For the dropweight, crank stringing machine

Discussion in 'Stringing Techniques / Stringing Machines' started by Ray_cn, Jun 20, 2012.

  1. Ray_cn

    Ray_cn New User

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    Hi, I'm from beijing, china. Doing some research about stringing machine.

    Recently I found there has a confused concept in how to choose the stringin machine. Someone thought that dropweight is more accurate than crank because of the Constant Pull. But after reading some paper about the constant pull and dropweight, such as "The_Importance_Of_Constant_Pull.pdf"(google), i think it's a wrong concept about the dropweight with constant pull.

    I read the "The physics of a dropweight tensioner ", It's great. Explained the princple of the dropweight lever.
    http://tt.tennis-warehouse.com/showthread.php?t=170414

    But I think it lost a variable about "string elongated", many people using Pre-Stretch is to solve this problem.

    CP(ConstantPull) is to solve this problem too.

    I just thought here has a mis-info about the DP(dropweight) with CP(ConstantPull).

    In my opinion, the CP is 1. Constant Tension, 2. Continuously Pull(for a time scale).

    CP is a time sensitive method, not easy to control. Here just talk about the princple of the CP and DP machine.

    Pre-Stretch is better. Using Pre-stretch is good choice for most stringer, it is easy to control and more accurately.

    As shown in the pic,
    Left is constant tension, continuously pull whether the string is elongated or not for a time. Because the weight is same, the R is same.

    Right has a lever, if the string is elongated for a time, the lever will not be hoding the H position. The string tension will not be same as before. f = (M g / r) (cos Q) R(from lethalfang). If the tension lost too much, for example Q=-90, the string tension is 0.

    So if add the "string elongated" variable, the DP is not a accurate system. It need people to adjust the tension.

    Some one said crank is not accurate because it is locked at the tension. But it is same as DP, it is losing tension after locked.

    kwun(badmintoncentral) made a caculate about the DP error. About 1.5%
    "force = weight * cos(alpha)

    the alpha is the same alpha that you listed in your diagram.

    but if you look at how the value of cosine changes, you will realize that even when alpha = 10 degrees (which is quite a lot), cos(10 deg) is only 0.9848, which amount to a error of 1.5%. that is hardly of any concern at all."

    I also do that for crank system.
    "As you said, if the string is elongated to 10deg, the r of the gripper is about 3cm.
    10/360*2*3.14*3=0.523cm, it means the string be elongated about 0.523cm

    For the dropweight machine, length of one string from the racket head to the gripper is about 40cm, if using a crank machine to pull the 40cm string, string elongated same, it is 0.523/40, the error is about 0.13%.
    "

    So the error for DP and crank is almost same.

    But for the crank machine, the string length from the racket head to the gripper is much less than 40 cm, it is much shorter than the dropweight, shorter string length mean tension lose less.

    After some research about electronic machine, I think the electronic is almost same as crank. Crank using hand and brand, electronic using moto and programmed chip.

    Then I got this machine choice instruction, Accurate, Performance, Price:
    Electronic >> Crank >> DropWeight >> Awls/Puller

    [​IMG]

    I also read the Stringway DropWeight Constant Pull machine. I think call it DropWeight+Constant Pull machine is better. Its point is "Lifts automatically at the position of the tenionhead."

    If I'm right, its princple is to put the string elongated at the left, then the lever at the right will hold the H position, the tension will be same even the string elongated. So it has a particular function to fix the dropweight problem. Most other dropweight machine didn't has that function, so they are DP machine, but no CP function.
    It's long... time didn't write english, hope it can explain clearly :p
    http://www.stringway-nl.com/USA/
    [​IMG]
     
  2. SwankPeRFection

    SwankPeRFection Hall of Fame

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    I think you're overlooking something here. With a lockout machine, once it's locked, elongation of string can still happen. With an electronic, the continuous pull on the string will negate the loss of tension cause by elongation. The same thing can take place with a drop weight if you wait for it to drop past horizontal and then ratchet up to zero back to horizontal. If you wait a good 10 seconds or so, elongation stops or slows down considerably and then you can clamp. This is how I string on both electronic heads and drop weights. It takes a bit longer, but the end result is a string bed that's pretty exact. If you rush and clamp at a faster rate, elongation becomes a larger variable and offsets your pulled tension on the loose side of the scale, usually well below what you wanted. This is why on a lockout, it's not unheard of to ask for 60 and get back low 50's or worse, depending on the pace of the stringer.
     
  3. Ray_cn

    Ray_cn New User

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    Yes, I think your work is great to wait the elongation time. Many stringer in china just thought faster is better.

    I think if operate the crank more slowly, for example from the 58lbs to 60lbs pulling at a slowly speed, 10seconds as your experience not 1second to finish it, I think it could get a correct tension too. Don't need release/repull, or ratchet up the lever back to the horizon position. But it need some more experience to control the speed.


