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  1. #1
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    Default Digital Scales/Tension Calibrator - which reading?

    There's one thing I've always wondered, when using a digital scale to calibrate the tension on a stringing machine (mine is a crank tensioner) - Do you take the highest reading, the median reading or the reading when it settles down?

    For example, if I dial in 25lb on my machine and my digital scale initially shoots to say 26lb intially but quickly settles down to 25lb. Do you take 26lb, 25.5lb or 25lb as the correct reading?

    (Obviously I'm exaggerating with the differences, but just to illustrate the point)

    I have three digital scales, all give readings to within about +/- 0.2lb of each other usually and I've always taken the reading when it settles down but as there will be some deformation/strain in either the hook/chain, string, mechanism etc I'm just wondering if there is any "relaxing" taking place. If so, should I actually be taking the initial reading/median reading?

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    Regular Member Mark A's Avatar
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    You should aim to have the tension correct at the moment you clamp the string. In practice this usually means over-shooting, the amount being dictated by your clamping speed.

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    Yep, I agree, but I think that's probably a separate issue?

    I guess what you're saying is, if we assume the machine is 100% calibrated and accurate, to get the tension we require accurately (say 25lb), we need to clamp the string quickly before the tension starts to relax/drop. I totally agree with this but this is during the stringing process, not calibrating.

    I'm asking about calibrating the machine (using a digital scale) to make sure it is actually giving us 25lb when we dial in 25lb - assuming the scale is accurate.

    The digital scale reading always fluctuates slightly as you apply the tension before settling down quickly. This usually only happens for about 1-2 secs after the tensioner locks out. Obviously the digital scale itself will have a different rate of relaxing/strain compared to a piece of string. But that factor aside I'm just wondering what others usually take as the reading (max, med, settled reading)?

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    The reading should be taken as soon as the lockout occurs

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    There are 3 ways to calibrate your machine. Let's use a 25lbs calibration for examples.

    1) Calibrate so when the tensionner locks out, it reads 25lbs exactly.

    2) Calibrate so when the tensionner locks out, it reads higher than 25lbs, but reads 25lbs when you would clamp the string.

    3) Calibrate so when the tensionner locks out, it reads higher than 25lbs, but settles down to 25lbs (after ~10 seconds).

    When I had a crank machine, I used #3, because I figured that even when my string is clamped, it keeps elongating and losing some tension.

    On TennisTalk, they preach method #1, and they are pretty aggressive about it too. Their reasoning is, different strings stretch differently. So one string might be at 25 lbs after 5 seconds, another might be at 26lbs or 23lbs. This introduces some greater tension variability according to the string you're using, because if you pull with a higher tension (to take the reading when it settles down), your overall tension could be further from your reference tension. This probably makes more sense in tennis, where they use tensions that are twice our tensions, but I still don't buy it.

    But I think everyone will agree that no matter which method you use, the most important thing is to give consistent results. That way, if someone brings you their racket and ask for 25lbs everytime, it'll be the same everytime. If a new customer finds your 25lbs is too loose, they can just ask you for 26lbs (or w/e) everytime.
    Last edited by yan.v; 07-15-2012 at 09:49 AM.

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    Regular Member Mark A's Avatar
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    Quote Originally Posted by yan.v View Post
    When I had a crank machine, I used #3, because I figured that even when my string is clamped, it keeps elongating and losing some tension.
    This happens on all machines, regardless of mechanism. Adding extra just for the cranks makes no difference after the string is clamped.

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    Quote Originally Posted by Mark A View Post
    This happens on all machines, regardless of mechanism. Adding extra just for the cranks makes no difference after the string is clamped.
    It actually does. If you pull at (let's say 27 is the magic number at which you need to pull for the string to settle at 25) 27 instead of 25, the tension will be closer to 25 when it settles than if you pull at 25.

    With that method though, the tension will settle near 25, but if you had an electronic machine, it would probably settle to a bit lower tension than that.

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    Regular Member Mark A's Avatar
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    Quote Originally Posted by yan.v View Post
    It actually does. If you pull at (let's say 27 is the magic number at which you need to pull for the string to settle at 25) 27 instead of 25, the tension will be closer to 25 when it settles than if you pull at 25.
    This is covered by your Option 2: add extra so the tension lands on 25 by the time you clamp. Option 3 would add even more tension, so it would be more than 25 when you clamp, and there's no need; once you clamp, the tensioner is out of the picture, whether it's electronic or manual.

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    Quote Originally Posted by Mark A View Post
    This is covered by your Option 2: add extra so the tension lands on 25 by the time you clamp. Option 3 would add even more tension, so it would be more than 25 when you clamp, and there's no need; once you clamp, the tensioner is out of the picture, whether it's electronic or manual.
    Yes I agree. My method was probably overkill since the tension would probably result in a tension that was higher than what it would have been with an electronic machine. Luckily the difference isn't big since most of the tension is loss within the first 5 seconds.

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    New Member JacksonW's Avatar
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    But sometime you get difference in measurement due to adjustment of your scale. so you must calibrate your scale with known weights so that you get accurate measurement.

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    New Member JacksonW's Avatar
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    You can also use a pull gauge scale for finding weights and tension calibration. Because these scales are made for this purpose and you can easily get accurate measurement.

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