constant pull phraseology

[barry]

No. Not conjecture. Those in the industry who read the trade publications just accept it as common knowledge. Try asking Ken at Babolat or Albert over at GSS and see what they say. You'll learn what I am stating is not just "conjecture." There is substance behind the point I am trying to make. Since you prefer for me to locate a source, how about the USRSA? They say "Constant-pull machines pull the string to the desired tension, but when the string starts to equalize and lose tension, it pulls a little more again to stay at reference tension." It's in the 2004 String Machine Selection Guide. http://www.racquetsportsindustry.com/issues/200409/200409machine_guide.html This is obviously an adjustment that is more complex than a hobby drop weight machine continuing to pull because of gravity.

Still, I believe they put an asterisk in the constant pull column of the guide because the manufacturers want it that way. It sounds better. The USRSA knows where the truth lies.

I read on another post, the USRSA has said nothing negative about either LF or Eagnas machines. Earlier there were comments to that effect. The USRSA says if you want the machines rated, then the vendor has to send them a machine to review! Guest LF and Eagnas decided not too.
It is very obvious the USRSA has more knowledge on stringing machines and better metrics than you or I. I tend to believe what they document, since they are unbias.

 

[Stan]

My understanding of constant pull machines is as ADC states, FWIW.

 

[David Pavlich]

No. >>This is obviously an adjustment that is more complex than a hobby drop weight machine continuing to pull because of gravity.<<

A drop weight doesn't have to make an adjustment since the laws of physics are a constant and undeniable. Whereas, each electronic machine has a characteristic called "hysterisis". Explained by Albert, it is basically the amount of tension creep that takes place before an electronic machine pulls again to get to the reference tension. Babolat's latest machines (Sensor and Star 5) are very sensitive in this area where as others are not as sensitive.

Since you enjoy hypotheticals, let's do this one: A very good pro stringer is in the midst of doing Andy Roddick's frames. The first main he clamps, he catches at the exact moment the machine pulls after it reaches it's hysterisis setting. Then the next main he clamps he catches just before the machine is to adjust for the tension creep. Oops! Two unequal strings. Probably off by tenths of a pound. So, does that make it a bad string job? No. It's picking nits which is what this hypothetical is doing.

So what you get with "lesser" electronics is a variance in reference tension depending on the hysterisis. Not so with a drop weight. It pulls the reference tension when the arm is lowered. It may be off a few tenths of a pound because of the angle of the arm, but it pulls constantly...more constantly than my Sensor because the drop weight has no electronic settings to interfere with the tensioning.

If you wish to discuss the accuracy of each machine, then, as I stated in my initial post in this thread, you have to bring in clamps and mounts. This is where the hobby machines fall off of the spectrum.

In the end, a drop weight is CONSTANTLY PULLING. That is undeniable...it's physics 101. An electronic, in the strictest sense, isn't because of hysterisis. Sure, it compensates, but the drop weight doesn't have to. It is the purest form of CP. We aren't discussing accuracy; we are discussing constant pull and you cannot, if you are intellectually honest, say that a drop weight is not a CP machine. Any physics profs out there care to tell me that I'm wrong?

David

 

[hangzhou]

David:

Do you think lock out machine as CP machine, Yes or No?
I guess your answer would be no, right? But according your logic, lock out machine should be viewed as CP machine as well. After you pull the string and lock the tension head, there is tension on the string just like you pulling rubber band with your two hands. Before clamping the string, string will creep or yield to such stress, thus the true tension will drop. But the tension head is still holding the string or pulling the string. If not then the string will go back to its original length and tension will disappear. So there is tension on the string and this true tension will decrease. Just like regular drop weight machine, crank machine has to be CP machine using your approach.

Then every machine is CP machine, including crank, regular drop weight, LF and electronic mahcines. Then CP concept become meaningless...

 

[A Defenseless Creature]

It is unbelievable that seemingly even the well educated are having trouble with the intended use of the term "constant pull machine" within the industry. It's not that hard of a concept to grasp. Really it's not that hard people, but most of you amaze me in that you still can not come to grips with the reality.

I am through trying to use this forum as an educational setting. It's obviously not going to happen. As for the hypothetical David presents, he is correct, I enjoy them. I also agree that to create the most accurate and consistent string job a number of factors need to be considered. Factors that are not involved in this discussion. Yes drop weight machines and gravity are constantly pulling, BUT they are NOT pulling to the set reference tension. Pulling to the set reference tension is what we should be talking about, yet people just don't seem to get it.

No David, your Sensor is not constantly pulling. That's the whole point. It is pulling to and maintaining the set reference tension. Something more complex than most simple gravity driven machines can achieve. In a sense this is the industry definition of constant pull and should NOT be confused with "Constantly Pulling." Two different terms entirely!!!!

It's been fun.

 

[barry]

David:

Do you think lock out machine as CP machine, Yes or No?
I guess your answer would be no, right? But according your logic, lock out machine should be viewed as CP machine as well. After you pull the string and lock the tension head, there is tension on the string just like you pulling rubber band with your two hands. Before clamping the string, string will creep or yield to such stress, thus the true tension will drop. But the tension head is still holding the string or pulling the string. If not then the string will go back to its original length and tension will disappear. So there is tension on the string and this true tension will decrease. Just like regular drop weight machine, crank machine has to be CP machine using your approach.

Then every machine is CP machine, including crank, regular drop weight, LF and electronic mahcines. Then CP concept become meaningless...

Constant pull definition
A “constant pull” machine uses either gravity or electric tensioning and continues to pull tension as the string stretches, and, until the tensioning head has been “deactivated”.

Lock out machines deactivates the tension once the desired tension is set, which does not qualify them as constant pull machines. Drop weight and most electronic machines continue to pull until the strings are clamped off.

Hard to believe you guys can't understand such a simple concept as constant pull. The USRSA defined it for us correctly.

So to answer the origianl question. All drop weight machines are constant pull! Lock out machines are not!