     
  4. Ray_cn

    Ray_cn New User

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    I think your procedure is waiting 10 senconds for elongation stop then ratchet up to zero back to horizontal, then clamp the string.
    So after the crank locked, just wait 10seconds too. Then releae and repull. It's same as dropweight operation. Easy than control the pulling speed.

    Because the spring in the crank is pulling the string as what the gravity do in the dropweight.
    [​IMG]
     
  5. Ray_cn

    Ray_cn New User

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    Sorry, waiting the crank elongation maybe not good idea after I learned more detail about a real crank tension head.

    Here is a crank tension head. The whole tension head is locked. But the spring-lever-string is still working, that mean string is elongating and spring still pulling as what happened in dropweight. one is spring, one is gravity.

    But the 3 points limit the spring loosing length. 1.lever stopper 2.lever shaft 3.lever-gripper connector. Then the spring pulling(tension loosing) will stop when the gripper return to the position before pulling the string. The spring can't loose to the zero but the weight lever could drop to -90degree.

    But if the string elongation is less than the limit of the spring loosing. It's same as in dropweight. Then we can wait the string elongation stop in crank then repull.

    So I think the crank has continually pulling but shorter. The dropweight has continually pulling but longer.

    Then I think waiting elongating in the crank is not good idea except we know the string elongation limit, if shorter, it's ok. If want to using the constant pull with constant tension, pull again or pulling slowly is better.
    [​IMG]
     
  6. yan.v

    yan.v New User

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    This person came on Badminton Central trying to tell everyone that in all situations, crank machines are more precise than drop weight machines and that ultimately, it was the same as electronic machines.

    Unless you agree with him, there is no way out of it, as he will keep arguing, insulting people and using racist comments until he gets banned.

    Just a heads up.
     
  7. struggle

    struggle Hall of Fame

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    fun fun!! !!!!
     
  8. Chotobaka

    Chotobaka Hall of Fame

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    I love a good train wreck...
     
  9. Ray_cn

    Ray_cn New User

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    Sorry, it's your opinion, not mine.

    I'm learning the techniques of the stringing machine. So want to discuss with those who care about the techniques too.

    If something is wrong, it's ok, i admit my mistake. Not everyone can get A for everytime. That will help me to get correct knowlege and doing correctly.

    My english is poor, so I draw many charts about the machine to make the discussion easy, and that mean i'm seriously about the knowlege. And when I drawing these pics, it make me understand the machine more clearly.

    So what is your point about these techniques? My english is poor, could you please show me something about your point?



     
  10. yan.v

    yan.v New User

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    Hi Ray,

    I'm sorry the situation had to go down that way, and as I have said, the language barrier does not help.

    I did find the discussion in the thread you have created to be food for thought and a decent discussion. However, I think you went too far when you started posting that everywhere even though people did not agree, and then resorting to insults when we pointed out that it was not right to post that information in stickies, at least until the people who created or manage these stickies agree.

    As for the techniques and difference in accuracy between machines, I feel I have explained my points well in the thread on BC, so I will not type it again. It may not be formulated perfectly since English is not my primary language which could explain why you do not understand (or maybe you just disagree), however people usually understand what I mean pretty well.

    In any case, I'll just agree to disagree and leave it at that.
     
  11. Ray_cn

    Ray_cn New User

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    Let's talking about the technique of the stringing machine, not how to control one's freedom of speech, ok?

    I post mine, you can post yours too.

     
  12. Irvin

    Irvin G.O.A.T.

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    I would agree with whoever it was that said cranks are more accurate than drop weights. Not sure what you were talking about though with the electronic machines. A crank does not pull at a constant tension as electronic machines do.
     
  13. Ray_cn

    Ray_cn New User

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    I reply in here, focus on the principle of the crank and dropweight. Sorry my english :oops:

    I mean when the crank move to the tension, the string will pull the gripper up, then release the lock from the ratcht on the gripper, the head locked. During this procedure, the arm will go against the stopper as shown in that video.

    When the head locked, I think the green part, spring,arm,gripper,string are not locked. The compressed spring is still pushing the arm, the gripper on the arm is still pulling the string according to the lever theory. So if the string elongated, the compressed spring will push the arm closer to the stopper. That mean the compressed spring loosing tension and the string elongating.I think the compressed spring loosing speed is faster than the string elongating speed, so the spring is pulling the string continually.

    As you said many people thought the pulling stopped because the head stopped, I also think it is stopped before, but after I draw these chart, I think it is not stopped. Because the green part is not locked. But the stopper limit the distance of the continually pulling.

    I learned a method from your reply, "raise the tension on the dial after it is locked ", I think it is a Pre-Stretch function. Stringer can do this instead of repull. Dial to a higher tension and back is easy.

    To fix the string elongation, Temperature and humidity, Tension, Time are important(Stress relaxation,still learning). Increase these parameters will help the string to elongate completely.

