Constant pull vs Lockout

Discussion in 'Stringing Techniques / Stringing Machines' started by Irvin, Aug 2, 2011.

  1. Irvin

    Irvin G.O.A.T.

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    My guess is less than one year. And yes string jobs do not normally berak at the knot but then again you don't have a constant tension on the string for a year either. When you clamp off the only force left is the frame. The string under its preset tension is the only force except for hitting the ball. I think less than one year. I will keep the bucket suspended in my basement storage area - temperature controlled (somewhat) and no sunlight what so ever.

    Irvin
     
  2. Posture Guy

    Posture Guy Professional

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    again, I'm no civil engineer, but isn't all matter 'elastic' to some degree? A steel beam is elastic if you put enough force on it, especially at certain temperatures.

    if any material would ultimately deform under load given enough time, then how do buildings stand? Especially those that have been up for hundreds of years? it seems like there has to be a demand over and above the material's intrinsic ability to withstand such demand to create such deformation.

    and I don't believe a paperclip will ever create such deformation in a thick rubber band. At least not in our lifetime.
     
  3. diredesire

    diredesire Super Moderator

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    Cool, i'm interested to see how it fares. I'd also rig up a poly experiment if at all possible :)
     
  4. SW Stringer

    SW Stringer Semi-Pro

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    String tests

    All installed string in a racquet is under "constant tension" which decreases very granually after the larger losses of the first hour. Brody and Cross calculate from their laboratory testing that the tension in a string initially tensioned at 62 or 40 pounds will drop to near zero in about 3 thousand billion years. My own testing of a Wilson OS racquet which I strung 9 years ago at 45 lbs shows about a 12 percent drop in tension which includes the higher initial losses after stringing. So that's nine years under tension and it hasn't broken yet. I have a Wilson T-2000 that's 38 years old with original string in the closet - still no broken strings due to tension.

    Another test that everyone is familiar with - The Golden Gate Bridge - has been standing for 74 years and hasn't fallen down yet due to constant tension in it's cables. Luckily the bridge was designed by engineers who preferred to drink rather than gargle at the Fountain of Knowledge.
     
  5. Kevo

    Kevo Hall of Fame

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    I think the biggest difference between CP and LO is the greater and more variable tension loss that occurs before clamping in the LO machine. Since in a CP machine the loss only occurs after clamping, there is noticeable difference. Remember that in a lock out, the tension loss starts as soon as the lock engages, and that loss happens in a longer length of string since the segment losing tension goes all the way to the tension head. Then when you clamp the string, you are starting with something less than the reference, and the loss isn't even comparable to what happens on the CP machine, because it initially occurred in a longer section of string. This also means the initial installed tension is variable on each section of string based on the length to the tension head.

    As far as which is better or worse, I don't think there's any question that technically speaking the CP is better, since each string will have a known tension at clamp time, but if you like the feel of a LO better, who cares about technicalities.
     
  6. barry

    barry Hall of Fame

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    I did a simple experiment with a digital fish scale. I connected one end to the center post, and the other end directly to the wise unit using a 17 gauge scrap string. I dialed in 50 pounds on my constant pull Wise unit and the meter read between 50 and 50.5 pounds. Then I disabled constant pull and the meter read 50 pounds constant at lockout. Since I clamp a string in less than 8 seconds, I never saw any variation. Plus no matter what you do, the lockout will occur when you clamp the string. If anything, the Wise CP may be less accurate than the CP, since the lockout was constant at 50 pounds, whereas the CP was fluctuating ½ pound. Point is if you have a well calibrated machine, with an experienced stringer, I doubt anyone could tell the difference if a racket was string on a klipper or a Star machine. The Star would take less time, but otherwise tension is tension.

    Another experiment I did was to setup a racket on my drop weight machine and let a string hang overnight with the weight. I thought the bar would move maybe a 1/2 inch after 24 hours. After the initial 5 seconds, there was never any noticeable movement.

    Kind of makes me wonder about CP, but I have all three type tensioners to play with, and still think electronic is way faster and easier to use. Like they say, perception is reality!
     
  7. dancraig

    dancraig Hall of Fame

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    For you that are recent members, barry is one of the original stringing members here. His posts have helped many people learn about stringing.
     