 

[Newberry]

I've never strung a racquet in my life- and I don't own a stringer, but I am a curious bystander of this thread.

Genuinely trying to understand here, but after watching the videos of a constant pull electronic stringer, I wonder how long the machine is allowed to "take up" the excess stretch?

For instance, if the machine tensions and is allowed to sit for 20 seconds, and does three "adjustments", but a subsuquent pull takes a bit longer and the machine tensions for twice that time and makes five adjustments (because the string continues to stretch) doesn't your consistency suffer?

Doesn't the string continue to stretch for days after its installed? It would seem that this would make contant pull a bit "over the top" as far as really improving the string job?

Taking a lockout machine for an example, its cranked to tension, locks out, and that particular length of string will stretch X amount. No adjustment is made by the machine, but as long as the material is consistent, the length of string being tensioned is the same, & the time under tension is similar, wouldn't each pull stretch the same amount, and produce a more consistent string job?

Just trying to understand thanks!

 

[wonder_wall]

In the end, a drop weight is CONSTANTLY PULLING. That is undeniable...it's physics 101.

In the same sense, it's physics 101 that two fixed clamps holding a string are constantly pulling (hangzhou's point to you).

Let's start with one of your claims that we can really put our finger on: You believe the machine is a constant pull machine independent of arm angle, you've said that very specifically here: "in the strictest terms, the drop weight is constantly pulling regardless of the angle of the arm."

It seems you want to reduce the term to mean nothing about what happens pull to pull, as you call that a mere "accuracy" issue. So according to you, even if a Klippermate is well-known to produce consecutive pulls that can easily be three or even five pounds apart, and to fix that you have to re-pull, that's a matter of inconsequence to you, all that matters is what happens DURING THE PULL.

Strange, but let's take your position for a sec then.

The "slope" of the line in the chart I gave which I'll copy again below tells you how much tension is lost AS TIME PASSES at a given starting point on the curve (USING ANGLE AS A PROXY FOR TIME).

At 60 lbs and if you start 20 degrees down, if you pass through let's say one degree due to string stretch, you are GUARANTEED TO LOSE a bit over 1/3 pound. If you go through 2 degrees, you are guaranteed to lose 3/4 pound.

At 70 lbs same thing: 1 degree of movement takes off 0.43 lb, 2 degrees 0.88lb.

In other words, WITH A STRETCHIER STRING AND STARTING FROM AN ANGLE SUFFICIENTLY AWAY FROM HORIZONTAL IT'S NOT ENTIRELY CLEAR IF ANYTHING WOULD BE HAPPENING DIFFERENTLY FROM WHAT HAPPENS ON A CRANK.

Now, David, I think you'll agree that terms should mean something, and you've said a crank is definitely not constant pull, so I believe in order to continue arguing the point, you will have to change your position to say, well, when close enough to horizontal it is constant pull. Please tell me if you agree or disagree...

Pic reproduced again, I'm optimistically hoping some people on here are color-blind, so changed the curve to thick, black line:

 

[David Pavlich]

Last post here:

A drop weight machine, once the arm is past the breakover point, is constantly pulling because gravity is a constant. I've purposely left out the accuracy part of the debate which I did in my first post. It may not be pulling the correct tension due to operator error, but it is still pulling the tension that the arm angle is allowing it to pull. In other words, the arm set at 60 lbs may be pulling at 50 lbs because of any number of errors, but it will continue to pull at 50 lbs because gravity hasn't changed while the arm is hanging there holding onto the string. This is 4th grade science.

Now if you want to talk about the stretch that occurs at a specific angle, I suppose that if you want to take 3 hours to string a frame, then you may have an argument. But in the real world, it tension..clamp, not tension, go have a sangwich, then clamp. I'll concede that tenths of a pound may be lost. However, it is still constantly pulling.

If you grab an 8 lb sledge hammer and hold it at arm's length, it is going to pull you arm down and will continue to pull your arm down with the same force no matter how strong or weak you are and will eventually wear you down so that you drop it. The hammer isn't getting heavier, your arm is getting weaker. Is that difficult to understand?

Next, a clamp or a crank machine holds the string in place, it's static, stationary, it doesn't compensate for tension creep. Not meant to offend, but Hangzou is wrong. A crank machine is not a CP machine. Your assertion that I should change my position is wrong. My argument is backed by the laws of physics.

You can all get hung up on semantics, but physical law is on my side. I'm a long standing member of the USRSA, an MRT, and if Greg Raven or David Bone or Crawford Lindsey would like to tell me that a Klipper isn't constantly pulling, I'll tell them the same thing...go back to school and take a basic science course. Gravity is constant, therefore the arm of a drop weight machine is going to pull at a specific tension as set by the operator, unless you go have that ham sangwich between pulls.

And for the last time, my argument leaves out accuracy (I have to repeat this because the subject of accuracy keeps coming up when arguing against my side of this even though I've REPEATEDLY stated that accuracy is not a concern for my argument). If you want to make that part of this, start another thread. Then I will tell you why I use a Sensor instead of a Klipper.

David

 

[barry]

Last post here:

A drop weight machine, once the arm is past the breakover point, is constantly pulling because gravity is a constant. I've purposely left out the accuracy part of the debate which I did in my first post. It may not be pulling the correct tension due to operator error, but it is still pulling the tension that the arm angle is allowing it to pull. In other words, the arm set at 60 lbs may be pulling at 50 lbs because of any number of errors, but it will continue to pull at 50 lbs because gravity hasn't changed while the arm is hanging there holding onto the string. This is 4th grade science.

Now if you want to talk about the stretch that occurs at a specific angle, I suppose that if you want to take 3 hours to string a frame, then you may have an argument. But in the real world, it tension..clamp, not tension, go have a sangwich, then clamp. I'll concede that tenths of a pound may be lost. However, it is still constantly pulling.