    "Constant Pull" and "Constant Tension" is about the "Tiem" and "Tension" parameters. But I think "Constant Pull" is not a clearly concept, because for different strings, the elongation speed maybe different, so the pull speed maybe different too, so the "constant pull" maybe not clearly for this difference. For example, if it is pulling "Constant" we sholud know what the pulling speed is. So why we not say "speed" directly, as "speed" key in some electronic machine. I think the concept "Pre-Stretch" and "Speed adjustment" are better than "Constant Pull". Clearly and easy to control. For waiting the elongation in dropweight or crank, using time is clearly. Because it is pulling at a decreasing tension. Pulling with decreasing tension is slow than pulling with set tension or higher tension.

    As in the chart, I think crank and dropweight are same in princple. if the string tension fall slightly and weight pulling continually in dropweight, it will happen in crank too. Only when string elongated too much in dropweight, it will not be happened in crank because of the stopper limit the distance.


    [​IMG]
    [​IMG]
     
  14. Ray_cn

    Ray_cn New User

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  15. SwankPeRFection

    SwankPeRFection Hall of Fame

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    Remind me to bring my own stringer if I'm ever in Atlanta for extended periods of time. Wouldn't want you stringing my stuff. ;)

    Constant pull machines are always more accurate if used properly. If used poorly, ALL machines won't be accurate. Now, when I say accurate, I mean getting the string tension you asked for out of the job once completed and also being able to duplicate those results. It's been my experience that when I've had jobs done by the same stringers on an electronic vs crank, the crank always puts out sub-par (i.e. for me means looser) string beds when you ask for the same tension on both machines. Fact remains that with cranks you lose tension from the string stretching out after you lockout. This doesn't happen with constant pull machines (electronic or drop weight). I don't care how many diagrams anyone puts out or how many years you've been stringing. I know from both personal experience and from what I've gotten back from stringers and from what I've gotten back from those same machines when I just strung them myself instead. When I can take a racquet off a drop weight or electronic machine and measure the tension and get back within a pound or two loose from what I strung it at and then take the same racquet off a lockout crank and get tensions off by as much as 8-10 pounds, something's off with the technology.

    If you don't belive me that, then take a stringing machine calibrator and put it on a crank and measure the tension. You'll see that you have to quickly watch the tension EXACTLY at the time of the lockout at peak pull. Any amount of time after that and the tension will show dropping on the calibrator. Do the same with a drop weight or an electronic and watch how the calibrator hardly moves to a lower tension in the same linear fashion as the crank. That's enough to prove my point.
     
  16. Ray_cn

    Ray_cn New User

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    Yes, I think your experience is very good.

    I learned a useful experience from your reply, "waiting 10s". I think after the "10s", we should "ratchet up to zero back to horizontal", sorry my english, i think it is to adjust the gripper and lift the weight arm back to the horizon. Maybe call it "re-horizon".

    For dropweight, if the string elongated, it has the additional operation "re-horizon".
    For crank, it also has a additional operation "re-pull".
    If only dropweight do the additional operation, the crank doesn't do that, it's not fair.

    If only waiting 10s, do nothing for dropweight, then waiting 10s for crank. I think they are almost same. (Because the lever system is not excatly same, L1,L2 not equal to L1',L2'. the time maybe a little different.) But the crank has a stopper. So the pulling time maybe end before 10s in crank. For crank factory, increase the stopper distance maybe not a good idea, because using Pre-stretch or speed control is enough.

    For dropweight, the pull tension is decreasing according to the lever theroy f = (M g / r) (cos Q) R. Q is bigger then the tension is smaller during elongating. Actually it happend in crank too, head locked, but spring is loosing.

    But electronic is always puling at set tension. That's why electronic is more accurate. Pulling 10s at a set tension is more accurate than pulling at a decreasing tension.

    All these is in princple, as you said, a good skilled stringer is the key for stringing.


     
  17. Irvin

    Irvin G.O.A.T.

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    'Ray_cn' I just connected my tension gauge up to the lockout. When the string locks out the tension starts falling. The spring does not compensate for the stretch. When the tensioner locks out the brake keeps everything from moving forward or backward. The gripper and spring arm are still free to rotate on the shaft but the spring, arm, and gripper doesn't apply enough movement on the to keep the tension constant.
     
  18. Irvin

    Irvin G.O.A.T.

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    Most of what you way is true. With a lockout or electronic tensioner it is much easier to repeat the exact same tension when changing the tension between rackets. With a drop weight getting weight in the exact same spot is difficult. Once you tension a string and clamp it off tension start to fall no matter what you used to pull tension. Most of your tension is lost very soon after it is stretched. If you pull tension with a drop weight at 60 pounds when you clamp it off you may have something close to 60 pounds. If you pull tension a second time with a lockout when you are ready to clamp you will have 60 pounds time after time after time.

    Most stringers that use lockout machine pull once and clamp the string. If used that way you will have lower tensions depending on how fast or slow the pulling speed was.

    EDIT: Also with electronic when you pull tension it reaches a set point and stops and the string starts to stretch. When the string stretches far enough for the tension to fall far enough the tensioner pulls again. So it will go up and down and when you are ready to clamp off you may have about what you set on the tensioner.
     
