Tension loss with crank machine

Discussion in 'Stringing Techniques / Stringing Machines' started by mars76, Oct 6, 2010.

  1. mars76

    mars76 Rookie

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    Hi All,

    I tried calibrating my crank based Stringing machine and i have set the tension to 50lb and when i started pulling the tension head as soon as the scale showed 50lb the tension puller got locked.

    How ever then there is a tension drop of around 6lb !! (the digital scale dropped to 44lb) Is this normal ?? Or does it has any thing to do with the test string i have tried for calibrating ..

    thanks
     
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  2. Irvin

    Irvin G.O.A.T.

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    No matter what type of tension head you have when the pulling force is removed the string will relax and you will lose tension. Problem with a crank is that pulling force is removed immediately the the lockout occurs unlike a constant pull which pulls until the string is clamped.

    Irvin
     
    #2
  3. MAX PLY

    MAX PLY Hall of Fame

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    And the tension loss will vary from string to string, depending on what it is made of. It is simply one of those variables you need to account for in stringing (and that is true irrespective of your machine type). However, I use kevlar string on my calibrator since kevlar stretches very little and is pretty durable. I feel that a string that doesn't stretch much gives me the "truest" reference tension and I calibrate on that basis.
     
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  4. dgdawg

    dgdawg Professional

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    +1 for MAX PLY's kevlar suggestion. This will give you the most accurate reading from a calibration stand point.
     
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  5. mars76

    mars76 Rookie

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    Thanks a lot guys..

    I will try with kevlar.
     
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  6. Technatic

    Technatic Semi-Pro

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    Loss of tension on crank machines

    Your experience is perfectly right, the tension drops directly after the system locks.
    The difficulty for stringers is that the final loss of tension depends strongly on the type of string and can be betweeb 6 and 17 lbs.
    A stringer can only compensate for the loss when he knows how much a certain string looses.

    The graphs below show how a crank machine pulls tension and how much is lost.
    The graph at the bottom shows a simple automatic CP dropweight with the same strings.

    [​IMG]

    [​IMG]

    [​IMG]
     
    #6
  7. dgdawg

    dgdawg Professional

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    Ha ha ha......I love posts like this.
    Forgive my if I'm getting "off topic", but I guess this does fit the "theme" of the OP.
    Please, no disrespect intended......but there are so many variables that go into one string job, they ALL contribute to the SBS.
    I think it's good to be familiar with these variables, and the diff things that contribute to tension loss.
    SBS is ALL RELITIVE.
    Relitive to: Type of string, size of the head, type of tensioning system, angle of pull, M's v.s.X's, gauge of string, drawback of clamp bases, I could go on and on.
    You could unwind 20' of string off a spool, cut it into 10, 2' lengths, measure the elasticity of those lengths and get 10 diff readings.
    You could take 2 stringers, on the same machine, with the same methods and tendencies, and get 2 diff results.
    You pull M's and X's at a spicific tension, you will get 2 diff readings (if you could even get readings).
    My point is, I think this stringing thing gets "over analyzed" to the point that ppl get hung up on a spicific element of the "craft" and forget there are 10 other factors involved.
    The key (IMPO) is consistency. The objective should be (again, IMPO) to pump out as consistent a job as possible.
    I would like to think that, when a customer brings a frame to me, it will play the same way it did last time they brought it to me. That is my goal, anyway.
    I am not an expert, and I'm not a physicist. I do consider myself a professional but I'm sure there will be ppl that disagree with everything I just said, and that's what makes a public forum a public forum.

    Disclaimer: This is only MY opinion
     
    #7
  8. Technatic

    Technatic Semi-Pro

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    Hi dgdawg

    If you love these kind of posts I hope that you do not mind when I disagree a little (otherwise there would not be a discussion).

    I think that you put the matter up side down;
    The SBS is certainly not relative it is the absolute value that the stringer feels when he plays.

    Therefore more and more stringers change to “stringing on stiffness” instead of on tension.
    Stringing on tension means that all the variables that you mention have influence on the end result which means a difference of +/- ??? % when you measure the stiffness of 10 stringers with there machines at the same tension. And ??? is more than 10!!

    Stringing on stiffness means that you choose the right stiffness for a player and calculate the tensions for specific racquets from there.
    I know stringers who check the stiffness with a Stringlab / ERT 300 and can obtain the desired stiffness +/- 1 kg/cm (dt value).

    To calculate the tensions depending on the size of the racquet and the number of strings they use the Tension Advisor.
    [​IMG]

    I disagree with the fact that consistency is important, it is the SBS value that should be consistent certainly when you string for many different players.

    Of course only my opinion also!
    What do you think?


    These threads tell more about stringing stiffness:
    http://tt.tennis-warehouse.com/showthread.php?t=338693

    http://tt.tennis-warehouse.com/showthread.php?t=298443
     
    #8
  9. Fearsome Forehand

    Fearsome Forehand Professional

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    The above graphs indicate the OP's cholesterol is high.:)

    I'm lucky that I never worry about stuff like this. I just string a racket. If it comes out tight with no misweaves and plays well, I'm happy.
     
