[brittonc82]

I am going to start building strings for my bows. I'm a little unsure about a few things. When you put twists in the string it has to shorten the length, so do you build it a little longer to start with? And how do you pre-tension the string? Any help would be appreciated. I will be using BCY 452x string

 

[rick prather]

Finished string length times .75= # of twists needed. # of twists times .0125 = amount to add to length before twists.
The pre-tension should be done before serving and be done on a stretcher.

 

[broadheadnut]

I take the finished string length and multiply by .01. That gives you how much to add to the string. Then take your finished length and divide by 1.2 to get your twist count

 

[Ray knight]

Finished string length times .75= # of twists needed. # of twists times .0125 = amount to add to length before twists.
The pre-tension should be done before serving and be done on a stretcher.

What material do you normally use? Thats quite a bit off from where i build most modern materials at 24 strands. 60" String i would set at 60.5" and 39.5 twists. On your formula you would set the jig at 60 9/16" and 45 twists. So only 1/16" longer jig setting but 5.5 more twists. Seems like it may come out a bit short with most newer materials? To add confusion - you need to compensate for strand count (higher strand counts will shrink more from twisting) and material. Stiffer materials will need the jig set longer or less twists. Fun right!!!

 

[nuts&bolts]

I am going to start building strings for my bows. I'm a little unsure about a few things. When you put twists in the string it has to shorten the length, so do you build it a little longer to start with? And how do you pre-tension the string? Any help would be appreciated. I will be using BCY 452x string

10 foot length of unistrut or super strut electrical channel.

BCY Micro Stretcher.








or draw board and a spring scale.





I use a 300 lb VIKING scale, to read up to 300 lbs.


I have a S beam load cell
and digital readout that I need to wire up
for LAB grade accuracy.

 

[dwagoner]

What material do you normally use? Thats quite a bit off from where i build most modern materials at 24 strands. 60" String i would set at 60.5" and 39.5 twists. On your formula you would set the jig at 60 9/16" and 45 twists. So only 1/16" longer jig setting but 5.5 more twists. Seems like it may come out a bit short with most newer materials? To add confusion - you need to compensate for strand count (higher strand counts will shrink more from twisting) and material. Stiffer materials will need the jig set longer or less twists. Fun right!!!

his formula is used alot for 1.33 ratios...... thats the basic for that rate

Finished string length times .75= # of twists needed. # of twists times .0125 = amount to add to length before twists.
The pre-tension should be done before serving and be done on a stretcher.

 

[bigkuntry72]

10 foot length of unistrut or super strut electrical channel.

BCY Micro Stretcher.

What is this one Alan and how do you know the tension?? We have one at work that we use just for redoing crossbow center servings??

 

[nuts&bolts]

What is this one Alan and how do you know the tension?? We have one at work that we use just for redoing crossbow center servings??

This is the BCY micro stretcher.

I use a spring scale.

Some folks use a DIE compression spring,
and read how much the spring is compressed,
after calibrating the "squeeze amount of the spring" to a linear spring scale.

So,
if you use a draw board (boat winch) and hook up the compression spring,
and you squeeze the compression spring say 1/2-inch,
and the inline VIKING spring scale says that you are squeezing the compression spring 300 lbs,
now you know that when you squeeze the DIE Compression Spring 1/2-inch less than the full size length,
you have 300 lbs.

 

[dwagoner]

What is this one Alan and how do you know the tension?? We have one at work that we use just for redoing crossbow center servings??

micro stretcher is weak.....look at the angle of the bars. its not sturdy at all......no supports.....you can bend that easily......

 

[carlielos]

micro stretcher is weak.....look at the angle of the bars. its not sturdy at all......no supports.....you can bend that easily......

My thought at 1st glance too, just needs gussets' installed for added stiffness!

 

[ron w]

I have a question or two in this area, for the experienced builders....
when you twist a string up under tension, where do you set the pretension at?. I ask this realizing that as you twist, the tension increases because the string gets shorter. do you just let the spring compress as you twist and let the string load tension as the twists increase in number?......I can't really see it working any other way.....what am i missing? do set up to end at a certain tension, or set up to begin with a certain tension,....knowing that. as N&B posted, you have to find out how much compression your spring adds to tension in the string as you twist.
last time I built strings was back when you just twisted up your string, off the jig and put it on the jig with as much tension as you could get and serve it. now I see that we are twisting under tension....this is new to me. it certainly makes sense, but new to me, never the less... and raises the above questions.

 

[rick prather]

What material do you normally use? Thats quite a bit off from where i build most modern materials at 24 strands. 60" String i would set at 60.5" and 39.5 twists. On your formula you would set the jig at 60 9/16" and 45 twists. So only 1/16" longer jig setting but 5.5 more twists. Seems like it may come out a bit short with most newer materials? To add confusion - you need to compensate for strand count (higher strand counts will shrink more from twisting) and material. Stiffer materials will need the jig set longer or less twists. Fun right!!!

With that many twists. is 5.5 more or less a big deal? As long as the length is correct before serving. Actually I twist slightly short, then burnish,then serve. By slightly I mean maybe a 1/32 nd. in.. I make them for me only so I can do what I want right? LOL.

 

[brittonc82]

So does it need to be pretensions at 300 lbs? And for how long?

 

[nuts&bolts]

I have a question or two in this area, for the experienced builders....
when you twist a string up under tension, where do you set the pretension at?. I ask this realizing that as you twist, the tension increases because the string gets shorter. do you just let the spring compress as you twist and let the string load tension as the twists increase in number?......I can't really see it working any other way.....what am i missing? do set up to end at a certain tension, or set up to begin with a certain tension,....knowing that. as N&B posted, you have to find out how much compression your spring adds to tension in the string as you twist.
last time I built strings was back when you just twisted up your string, off the jig and put it on the jig with as much tension as you could get and serve it. now I see that we are twisting under tension....this is new to me. it certainly makes sense, but new to me, never the less... and raises the above questions.

As the TWISTS get more and more,
then stretching tension goes UP.

Many like to use a die compression spring.

I built my 16 foot long bench,
so I have MORE than enough room to rig up a 300 lb VIKING inline spring scale
so I can MONITOR the stretching tension.

If you can afford one,
the pneumatic stretcher from Specialty Archery will keep a CONSTANT stretching tension, cuz of the pressure bleed on the air cylinder.

Too expensive for the home builder.

I'm picky,
so I purchased a S-Beam load cell, and digital readout,
so I can REALLY monitor the tension when adding twists,
so I can REALLY monitor the change in stretching tension, when I let the bundle sit on the stretcher.

 

[bigkuntry72]

This is the BCY micro stretcher.

I use a spring scale.

Some folks use a DIE compression spring,
and read how much the spring is compressed,
after calibrating the "squeeze amount of the spring" to a linear spring scale.

So,
if you use a draw board (boat winch) and hook up the compression spring,
and you squeeze the compression spring say 1/2-inch,
and the inline VIKING spring scale says that you are squeezing the compression spring 300 lbs,
now you know that when you squeeze the DIE Compression Spring 1/2-inch less than the full size length,
you have 300 lbs.

Thanks N&B i may look into getting one with a spring glad to know what I'm working with now I really wanna get into building strings so I guess that is a great starting point.