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Why +2lbs On The Cross?

Discussion in 'Badminton String' started by kwun, Apr 7, 2003.

  1. Blitzzards

    Blitzzards Regular Member

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    You can get constant tension pull out of a crank machine simply by double or triple pulling on the string. The tension lost for most crank machines normally happen only on the first pull where you are pulling on a previously untensioned string which has still some slack in it. The second and third pull will have increasingly short travel distance on the crank until all succeeding pulls have the same travel distance which is when you have constant pull tension.

    The only hassle with the crank tensioner is that the constant tension pull is more or less manual and not automatic.
     
  2. DinkAlot

    DinkAlot dcbadminton
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    If you are a good stringer, it's not that big of a difference. The key is the stringer.
    Personally, this Panda would use a crank over drop weight just because it saves time.

    If you are used to crank machines, then it's not significant at all.

    If Panda had to use a crank machine, he would just "overclock" it. Say Panda wants 30lbs. ECP, then he would go 34-35lbs. on a crank to get similar tension.



     
  3. dunmaster

    dunmaster Regular Member

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    You can definitely achieve the same or better result with a crank machine, which is a lot faster than drop weight machine. Besides what DinkAlot mentioned, this is what I normally do:

    - first of all, develop a constant and steady pull motion with your machine, which means that make sure every pull you are making is as the same as possible. You should be able to feel the higher tension when the "tension head (right term?)" is about to lock.

    - with this repeatable motion in place, perform a good tension calibration with a good tension gauge and the same string as you are going to use.

    NOW, here is the key: when you perform calibration, use the close-to-steady number on the gauge a few seconds AFTER the crank stopped!

    for example, if you want 30 lbs, the gauge may say 35-36 lbs right after it locks. It will drop quickly and then slow down to a close-to-steady number. Calibrate the system to that number.

    NOTE: this will be pending on your experience and speed of making the pull. Normally, a few trials and errors will be fine. ALSO, different string has different tension loss speed and amount. You will need experience to get a hang of them.

    Hope this is useful.
     
  4. gavias

    gavias Regular Member

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    Thank you for your answers. Two more questions:

    1- The crank machines have to be calibrated frequently?

    2- How often they break?
     
  5. gavias

    gavias Regular Member

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    ... The string grip in the crank machines could be adjusted? I am asking, because I am think in buying a pros pro crank machine, but I don't know the efficiency of the grip.
     
  6. dunmaster

    dunmaster Regular Member

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    calibration frequency is pending upon the care you give to the machine and usage. there isn't a certain rule, but I normally do a check (verification of the reading) once a month or sooner (like every 2 weeks).

    the machine normally lasts LONG time (10+ years), with proper care and storage location.

    for the string grip. assume you are talking about the two parallel plates that hold the string. If so, yes, they can be adjusted for different string diameter. often time, you don't have to do anything about them, unless they are slipping or out of alignment. again, this is something that normally doesn't go bad at all.
     
  7. chip167

    chip167 Regular Member

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    Hi everyone, I have read most of this thread but not all, so forgive me if this question has come up already...

    I am not a stringer, so I wondered, when a player gives you a racket and asks for it strung at say 24lbs, do you string at 24x26, or 22x24? Or 23x25?

    Thanks!
     
  8. Blitzzards

    Blitzzards Regular Member

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    Here is your answer. Please use a little bit of mathematical logic to calculate your specific number:

     
  9. clawhammers

    clawhammers Regular Member

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    I wonder why YY has not suggested this +2 Lbs on the cross anymore in its annual catalogue

    Instead YY suggests to use same string tension for main and cross strings.

    cmiiw
     
  10. crawshaws

    crawshaws Regular Member

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    This 1lb higher tension on the crosses issue has been bothering me, so I also did some calculations (I'm an engineer).
    I agree with the first part of your calcs (the mains are forced by the crosses to stretch about 0,6 mm over their length), HOWEVER, I think your next steps are incorrect.
    A 0.25% extra strain (strain = change in length/original length) doesn't give 0.25% extra tension.
    Actually Tension is proportional to Strain x Young's Modulus (YM is effectively the "spring constant" of the string material. I went though the theoretical calculations but the problem is finding reliable values for Young's Modulus for the string materials (they range from 6 Gpa to 28 GPa...too broad a range to be useful!). So...I did some experiments:
    What I found was that adding 5lb (20lb to 25lb) of tension on a 480mm length of BG-65 stretches it 4,5mm. Since we can assume the BG-65 is elastic in this tension range, we would see 2,25mm stretch over a 240mm length (the length of a long main) with +5lb...so, calculating 5 x 0,6/2,25 = 1.3lb would stretch a main by 0,6mm (the length we agree the mains get stretched).
    The conclusion from this analysis is that the crosses should be strung 1.3lbs higher tension than the mains to end up with the same tension on the long mains as the crosses.
    By the way, reversing out the YM gives a value around 13 GPa.
     