If you grab an 8 lb sledge hammer and hold it at arm's length, it is going to pull you arm down and will continue to pull your arm down with the same force no matter how strong or weak you are and will eventually wear you down so that you drop it. The hammer isn't getting heavier, your arm is getting weaker. Is that difficult to understand?

Next, a clamp or a crank machine holds the string in place, it's static, stationary, it doesn't compensate for tension creep. Not meant to offend, but Hangzou is wrong. A crank machine is not a CP machine. Your assertion that I should change my position is wrong. My argument is backed by the laws of physics.

You can all get hung up on semantics, but physical law is on my side. I'm a long standing member of the USRSA, an MRT, and if Greg Raven or David Bone or Crawford Lindsey would like to tell me that a Klipper isn't constantly pulling, I'll tell them the same thing...go back to school and take a basic science course. Gravity is constant, therefore the arm of a drop weight machine is going to pull at a specific tension as set by the operator, unless you go have that ham sangwich between pulls.

And for the last time, my argument leaves out accuracy (I have to repeat this because the subject of accuracy keeps coming up when arguing against my side of this even though I've REPEATEDLY stated that accuracy is not a concern for my argument). If you want to make that part of this, start another thread. Then I will tell you why I use a Sensor instead of a Klipper.

David

David I think you finally “hammered” it home! All drop weight machines are constant pull! Lock out machines are not!!

 

[wonder_wall]

...in the real world, it tension..clamp, not tension, go have a sangwich, then clamp. I'll concede that tenths of a pound may be lost...

So, you're saying in my example of 1 or 2 degree change and almost a pound lost at 2 degree change, it's irrelevant because it will take a half hour or more to move through 2 degrees? Really? Even with like let's say 17 gauge nylon multifilament at 70 lbs?

If there's a string that I can prove to you could move 2 degrees in say 30 seconds, would you be more convinced it's a relevant point? (Offhand, don't know if there is, but could check it out, quite sure you're wrong about it taking 1/2 hour...)

Keep in mind also, I started at 20 degrees only, I could make the situation way worse for the drop weight machine if I started at 45 degrees or more. According to your claim, it still would not matter? According to your initial claim keep in mind, I can use any starting deviation I want and make the situation much worse for your argument.

I can check these things out and get back to you, think you can easily be proven wrong.

 

[SW Stringer]

Newberry posits: "Taking a lockout machine for an example, its cranked to tension, locks out, and that particular length of string will stretch X amount. No adjustment is made by the machine, but as long as the material is consistent, the length of string being tensioned is the same, & the time under tension is similar, wouldn't each pull stretch the same amount, and produce a more consistent string job?"

You've hit the nail on the head, and on stretchy string if one doesn't clamp off at the same time interval after reaching tension (on a CP elecronic) the variation in tension from string to string will vary more than the lockout machine. In my opinion, the Wise head set to lockout mode will give more consistent stringbed stiffness than it will in CP mode for that very same reason. Any of you Wise owners out there want to test that hypothesis?

 

[David Pavlich]

So, you're saying in my example of 1 or 2 degree change and almost a pound lost at 2 degree change, it's irrelevant because it will take a half hour or more to move through 2 degrees? Really? Even with like let's say 17 gauge nylon multifilament at 70 lbs?

If there's a string that I can prove to you could move 2 degrees in say 30 seconds, would you be more convinced it's a relevant point? (Offhand, don't know if there is, but could check it out, quite sure you're wrong about it taking 1/2 hour...)

Keep in mind also, I started at 20 degrees only, I could make the situation way worse for the drop weight machine if I started at 45 degrees or more. According to your claim, it still would not matter? According to your initial claim keep in mind, I can use any starting deviation I want and make the situation much worse for your argument.

I can check these things out and get back to you, think you can easily be proven wrong.

You could "what if" this to death. If you use a drop weight, do you stand there for a while before you clamp off or do you tension and clamp like any stringer would? Do you put the arm at 20 degrees one time and then 45 the next or do you do it the corrrect way?

Hey, I could take my machine to the top of Mt Wilson and get a different RDC reading than if I strung it here at sea level. How much do you want to move statistics around? We could do this until our fingers turn into nubs. Maybe we can throw in humidity.

Theory is fine. In the world of stringing, good stringers strive to do what is supposed to be done correctly. Look at your figures from that standpoint which is where I base all of this stuff.

Look, the drop weight pulls continually, just like I stated in my first post. I've seen statistics demonstrating the tiny differences from one degree to the next. If you stand around watching the string stretch while it's under tension from the tension head, that's fine. I don't have time to do that. Besides, the Sensor will release tension after so long, so it wouldn't work for me.

All I said was that the drop weight pulls continually, again. If you want to keep bringing up the differences because of operator error, then fine. I am going to give you the benefit of the doubt and say that I believe that you don't string like that. I'm willing to be that you do your best to make sure everything is correct. In the real world, which is where I do my stringing, gravity is a constant and will pull the same everytime...if the operator does his or her part.

David

 

[David Pavlich]

Newberry posits: "Taking a lockout machine for an example, its cranked to tension, locks out, and that particular length of string will stretch X amount. No adjustment is made by the machine, but as long as the material is consistent, the length of string being tensioned is the same, & the time under tension is similar, wouldn't each pull stretch the same amount, and produce a more consistent string job?"

You've hit the nail on the head, and on stretchy string if one doesn't clamp off at the same time interval after reaching tension (on a CP elecronic) the variation in tension from string to string will vary more than the lockout machine. In my opinion, the Wise head set to lockout mode will give more consistent stringbed stiffness than it will in CP mode for that very same reason. Any of you Wise owners out there want to test that hypothesis?

Yes, you can get a consistent string job from a crank machine. I had one and it did just fine. However, I like the consistency of the electronics and the speed associated with a good one.

Also keep in mind that there has got to be a reason that the stringing cabins at the top tournaments have good electronic machines. They are constant pull and don't lock out.

