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How much to calibrate over-crank to

Discussion in 'Badminton Stringing Techniques & Tools' started by Blitzzards, Jan 26, 2012.

  1. Blitzzards

    Blitzzards Regular Member

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    I have recently been calibrating my crank machine to give me the tension/stiffness close to that of an Electric Constant Pull's. What I have noticed is that with the pull set at exact tension (i.e. when I crank at 30lbs and have the gauge also read 30lbs), the string bed comes out about 2lbs lower thus feeling like 28lbs in my case. Thus on my next calibration, I set the crank to pull 2lbs higher than whatever tension I set on the dial.

    However what I noticed next is that when I'm trying to crank the string into tension while observing the registered tension on the gauge, about half the time the tension does not even reach the +2lbs which I have dialled in, even if I use the same technique on every crank. In the half of the tries that I did not reach the set tension, I compensated by cranking another time while pulling the string through (so the gripper grips more string on this second crank) but the tension registered is usually 0.5 to 1lb too high than the +2lbs that I set :confused:

    In other words, I realised that everytime I string, I am actually not applying the exact tension that I intended to on every crank. My question is, how much should I over-calibrate my tension head to pull to compensate for the natural inconsistency of the crank tensioner? I have heard of the +3lbs rule for crank, but does that apply to compensating for all of the inconsistencies? Or should I work on getting a more consistent cranking action (which may not be possible as everything is hand worked, and human error always creeps in)?

    In fact I'm already starting to look into purchasing an electronic tension head, but in the mean time, I would like to tackle this so that I will appreciate the consistency of the electronic constant pull more :D

    Appreciate all help I can get in this matter.
     
  2. silentheart

    silentheart Regular Member

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    1) I assume you have a eagnas machine?
    2) If a crank machine is calibrated correctly, it should lock at desired tension. Yes, it will drop tension right away. You need to adjust the beak pad as closely to the disk as possible wile you can crank freely.
    3) With #2, your var should be less than 1/2 lb difference every pull.
    4) Should you calibrate 1 or 2 lb over? My answer to you is depend. If you are quick at clamping, you will need 1 lb over. if you take your time clamping, 2 lb over. Do not go 3 lb over because you are putting the racquet at risk because if you string at 27 lb, the frame actually take 30 lb before the break apply. That just might be the straw that breaks camel's back.
    5) Get a professional to calibrate for you. That way, you get a consistent pull every time. Even if it cost you $60.
     
  3. Mark A

    Mark A Regular Member

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    I'm about to get a WISE, but I can impart some crank-related wisdom.

    As far as overclocking the crank, I would have the thing overshoot and then land on your desired tension after a generous two-count - you want the "true" tension to be there at the moment you clamp the string, and the two-count leaves enough time for you to manipulate your clamps. There are people who insist on having the correct tension show up after a minute under tension, but this is pointless - if it reads 30 lb when you clamp off, it'll be 30 lb whether it's crank or electric.

    Technique-wise, it's very important to develop a consistent pull - there is considerable variance in the tension with pull speed, and the slower you can pull the crank, the better (especially on crosses, where friction plays a part). Personally, I start the pulls quick, then slow down as the lockout gets close. I have a video somewhere in this forum of my crank use, if it helps.
     
  4. silentheart

    silentheart Regular Member

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    good call! mark.
     
  5. dunmaster

    dunmaster Regular Member

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    definitely agree! consistency is the key here, and mechanical break is very subjective to how you move the crank. you should be able to feel the "pull" on the crank when it's about to lock-in.

    What I have also experienced is that when you are stringing racket with different string, the amount of over-calibrate is also different. therefore, it's always recommended to use the same string to validate (OR calibrate) the desired over calibration.
     
  6. Mark A

    Mark A Regular Member

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    This is why I keep a very old piece of squash string just for calibration - it's been pulled so many times that there's absolutely no slack left in it, so it's perfect. Well, Kevlar would be PERFECT perfect, but I can count on one hand the number of Kevlar jobs I've done.
     
  7. _Rav_

    _Rav_ Regular Member

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    I tend to double pull mine, but then i'm not going for any speed records. Pull till it locks out, then support the crank handle while you release the brake (to stop it slipping back and losing the tension) then pull again until it locks out, then clamp quickly and carefully.
     
  8. Blitzzards

    Blitzzards Regular Member

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    Thanks to all for the insights. My machine is an AFE oem, similar to kwun's, which has a very short crank path, master SH.

    In the mean time, I recalibrated the crank to 1lb maximum overpull, considering that I crank multiple times until I can apply no much more tension to the calibrated string. With these settings, I strung another racquet to 33lbs with the same multiple crank action on every string and when I was done, I noticed that the result gave me 33lbs right after I took out the racquet, then it settles to 32lbs overnight.

    What I wonder now is, if I keep this multiple crank action "setting" and calibrate the overpull to 2lbs maximum, will I theoretically get the true tension?

