Are drop weight tension-selectors accurate?

Discussion in 'Stringing Techniques / Stringing Machines' started by pmacias, Jun 30, 2009.

  1. pmacias

    pmacias New User

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    I strung for many years on an AG drop weight machine. Not long after I bought it, I borrowed somebody's callibrator and was shocked at how off this machine was. In other words, if I set the weight at 62 I'd get something more like 55 according to the callibrator. I found a pretty reliable remedy which involved using both the tennis and badmitten weights, blah, blah.

    ANYWAY, I just bought a new machine--an upgrade: Gamma Progression II 602FC. I'm putting the thing together and wondering if I'm going to have the same situation: set the weight at my beloved 62 pounds but get something more like 55 pounds.

    Anybody's thoughts on this???
     
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  2. TenniseaWilliams

    TenniseaWilliams Professional

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    I would test it. The 602FC might be high end enough to be pretty close, but it is nice to know how far off your machine is compared to other stringers, assuming they are somewhat calibrated.
     
    Last edited: Jun 30, 2009
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  3. scotus

    scotus Legend

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    Your observation is significant in that the two dropweight machines apply the same tension, regardless of the number the calibrator indicates. That is, the callibrator shows 55 lbs for both and did not show any difference between the two machines.

    So you must ask yourself 2 questions.

    1. If indeed there is a discrepancy between the stringing machines and the calibrator, is it possible that the calibrator is in the wrong? Remember, it is 2 against 1.

    2. Is there a chance that both the calibrator and the two stringing machines are correct? That is, are you reading the tension from the correct end of the weight?
     
    Last edited: Jun 30, 2009
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  4. pmacias

    pmacias New User

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    No, I haven't calibrated the Gamma machine yet. Sorry, that was my lack of clarity. I'm just wondering if in general drop weights are known to be pretty inaccurate. Or, are some drop-weight machines, maybe higher end ones, actually pretty accurate.

    Of course, this is all out of curiosity. I don't string for other people anymore--just myself--so accuracy isn't really an issue. In other words, after a few jobs, whether the machine is accurate or not, I know I'll find a setting that gives me about 62 pounds.
     
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  5. Audiophile

    Audiophile Rookie

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    I have a Stringway dropweight (Laserfibre was marketing and selling them here in the US a while back) and have put the little Gamma calibrator I have on it several times. It has always been about as dead on as I can read. I've tried from 45 lbs. on up to 65 lbs.

    Dropweights are supposed to be very accurate, assuming they were engineered correctly. I'm not aware of any drop weight that even can be calibrated, not to say there isn't one out there. Will be interested to know when you get the Gamma together how it turns out. Best of Luck.
     
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  6. Bud

    Bud Bionic Poster

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    You hit the nail on the head. You won't get any stringing machine that's more accurate than a DW, assuming it's engineered and manufactured correctly. It will never go out of adjustment unless the weight is damaged, the rotating mechanism is severely under-lubricated or the gravity constant changes (highly unlikely!)
     
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  7. Bud

    Bud Bionic Poster

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    Hopefully, you know that on many dropweight machines, the tennis racquet weight and the badminton weight must both be on the bar when stringing tennis racquets. When stringing badminton racquets, only the smaller weight should be on the bar.

    I'd find it very hard to believe it was not user error... but possibly equipment malfunction (tension tester/calibrator). There is little that can go wrong with a manual dropweight machine.

    Looking at your numbers... I went and looked at my X-2... and if I was to remove the badminton weight from the bar and just string with the tennis weight... the final tension would be at least 5 lbs. too little (since the edge of the weight is now reading 60 lbs... when in actuality it's 55 lbs. (with the badminton weight on the bar). This error would compound at higher tension (as the weight is moved further toward the end of the bar). That is suspiciously close to the 7 lbs. you discovered.

    So, were both the tennis and badminton weights on the bar and jammed up directly next to one another when you discovered the 7 lb. error?
     
    Last edited: Jul 1, 2009
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  8. jmverdugo

    jmverdugo Hall of Fame

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    I have had my drop weight for about 3 years now. I have a calibrator too so I check it from time to time, it is always good. Maybe you are using the wrong side of the weight to set the tension?. You are supposed to use the machine side of the weight to match the tension desired on the stick.
     