  8. SW Stringer

    SW Stringer Semi-Pro

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    Kevo says: " I think . . . Remember that in a lock out, the tension loss starts as soon as the lock engages, and that loss happens in a longer length of string since the segment losing tension goes all the way to the tension head. Then when you clamp the string, you are starting with something less than the reference, and the loss isn't even comparable to what happens on the CP machine, because it initially occurred in a longer section of string. This also means the initial installed tension is variable on each section of string based on the length to the tension head. . . . "

    I'm having trouble following your "Irvin-esque" logic here. By that I mean disconnected logic, hand waving and so many words that could have been condensed to fewer with more clarity, that although quite entertaining, still makes no sense. Do you have any test data to back up your assertions like Barry did in his post. Your point could become more clear with actual measurements. Thanks.
     
  9. Posture Guy

    Posture Guy Professional

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    that is just a great freaking line, I'm gonna be using that one.

    note: that is not a comment on any of the discussions on this thread. Just liked the line.
     
  10. Irvin

    Irvin G.O.A.T.

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    Since I have been asked I will. When I pull tension on a string whether it is with my Wise (constant Pull) or my crank / lockout tension the length of string is the same. I made sure to measure the distance where the lockout was and mounted my Wise tensioner to be the same.

    When tension is pulled by the Wise it keeps a relatively constant tension (give or take a small amount) until the string is clamped off. It normally takes me about 5 or 6 seconds to move a clamp and reposition it. During that time the tension on the string goes up and down as the string loses tension and the Wise pulls more. As soon as you clamp the string you isolate the string into two sections. The part of the string on the tensioner side of the clamp is constant until the tensioner is released. When tension is released the clamp with draw back because of the drawback from the string in the racket. The elasticity of the string is now the only thing creating tension any tension. When tension is pulled on the next string most of the drawback is recovered and the process starts again on the next string.

    Now tennis string is not like a rubber band in as much as tennis string offers more resistance to change. But it will yield to pressure. Watch this video made by 'YULitle.'

    http://www.youtube.com/watch?v=gwjDUQAGZMY

    I don't believe that. The next time you start your mains and pull tension on the first string before you clamp it release tension and look at all the slack you have in the string. The reason for the slack is the strings resistance to change. When tension is pulled on a tennis string the string pulls back with the same force. If it didn't the tensioner would never stop pulling. But the string continues to resist changing in length. When the tensioner stops pulling the string will continue changing because there is still a force on the string. That force is the elasticity in the string but that force will continue to drop as the string starts stretching or changing.

    Now let's look at what happens when you pull with a lockout stringer. Initially the same as a constant pull tensioner but after the tensioner locks the string starts to change it length and the tension on the string starts falling. If you clamp the string at this point you will have a lower stretch in the string than what you had with a constant pull. This lower stretch in the strings will produce a lower SBS.

    But if you pull tension again before you clamp you will have pulled the stretch to the same amount you would have had with a constant pull and you can achieve the same feel (SBS) with a lockout stringer as you had with a constant pull.

    Irvin
     
  11. Scooter

    Scooter New User

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    A steel beam is elastic under any load at all. Even the smallest loads will cause the smallest deformations. Elastic is a state in which the material will fully recover from deformation. Under enough stress it can enter a plastic state, which is where the materials fibers cannot take any more stress and then energy is released via permanment deformation.

    Generally buildings are designed such that the materials never reach the plastic state.

    Some materials can be of a viscoelastic behavior, which means that it uses stress relaxation, which is deformation over a period of time.


    Basically barring any sort of material deterioration, a constant load on a material should not eventually break it, unless it was poorly designed. In fact if tennis strings are viscoelastic (which i believe it is, because tension will slowly drop over years if you are not using it) the strings will be under less stress eventually, in which case it definetly wont snap on its own.

    This is all just the basics, and of course there is much more detail. A racquet string could surely break if left alone for years under many extreme temperature changes causing cyclic loading, which will weaken the material.
     
  12. Irvin

    Irvin G.O.A.T.

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    'Scooter' you seem to know what you are talking about. Thanks for your input. Let's assume that rather than a racket be left alone it was subjected to a constant pulling force. So rather than the tension dropping the string got stretched longer and longer. I believe sooner or later it will reach the plasticity limit state of the string and break. What's your take?

