And i got to braid a Dacron release cord from the broken string,and the string didn't even slap me in the face as it broke so it's all cool :)

Title: Re: Crossbow string
Post by Thomas on Feb 9th, 2013 at 11:17am
jlasud

Pretty sure you already know that traditional crossbows use an endless string which means continuous loops are wound around two spaced pins until you get the required number of strands. The beginning and the end of the string having previously been tied off to the side are then over lapped and then overlaid by the nock serving on one end. This means the end loops contain only half the number of strands.

Because the payload of my 100# “single string” bullet crossbow is only 12 grams I have 52 strands of B50 or 26 on the nock loops. The nock serving is braided spectra overlaid with cotton coxcombing. All of this may sound like overkill but I have got at least 2500 shots off this string.

Tom      

Title: Re: Crossbow string
Post by Mauro Fiorentini on Feb 11th, 2013 at 1:14pm
Topic added to the PW Index!
Greetings,
Mauro.

Title: Re: Crossbow string
Post by Bill Skinner on Feb 11th, 2013 at 6:58pm
For a bow, you want the string to have a minimum of EIGHT times the draw weight, that means if the bow draws 50 pounds, the string should have a breaking strength of 400 pounds, minimum.  This is at the weakest point, usually where the string touches the limbs.  So, a 50 strand string for a crossbow means it has 50 strands at the nock on the limb, 100 strands where the bolt rests.  I don't know if a "Flemish" string can be used on a crossbow, if it can, it should solve your problems.  And, FWIW, Flemish twisted strings are used on English longbows that pull the same as your crossbow.  

Title: Re: Crossbow string
Post by squirrelslinger on Feb 12th, 2013 at 3:27pm

Mauro Fiorentini wrote on Feb 11th, 2013 at 1:14pm:
Topic added to the PW Index!
Greetings,
Mauro.

What? Dacron and Spectra are now primitive? what plant/animal/mineral do i get them?
-Squirrel

Title: Re: Crossbow string
Post by Masiakasaurus on Feb 12th, 2013 at 4:17pm
They are "primitive," defined in webster's as closely approximating an early ancestral type or being little evolved. Nobody said anything about ancient, traditional, or historically accurate. That's why we talk about steel knives and rubber banded slingshots here, too.

Title: Re: Crossbow string
Post by Dan on Feb 12th, 2013 at 6:23pm

squirrelslinger wrote on Feb 12th, 2013 at 3:27pm:

Mauro Fiorentini wrote on Feb 11th, 2013 at 1:14pm:
Topic added to the PW Index!
Greetings,
Mauro.

What? Dacron and Spectra are now primitive? what plant/animal/mineral do i get them?
-Squirrel


You can get the them from plants and animals that have been underground for awhile and have turned into petroleum.  ;)


One of my youth leaders said "Everyone is purist to a certain extent".

He said his space age compound was traditional... in comparison to the xbows that most of the other guys in the family competion were using.

As primitve weaponeers, sometimes we expieriment with some of the newer stuff as well.  :)

Title: Re: Crossbow string
Post by Bill Skinner on Feb 12th, 2013 at 9:45pm
If it will make you feel better, silk is very close to B50, it stretches until it stabilizes, you need more strands and it is waterproof.  If you want something like Spectra or Kevlar, use linen.  High quality linen does not stretch, even when wet.  It will rot, unlike the modern materials.  FWIW, good linen thread of the proper diameter and strength is hard to come by in England and almost impossible to find in North America, and that's more countries than the US. ;D

The English Warbow Society allows Fastflite strings, mostly because a broken string on a warbow usually means large pieces of wood flying in all directions at a pretty good velocity.  Pretty much everything else has to match what was available to the archers of the time, with a few exceptions that are classed as modern warbows.  That means a selfbow made of certain woods, horn nocks on the bows, geese feathers on the arrows and forged points that match a historical point type.  Turkey feathers were rather grudgingly added not too long ago.  

Title: Re: Crossbow string
Post by jlasud on Feb 15th, 2013 at 10:38am
Thanks guys! I'll post a pic when the new string will be ready,and installed. Hopefully it'll last.
Thomas,better to be overkill than underkill. And for sure 12 grams ammo,is a bit too lightweight.
I used 21-27g bolts,and i want to try ~35g bolts to see which weight is ideal.
21-27grams fly like bullets,well more like lead glans. :)

Title: Re: Crossbow string
Post by Thomas on Feb 16th, 2013 at 12:51am

jlasud wrote on Feb 15th, 2013 at 10:38am:
Thanks guys! I'll post a pic when the new string will be ready,and installed. Hopefully it'll last.
Thomas,better to be overkill than underkill. And for sure 12 grams ammo,is a bit too lightweight.
I used 21-27g bolts,and i want to try ~35g bolts to see which weight is ideal.
21-27grams fly like bullets,well more like lead glans. :)


Jlasud

When I said 12 gram payload I was referring to 3.4 grams for a 9.5mm (.375”) steel ball bearing plus the 9 gram shuttle on the bowstring that holds the ball for firing. This crossbow has been dry fired several times thanks to the tiny ammo escaping just before the trigger pull.