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  9. diredesire

    diredesire Super Moderator

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    I'm going to chime in and second this post. Bud said just about everything I was going to.

    A) It's more likely the calibrator is off, it is basically a simple spring reference device, you need to confirm it against a known weight before you can trust it, especially when seeing errors such as these.
    B) It could have been user error. Any DW I've worked with (which is not really that many... at least 3 that I can think of..) have worked with both badminton/tennis weights on at the same time. (That I can recall)
    C) You should calibrate your calibrator against another calibrator that is known good. Several stringers have two calibrators, one digital, one "analog."
     
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  10. pmacias

    pmacias New User

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    Thank you guys! I got just what I wanted here: drop-weight machines are known to be accurate. Regarding my findings with my prior machine, I was fifteen years old with my head partially up my #$%; in other words, I think I failed to recognize when opening and putting the machine together that both weights needed to be used up against each other. I was pretty excited. Ironically, I "calibrated" the machine by using both weights, just not against each other, about an inch away from each other instead. So yes, user error I think explains what I found with my AG machine. Now, when I fire up my new Gamma, I'm going to set it at 62 and feel pretty good about what the results will be. Thanks for the feedback.
     
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  11. BurghKing

    BurghKing Rookie

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    Not to beat a dead horse, but user error on the dropweights is usually the cause for the tension being off. Also, the floating clamps are notorious for the not being as accurate as a fixed clamp. Try taking your calibrator to a shop to be calibrated just to be sure.
     
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  12. TenniseaWilliams

    TenniseaWilliams Professional

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    I was surprised at the results on my inexpensive dropweight. I loaned my scale (a digital ultrasport 50, ordered from a well known stringing site) to a friend with the same model stringing machine, and he had similiar results.

    I contacted the manf, he very politely told me I was an idiot, my scale was bad, I wasn't doing it right, etc. I exchanged emails with him, trying to figure out what I was doing wrong.

    My new travel stringer (an ancient LF/SW eco) tests within a pound on my scale. Does it really matter that much? Probably not, but I like to think I do what I can.
     
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  13. dancraig

    dancraig Hall of Fame

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    On some dropweights, the numbered scale is attached to the bar. It can be attached in the wrong spot and cause the tension pulled to be inaccurate.
     
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  14. SpinDog

    SpinDog Rookie

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    I know that your question was answered but out of curiosity I decided to check my own machine. I have a Gamma Progression II 602FC and an UltraSport50. I just set my machine up for 60lbs. I positioned the edge of the weight right between the hash marks at 60lbs. The UltraSport50 read 59.8 lbs.
     
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  15. Bud

    Bud Bionic Poster

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    I thought this may have been the issue :)
     
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  16. TenniseaWilliams

    TenniseaWilliams Professional

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    Has anybody else tested a dropweight with a nice scale like the UltraSport?

    I would assume any inaccuracy would be linear on a dropweight but it might be interesting to see measurements at 40lbs and at 70lbs as well. I have tested a very expensive (but old) electronic that was pretty much spot on at 70, but way low at 40.
     
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  17. SpinDog

    SpinDog Rookie

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    Gamma Progression II 602FC:

    At 40 lbs reference tension the actual measured tension was 40.3 lbs. At 70 lbs reference tension the actual measured tension was 70.4 lbs. The bar was as close to horizontal as I could get it but not exactly which would account for a slight error. The accuracy of the UltraSport50 can be +- .2 lbs. For all practical purposes the machine was right on target.
     
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  18. Il Mostro

    Il Mostro Banned

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    ^^^^^^
    Pretty phenomenal results.
     
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  19. SpinDog

    SpinDog Rookie

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    Yea, there goes my alibi! :???:
     
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  20. Koz

    Koz Rookie

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    It's Science

    [​IMG]
     
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  21. Il Mostro

    Il Mostro Banned

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    LOL. :) Yes it is science, but also more than a fair amount of technique in getting the arm parallel and in the same position every time.
     
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  22. TenniseaWilliams

    TenniseaWilliams Professional

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    It's also manufacturing tolerances.
     
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