    Last edited: Jun 25, 2012
  19. ART ART

    ART ART Semi-Pro

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    One question:

    Without using a calibrator or digital measure weight,

    Is there any formula/method to know the force(in kilos) that a drop-weight machine, is doing ?
     
  20. tball

    tball Semi-Pro

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    String elongation is easy to see on a drop-weight: just let it pull, and leave it there for 10 minutes.

    People who have crank machines, is there any way you could detect elongation on your machine?
     
  21. SwankPeRFection

    SwankPeRFection Hall of Fame

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    You still don't get it. If you do it right, the wait for elongation drop (10 seconds or whatever) takes the dropweight from slightly above horizon to horizon (i.e. exact weight and location of bar). If (and I say "if") the bar goes past horizontal and stops stretching the string and you ratchet backup, I always ratchet up and see if it drops again and usually it doesn't or is hardly noticible. It's the technique that's used. It's not as cut and dry as just let it drop past horizontal and then lift it back up. This is why I said that if your skill with your machine isn't good enough, you're going to get crappy results. Being OCD, it's not very hard for me not to rush a string job and pay close attention to repetition of steps for each pull. So again, you're overlooking a few factors here that aren't as you perceive them to be.
     
  22. SwankPeRFection

    SwankPeRFection Hall of Fame

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    Visually during the stringing process, no. If they do a test using a calibrator as Irvin did after my suggestion in my previous post, you will see it, as he did.

    I think those of you who don't see that a drop weight can be as consistant as an electronic (as long as the weight measurement is correct), haven't spent considerable time "dialing in" your technique with said drop weight to see what works and what doesn't. Don't get me wrong, you can't bust out a new one first time using it and get perfect results, unless you've used them contantly, but after a couple of jobs, you learn to dial in the perfect string job out of the machine. It can be very consistant. Of course, this has a lot to do with the machine design and the technique of the user. Those are the biggest factors with these machines. Think of them as crude strick shifts with no traction control, no power brakes, cable clutch car vs an automatic DSG, traction control, power brakes, etc. The skill of the driver doesn't need to be high to use the second car effectively, but the first one requires some skill to maintain effective behavior on the track.
     
  23. Irvin

    Irvin G.O.A.T.

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    I was not measuring elongation I measured actual tension loss. If the string stretched under a constant tension you would not see a difference. If you want to see the elongation in the string you could watch the spring arm but the movement is slight as the spring continues to push it.
     
  24. SwankPeRFection

    SwankPeRFection Hall of Fame

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    Right, "constant tension" (i.e. something that a crank does not apply). If you use a lockout and pull tension for 50lbs, after the lockout happens and the string stretches between the last grommet it goes around or the last clamp point and the tension head point, it will lose tension. This is the point I was trying to make sure people understand. The only way to negate this stretch and in turn the native tension loss associated with it is to somehow offset it by continually pulling on the string at the same tension until it stops stretching or slows down this stretching considerably. This is easier to do with poly strings, not so easy with syn guts or the like. Does this make sense to everyone?
     
  25. Irvin

    Irvin G.O.A.T.

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    You are getting close a lockout does not have the ability to pull tension once it is locked out (so to speak.) But after the lockout happens the string DOES NOT STRETCH it stays exactly where it was when it was when brake on the tensioner was engaged. You can see that string does not stretch in this video up to about 1 min 35 second into the video.

    http://www.youtube.com/watch?v=3aYI5DXQxSA&feature=plcp

    Now if you want to see the elongation of the string watch the video at 1.35

    What some people are failing to recognize is the lockout always pull to the set value time after time unlike a 'so called' constant pull which does not. I have a Wise electronic tensioner also. If I set it to 60 pounds it will pull to about 60.1 lbs and stop. When the tension drop to about 59.75 it will pull again to 60.1 pounds. That is not a constant tension.

    Just after I made that video (linked to above) it was shown at the GSS Symposium that by using a lockout stringer, with the method I demonstrated, one could replicate the same result as a racket strung on an electronic.

    All three stringers (lockout, drop weight, and electronic) have their own distinct advantages don't sell any of them short. Arguing which one is the best is a waste of time. There will always be those that like one better than all the others for different reasons.

    EDIT:
    With an electronic tensioner it is easy to do no matter what string you are using.
     
    Last edited: Jun 25, 2012
  26. SwankPeRFection

    SwankPeRFection Hall of Fame

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    In the video, when he's measuring the gap, he's already locked the clamp onto the turntable. Also, from the looks of it, it looks like the type of string he's using doesn't seep to stretch a whole lot. So, it's not really a good indicator. Besides, I've seen that video a while back.

    The point I'm trying to get you all to realize (and I'm surprised you keep arguing about it because you've noticed it yourself) is this. A calibrator shows string stretch on each machine when hooked up by it showing tension loss after lockout (on a lockout machine). Constant pulls can compensate for this CONSTANTLY, lockouts don't. While you can put twice or three times or a billion times to offset for this, that's not what I'm saying. Read CAREFULLY.
     