  11. kwun

    kwun Administrator

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    did you take into account string density in your calculation?

    the main strings are closer together and the crosses are further apart. the effective tension for the mains are thus higher.
     
  12. Mark A

    Mark A Regular Member

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    Interestingly, Victor (and others) has the V limit two pounds lower than the H limit.
     
  13. crawshaws

    crawshaws Regular Member

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    The mains are tensioned when there's no crosses in the way (using the Yonex pattern). When the crosses are tensioned they are zig-zagging through the mains.This isn't so with the Victor pattern, where several of the bottom crosses are done first.
     
  14. j4ckie

    j4ckie Regular Member

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    While not super-productive concerning the ongoing discussion, I tried different tensions on my BS09s, trying to find a satisfying tension for the BG66UM where it doesn't feel dead after 3 sessions but I can still smash harder than a small girl :D
    Anyhow, during that, I varied the main/cross string tensions as well, as I was wasting string anyway....and had interesting results. The stringjob yielding the best head shape was a 12x12,4kg one [26.4/27.28lbs]. The 29x30 one was better in playability, but too hard for my taste, and the most recent one resulted in the best feeling of all - a 27x29lbs one. Even though the head shape is very slightly off, it just feels more alive than any other previous tension.
    I would try and guess that it's due to the cross strings being slightly tighter than the mains, giving a bit more feedback than a more homogeneous stringjob while retaining most of the repulsion of the softer mains. Personally, I'm very surprised by this, as I was pretty sure a string job with the perfect head shape would yield the best results, and I still have no real 'scientific' explanation for it.
    Still, fact is, the 27x29 feels more alive (harder too) than a 27x27, more repulsive and slightly more direct than a 28x28, and more powerful than a 29x29 (while not as hard and direct).

    Stringing was done on a Signum Pro machine modded with a WISE tension head. Same pattern and equipment for every one of those stringjobs, of course. :)
     
  15. Mark A

    Mark A Regular Member

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    If you're a top-downer like me, keeping the "corners" of the iso-frame is the tricky bit. I've found that 27.5/30 with 26->30 from the top cross does OK in this regard. IMO the crosses stretch the mains, so the mains need extra - end of story.

    A TD will probably never keep the frame shape, but my width/length ratio is good and I'd rather have stress end up at the bottom of the frame than the top.
     
  16. j4ckie

    j4ckie Regular Member

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    Yep, top-down with lowered tension at the beginning. For others I wouldn't add quite as much tension as on mine, as it DOES deform the frame, but enough to even out the difference created by lengthening the mains and pulling at worse angles than on the mains (0.4-0.6kg usually).
     
  17. Mark A

    Mark A Regular Member

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    I don't use the WISE prestretch, but I'm considering using it to see if more of the cross friction is pulled out - I'm wondering how much of the target tension is lost to that friction (even with ECP and the "massage" technique).
     
  18. j4ckie

    j4ckie Regular Member

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    Hard to put a number on it, but I find that with 10% pre-stretch I need to add very little on the crosses to get a pretty homogeneous stringjob. Without the pre-stretch, I would need to 'massage' the strings (taking much time, which I don't really want to spend^^) and probably still end up short in comparison...
     
  19. crawshaws

    crawshaws Regular Member

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    If the mains are done first and tied off, the crosses will stretch the mains and cause the mains tension to increase. This is basic mechanics of materials: Stress (which is Tension/String Cross Section Area) = Young's Modulus x Strain. So for a homogenous string bed, the mains should be tensioned LESS than the crosses.
     
  20. j4ckie

    j4ckie Regular Member

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    Yep, that's what everyone does....and I'm studying to be an engineer as well, so no need to explain the basics of mechanics to me ;) I'm just surprised a rather big difference in tension lead to such a great result, as I would've expected it to feel slightly 'off' with the crosses being tighter (even taking into account that the mains have tightened by pulling the crosses).
     

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