    Irvin
     
  13. Scooter

    Scooter New User

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    Well, there is two ways to look at this, not sure which one you mean.

    is this constant pulling force based on an initial stretch? For example lets take an exaggerated example and say you tie a string between two points such that it has very high tension in it (think of a rope between two trees perhaps?) in this case assume the force is high enough to cause any sort of plastic deformation and that it is the type of material that will stretch over time like i discussed in my previous post. in this cause energy is being released and the rope between two trees would eventually sag if it stretches (obviously exaggerated, but you get the point). to keep the force the same you would need to increase the distance between the "two trees" so the rope is taut.

    but if you mean taking a string, hanging it from the roof, then attaching a large weight at the end of it, yes then in this case it could get longer and longer until failure since the force is constant and stress can not be released through deformation.

    when it comes to tennis strings, it is the first scenario, since nothing keeps the force the same in the strings after some stress is released through deformation. nothing re-tightens the strings

    also the string in the racquet is one piece. you cant just have one main or cross elongating, the whole string everywhere would elongate in your theory. every cross, every main.
     
  14. Irvin

    Irvin G.O.A.T.

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    'Scooter' I agree with you completely. I was saying earlier that if a constant force was pulling on a string it would stretch until it broke. Like the weight on the rubber band I thought a 65 lb weight hung on a tennis string would eventually break the string as long as the weight never touches the ground to take the constant pulling forrce off the string.

    I am getting ready to go on vacation and will start a test on this when I get back.

    Irvin
     
  15. True Gut

    True Gut New User

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    Dang. Gone just two days and missed so much.
    Irving - do that bucket experiement! In your rubber band test, the weight you hung was greater than the elastic limit of the band, so it deformed permanently and eventually broke.
    How about this one. Take a fishing line that you know the test strength of (like 20 lb test for example - and not an old dried out that has been sitting in a drawer for 5 years) and hang a 10 lb weight on it. Will it just keep stretching till it breaks? Just be prepared to wait a while.
     
  16. Irvin

    Irvin G.O.A.T.

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    I am leaving to go on vacation tomorrow and I will do the bucket experiment when I get back. The rubber band did not deform permanently. After it broke it was the same length as it was before. But it did break.

    Irvin
     
  17. True Gut

    True Gut New User

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    Have fun. But be careful driving over any suspension bridges tho. You also might want to check all the pictures on your walls to make sure they don't fall while you are gone. And don't walk under any chandeliers. And don't drive into any real droopy overhead power lines. ;) The proof of what we are saying is all around you.
    Quick test. Try hanging that weight with ten rubber bands before you leave home. It won't be any closer to the floor when you get home..
     
  18. fortun8son

    fortun8son Hall of Fame

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    Ok, I admit my logic was flawed and my argument poorly reasoned.
    I'll try again.
    I do not believe that the concept of CP is inherently better than the concept of LO.
    As barry's above experiment proves.
     
  19. Scooter

    Scooter New User

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    Ah well in that cause it is certainly possible within the realm of material behavior standpoint, but it would be quite a poor design of a tennis string if that happen under only 65lbs. Thus i think all new tennis strings these days would easily pass that test.

    as for your rubber band test, rubber bands are extremely elastic. I dont recall, but will likely look it up soon out of interest, but i would assume it is more than possible for the material to fail either before plastic state or at the very start due to its properties, thus any plastic deformation is not noticeable. it isnt like a plastic bag which you can stretch alot before it breaks.

    plastic deformations are miniscule, especially in highly elastic objects. something as small as a rubber band, i doubt the plastic deformation could be observed by our mere eyes. I will look into it perhaps!

    enjoy your vacation
     
  20. Irvin

    Irvin G.O.A.T.

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    I did hang that 5 lb weight from 10 rubber bands so far it has dropped 0.25" in the first 45 min there was no noticeable stretch after the initial stretch. I will let you know what happens when I get back.

    If a tennis string is subjected to no more an initial 65 lb force I would agree with you but that is not what we are talking about. I think if the force remains constant long enough the string will break.

    In a tennis racket the string will not break because the elasticity of the string is the only force. As the string stretches the pulling force goes down, the tension drop slows, and because there is less tension the string would not fail from the force created by the string. If there were some outside force acting on the string causing a constant 65 lb force I think it will break.

    Irvin
     
  21. Scooter

    Scooter New User

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    It is all completely dependent on the material of the strings.