  27. Irvin

    Irvin G.O.A.T.

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    In the video when I measured the gap I did not have the clamp locked on the turntable. LOL It was not 'him' it was me. The string was Gosen OGSM which does stretch a lot. When pulling tenison (before lockout) there is a lot of stretch. Tension loss and stretch, it's one or the other not both. If the string is stretched under constant pull there is no loss in tension if there is loss of tension (as in a lockout) it was not stretched. On a drop weight there is stretch but no loss of tension. On a lockout there is loss of tension but no stretch (unless you pull again.) Constant pull don't compensate for stretch they cause it. lockouts can also compensate for tension loss by stretching the string on subsequent pulls.
     
  28. seekay

    seekay Semi-Pro

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    ISOSpeed Baseline demonstrates this to great effect. I once tied a length of it to my calibrator and pulled it to 60lb on a crank. Within 5 seconds, it had lost 10% of its tension, eventually settling around 52lb. That can be worked around, as discussed, but a stringer going for speed on a lockout machine isn't going to be accurate. They can, however, be precise.

    Based on my limited experience using all three types, I feel that:

    A drop weight should be very accurate, but it's possible for the tensions to subtly vary from string to string (while still being near reference).

    A lockout machine makes it easy to pull the same way every time (precision), but not necessarily ending up near the reference tension.

    A good electronic tensioner should be both accurate and precise every time. It's possible to match the results with either a drop weight or lock out machine, but the electronic machine makes it easier for the operator.
     
  29. Rabbit

    Rabbit G.O.A.T.

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    Quoted for accuracy and truth.

    Personally, I have strung on all 3 types, dropweight, lockout, and electronic. Here is my order of preference:

    1. Electronic - too easy to use not to like it and results are by far the most consistent

    2. Lockout - speed and ease of use are really nice along with dependability. Results are great.

    3. Dropweight - fun to start, but gets to be a PITA. Results aren't as consistent as the other two, but it's a great place to see if you want to string without dropping a house note.

    In the end, it's all what you get used to. I enjoy the "sport" of stringing and have invested my time in it. I started out with a dropweight and wound up with a Neos and then a Wise. For my money, you cannot beat an electronic tensioner. And, with stringing machines, the old adage "you get what you pay for" is as the golden rule. I'm quite sure if I stepped up to a Star 5, I'd think it was hands down better than my Neos.

    Edit: I will add, just for emphasis, that I've strung for myself and others on all 3. Of the 3, the Neos/Wise combination gives the best results and most satisfaction with my customers. The Neos was second, and the dropweight...well let's just say that they were getting a deal.
     
    Last edited: Jun 25, 2012
  30. Wikky

    Wikky Rookie

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    I suppose they could pull a string and then measure the pitch of the string by plucking it, come back 10 minutes later and see if it has the same or higher frequency. I doubt it would be any different though.

    I would personally rather string on a drop weight/CP any day rather than a crank as long as it had a supportive mount and good fixed clamps. There are just to many variables in a crank machine for me to feel that I am doing a consistent job over a days worth of racquets.
     
  31. sstchur

    sstchur Hall of Fame

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    The thing is, constant pull is time sensitive. The natural elongation properties of a given string are not. I have both machines, and I use my electronic more because I enjoy using it more. But I don't necessarily believe it is "more accurate."

    If I pull tension on the electronic at 60, indeed it will remain at 60 while it's pulling (save for very small ups and downs while the tensioner is adjusting). But the key is that the longer I wait before I clamp off and release the tensioner, the more I've stretched the string. Suppose I pull one string and wait for the tensioner to beep, and immediately clamp and release, and move on to the next string. I attempt to repeat, but suppose something or someone distracts me, even only briefly, 3 or 4 seconds say. That's still 3 or 4 more seconds of stretch on one string than on the other.

    With a lock out, I pull tension, it locks out, and the string naturally beings to relax. Doesn't matter when I clamp off. Nature is going to make that string relax at the same rate every time. Nature is pretty consistent that way.

    So every time I pull tension and it locks out, I'm getting the same rate of tension loss (or relaxation or whatever you want to call it). In that sense, a lock out is very consistent.

    It wouldn't be fair not to mention that just as there is human variability in how much time you wait before clamping and release with constant pull, so also there is variability in how slowly and steadily one can crack on a lock out.

    Is it easier to crank consistently, or is it easier to "move between strings" in roughly the same amount of time. I'm not claiming an answer to that question one way or the other.

    But I don't agree with people say "undoubtedly, unequivocally, 100% constant pull is superior and more accurate and over all better than lock out."

    It just isn't true. Both mechanisms are valid. Both have a degree of human variability. Neither is "good" nor "bad." They are different. But I believe you can be reasonably consistent with either one. And truth be told, the VAST majority of club players cannot tell any difference one way or another.
     
