Stringway ML100 constant pull tension measurements

Discussion in 'Stringing Techniques / Stringing Machines' started by Joonas, Dec 9, 2013.

  1. Joonas

    Joonas Semi-Pro

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    I decided to post this in the general thread instead of Stringway users thread. Perhaps it is useful to some one who is not yet an SW user.

    First of all apologies for loosely commenting on this on some thread before. I double checked the pulling accuracy of ML100 automatic constant pull machine and results are not that I stated before here. Now I took the measurements many times, from different attach points of the scale and repeated.

    Stringway claims that the pulling tension is not dependent on the angle of the weight lever. I wanted to believe this and enjoy stringing with "most accurate machine in the world".

    I set the tension to 25kg and checked the tension first the lever in quite down position - not "flooring the lever however. The tension read 24,45kg. Not too far from 25kg but not 25kg.

    Then I checked the tension with lever on clearly higher position. Now the reading was 26,93kg.

    The difference between positions is about 2,5kg.

    Most of the time when stringing racquets you end up using more or less same angle and in my case it is more at high than low. So obviously I am tensioning little higher than what I believed to. This explains why I get usually higher tension when measured with Racquettune than my set tension is.

    Now I don't know if this is a big problem for me. At least I know how it is. But naturally it annoys a bit when you don't have what you believed you had.

    Pics of the measurements can be seen here: https://plus.google.com/photos/103578011377325984720/albums/5955521540171399617
    The angle of lever is bit hard to see but gives you the idea however.
     
    #1
  2. tennis4

    tennis4 Rookie

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    By examining the pictures you posted here, I found the contact points of the lugguage scale hanger and the racquet support columnn are not always the same across all the pictures, ie, the support column is hooked at the hanger's right corner in picture 1, picture 2 the contact point is near the middle of the hanger.

    I would redo the experiment while trying to use the same contact point for all scenarios.
     
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  3. Maui19

    Maui19 Hall of Fame

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    I got similar results. The actual measurements were sensitive to setup and the angle of the pull, but the results were in line with what Joonas found. My bar was set at 48 lbs, and my test readings ranged from 47.0 (low bar) to 50.3 (high bar).

    Not earth shattering, but not what I was expecting when I paid $1,000 for this machine.

    In the end, I like the stringer so far, but they need to stop telling people it is as accurate as a drop weight machine.
     
    Last edited: Dec 10, 2013
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  4. verbouge

    verbouge Rookie

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    I, too, have found the same thing. It IS disappointing, but I've used that machine so much, I've come to love it. I find that for my machine, the reading is most accurate when the top of the red tension head is level to the floor. So if the bar goes too far, I take up the slack and reset the head higher, all in one motion.

    This detracts from the "peace of mind" and "ease of use" of the ML 100, for sure. I still find the stringbeds resulting from this machine are very close to what I intend, and that the true constant pull of the machine results in less tension loss as I play.

    It would be best if Stringway were to come clean with this, and either include this information in the instructions, or remedy the underlying problem through engineering.

    By the way, I also own an MS200. Although this is a fabulous machine, and I have strung many hundreds of racquets on it, the same is true regarding the position of the tension head. I use the same work around for this machine as for the ML100.
     
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  5. Irvin

    Irvin G.O.A.T.

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    It seems strange to me that so many people have believed this "automatic drop weight" for so long and never bothered to test it. Don't believe anything you hear and only half of what you see.

    BUT on the other hand how many times have he heard the tension is just a number. If you set the tension to x lbs and you like it then that's a good thing. If it feels good do it. And if you like an SBS of 32 and you can attain that ay y lbs what's your problem?
     
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  6. tennis4

    tennis4 Rookie

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    Guess what, I believe all of them that the accuracy is conditional. Without knowing the pulling mechanism in details, I just find it amazing or hard to believe what Stringway said about "automatic".
     
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  7. struggle

    struggle Hall of Fame

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    i never believed it. but i figured it was close enough and having used a traditional DW in the past I'd have tried to be consistent just the same.

    this is hypothetical, i've never used one (stringway), just figured...

    edit: perhaps someone with "positive" results can reply, in regards to the numbers, I understand most folks love their Stringway machines. all good with me.
     
    Last edited: Dec 10, 2013
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  8. Power Player

    Power Player Talk Tennis Guru

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    I get so close that the differential does not affect me at all.

    ****I don't string for a living, just for myself*****
     
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  9. bbulla

    bbulla Rookie

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    I have an ML100 as my 'other' machine, and got an electronic tension calibrator to test the machine. I set the weight to 58lbs, and it measured out at 59lbs. That was consistent to all the other markings on the 'ruler' for setting tensions on the Stringway. So now I know when I want 50, I actually set it to 49. I would imagine there are tolerances in the manufacturing process that would cause this.

    As far as the 'angle' of the arm, I have found that regardless of the angle it still pulls the same tension....as advertised.