    Since most tennis strings are plastic based, to avoid large deformations they must be able to take significant force so they dont reach "plastic state"

    i would say there is just too many variables about tennis strings material behaviour to make a call on it. Under some forces, yes what you say could happen, but where do you draw the line on that force? will 40 lbs do the same eventually? 10? 5? why not just the weight of the string itself hanging for countless years? I can guarantee that such low forces will never break the string over time, but there is a threshold somewhere, which will be completely different for every type of string.

    My final thoughts: depends on the string, but 65 lb force will not guarantee a break if applied long enough. It might not even break any string, the string could reach an equilibrium where any stress relaxation (elongation) is used up, but the elastic portion can still hold it. I have no idea, but any guesses or experiments will only give us a small insight to that one type of string used, as every string will be much different.
     
  22. diredesire

    diredesire Super Moderator

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    Hey Barry, good experiment. I have a few questions, though.

    How accurate is your fish scale, what is the resolution? Can you try the same in ounces, grams? What is the approximate sampling rate? 1/10s?

    Has it been calibrated to a known weight? Or is this an "out of the box" reading?

    The reason I ask is because I think experiments like the one you ran are great, but they have to have some sort of validity to them. Basement experiments are only so useful, especially since the measurement tools are generally very poor in terms of resolution and accuracy.

    We also have to make the conditions as realistic as possible, IMO. I think the test should be performed through a tennis racquet, although if your fish scale is similar/identical to mine, it's actually pretty hard to get enough room :p

    What you say about lockout @ clamp is true, though. I disagree with your comments about a klipper vs a star, though. The tensioner may be a smaller variable in that case to the rest of the system. Some machines simply have much worse drawback (in clamps), and/or a worse support system, which would only serve to exaggerate the effect in this thread: http://tt.tennis-warehouse.com/showthread.php?t=397033

    Your dropweight experiment is an interesting one. I think the types of effects that we're discussing here would likely be much more apparent on longer lengths of string, but the theory still holds, IMHO. What type of string did you use, btw?
     
  23. barry

    barry Hall of Fame

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    The fish scales to a tenth of a pound. My setting was 50 pounds when doing the test. The Wise in constant pull showed between 50 and 50.5 pounds the same Wise in lockout stayed at 50 pounds. Since the same scale was used, it should be a good reference value. It was done with a 17 gauge poly string; Simple test, maybe some else with a Wise could report their finding, just turn on and off CP.

    My goal was to verify CP is real, or just a marketing term. Either way, I will never give up the electronic tensioner, just too easy and fast to use.
     
  24. Tennishacker

    Tennishacker Professional

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    Answer is easy.

    If you have the money, get CP, if not get a Lockout.
     
  25. max pl

    max pl Rookie

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    drop weights are constant pull and are cheaper than cranks for the most part.
     
  26. rjw

    rjw Professional

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    I've found that the few polys that I've strung have very little stretch, so that might be why you are not seeing any drop while in LO mode?

    I've only tested with multi and syn gut, which do drop a bit on my LO crank machine.

    I am curious to know if with a Wise in LO mode, if multis and synguts would lose a little. If not, then I'll never upgrade, unless mass production was a priority over feel.

    I've said this in a few threads, and I've only strung racquets for 4 other players, besides myself, but so far, we all agree that our racquets now have a lot more feel than when they were strung on high end CP machines, although it might be due to running lower tension on cross than on mains. (note: dt was the same as cp results so it is not necessarily due to lower tension)

    I think that a couple of stringers on this forum might agree, but probably not many.

    It's whatever makes you feel warm and fuzzy, I guess !
     
    Last edited: Sep 17, 2011
  27. diredesire

    diredesire Super Moderator

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    That's actually why I asked. I find that Poly is pretty bad at holding tension in absolute terms, but in terms of stretch, they're pretty bad as well. Thus, I'm curious as to how much variance you're going to see over very short periods of time (<5-10s). I'd be very interested to see the same experiment done on a syn gut. A syn gut should exaggerate/show the stretch phenomenon in a more realistic fashion. However, if you're just stringing polys, then it's a moot point.
     
  28. Rabbit

    Rabbit G.O.A.T.

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    I've tried it with quite a few strings on my wise. Poly,syngut, and multis all lose considerable tension a lot more and faster than I ever would have believed. Gut shows the least.
     
  29. Kevo

    Kevo Hall of Fame

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    I also wonder if the string barry used was the same piece. With poly it would be important I think to use a new never tensioned length of string.

    It would also be interesting in the LO scenario to use varying pull speeds from really slow to fast.