  32. SwankPeRFection

    SwankPeRFection Hall of Fame

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    And that's the part I don't agree with. Based on calibrator scale findings, this "relaxation" you're talking about is still stretch and is still time sesitive. If relaxation after lockout didn't affect tension, then a calibrator scale wouldn't peak and then drop off. By your example, it would peak and then remain there and it most certainly doesn't behave this way.

    On a crank, if you crank and it locks out and then clamp quickly and then take the same process but wait a bit before you clamp the next string you pulled, you'll get tension difference between the two.

    I think perhaps using the term string stretch is throwing people off to think that is a pulling motion to elongate, but whether this happens via the constant pull head or by simple relaxation of the string after lockout, it's really the same thing. The only big difference is that with constant pull, that "constant pull" negates the tension loss the string gets from relaxation. You really have to visualize it to see it clearly.

    If we had a calibrator scale video showing this on each of the three machine types, you'd see what I meant.
     
  33. sstchur

    sstchur Hall of Fame

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    I'm not talking about stretch in any sense. When you crank, you are stretching the string. Once it locks out, nothing is being stretched. Rather, the string is now relaxing, based on its natural properties. This will be consistent because it's the natural properties of the string.

    I did say that there is human variability during the stretch process, but that was was a side comment, and not my main point.

    Afterwards (after lock out) there isn't any stretch going on (the tension is never increasing after lock -- this is quite plain to see when you hook up a calibarator). Indeed, I've connected many a calibrator to both types of machines. It's easy to see what happens. Yes, the tension loss after lock out is significant, surprising even. But one thing it isn't, is inconsistent. That string is naturally going to relax at the same rate each time.

    EDIT: Also, you said:

    This is not at all what I am saying. In no way did I say or imply that tension peaks at lock out and remains there. If that is how people are interpreting it, I did not explain myself well.
     
  34. Ray_cn

    Ray_cn New User

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    Thanks Irvin, I will repeat your operation to see the detail of the arm-gripper movement when I get the tension head.

    Now here is what I learned from here:
    1. After the string get a set tension, e.g.60lbs, string elongation is alwasy happen, whether pulling continually or not. If pulling continually , the elongation will finish faster than not.

    2. Dropweight is continually pulling with decreasing tension. Cos(a) is not linear, from horizon to 25degree, tension now is 0.91, ~1% lost. 60lbs, now it is 54.4lbs.
    That mean, at horizon, pulling at 60lbs, at 25degree, pulling at 54.4lbs, continually pulling with decreased tension. It's easy to detect the string elongation and current tension.

    3. Crank is continually pulling with decreasing tension too. But the stopper limit the spring so it is not easy to notice that. I think the distance between the arm and the stopper is different while locked or not. So measure the distance will detect the elongation. Or the rotated angle of the gripper after locked. It's not easy to detect the elongation for crank. But not mean it is not pulling continually. If it is not pulling, release the lock, the head will not go toward the racket. Will confirm the detail when my tension head arrived.

    4. For dropweight, waiting 10s, then "re-horizon", for the crank, waiting 10s then "re-pull". The time maybe a little different. I think they are same operation for getting a accurate tension. It need a good experience stringer for time control.

    5. For crank, pulling slowly before locked, e.g. 10s from 58lbs to 60lbs then locked. Maybe a useful method too. But need a good experience too.

    Learning many from here, thanks for all the discussion hope i could be a good stringer as you all in future :D

    For ART, Here is a formula: f = (M g / r) (cos Q) R http://tt.tennis-warehouse.com/showthread.php?t=170414
    Maybe put a soft ruler on the indicator is easy to get the current tension if the arm is not at the horizon position. If Dropweight factory could change the indicator to a scale ruler with degree and tension percent of the horizon is better. i.e cos(20)=0.94 , current tension = horizon tension *0.94, or cos(40)=0.77, then current tension = horizon tension *0.77
    Assume the circumference is 18cm, sorry the 40degree should be at the left of the 20degree.
    [​IMG]
     
  35. Rabbit

    Rabbit G.O.A.T.

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    You are 100% correct and great posts. I had an epiphany when reading your posts. A lockout is basically the same as a strung frame. In other words, once tension is pulled, it's exactly like if the frame were strung and just sitting there. In both cases, there is no further force or action on the string. It is basically inert (for lack of a better word).

    So, you are exactly right. The string begins to act as if it were installed in the frame and tied off. The difference is that you have a clamp on the string until you pull tension on the next.

    I too would rather string with an electronic tensioner as it is easier and more enjoyable. But I completely understand your point and agree with you.

    Again, great insight.
     
  36. Irvin

    Irvin G.O.A.T.

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    ^^The lockout is like a strung frame with a method to tighten the string after it is strung.

    Imagine, if you can, a drop weight machine with the ability to pull tension slowly on a string and then after a any set amount of time the arm drops and stops exactly at horizontal with absolutely no overshoot what-so-ever. Also that drop weight had a method to set the tension at exactly any amount in pounds or kilograms no matter what the altitude was. Now you have the ability to use a drop weight to match a string job as good as you can string on a lockout.
     