David

 

[fwtennis]

SW and Newberry, not exactly. Strings do not stretch forever. If they did all racquets would eventually end up with strings that look like butterfly nets. My understanding that the effects of constant pull on a standard string are maximized within 5 – 7 seconds of reference tension pressure on the string. Whatever stretching a string is going to do at 60 pounds for example, will be done in that time. Letting it sit under tension for minutes will have no noticeable difference than the 5 – 7 seconds. A multi-fiber string might need a few seconds more.

On a lock out, how fast or slow you crank plays a big part in consistency. The faster you pull, the more tension you lose. So if you do not pull at the same speed every time, that could conceivably throw your tensions all over the place on each string. Lock out on the Wise is the best way to go since it pulls at a consistent speed every time. But if you are going to buy a Wise, why use lock out unless you are trying to match a racquet strung last on another lock out. Pick one and go with it because the results between the two styles are noticeably different.

 

[wonder_wall]

Now if you want to talk about the stretch that occurs at a specific angle, I suppose that if you want to take 3 hours to string a frame, then you may have an argument. But in the real world, it tension..clamp, not tension, go have a sangwich, then clamp. I'll concede that tenths of a pound may be lost. However, it is still constantly pulling.

So, it's "case closed" time with David apparently, even though apparently a bunch of people out here care about this discussion. Very nice to have such dignified opposition, and after he asked for the discussion no less.

David is unwilling to debate on the other side of the issue. It's unfortunate since he's the only one who has stated an opinion of "constant pull" on the other side that can actually be pinned down. We can't debate against things that don't even mean anything.

My opinion and apparently numerous other people's opinion of what constant pull is VERY EASY TO DESCRIBE AND QUANTIFY: pulling to a set tension, like a crank, but then maintaining that same set tension. VERY SIMPLE TO DESCRIBE, very clear, not subject to much interpretation.

If we plot time and tension, we have something that is more or less A LINE.

Your description of constant pull, David (calling out to the air), is not so easy to describe.

So far, we've got, "it operates that way on a drop weight regardless of arm angle," "gravity," "weight," "pulling," and your grand finish: we're not having sandwiches between tensioning and clamping so who cares if a drop weight is losing tension in that interval.

WELL DAVID, I DON'T THINK 3/4 LB PER 1MM STRING STRETCH COULD FAIRLY BE DESCRIBED AS TENTHS AND THE INTERVAL OF TIME YOU DON'T CARE ABOUT IS PRECISELY WHAT IS UNDER DISCUSSION AND THE DIFFERENCE IN BEHAVIOR BETWEEN WHATEVER YOUR IDEA IS OF CONSTANT PULL AND A LOCKOUT IN THAT PERIOD OF TIME **IS** THE DISCUSSION.

What I'm trying to show you that a drop weight machine does not even fit YOUR OWN HAZY DEFINITION OF WHAT CONSTANT PULL IS!

And I say that because I can show you that a drop weight ACTS LIKE A CRANK when the angle is off enough.

Here's some numbers.

70 lbs tension, 38 degrees off perfect horizontal (in the next chapter, I can keep making David's point look worse by increasing the angle). According to David's argument the behavior of this system is "constant pull" because it keeps pulling over time, via a weight (of five pounds or so), involving gravity.

Here's what it actually does over time: 55lbs initial tension, 1 degree of movement of the arm equals about 1mm of string creep (assuming 2.25 radius hub). AND FOR EACH MM OF STRING STRETCH 3/4 lb is lost in tension (and for each degree).

This apparently doesn't matter though, because we're not having sandwiches in this interval and you claim 3/4 lb per mm of string stretch constitutes tenths anyway, so who cares.

Can anyone tell me that a crank would lose more tension than 3/4lb per mm of string stretch? This is something very precisely knowable.

Since we all agree that if it's a crank it's not constant pull, David would have to agree that if it acts like a lockout machine it can't very well be constant pull, because HIS OWN HAZY DISTINCTION is defined by differentiation with a lockout machine.

So, David would have to change his argument to something wherein the drop weight only fits when very close to horizontal and remains there throughout the tensioning cycle.

So, David, sandwiches or not, I think you're defeated by your own definition.

 

[Steve Huff]

All of these posts are too much for me to read through, but I think I have an idea what a constant pull machine is.

1. I have a Serrano 550B. It is a drop weight machine (65 yrs old). The weights are heavy, near the floor, requires a foot pedal to lift them up. It IS a constant pull machine. I don't think you could measure to the tenth (maybe 100th) of a pound difference between the tension when the weight is lifted and when it settles.
2. My Wise Tensioner is "considered" a constant pull machine. David's point that it depends on the sensitivity is correct. The tension has to drop an tiny bit for it to "sense" that it needs to pull again. So, maybe to some, it wouldn't be a true constant pull. An expensive Babolat may have greater sensitivity (may start repulling after it senses 1/1000th pound difference, I dont' know), but I'm pretty sure it operates the same way.
3. The Laserfibre standup uses a spring similar to a garage door, but on a smaller scale. You push a foot pedal to compress it, let it go to let it uncoil (I think that's the direction). It pulls constantly, at a preset tension. It IS constantly pulling at that preset tension. It IS a constant pull.
4. A simple drop weight pulls tension as the weight falls. When I first began stringing, I would let the weight settle just above where it became vertical. As it settled further and when I released the clamp, it would resettle at vertical. It took some practice, but after a while, it became pretty intuitive. Someone stated that it has to be able to be duplicated by multiple users to be a true "constant pull". That's like saying an automobile isn't really an automobile in some people's hands. If used correctly, it's pulling at a constant rate when I clamped the string. You might argue that the release of the clamp caused it to drop more. Agreed. The machine was still pulling at the same force, there was just a section of string (what was in the clamp) that hadn't been tensioned yet.
5. My old Ektelon H quit pulling when it reached a certain tension. It was NOT a constant pull--it quit pulling.

Just my 2 cents. The electronic machines are still "Constant Pull" enough for me. So are LF's spring, and so are cheap dropweights.

