Common mistakes with dropweight machines?

Discussion in 'Badminton Stringing Techniques & Tools' started by s_mair, Apr 7, 2015.

  1. s_mair

    s_mair Regular Member

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    After thinking about it for several months, reading a lot of the threads in the BC stringing-forum (and in parallel getting more and more annoyed by the local stringers around here), I finally decided to start stringing my own rackets and ended up buying a Pro’s Pro Challenger dropweight machine. I used the easter holidays, a old racket of mine and a roll of the cheapest strings I could find and simply started stringing.

    Trial run No. 1 (2 piece Yonex pattern): After nearly 3 hours I finally arrived at the second to last cross string…. and…. tadaaaa… it snapped! Most probably because I somehow damaged the string inside one of the shared grommets while desperately trying to get the second string through (with the “help” of an awl). Result: My neck was hurting, my fingers were sore and shaky so I was really done for that day and seriously considered sending back the whole stuff and quitting stringing for good.

    Trial run No. 2 (1 piece Haribito “non-professional” pattern): I cut out the remainings from trial run 1 and started again from scratch. Everything was working much more smoothly and I was proceeding much faster. And after around 2 hours I had finished my first actual stringing job! The stringbed felt solid, the ping frequency was at about 950 Hz (tension used was 20 x 22 lbs. with a 0.68 mm string) so all in all: I was really, really pleased with myself!

    Now, my first priority is to achieve a solid consistency before trying to optimize the time needed. And before I lay my hand on one of my main rackets (a Voltric 80 and a TK9000), I want to get the feeling that I somehow have a bit of control of what I am doing.

    Now for the questions:

    1.) What do you think are the most common mistakes that you can make while stringing on a dropweight machine that cause inconsistencies of any kind? Or put it the other way round – what are the most important things you have to look for very carefully during stringing to achieve a best possible result in the end?

    2.) After finishing a stringing job, how do you quickly check if the result is as expected and that the tension is consistent over the whole stringbed?

    In general, I am really impressed about the amount of knowledge that is available in this forum. I am sure that without all the things I read here, I would not have had the slightest chance to actually succeeding in only the second attempt. A big thanks to all of you for sharing your expertise here!

    Cheers,
    Simon
     
  2. ucantseeme

    ucantseeme Regular Member

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    I think that the most common mistakes are:

    - clamping to far away from the frame ->tension loss
    - not well adjusted clamps -> slipping or crimping the string
    - not straightening every cross after each pull, you must massage the string
    - don't get the right adjustment to bring the leverage of your drop weight machine in a horizontal position
    - don't give the machine enough time to remove some slack off the string
    - wrong clamping like first base than clamp, wrong releasing clamp like first clamp than base
    - the knots are often a problem. Try to learn parnell knot and a good starting knot
    - use a stringmover instead of an awl
    - use scrap string to threaten blocked holes instead of an awl
    - prefer fixed clamps over flying ones to avoid tension loss

    You can check the result with pinging the stringbed and compare your result with other. Something under 1000hz is always suspect. You can't check if you did a every string with the same tension. That is impossible. I doubt that any stringer will produce a stringing job where every string has the exactly same pulled tension.
     
  3. ucantseeme

    ucantseeme Regular Member

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    Found the data of my last 22x22 job with BG80 Power. Frequency: 1131HZ. I don't want to blame you or say that my job is the right result but we have a difference of close to 180Hz which is much. And more than 3lbs difference.
     
  4. s_mair

    s_mair Regular Member

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    That is indeed quite a significant difference, thanks for checking. I will have a close look on the frequency with the next jobs. As for the other hints there are also some amongst them which I will focus on more next time. I have definitely learned my lesson that an awl should be used with a lot of caution...
     
  5. Mark A

    Mark A Regular Member

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    Dropweights don't really have any special technique requirements (unlike cranks) - just make sure the arm is level. However, when pulling crosses - as ucantseeme said - the cross must be straight when the arm is level; press the cross toward the previous cross before starting the pull, and slowly let it out as the tension increases.

    ucantseeme has covered pretty much everything else, but it's not bad practice to add a pound or two for knots as long as you do it consistently.

    Best way to do this is to check the frequency, especially against other rackets you've just done at the same tension - a racket loses around 1% of its tension during the first hour, and this is within the margin of error for a good string job.
     