  37. SwankPeRFection

    SwankPeRFection Hall of Fame

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    And I don't think I've ever said that it is inconsistant and I certainly agree with you that the only variable in that which would show differences in the tension loss is the length of string between the two tension points (i.e. longer mains or crosses will relax more than shorter ones because there's more material there to work with). That's never been a point I've tried to make about crank machines. My gripe with them is that you get inconsistant string bed stiffness from them as opposed to constant pull ones. What that means is NOT that the inconsistancy is all over the string bed. What that means is that what I ask for in string bed stiffness and what I get from a crank is far less looser than what I get from a constant pull machine. With that also comes the idea that I don't have to ask for an initially higher LBS increase just to offset that relaxation that happens after lockout that's inherent to cranks.

    Along with this comes a VERY important aspect. Strings have their own sweetspot for elasticity and response. If I have to pull the **** out of a string to get the same overall string bed stiffness that I'm after with a crank, there's a good chance that I'll "deaded" the liveliness of that string after a certain point, not to mention the added stress to a frame if I have to go over the max tension scale on it to get the end result after resting. If I can accomplish the same by pull for a longer and more constant pull rate with less weight, it'll be more efficient then overloading a string with a ton of weight just to hope that it doesn't relax way below what I want out of it.

    This is what I'm trying to get across, not that cranks are all over the place in consistancy within the bed of the racquet you're stringing. That was NEVER a point I was trying to make. The inconsistancy is the vast stiffness difference you see in the stringbed from a crank vs the same racquet strung at the same tension on a constant pull machine.

    The bottom line is, a lot of people who always got their frames strung on cranks all of a sudden realize that they actually play with a string bed that's looser than what they originally thought. People asking for 60lbs on crank are now asking for 52-54LBS on constant pull because they're seeing the same feel and string bed stiffness out of that as they were from the higher "pull" tensions they were on a crank. This is what I'm trying to say... as long as you get that, then we're all on the same page.
     
  38. SwankPeRFection

    SwankPeRFection Hall of Fame

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    lol, you're seriously going to argue altitude as a gravity negator for using a drop weight machine? :lol: :rolleyes:

    Unless you're stringing in space, this isn't an issue, AT ALL.
     
  39. sstchur

    sstchur Hall of Fame

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    Oh I never meant to imply that the overall string bed will feel that same on a lock out as on a constant pull. Most definitely the resulting string bed you get from a lock out is softer than what you get from constant pull. I think everyone gets that, and I don't think anyone will argue.

    But I also don't think it matters. I don't fool myself into believing, that if I set my machine at 60lbs, that every strings is going to end up at exactly 60lbs. That is not (and never has been) my goal when I string a racquet. We call the tension a "reference" tension for a reason.

    If I string the Mains at tension M and the Crosses at tension C, what matters to me is the resulting string bed feel. Do I like how M & C feel? And can I reproduce it?

    The answer to the 2nd question is yes, whether I'm using lock out or cp. The answer to the first question is purely subjective.

    I think where we disagree is that you seem to be saying that 60CP is somehow "more true" or "better" than 60LO. I don't believe this. I concede that they're different from each other (maybe even significantly so), but I don't concede that one is better than the other.

    And I also don't concede that 60LO is going to vary each time you do it. 60LO is 60LO. It's neither good nor bad. It's absolutely reproduce-able, every time.

    And 60CP is 60CP. Surely stiffer than 60LO, and equally as reproduce-able, but not inherently "better" IMO.

    The many many nuances of the resulting string bed aren't of really high importance (to me). If I set my machine to "foo", all that matters is:

    1. I like how tension "foo" feels, and
    2. That I can reproduce tension "foo" next time around

    Tension "foo" might be (scientifically speaking) tension "bar" in reality, but I don't care. And neither do my customers. And in fact, I think the string bed is far more complex than simply tension "foo." But that's another discussion, and not one I'm interested in right now.
     
  40. Irvin

    Irvin G.O.A.T.

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    Just for the record I don't agree. Let me point out a graph from the pdf file mentioned in the OP's first post:

    [​IMG]

    From this graph I can understand why people believe a lockout stringer will produce a softer stringbed. Everyone can clearly see that most of the string's relaxation is in the first ten seconds. So if I pull tension with a lockout and clamp off the string according to this graph if I set the tension to about 67 lbs after ten seconds it will drop down to about 54 pounds there about. But after 10 second the string has relaxed and there is no appreciable amount of tension loss. What do you think happens if you pull tension again after 10 seconds?

    EDIT: Also 60CP on an electronic constant pull is not 60CP. For those of you who know anything about an electronic CP you should know the tensioner cuts in at a point somewhere below the set tension (60CPL) and stops again somewhere above the set tension (60CPH.) Therefore 60CP is somewhere between 60CPL and 60CPH. Where as 60LO is 60LO time and time again.
     