Tom


Title: Re: Crossbow string
Post by jlasud on Feb 16th, 2013 at 2:45am
I see.Have you tried heavier ammo? If not,try it. Maybe  cast lead bbs.
I got the point that your string is plenty strong for it's draw weight.

Title: Re: Crossbow string
Post by Thomas on Feb 16th, 2013 at 8:30pm

jlasud wrote on Feb 16th, 2013 at 2:45am:
I see.Have you tried heavier ammo? If not,try it. Maybe  cast lead bbs.
I got the point that your string is plenty strong for it's draw weight.


jlasud

I started with .400” lead balls (6 grams), 100 for $12 U.S. but they deformed easy and made accuracy testing futile. The steel ball bearings were $7 U.S. for 250 and are easily recovered from my target stand which has some scrap carpet hung inside.

My son David and I had an impromptu shooting match today and we both managed to place some shots through previous holes, (well slightly enlarged) at just under 10m, it is good cheap fun.

Tom      

Title: Re: Crossbow string
Post by jlasud on Feb 19th, 2013 at 12:39am
it sure is fun! from the few shots i got from the first ,weak string,i experienced a crossbows accuracy. Point and click.
Something magical for someone practicing slinging and archery :)
The new string made of 50 strands of dacron is ready and today i'll get the bastard string and install it.
This week some time i'll be back with some pics.
Long ago I also made a slide for ball ammo.I'll try that too.
A pic of the slider you use,would be nice ;)

Title: Re: Crossbow string
Post by squirrelslinger on Feb 19th, 2013 at 7:52pm
I love crossbow accuracy, but I hate the loading time and diffuculty.

Title: Re: Crossbow string
Post by Thomas on Feb 19th, 2013 at 7:59pm
jlassud

My shuttle “slider” design has gone through more than six revisions but the big accuracy breakthrough was the groove shape shown in pictures. This newest shuttle is made of uhmwpe and allows it and the string to be easily separated. The same material is used on the pressure pad at the top which keeps the shuttle from buckling before release. Another helpful feature which helped in my experiments is the replaceable groove track which is attached with spray adhesive. The track shown is of $1.50 rosewood cutoff from a local supplier.
     

SLIDE_AND_TRACK_008.jpg (240 KB | )

Title: Re: Crossbow string
Post by Thomas on Feb 19th, 2013 at 8:08pm

View of track profile      
SLIDE_AND_TRACK_005.jpg (253 KB | )

Title: Re: Crossbow string
Post by Thomas on Feb 19th, 2013 at 8:21pm
The release pin is at the far left in the slot. In other words the actual release hook “nut” is about 25mm behind the string. The steel ball projectile is seated in a 90deg cone at the right side.          
SLIDE_AND_TRACK_016_001.jpg (245 KB | )

Title: Re: Crossbow string
Post by squirrelslinger on Feb 20th, 2013 at 3:24pm
Dude. I love that thing. How did you make it? machined it? It looks VERY cool.

Title: Re: Crossbow string
Post by Thomas on Feb 20th, 2013 at 6:21pm
squirrelslinger

Other than a drill press for the holes, commercial bolts, dowel pins and steel plate
every thing else is hand done. The red item activates a magnetic auto safety. The stock “tiller” will not be shaped and finished until the tinkering is done. Lock was designed on a $28 Win 95 2d cad. By the way the steel bow “prod” is from Alchem.

Tom        

innercase.jpg (346 KB | )

Title: Re: Crossbow string
Post by jlasud on Feb 21st, 2013 at 3:19pm
Wow,serious piece of hardware,and workmanship!
I played around with my new toy,and i also used ~1" pieces of 1/2" thick dowel and put a 18g(bit more than half ounce) lead balls in from of them. The piece of dowel acted as a sabot,and i could shot like this,without any modification to the xbow.
I was building this,i though,i'm going to make a regular medieval crossbow,rather than a stone bow because with a sled i can shot bolts and ball ammo too.
Nyilpuska_002.jpg (86 KB | )

Title: Re: Crossbow string
Post by jlasud on Feb 21st, 2013 at 3:20pm
Loaded.
Nyilpuska_003.jpg (88 KB | )

Title: Re: Crossbow string
Post by squirrelslinger on Feb 21st, 2013 at 5:22pm
Coolio! I now own a small 50 pound pistol crossbow, can put a 10 gram plastic bolt(with a metal tip ;)) through 1/4th plywood easily. Who said they were weak???
They penetrate my target deeper than arrows, and given the shafts are close to the same size (arrows a bit bigger) the darts MUST be moving faster to match penetration.
I am going to make some wood ones tonight, my cut-down 8 gram POC shafts will also penetrate, with no point of fletch.
-Squirrel

Title: Re: Crossbow string
Post by jlasud on Feb 22nd, 2013 at 10:31am
The above one is ~170#

Title: Re: Crossbow string
Post by squirrelslinger on Feb 24th, 2013 at 9:06pm
Nice. I wound up using edited bamboo skewers( under 1 cent each:)) for me darts, clocked (by shooting alongside of an arrow of known FPS from my uncle's gun-testing assembly) at about >200 fps. the darts weigh less than 3 grams.
-Squirrel

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