 

[Newberry]

SW and Newberry, not exactly. Strings do not stretch forever. If they did all racquets would eventually end up with strings that look like butterfly nets. My understanding that the effects of constant pull on a standard string are maximized within 5 – 7 seconds of reference tension pressure on the string. Whatever stretching a string is going to do at 60 pounds for example, will be done in that time. Letting it sit under tension for minutes will have no noticeable difference than the 5 – 7 seconds. A multi-fiber string might need a few seconds more.

Again, I don't have any stringing experience, but I have noticed that a new string job will feel "looser" up to a week after the new strings are installed. I have some old racquets (with old string!) that I bet have lost 10 pounds in tension. The longer strings always seem looser than the shorter ones.
I'm sure they wouldn't ever look like "butterfly nets" as the string does need some tension to stretch and wouldn't stretch at all if it were loose in the frame.

One of my other hobbies is archery, and I build my own bowstrings from multiple fibers. The material I prefer is a blend of Dyneema and Vectran. The fibers are rated at 75lbs per strand and I generally use 22 strands for over 1600lbs of rated capacity (you actually have to halve that number but thats a whole other discussion!)

Vectran is a very stable fiber, but, even at 100lbs on my tension jig, it will stretch for over an hour. I can't imagine that a strand of less stable racquet string would equalize in less than 7 seconds, but I guess it all depends on what kind of percentage you are looking at.

If stringing a racquet is anything like building a bowstring, its all about consistency. Each strand of a bowstring has to have consistent tension, or it creates an "unbalanced" string.
I would guess that a string job on a racquet is similar.

That kind of thinking tends to make all this constant pull a moot point IMHO. Not many strings on a racquet are the same length, and each will continue to stretch a given amount after the stringjob. The best you could hope for is a consistent "taper" that is the two longest mains are the same, then the next two are the same and so forth. I don't see how you will ever have the longest main with the same "one day old settled" string tension as the shortest main. But I could be wrong...

 

[hangzhou]

Last post here:

A drop weight machine, once the arm is past the breakover point, is constantly pulling because gravity is a constant. I've purposely left out the accuracy part of the debate which I did in my first post. It may not be pulling the correct tension due to operator error, but it is still pulling the tension that the arm angle is allowing it to pull. In other words, the arm set at 60 lbs may be pulling at 50 lbs because of any number of errors, but it will continue to pull at 50 lbs because gravity hasn't changed while the arm is hanging there holding onto the string. This is 4th grade science.

Now if you want to talk about the stretch that occurs at a specific angle, I suppose that if you want to take 3 hours to string a frame, then you may have an argument. But in the real world, it tension..clamp, not tension, go have a sangwich, then clamp. I'll concede that tenths of a pound may be lost. However, it is still constantly pulling.

If you grab an 8 lb sledge hammer and hold it at arm's length, it is going to pull you arm down and will continue to pull your arm down with the same force no matter how strong or weak you are and will eventually wear you down so that you drop it. The hammer isn't getting heavier, your arm is getting weaker. Is that difficult to understand?

Next, a clamp or a crank machine holds the string in place, it's static, stationary, it doesn't compensate for tension creep. Not meant to offend, but Hangzou is wrong. A crank machine is not a CP machine. Your assertion that I should change my position is wrong. My argument is backed by the laws of physics.

You can all get hung up on semantics, but physical law is on my side. I'm a long standing member of the USRSA, an MRT, and if Greg Raven or David Bone or Crawford Lindsey would like to tell me that a Klipper isn't constantly pulling, I'll tell them the same thing...go back to school and take a basic science course. Gravity is constant, therefore the arm of a drop weight machine is going to pull at a specific tension as set by the operator, unless you go have that ham sangwich between pulls.

And for the last time, my argument leaves out accuracy (I have to repeat this because the subject of accuracy keeps coming up when arguing against my side of this even though I've REPEATEDLY stated that accuracy is not a concern for my argument). If you want to make that part of this, start another thread. Then I will tell you why I use a Sensor instead of a Klipper.

David

Dave:

Here are the difference between us:

I stated and believe: lock out machines are not CP machines, regular drop weight machines are not CP machines. Electronic machines with loadcell or similar device are CP machines, LF machines should belong to this group.

You stated: Lock out machines are not CP machines, but regular drop weight machines are CP machines(This is the part that I don't agree).

My logic of CP machines: whether the machine can pull to reference tension and stay within designed tolerance, i.e. compensate the tension due to string creep.

You logic of regular drop weight machines being CP machines: gravity is constantly pulling the string.

My question or challenge to you is(Not meant to offend): Is the string pulled constantly by the lock out machine before clamping?

If yes, then they are same as regular drop weight machines, and should be consider as CP machines according to your logic

If not, where does the tension or stress on the string come from?

My point is that on lock out machines, the string is pulled all the time just like regular drop weight machines. Every machine works same way to stretch the string either by crank head, drop weight, or electronic motor. The string is under constantly stress or pulling. Without pulling force, the string will go back to its original length, thus tension will drop to zero.

So there is no way to differentiate these machines just based on whether string being constantly pulled because they are under stress or pulled all the time.

Operator's capability and string characteristics should be left out for this discussion.

 

[Audiodude]

So, it's "case closed" time with David apparently, even though apparently a bunch of people out here care about this discussion. Very nice to have such dignified opposition, and after he asked for the discussion no less.

David is unwilling to debate on the other side of the issue. It's unfortunate since he's the only one who has stated an opinion of "constant pull" on the other side that can actually be pinned down. We can't debate against things that don't even mean anything.

My opinion and apparently numerous other people's opinion of what constant pull is VERY EASY TO DESCRIBE AND QUANTIFY: pulling to a set tension, like a crank, but then maintaining that same set tension. VERY SIMPLE TO DESCRIBE, very clear, not subject to much interpretation.

If we plot time and tension, we have something that is more or less A LINE.

Your description of constant pull, David (calling out to the air), is not so easy to describe.