    I think it's pretty well understood from existing literature that strings start losing tension immediately. Of course I don't have a digital scale I can use for testing, but I'd give it a shot if I did. I'd have to figure out a way to simulate lock out though since I have a Stringway machine.
     
  30. Technatic

    Technatic Semi-Pro

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    Remaining elongation

    Hi guys,

    Very interesting discussion I would like to add my 2 cts perhaps it is useful.

    = The loss of tension depends completely on the remaining- and the elastic- elongation that occur when a string is stretched .
    * When the ball hits the strings and the tension exceeds the stringing tension a little bit remaining elongation occurs, the strings gets a little longer, and the tension goes down.
    * The elastic elongation maintains the tension in the string in the racquet, the higher this elasticity the lower the loss of tension.

    Monofilament strings show a lower elasticity and the remaining elongation is very different.
    A stiff mono is ok, but a stretchy one shows huge remaining elongation, these are actually useless strings which loose their tension rapidly.

    This file shows the elongation characteristics of monos and multis, the text is in Dutch.
    Remaining elongation = blijvende rek.
    Elastic elongation = elastische rek.

    www.stringway-nl.com/nl/TAonline/Int snaren rek..pdf

    As you can see the difference in “blijvende rek 20-40 kg” (remaining elongation) in the monos is huge and “elastische rek 20-40 kg” is lower (about 1 %) for monos then for multis (1,5 to 2 %)

    These figures are the reason that the monos loose tension much faster then multis

    = About the loss of tension during pulling:
    Some strings loose tension quickly and others stretch slowly, this depends mainly upon the friction inside the string, which slows down the elongation.

    The graphs show the tension during pulling with a LO tension unit.
    The type of string and the loss of tension is mentioned at the bottom of the graph.

    [​IMG]

    [​IMG]

    As you can see the upper nylon looses tension very quickly and the lower much slower.
    The upper mono looses 10 lbs slowly and the lower 13,2 lbs faster.

    As you can see all 4 strings stop loosing tension 10 seconds after pulling tension.

    Hope this is understandable if not please let me know.
     
  31. Posture Guy

    Posture Guy Professional

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    this is very interesting.

    it appears that 90% of the tension loss actually occurs in the first 4-5 seconds after lockout. it makes me wonder how much of that can be mitigated by either pulling more slowly before locking out (for example, increasing the elapsed time from start to stop of pulling from say 1 second to 4 seconds), or what double pulling would do.

    would also like to see those numbers for tension loss after lockout from a constant pull machine.
     
  32. Technatic

    Technatic Semi-Pro

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    Tension on CP units

    Indeed, when you pull slower on a lock out than the elongation is generated in the string there will be no loss.
    That is why they say: “ A fast stringers is a soft stringer”.

    If you do a double pull you loose less tension because all the remaining elongation that was developed in the first pull will not occur again.

    These graphs show the tension on an automatic drop weight tensioner and on an electronic CP tensioner.
    As you can see the CP accuracy of a automatic drop weight ist hard to beat.

    [​IMG]
     
  33. Irvin

    Irvin G.O.A.T.

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    I find it very very hard to believe that a high end electronic tensioner will allow the tension to drop 2 kg in a 3 second period before the tensioner re-tensions the string. But this is what I see from 9 to 12 seconds in the second graph in post #132. Am I reading this wrong?

    Irvin
     
    Last edited: Oct 13, 2011
  34. garywsyu

    garywsyu New User

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    It is easy to tell from the aboved graphical illustrations showing the tensional flunctuation of strings under different pulling systems.

    But it is understandable that the motorised actuator on high end electronic tensioner working up and down to maintain a "steady" tension in every 3 seconds interval.

    Thanks Technatic for bringing in such information.
     
  35. gamerluke

    gamerluke Rookie

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    Sorry to revive a very old thread. This was fascinating, though, and Irvin you never reported your rubber band test result after you came back from vacation (or your bucket test). Do you remember what happened?
     
  36. Irvin

    Irvin G.O.A.T.

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    Lol have no idea but I do remember discussing that vaguely
     
  37. gamerluke

    gamerluke Rookie

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    Dangit...must...know...what...happened...to...rubber...band...
     
  38. Irvin

    Irvin G.O.A.T.

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    Well there is a way to find out. I don't think mine broke or touched the floor but I am not sure.
     

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