    Last edited: Oct 7, 2010
    #9
  10. Pinkskunk

    Pinkskunk Rookie

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    Who Makes "smart Weight Tensioner" ?
     
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  11. dgdawg

    dgdawg Professional

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    Hey Technatic-I don't mind at all that you disagree. As you stated, that's what makes it a "discussion".
    I've used the ERT 300. I was intrigued by it....until a customer brought his over for me to check out. I strung his racquet and measured it about 15 times with the ERT. I got 13 diff results. I read the instructions over and over....it just didn't work.
    As I mentioned, I'm not an expert....I do consider myself a professional and....pretty knowledgeable...but far from what I would call an expert.
    Please forgive me, I don't want to come off as arrogant or disrespectful, but I could not disagree more with any comment I've ever heard: "I disagree with the fact that consistency is important". In IMO (and the opinion of ppl I do consider experts) consistency is the most important thing.
    You can calculate everything you want, factor in elasticity ratios, but if you're not consistent with tensioning rates and clamping time, along with draw back on clamp bases, you're going to have different results.
    I guess, my friend (I say this sincerely) this is one topic we will have to agree to disagree.
    I will maintain, until experts prove me incorrect, that consistency is the main factor in achieving consistent string jobs.
     
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  12. Ash_Smith

    Ash_Smith Hall of Fame

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    I think (hope) Technatic was meaning that consistency of SBS is important - this would suggest therefore that your consistency when stringing is also important - without consistent technique you won't get consistent SBS - I hope that's what he was getting at anyway!

    In respect of the ERT - it's a great tool for measuring your consistency - I check each racquet as it comes off the machine and record it in my customer database. Then, when they come in next time I have a record of the tension and SBS - this allows me to try to match it if that's what they want or change it accordingly.

    Cheers

    Ash
     
    #12
  13. Technatic

    Technatic Semi-Pro

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    Sorry for this misunderstanding.
    No need to explain because Ash already said exaclty what I meant.

    Btw: Measuring tools like the Stringlab and the ERT300 are quite vulnarable tools which have to do a difficult job:
    The tool has to generate the natural frequency of the tool on the stiffness of the strings and measure this frequency.
    After that it has to calculate the stiffness of the string bed with the formula C=6,28*m*f^2.

    If there is a lot of difference in the measuring result there is something wrong with the Piezo elements or the mounting of the piezo in the housing.
     
    #13
  14. SW Stringer

    SW Stringer Semi-Pro

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    Technatic, interesting post, this is the first time that I've seen an equation for calculating SBS for the ERT devices. Is m the combined mass of the strings and the ERT device in kilograms? I have a racquet that pinged at 523 Hz (natural freq of stringbed alone) and using m=0.015 kg I get a C = 27900 which is obviously too high. Do you know of any way of calculating an ERT number from the natural frequency of the stringbed alone, knowing the mass or density of the strings? I've got years worth of stringbed frequency data that I'd like to convert over to a standard SBS number such as the ERT's use.
     
    Last edited: Oct 8, 2010
    #14
  15. Technatic

    Technatic Semi-Pro

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    Calculating stiffness from frequency.

    _______________________________________

    I see that you did not get an answer to your question:
    Laserfibre and Stringway both offer “Automatic Constant Pull” drop weight systems. Stringway calls his “drop weight” a “smart weight” and his foot operated machine a “smart spring” machine.

    I think that your calculation could well be the right stiffness.
    m = mass in kg and you get stiffness C in N/m.

    This means that your stiffness is 27,9 kg/cm or Dt value. And this is the stiffness of the stringbed alone, because it acts as the spring in this system.

    The value is a little low what is the range of frequencies that you measured in those years.

    If you look at this route map you can see the stiffnesses for different types of man – players.

    [​IMG]
     
    #15
  16. SW Stringer

    SW Stringer Semi-Pro

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    Technatic, It looks like the DT number is the stiffness number C, divided by 1000. I checked a Wilson N3 (113 in^2) strung with Wilson NXT 16 at 60 pounds (644 HZ) which works out to about 40 DT units at a 4% stretch factor. I compared that number to Wilson N3's in the Stringforum dot net database of DT values and it's in the same range. Also comparing racquets of the same or similar head size using Wilson NXT 16 at 60 pounds an excellent correlation was found there too. Thanks for solving my dilemna. The 523 Hz number was from a racquetball racquet - normal tension range is 28 to 45 pounds hence the lower frequency.
     
    Last edited: Oct 11, 2010
    #16
  17. Bud

    Bud Bionic Poster

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    Completely normal and the amount of tension loss depends on the string type. Crank type machines usually string about 10% lower than CP/DW machines.
     
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  18. Rabbit

    Rabbit G.O.A.T.