So far, we've got, "it operates that way on a drop weight regardless of arm angle," "gravity," "weight," "pulling," and your grand finish: we're not having sandwiches between tensioning and clamping so who cares if a drop weight is losing tension in that interval.

WELL DAVID, I DON'T THINK 3/4 LB PER 1MM STRING STRETCH COULD FAIRLY BE DESCRIBED AS TENTHS AND THE INTERVAL OF TIME YOU DON'T CARE ABOUT IS PRECISELY WHAT IS UNDER DISCUSSION AND THE DIFFERENCE IN BEHAVIOR BETWEEN WHATEVER YOUR IDEA IS OF CONSTANT PULL AND A LOCKOUT IN THAT PERIOD OF TIME **IS** THE DISCUSSION.

What I'm trying to show you that a drop weight machine does not even fit YOUR OWN HAZY DEFINITION OF WHAT CONSTANT PULL IS!

And I say that because I can show you that a drop weight ACTS LIKE A CRANK when the angle is off enough.

Here's some numbers.

70 lbs tension, 38 degrees off perfect horizontal (in the next chapter, I can keep making David's point look worse by increasing the angle). According to David's argument the behavior of this system is "constant pull" because it keeps pulling over time, via a weight (of five pounds or so), involving gravity.

Here's what it actually does over time: 55lbs initial tension, 1 degree of movement of the arm equals about 1mm of string creep (assuming 2.25 radius hub). AND FOR EACH MM OF STRING STRETCH 3/4 lb is lost in tension (and for each degree).

This apparently doesn't matter though, because we're not having sandwiches in this interval and you claim 3/4 lb per mm of string stretch constitutes tenths anyway, so who cares.

Can anyone tell me that a crank would lose more tension than 3/4lb per mm of string stretch? This is something very precisely knowable.

Since we all agree that if it's a crank it's not constant pull, David would have to agree that if it acts like a lockout machine it can't very well be constant pull, because HIS OWN HAZY DISTINCTION is defined by differentiation with a lockout machine.

So, David would have to change his argument to something wherein the drop weight only fits when very close to horizontal and remains there throughout the tensioning cycle.

So, David, sandwiches or not, I think you're defeated by your own definition.

Any decent stringer will easily be able to get a dropweight within five degrees of level after stringing only a few racquets. Using 38 degrees off horizontal as an example is laughable.

55 pounds of tension is 55 pounds of tension. "String creep" will vary dramatically from one type of string to another. Stretching a Kevlar string 1mm would result in much more tension than stretching a multi-filament string 1mm. It comes down to this: Operated properly, A conventional dropweight is as much a constant pull machine as a Laserfibre and will produce very similar results, if everything else (Clamps and mounting), is equal. 38 degrees off of horizontal would not be considered proper operation. 10 degrees is unacceptable in my opinion. I've used a couple of different dropweights and never had a problem getting pretty darn close to horizontal, with very little effort. It's just not that hard to do.

 

[Newberry]

I would have to respectfully disagree with hangzhou.
A string in a lockout machine stretches one millimeter....the machine does not change. The tension on the string drops to a value less than the original pull.

A string in a drop weight stretches one millimeter.... the weight will drop a small amount. The string will not be at the exact same tension as before, but it will continue to drop as long as the string stretches.

As long as the user re-orients the weight bar to horizontal, the string will be re-tensioned to the correct weight.

If the lockout machine is released, and the string re-pulled, it should pull just a bit further the second time, accounting for any stretch that occurred the first pull, but it does not pull dynamically, like the drop weight.

This thread has sure been an interesting one!

 

[hangzhou]

I totally don't agree with Mr. Newberry:

I would have to respectfully disagree with hangzhou.
A string in a lockout machine stretches one millimeter....the machine does not change. The tension on the string drops to a value less than the original pull.

You agree thatt there is tension on string and that tension will drop to a value. Now where does this tension come from? Is this tension created by the pulling generated by the crank head? Is the crank head continuesly or constantly pulling the string so to maintain that one millimeter stretch?

If the crank head don't constantly pull the string, then tension on the string will go down to zero. Stringing is a process of pulling, be it crank head, drop weight, electronic motor. They have to pull the string to create stress or tension. The stress or tension in string does not come from nowhere...

A string in a drop weight stretches one millimeter.... the weight will drop a small amount. The string will not be at the exact same tension as before, but it will continue to drop as long as the string stretches.

As long as the user re-orients the weight bar to horizontal, the string will be re-tensioned to the correct weight.

I agree with you on this part.

 

[wonder_wall]

...Using 38 degrees off horizontal as an example is laughable...

Well, I started with 20 degrees but that didn't seem to move David. I'm just following the terms set forth by David's position, please see where I quoted his position: "in the strictest terms, the drop weight is constantly pulling regardless of the angle of the arm." I'm just trying to get David to admit he's wrong and then see how he changes his position. David is a person WHO I THINK is the most likely to participate in a conversation like this IN GOOD FAITH (at least I did before he said case closed or whatever).

For those apparently many out here unfamiliar, it's called a "conversation" or "discussion," perhaps "give and take," "debate." That's what this activity is called.

 

[Newberry]

I totally don't agree with Mr. Newberry:
You agree thatt there is tension on string and that tension will drop to a value. Now where does this tension come from?

No problem on the difference of opinions hangzhou, that's why they make coke and pepsi!

To discuss your question:

The tension in the lockout machine comes from the elasticity of the string material itself. If the machine locked out at 60lbs, and the string stretches, the tension is now less than 60lbs.
The machine is not moving, it is "locked".
If you cut the string the machine will do nothing. (the racquet might not be so lucky)

The tension in the dropweight comes from the weight. The string material reaches its stretch for 60lbs, the dropweight tries to reach the ground and an equilibrium is created. If the material stretches the weight drops. The operator re-levels and the tension is again at 60lbs
If you cut the string the weight will drop.

If you push down on the string in the lockout machine, the tension on the string increases, it it static.

If you push down on the string in the drop weight, the weight moves, it is dynamic.