    Last edited: Jun 26, 2012
  41. sstchur

    sstchur Hall of Fame

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    Irvin, your post confuses me. As far as I can tell, we're saying the same thing, and yet, you say "for the record, I don't agree."
     
  42. Irvin

    Irvin G.O.A.T.

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    ^^We are not saying the same thing. You are saying a racket strung on a LO will be softer than one strung on a CP I am saying it does not have to be IF you pull again (at 10 seconds.)
     
  43. sstchur

    sstchur Hall of Fame

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    Well sure, IF you pull again. Most people don't though. If you'll remember, I completely agree this method of using a lock out. I posted an experiment about a year or so ago, where I strung two of the exact same racquet with the same string on the same machine, and with one of them, I strung 10% higher, and on the other, I didn't increase tension, but I double pulled every string. Upon playing with each racquet, there was no significant/discernible difference to me.

    And I theorized that double pulling was a legitimate method of going from CP to LO (just as the USRSA recommens a roughly 10% increase when going from CP to LO).

    So I still believe we are saying that same thing. You agree that if you're not double pulling, a LO string bed will be softer than a CP, don't you?

    Double pulling is perfectly valid IMO, but we both know that most stringers using a lock out machine, aren't doing this.
     
  44. Irvin

    Irvin G.O.A.T.

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    Yes I do but what I have been saying all along (since post #25) is you have to double pull.

    EDIT: Unless of course you have a smart spring tensioner. http://truetension.com/TTSM.gif
     
    Last edited: Jun 26, 2012
  45. sstchur

    sstchur Hall of Fame

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    Ok fair enough. Admittedly, I had not been reading every single post in this thread, so I wasn't aware that you had been talking about double pulling all along.
     
  46. SwankPeRFection

    SwankPeRFection Hall of Fame

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    Nice graph, I think that shows exactly what we're all trying to agree upon. This is exactly what I was talking about. However, I would put money on it that a CP machine (drop weight or electronic) would maintain a pretty straight graph after the initial tension was reached (overlooking the drop in measurement while you re-ratchet the dropweight if needed to attain horizontal again if it drops below due to excessive relaxation/elongation/stretch of the string).

    The idea in my head is, if I ask for 60, give me 60. Don't give me freaking 50 or 52. I think because of that, it's been my experience that I can take a CP machine and return a more consistant request to myself or my clients without having to screw around with pulling twice or three times or how ever many times it takes to make sure the LO machine pulls the string and maintains it at the tension I set it to until I clamp. That's all I'm trying to say.

    Also, back to your previous video where you second pull after clamping... I dunnot how much of that slack or relaxation you're really pulling and getting it back to the set tension. I say this because we all know even if you don't lock the clamp to the table (which you said you didn't in the video even though I saw your hand go down to it momenteraly after clamping the string) the clamp base pivots enough to stop with force from string tension to keep it from slipping on the rails. What I would love to see is a graph like you have above where you're measuring the entire process from the initial pull, to clamp, to second pull, etc. I'd love to see what that would look like in regards to that reference tension you're asking the machine to give you. Then I'd like to see the same with the other two types of machines. I think it would show some really cool info that stringers could use to get a better understanding of what's actually going on with the string as you string on each various machine. You'd be surprised how many stringers just think that you're getting the same relative tension from ANY machine you use regardless of what you use and how you do it. :rolleyes: That's what I'm hoping to put to bed with this thread.

    Great info so far though...
     
  47. Irvin

    Irvin G.O.A.T.

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    Imagine a graph like the one above and at the ten second mark the tension goes back up to the initial lock out level and pretty much remains there. Same thing that happens when any CP machine when you clamp the string and remove the tensioner the tension starts to fall. But the fall after the first ten seconds will be much less and much slower.
     
    Last edited: Jun 26, 2012
  48. SwankPeRFection

    SwankPeRFection Hall of Fame

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    I don't want to imagine anything. If someone is going to provide hard scientific proof for one finding, there should be the same for all variances discussed. There is no room for imagination. It's about proper testing.

    Three pieces of string of equal length. Same distance between clamp and puller. Different machines all set to the same tension (crank and electronic calibrated prior to test).
     
  49. jxrojas

    jxrojas New User

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    Personally, I've been working with a lock out for the last month, and I do second pull after 7 to 10 seconds, but I do not clamp after the first pull. Using this, I've been able to get really consistent string jobs which come really close to the used reference tension; for example, yesterday I strung a K Six.One 95 with Solinco Tour Bite 1.20 @ 52/50 lbs and the tension read immediately after stringing was 51.7 lbs (using RacquetTune, which is quite precise).

    I think the bottom line of this matter is to just try to be as consistent as possible and always strive for quality over speed. That's what every stringer should strive for IMO, no matter if they use a CP, a Drop-weight or a LO.

    Jon
     
  50. Chotobaka

    Chotobaka Hall of Fame

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    Wow, what a blast from the past. True-Tension were brilliantly designed and seriously built pieces of equipment that were made for the long haul.
     

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