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String tension again

Discussion in 'Badminton String' started by OJ, Jan 20, 2001.

  1. OJ

    OJ Guest

    Strings and tension seems to be interesting topics on this board. I have experience that I would like to share and possibly get a reaction on.

    Over the years I have lived in many places and restrung my rackets in many different places and the reslut always differs. But when you order a specific tension you should get at least somewhere close to what you ecspect. Let me explain. If I order 9 kg tension (in Sweden we often measure in kg) the sales clerk might look at me and say something like: ”Is that all, we normaly don´t string less than 12 kg?”, or ”you can´t string a racket that hard. It will break”.

    This pussled me a lot so I tried to investigate the cause of this. And I came to the conclussion that there exist at least two different ways of measuring string tension. Now I string my rackets in a shop where they have a french machine of the brand Babolat, at 9,5 kg. Which is as hard as my friends who string at 14 kg at another place whith another machine.

    This all leads me to think that when you are discussing string tensions on this board you might you think have totaly different ideas about something that you actually agree about, and the other way around. Something like that.

    Anyway, does anyone else have the same expeience? Do you know how your string tension is measured? Is this a known fact? Do you know what I am talking about or am I maby a total idiot? (No, don´t answer that last one)

    I might have to add that I have an opinion already established in my mind, and my source is by me quite reliable. I still would like to hear other opinions and experiences.
     
  2. Mag

    Mag Moderator

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    Actually, something like this happened to me when I went to have my very first racquet restrung. Then I didn't know much about badminton and tension and such, so I just asked them to string it "pretty hard" (which I thought would automatically give me the mother of all smashes, of course it didn't). The racquet was a Prince Response, pretty good actually, a robust Y-joint graphite racquet. Anyway, when I returned to pick the racquet up the guy told me: "I strung it pretty hard as you asked, 16 kg. I could pull a little more but I don't want to risk breaking the frame."

    This still puzzles me. 16 kg would mean 35 lbs! I don't think so, not on that racquet... Sure it was strung hard and I found it a bit hard to play with for a while, but back then 20 lbs would probably have been too much for me. I haven't used this shop again (I've moved since), but to this day I still haven't used tensions over 26 lbs. So I guess there must be some other way of measuring, as OJ suggested.

    (This was in Stockholm, Sweden, by the way)
     
  3. kwun

    kwun Administrator

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    Hi Mag,

    even though 16kg seems a bit high, it is conceivable that prince Y-joint rackets can take it, or may be a bit lower. the Y-joint racket has less strings, so for the same tension, the racket frame is subject to less total force. therefore, to achieve the same "feel" as regular rackets, stringers usually string it at higher tension.

    this is one of the disadvantage of the prince racket shape. since higher tension is needed, the string doesn't last as long.

    cheers,
    kwun
     
  4. kwun

    kwun Administrator

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    OJ,

    i some what i agree with you. most stringers don't have their stringing machine calibrated very well. stringer A's machine's 24lb may be stringer B's machine's 20lb. also, the type of stringing machine also makes a difference, a free weight machine and electronic machines tend to be tighter than a cranked machine. i can explain why if you are interested.

    most professional stringers use crank machines, so it is likely that you'll see lower tensions.

    yes, indeed, talking about string tension is really not that accurate, but hey, we do it anyway. :)

    cheers,
    kwun
     
  5. cooler

    cooler Regular Member

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    kwun, can u give us a hint on why a cranked machines give less tension than free weight and electronic?
     
  6. kwun

    kwun Administrator

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    cooler,

    sure. it is hard to describe. let me know if i am not making sense.

    let's go through how the machines work and then we can talk about how the string react to tension.

    let's say, we want to pull our string @ 20lbs.

    the drop weight machine works by having a rotating weight that is attached to the string. the weight is "dropped" and when the bar holding the weight is resting at horizontal position and the string is no longer stretching, then the desired tension is achieved. when this happens, the string is held at a contant tension of 20lbs.

    the crank machine has a little spring at the end. when the stringer crank up the tension, the spring is compressed. the stringer pre-adjust the machine such that the moment 20lb is reach, a latch is activated and the position of the spring is held and the stringer can then release the crank.

    ok. the string. the string is woved together by a lot of small filaments/fibers. when tension is applied to the string, the string starts to stretch out slowly. when all the fibers are straightened, it will stop stretching. let's call this the limit point.

    ok. back to the machines. what happens with a drop weight machine is that, when the weight is dropped, the string will start stretching. it will slowly stretch to the limit point, while doing so, the stringer need to readjust the weight until the weight stops dropping. at this point, the string will stretch no more. and the stringer will clamp the string and work on the next segment.

    with a crank machine, it is different. the latch activates as soon as the tension becomes 20lbs. beyond that, the crank is disengaged, and the stringer can no longer apply more tension. however, the instance when the latch activates, the string has not reached the limit point yet and will continue to stretch. this is because the stretching process is slow. so after the latch is activated, the string will continue to stretch thus the resultant tension is lower.

    there are two observations.

    1. the tension coming from a drop weight machine is the "true" tension.
    2. the crank machine is faster since the stringer can start working on the next segment as soon as the string reach 20lbs. he/she doesn't need to wait till the string reach the limit point.

    i hope that make sense.

    cheers,
    kwun
     
  7. cooler

    cooler Regular Member

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    thanks kwun, it makes perfect sense, and u did a fine job explaining it. i personally havent work on a drop weight machine before but i did carried a belief that the drop weight is a truer form of stretching as it is straight forward, no pulley or spring activation. While some stringer brags about how fast they can string a racket, my taking longer, 2x longer using similar crank machine.
     
  8. Cheung

    Cheung Moderator

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    I just got a drop weight machine. It does string at a higher tension than the other racquets I have using a crank, even though the weight may say 25lbs
     
  9. cooler

    cooler Regular Member

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    I solve that problem by doing routine calibration using real free weight dumbell. At higher tension, i pull slowly. I think it's not what machine one use but who use the machine, drop weight or crank style mahines..
     
  10. Cheung

    Cheung Moderator

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    How exactly do you do the calibration? (sorry if this seems a simple question).
     
  11. cooler

    cooler Regular Member

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    I'm cheap but practical. I dont like the spring type weight scale, not accurate enough but good for weighing fish though. I tie a 25lb weigh with badminton string to the crank vise and pull to see when it lockup. I check the pound marker. Luckily, in my case it match up. If not, i think there is a screw to adjust the spring locking mechanism but i dont need to do that yet. I repeat the process for 20 and 30 lbs weight tests but i dont adjust the spring for those tests, i just need to know i far i'm off. 99% of my stringing is done between 22 to 26 lbs so the 25 lbs test is my base reference. My machine has 1/2 lb increment market but i can cut it down to 1/4 lb increment visually.
     

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