Completely different ways to a perfectly acceptable string job.

 

[wonder_wall]

...It took some practice, but after a while, it became pretty intuitive. Someone stated that it has to be able to be duplicated by multiple users to be a true "constant pull". That's like saying an automobile isn't really an automobile in some people's hands...

If cars worked like regular drop weight machines, you'd push the brakes and then have to assess the probability of the car actually stopping before the red light, in the middle of the intersection, or 50 feet past the red light. Or in some cases you'd simply go right through the intersection and the car would say "TRY AGAIN!"

 

[fwtennis]

Let’s keep this real simple. Set tension on a Babolat Sensor, a LF and a regular drop weight all to 60 pounds. Put the string in the tensioner on the Sensor and hit the button. It applies 60 pounds to the string and stops. It moves a little bit more, it is still 60 pounds. One more time, and it is still 60 pounds.

Put the string into the tensioner of the LF and let the arm come down. It stops 45 degrees below horizontal. It is 60 pounds. It drops 5 more degrees, it is still 60 pounds. It drops one last time 5 more degrees and it is still 60 pounds.

Put the string in the tensioner of the regular drop weight and let the arm come down. It stops 45 degrees below horizontal exactly like the LF. Is it 60 pounds? NO it is not. It is about 43 pounds. Gravity takes hold and Barry’s constant pull goes into effect and the arm drops 5 more degrees. Is it 60 pounds now? NO. Is it even holding constant at 43 pounds? NO. It is now about 38 pounds. Gravity does its thing one more time and “constantly pulls” the arm down 5 more degrees. Is it now 60 pounds? NO. 43? 38? NO. It is now about 33 pounds. Almost half the set tension. It is mathematical fact and not fuzzy physics. Folks, it’s going in the wrong direction.

In the first two examples, no matter what the tensioner does, no matter what the machine does, no matter what the string does, no matter what the stringer does, the first two examples automatically achieve the selected tension and it is automatically maintained at all times. The more the third example automatically pulls, the farther away you will be from the tension you want. How much simpler can this be explained. What is the point of constant pull on a Klippermate if the constant pulling takes you away from where you want to be.

 

[David Pavlich]

Well, I started with 20 degrees but that didn't seem to move David. I'm just following the terms set forth by David's position, please see where I quoted his position: "in the strictest terms, the drop weight is constantly pulling regardless of the angle of the arm." I'm just trying to get David to admit he's wrong and then see how he changes his position. David is a person WHO I THINK is the most likely to participate in a conversation like this IN GOOD FAITH (at least I did before he said case closed or whatever).

For those apparently many out here unfamiliar, it's called a "conversation" or "discussion," perhaps "give and take," "debate." That's what this activity is called.

So, in my quote above, "in the strictest terms, the drop weight is constantly pulling regardless of the angle of the arm.", you are saying that the arm isn't constantly pulling? Even at the out of the norm angles you bring to the mix, the machine IS STILL PULLING TENSION. I fail to understand what is wrong with those 17 words (maybe I should have stated that the arm was somewhere between break-over and 180 drgrees). You've pulled that quote out a couple of times now. What is the problem? Is it the fact that I didn't say it's pulling incorrectly or that it's not pulling the true reference tension? All I'm saying, time after time, is that as long as the tension arm is beyond the breakover point, it's pulling the string.

And I repeat, it is constanly pulling. Maybe not pulling the set reference tension, but this is all that I've said. I purposely left out accuracy as a qualifier for MY side of why I believe it is a constant pull machine.

If you will, answer this question: Is a drop weight constantly pulling on the string until clamped when it is beyond the breakover point and not at 180 degrees or beyond (0/360 at the top)? And for the fourth or fifth time, leave accuracy out of the equation. If you answer yes, it's pulling all the time that it is engaged until the string is clamped, then you and I agree.

I will never say nor have I ever said that a drop weight is as accurate as Sensor or Technifibre or an Aria. You insist on tossing in angles that aren't relative to the proper operation of a drop weight to prove your point and no, it doesn't move me because it's irrelevant since it's poor stringing practice. Your point is proven as such (poor stringing protocol will provide poor string jobs), but it has nothing to do with my point.

Once more, is a drop weight machine constantly pulling when it is beyond the break over point and less than 180 degrees? If you give the correct answer than you and I agree on the point that I've been making since the first post.

 

[hangzhou]

No problem on the difference of opinions hangzhou, that's why they make coke and pepsi!

To discuss your question:

The tension in the lockout machine comes from the elasticity of the string material itself. If the machine locked out at 60lbs, and the string stretches, the tension is now less than 60lbs.
The machine is not moving, it is "locked".
If you cut the string the machine will do nothing. (the racquet might not be so lucky)

The tension in the dropweight comes from the weight. The string material reaches its stretch for 60lbs, the dropweight tries to reach the ground and an equilibrium is created. If the material stretches the weight drops. The operator re-levels and the tension is again at 60lbs
If you cut the string the weight will drop.

If you push down on the string in the lockout machine, the tension on the string increases, it it static.

If you push down on the string in the drop weight, the weight moves, it is dynamic.

Completely different ways to a perfectly acceptable string job.

The tension on lock out machine is created by the crank head being moved away from racket. Not string itself. After locked out, the locking mechanism provides the force of pulling the string through crank head to maintain the stretches. String will go under creep and the tension will drop. But the locking mechanism is constantly pulling the string to maintain that stretched length. although the true tension has dropped already. Just image you pull a rubber band with your hands to centain distance, do you feel that you are pulling the band all the time to keep that distance? Sure, if you cut the rubber band, nothing will happen to you hands...

Now if you agree with this and compare to drop weight, you have to agree that string are pulled all the time regardless of pulling method, i.e. lock out, drop weight, electronic motor. Then using the notion of whether string being constantly pulled to differentiate machine is meaningless because they are same... Unless you change that notion to or as whether the pulling can deliver consistant results within designed tolerance...