    So as long as you adjust the weights according to some sort of measured scale and not just the 'ruler' that comes with the machine, I would say it is very accurate. It's definitely not any less accurate at pulling tension than more expensive electronic machines.
     
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  10. Maui19

    Maui19 Hall of Fame

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    I do have to add that the machine is a dream to string on, and I'm sure I won't have trouble getting the SBS I want. My annoyance is that I bought a machine that was supposed to do something and it doesn't. If I had known this, I probably would have gone in a different direction.

    I am also surprised this hasn't been discovered before.
     
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  11. bbulla

    bbulla Rookie

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    When I did my testing I was testing more for setting the weight in the right spot on the bar....not really considering the angle of the bar. Perhaps I will try it again and see if I can see what you are saying.
     
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  12. Joonas

    Joonas Semi-Pro

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    Ok guys. I was talking today to Fred Timmer from Stringway about this. Maybe my tone was bit too negative initially.

    To put it shortly there is mistake in the way I made the measurement. I attached the scale freely to other end post of frame support. That is fine but as the tension head moves on the vertical axle the angle of string is changing and multiplies from longer way. Fred pointed out that actual tension should be measured inside the frame. There is alway friction after grommet exit unless the path is exactly horizontal.

    This is what Fred answered to me:
    "The principle is that the horizontal component of the tension H multiplied with the lever V = W multiplied with the lever H.

    When the tensioner turns forward the tension Te has an angle with H and will be heigher than H.

    However; In the racquet the horizontal Tension H will be tension in the string bed, the vertical component V will pull the string down and cause a frictioni.

    So it is important to measure the horizontal component of the tension, because that is the actual tension working in the stringbed.

    Because of the friction we want to pull the tension in an horizontal line, but when the tensioner turns forward there will always be an angle."

    I have attached the drawing he refers to behind the same link as the original pix are https://plus.google.com/photos/103578011377325984720/albums/5955521540171399617?partnerid=gplp0

    Of course I had to verify his words. Now I set up scale inside the frame and made the same measurements. Now all the results within "normal" angles of lever were really close to ref 25kg. Overall lowest I measured 24,62which is 1,5% off from ref tension. Not too bad. Highest I got from very extreme up angle was 26,22 which is 4,9% higher than ref tension.

    Range between "normal" high and "normal" low were 25,12 - 24,63kg. This gave me back the confidence. I added few pictures of correct measurements inside of the frame.

    So no worries with tensions after all.
     
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  13. Irvin

    Irvin G.O.A.T.

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    Go on and make your measurements inside the frame. They will still be off and the farther you go from the center of frame the farther off they will be.
     
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  14. Maui19

    Maui19 Hall of Fame

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    I love it when things work out.
     
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  15. Joonas

    Joonas Semi-Pro

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    Irvin, did you read my latest post? I did do the measurements inside the frame and I explained the results. My luggage scale is so big that I would need a Big Bubba to move the position of the scale dramatically.

    But I am happy of 0,5kg delta in "normal" usable weight lever positions.

    Joonas
     
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  16. marco forehand

    marco forehand Rookie

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    Good on you for your follow up post. My experience has been that I get a very consistent string bed, using a Stringmeter to measure the results across the stringbed as well as an ERT 300. I have decided the Stringmeter is a better tool, for whatever that is worth.
    I had, because of the consistent results as I've measured them, never thought to try your original experiment. When I read your post, I was concerned at first, thought about it some, and decided the results speak for themselves.I wasn't going to get overly concerned.
    Still I appreciate the effort and the follow up on your part.
     
    #16
  17. Irvin

    Irvin G.O.A.T.

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    Sorry not I did not read all of it. It should be easy to test though. Use the setup you have and if you have a starting clamp you could measure all the mains I would think (and or crosses.)
     
    #17
  18. Joonas

    Joonas Semi-Pro

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    I was using fixed clamp and looping the string through grommet. But yes, a starting clamp would provide another easy way as well.
     
    #18
  19. A Defenseless Creature

    A Defenseless Creature Semi-Pro

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    You should also use a Kevlar string on your tension measuring device. synthetic strings have too much elasticity for best accuracy.
     
    #19
  20. Joonas

    Joonas Semi-Pro

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    Your comment might be good with lock-out machine.

    With constant pull it doesn't matter. Only thing with softer string like syn gut is that weight bar drops further down during tensioning. During the course tension stays the same. String is just getting longer and longer.

    I have measured with both syn gut and poly. Note also that after few measurements especially the poly has stretched to the point that it will hardly stretch any more.
     
    #20
  21. Irvin

    Irvin G.O.A.T.

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    If you don't have access to a stiffer string you need to make sure you use the initial reading.
     
    #21
  22. Joonas

    Joonas Semi-Pro

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    The reading doesn't change much. When I left the string under tension the drop was like 0.01 kg in half a minute. This was with already much stretched Poly (Signum Poly Plasma Pure 1.23)
     
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