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    Again, there are other factors as well. A dropweight with fixed clamps will produce a much tighter stringbed than a dropweight with floating clamps on the lower end. Simply stating a dropweight is better than a lockout machine is really disingenuous and misleading unless one considers the other components.

    It was my experience that there was a -8 pound difference when moving from a Gamma Dropweight to the Prince Neos. In other words, I had to back tension down by 8 pounds to get close to the Gamma's string job. The reference tension on the Neos strung racuets was more consistent and felt stiffer. The Gamma produced a much softer stringbed. The Gamma I had came with floating clamps. There was always noticeable drawback with the floating clamps.

    Now that I've moved to a Wise tension head, I've seen a further decrease in tension of about 6 pounds. Where I was stringing my frames at 54 with poly, I now string them at 48 to get the same approximate feel.

    What is different between the crank and the electric tension head is more consistency. The electronic tension head produces a more consistent string bed. The Wise has a feature that I really like. It has two modes, constant pull and lockout. So, if someone comes to me and says I'd like it strung at 55 with Prince SynGut, I can set the machine to 55 in lockout mode and observe the tension drop. I then reduce tension to the new number and string the frame. The final results are more consistent.

    The other really nice thing about an electric tension head with a digital readout is that you know what the tension is from start to finish. In other words, if you clamp off and start pulling and a clamp is set too loose, the tension creep/drop is visible and you know you have a problem. This is not the case with either a dropweight of any caliber or lockout machine. The digital readout then is invaluable when producing consistent results.

    To the OP, it's all what you get used to. If you're used to stringing on a Gamma dropweight as I was and setting the tenison at 65...great. If you're used to stringing on a Neos and setting the tension at 56.....great. And if you're stringing on a Wise and setting the tension at 50....great. Tension is only a number and is corrrelated to the machine you're using. IME, I find the most consistent results for an entire string job come from an electronic tension head used on a machine with a sound mounting system and fixed clamps.
     
    Last edited: Oct 11, 2010
    #18
  19. mad dog1

    mad dog1 Hall of Fame

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    actually, Bud didn't say one was better than the other. he simply stated that a crank machine usually string about 10% lower in tension than DW or CP machines. that's all.
     
    #19
  20. Rabbit

    Rabbit G.O.A.T.

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    Which is completely misleading if the dropweight in question is one with flying clamps per the omitted part of my post. In point of fact, a crank maching with fixed clamps will deliver a higher reference tension (+8 pounds) than a dropweight with flying clamps again per the omitted portion of my post.
     
    #20
  21. Technatic

    Technatic Semi-Pro

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    As you can see in the grahps a lock out can looses 8 to 17,8 lbs.

    A dropweight with good quality flying clamps really does not loose 8 lbs more than fixed clamps also because most of the drawback will be compensated on the next pull.

    you can read more about the quality in these treads:
    http://tt.tennis-warehouse.com/showthread.php?t=149446

    http://tt.tennis-warehouse.com/showthread.php?t=315762

    I even think that triple clamps loose less because they are not connected to the machine and the drawback in minimum.
     
    #21
  22. gotwheels

    gotwheels Semi-Pro

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    SW Stringer (& Technatic): In your reverse calculation back from stringbed frequency to DT (or stiffness C), was m the mass of the main & cross strings (stringbed weight)? Also, is your frequency from the Freqmess program?

    Technatic: I always enjoy your comments and find them usefull in understanding the relationship of the stringing process to performance of the stringbed.

    Good stuff!
     
    #22
  23. Technatic

    Technatic Semi-Pro

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    Hi Gotwheels,

    Good to hear that my posts are useful.
    I refer to the use of the Stringlab or ERT300

    In the calculation of the stiffness with a measuring tool like the Stringlab or ERT300 the mass in the calculation is the mass of tool + a percentage of the weight of the stringbed.
    You can understand that that part of the stringbed that is closer to the frame has less influence on the frequency.

    In the I-phone system only the mass of part of the mass of the stringbed should be in the calculation.
    I guess that you have to take 40 to 60 %.
     
    #23
  24. SW Stringer

    SW Stringer Semi-Pro

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    The m I used was the total weight of the installed strings (mains and crosses) which I calculated by subtracting the leftover lengths of string from cutting the tail of the knots from 40'. Since it was a 17 gauge multifilament I weighed the leftover stuff, measured it and came up with a mass per foot of 0.4447 grams. I get the frequency from a Korg instrument tuner, but Freqmess or Audacity (free audio processing software) would come up with the same number. I plugged the two numbers into the equation from Technatic's post and also checked my DT number with the Stringforum dot net DT database which showed close agreement for the racquet ,tension, and string that I used.
     
    #24
  25. Technatic

    Technatic Semi-Pro

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    Hi SW Stringer,

    This is interesting.
    There must be some inaccuracy because a stiffness of 27 kg/cm is too low for good playability. (If you are not a lady with an arminjury).

    Stiffness for a man should be 34 to 37.

    The question is; what could cause the deviation?
     
    #25

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