    One more thing I noticed is with my tension calibration gauge (the Eagnas style manual type), if I wrap one loop around the pulling hole as opposed to just looping "straight through", my calibration will now show less on the gauge. I have this idea that the loop around the gauge will effectively simulate the lose string over two grommets on a racquet, so in this case will calibrating my 1lb overpull on this loop give me more accuracy?

    I don't have a racquet to string in the next few days so I would like to get this discussed and analysed thoroughly before I test it :)
     
  9. silentheart

    silentheart Regular Member

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    These are my opinions
    1) since you have figure out the multiple pull will get you to the tension you want -1 lb. have you tried the racquet to see how it feel? because it might just plays the best for you.
    2) reg your question on 2 lb over calibration, yes, in thory.
    3) there is no such thing as accuracy. it is all relative. just because your crank is 1 lb below my ecp, it does not mean your macine is off.

    the fun of string yourself is to be able to make that little tweek yourself on the next stringing job. the satification of you have a racquet well done by yourself and enjoy the fruit of your 1 hr labor. the reasone i got the wilson machine is not to make money, it is to make sure i get and give consistent string job for myself and my friend that is not a blow job.
     
  10. Pete LSD

    Pete LSD Regular Member

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    I got great caibration resut by waiting for that minute ;). The tension versus time curve is real. The drop in tension is drastic during the first 10 seconds and slowly tapers off. The curve looks like a hyperbola.

     
  11. Pete LSD

    Pete LSD Regular Member

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    I can only speak for the Gamma tension head. Three pounds over reference at lockout will fall back to the original reference tension.
     
  12. Blitzzards

    Blitzzards Regular Member

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    Thanks all.

    Can't wait to recalibrate my crank tensioner again when I get home :D
     
  13. Blitzzards

    Blitzzards Regular Member

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    Thanks all.

    Can't wait to recalibrate my crank tensioner again when I get home :D
     
  14. Mark A

    Mark A Regular Member

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    Any string/string or string/frame interaction will cause friction, which might not be pulled out during cranking, so your result is hardly unexpected. I'd get rid of all extraneous looping during calibration, but this means you have to be even more pedantic when pulling crosses (i.e. get all the friction out).
     
  15. Mark A

    Mark A Regular Member

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    ^Two more important points:

    1. Make sure the turntable is absolutely still before lockout occurs - the string path has to be dead straight in the vertical plane;
    2. Wind all the tension off the spring once you've finished stringing - the spring gets tired if left under compression, and your tensions will begin to drift downward over time.
     
  16. dunmaster

    dunmaster Regular Member

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    Besides, since the lockout parts are all metal items, I often clean that part once a month to make sure they are free of dust or dirt or such. I don't recommend to put any oil on it, since it may affect the effective lockout over use.

    of course, when the machine is not in use, cover it up with cloth or box.
     
  17. Blitzzards

    Blitzzards Regular Member

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    OK, so I have now calibrated my crank tensioner to pull 2lbs extra for every twice [very] slow crank, and both successive cranks show me the same 2lbs extra compared to what I have dialled in. I noticed that after 5 minutes, the tension settles to 0.5lbs extra (compared to the over-crank's 2lbs extra). From my previous string job which gave me 1lb below intended even with 1lb over-crank, hopefully this new calibration will give me my true tension. I am hoping that with this 2lbs overpull, my finished string bed will give me +0.5lbs overall tension then settle to dialled tension overnight.

    PS. I do feel the difference between the 33lbs that I desired compared to the dropped tension of 32lbs on my previous string job, and I still prefer the extra 1lb that I dialled in and intended to hit :p
     
  18. Blitzzards

    Blitzzards Regular Member

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    So I "sacrificed" one of my still doing fine racquets and strung it at 33lbs with the above 2lb over-crank calibration..

    And it seems that the over night tension has yet again fallen below the 33lbs mark, but at least it sounds higher pitched than the previous 32lbs racquet I did (i.e. still higher tension overall; I have a spot on 33lbs racquet strung using ECP with BG75Ti sometime ago which I still keep for tension reference).

    Two things are apparent here now:

    1. Each and every racquet seems to have its individual own tension holding properties and calibrating a manual crank machine to account for all can be messy. I will get much better consistency with an ECP with light (10%) pre-stretch.

    2. Master PeteLSD is again correct in regards to the +3lbs rule :D
     
  19. Blitzzards

    Blitzzards Regular Member

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    On a side note, now that I am going to calibrate my crank to +3lbs per pull, I am wondering since I am fond of doing 33lbs string jobs, is it a good practice to leave an "over-tensioned" racquet on the stringing machine with the supports tightened around the frame after the string job and allow the tension to settle before taking it off (overnight for my case)?

    In my case for a 33lbs string job the very initial tension after completion will be around 36lbs which is pretty scary for racquets with slightly thin graphite in the frame such as the Armortecs which I tend to use a lot.
     
  20. Blitzzards

    Blitzzards Regular Member

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    After further analysis, I theorise that the actual tension (referencing a constant pull job) pulled by a crank would be:

    [tension pulled measured by gauge] - 2.5±0.5lbs

    However due to the variable factor in this formula, electric constant pull is still the better choice for a consistent string job.
     

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