  6. DarthHowie

    DarthHowie Regular Member

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    I would also like to add from Mark A and ucantseeme comments the following:

    If you don't wish to use an awl of string mover (kwun has a video with the string mover technique) to address shared grommets, you can always use tooth floss to thread the string through.

    and an illustrated example of what ucantseeme said:
    http://www.badmintoncentral.com/forums/showthread.php/150903-VIDEO-DarthHowie-Stringing-Overcome-Blocked-Cross-Grommet-Use-Scrap-String
     
  7. ucantseeme

    ucantseeme Regular Member

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    [MENTION=2950]DarthHowie[/MENTION] The ZF in your video as some deep marks above your shouldersupports. I don't think that it was your work. That makes me sad to see such expensive rackets with such wounds.:( Which makes me to add:

    - don't tighten your shouldersupports to much. Just firm without any deformation or pressure.
     
  8. DarthHowie

    DarthHowie Regular Member

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    [MENTION=59291]ucantseeme[/MENTION]
    Are you referring to the area in the red box in my picture for overcoming the blocked grommet video?
    If so...those are some chips from clashes and not from my supports. My chudek supports (with rubber tubing) leave no indentations whatsoever.

    Thanks for the tip. I tighten just enough and have load spreaders on both the head and throat.
     
  9. ucantseeme

    ucantseeme Regular Member

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    You get me wrong. I would never try to teach you and don't think that you would ever tighten the shoulder supports too much. You are a great stringer and I would be glad to try one of your jobs. My tip was for the OP.
    I was refering the area on the left of the red box. Amybe I should visit an oculist.:eek:
     

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  10. DarthHowie

    DarthHowie Regular Member

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    I welcome all advice. I learn from all. So much knowledge shared amongst the members. So much easier to learn now then before.
     
  11. s_mair

    s_mair Regular Member

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    Thanks for all the useful tips and advices. I have already used the string mover technique from kwun to tackle my shared-grommet-issues in trial #2 and it was a huge improvement to just endlessly fiddling around and hoping that the string will find its way through.
    Using floss or scrap string as described also sounds very intersting - will be tested in run #3!

    Regarding the fixation, I was totally surprised to see how soft a frame is and how easily it is deformed when tightening the supports only a little bit too much. I have also ordered a set of load spreaders from MBS.

    Just out of curiosity - how big is the difference in tension in case the arm is 5° or 10° out of level?
    You can surely do a mathematical calculation for it, but I guess that only calculating it that way completely ignores all the friction between the strings that is involved.
     
  12. ucantseeme

    ucantseeme Regular Member

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    If I'm not stupid it must be close and narrow to:

    pulled tension = adjusted tension * cos(angle in degrees)
     
  13. DuckFeet

    DuckFeet Regular Member

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    Calibrate your machine. Prep shared holes with awl before mounting.

    I got a cheap luggage weight thing off eBay for about a fiver and it shows 4lb higher than the scale on my machine.
     
  14. Mark A

    Mark A Regular Member

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    Even 10 degrees from level would lead to a tension loss of only 1.5%.

    That's nothing.
     
  15. _Rav_

    _Rav_ Regular Member

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    You could check the accuracy of your scales with a measured bucket of water. 1 litre of water is 1 kg, add a litre and check the scales reading each time up to 12-13 kg and you should get a feel for how far out they are, or not as the case may be.
     
  16. DuckFeet

    DuckFeet Regular Member

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    I've found the opposite. Few mm off the mark = +/-5deg at most = 1lb. Maybe I need to retest this!


    Re the bucket of water. I weighed from 100g to 11kg car wheels and it seemed close enough. I just don't think pros pro do QC.
     
  17. RedShuttle

    RedShuttle Regular Member

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    It seems impossible to pull the first bottom left hole with the arm in the way. Is there a good way to pull it or okay to just pull top left 1 & 2?
     
  18. Mark A

    Mark A Regular Member

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    Mine was strictly theoretical - 100(1-Tcos10) = 1.52% of T.

    I haven't used a dropweight for nearly a decade, though, so take it with a spoon of salt.
     
  19. s_mair

    s_mair Regular Member

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    The formula should be correct, so we are talking about a factor of "cos(deviation angle)". So even a massive deviation of 20° would cause a tension loss of only 5-6%. Putting aside any side effects like friction between strings and grommets of course.
    So it seems like other mistakes like a wrong clamping process or not straightening the crosses before tensioning have a much bigger impact on the final result. Very interesting, I would not have expected that.
     
  20. craigandy

    craigandy Regular Member

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    Is it the challenger 1 with the ratchet system? If so you have to be careful whilst tensioning because the ratchet locks the bar down if pushed or dropped hard, so if you pushed/dropped it down one ratchet click further than the click for horizontal it would be at least 5lbs or so more also if you forced it one click forward way before it reached horizontal it could still be 5lbs higher in tension. If no ratchet system then this should no be a problem.
     
    #20 craigandy, Apr 8, 2015
    Last edited: Apr 8, 2015

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