 

[wonder_wall]

...What is the problem? Is it the fact that I didn't say it's pulling incorrectly or that it's not pulling the true reference tension? All I'm saying, time after time, is that as long as the tension arm is beyond the breakover point, it's pulling the string...

Thanks for replying.

The problem is that if it's behaving exactly like a lockout machine, and you agree that a lockout machine is not constant pull, you have to change your definition or something.

I'm pointing out to you how the drop weight machine is characterized just as much BY LOSS OF TENSION OVER TIME as it is by CONSTANT TENSION OVER TIME. And I'm pointing out that it may well lose the same or more tension than the lockout, even though your basic claim is that the drop weight machine is "pulling" while the lockout is "not pulling." And if your constant pull machine actually loses the same or more tension than a lockout, which you say is definitely not constant pull. Well, then, Houston, don't you have a problem?

 

[David Pavlich]

[QUOTE=hangzhou

>>You logic of regular drop weight machines being CP machines: gravity is constantly pulling the string.<<

Is gravity, which is what powers the lever arm, not constantly pulling the string until clamped?

>>My question or challenge to you is(Not meant to offend): Is the string pulled constantly by the lock out machine before clamping?<<

No. I did several test with my lockout (which I still own). I took my calibrator and tied some fresh Prince syngut on the ends. I then set it up in my Gamma which was set at 60 lbs reference tension. I cranked it until it locked out. Immediately, and I mean immediately, you could see the gauge readings dropping. The Gamma does not compensate for tension creep...it quits pulling, in other words.

>>If yes, then they are same as regular drop weight machines, and should be consider as CP machines according to your logic<<

My tests show that, in fact, the above statement is wrong.

>>If not, where does the tension or stress on the string come from?<<

The stress, or tension, has been locked in place, minus the tension creep, by the clamp or by the tension head if you haven't clamped off. However, the string is losing tension because of tension creep. This happens with a Sensor also. However, because the Sensor doesn't stop pulling until the string is clamped, the remaining tension in the clamped off string is higher. And since a drop weight is still pulling until clamped, its string will also have a higher residual tension, unless you didn't lower the tension arm to the proper level. Then it isn't a form and function of the machine, it's poor operator performance. Of course, you already know this.


>>My point is that on lock out machines, the string is pulled all the time just like regular drop weight machines.<<

And my tests prove this statement false.

>> Every machine works same way to stretch the string either by crank head, drop weight, or electronic motor.<<

No, they don't. If you truly believe this, then you need to learn more about how each machine operates. You can alter the tension just by how quickly you crank a machine, which has been posted earlier. If you'd like, I can give you more examples as to how you can alter how a machine pulls.

>>The string is under constantly stress or pulling.<<

Yes, the string, once tensioned, is under stress, but it's not pulling. In fact, for a time, it's losing tension. If it were pulling, it would be getting tighter.

>>Without pulling force, the string will go back to its original length, thus tension will drop to zero.<<

No. Again, because the string is tensioned and then clamped, the tension imparted to the string is captured in the string because it has been held in place. It will drop tension but only to a certain point.

>>So there is no way to differentiate these machines just based on whether string being constantly pulled because they are under stress or pulled all the time.<<

I think the above takes care of this part of your reply.

>>Operator's capability and string characteristics should be left out for this discussion.<<

This is what I've been saying all along. I could have used Kevlar as my sample string, which has 3% or less elongation. Others talk about stretchy string. How about Kevlar? Hang a 50lb weight from it for a couple of hours and see how much longer it gets. Talk about skewing statistics! But I chose to leave it out of the discussion.

David

 

[David Pavlich]

David I think you finally “hammered” it home! All drop weight machines are constant pull! Lock out machines are not!!

No, and that's fine. Under normal strining operation, a drop weight continues to pull regardless of what others say. It is undeniable because physical law is what it is. Angles, tension creep, etc. are byproducts and have nothing to do with the point that I am making. Crank machines put in a set amount of tension, but upon lockout, the input tension immediately begins to drop.

But, let the discussion roll along!

David

 

[David Pavlich]

Thanks for replying.

The problem is that if it's behaving exactly like a lockout machine, and you agree that a lockout machine is not constant pull, you have to change your definition or something.

I'm pointing out to you how the drop weight machine is characterized just as much BY LOSS OF TENSION OVER TIME as it is by CONSTANT TENSION OVER TIME. And I'm pointing out that it may well lose the same or more tension than the lockout, even though your basic claim is that the drop weight machine is "pulling" while the lockout is "not pulling." And if your constant pull machine actually loses the same or more tension than a lockout, which you say is definitely not constant pull. Well, then, Houston, don't you have a problem?

The only way that this will be settled is to have a RDC standing by after a good stringer strings a frame with a lockout and a drop weight. I'm betting that the drop weight will have a higher RDC reading.

But, that still doesn't negate the fact that the drop weight is pulling the whole time until clamped. And because it's pulling, even if the angle is changing that tiny bit, it won't lose near as much tension as the crank machine.

As my reply to hangzou stated, I did the tests with my Gamma crank machine that showed, in no uncertain terms, that the split second that the machine locks out, the tension drops. I still have my old Klipper in the garage. If I think of it, I'll bring my tension gauge home and do a little test. The results will be based on proper technique with the arm in the proper location. I'll use Prince syngut w/duraflex 16 as I did with the Gamma tests. Should be interesting. I don't have a digital camera, otherwise I'd find a way to post it.

David

 

[SW Stringer]

hangzhou says: "If the crank head don't constantly pull the string, then tension on the string will go down to zero. Stringing is a process of pulling, be it crank head, drop weight, electronic motor. They have to pull the string to create stress or tension. The stress or tension in string does not come from nowhere... "

I get the impression some of us here don't have a full understanding of how the lockout tension head actually works. It's explained in great detail if you search the US Patent Archives for Franklin W. Held, patent #3,441,275, issued April 29, 1969. The interested parties will certainly want to look this up. But, in the meantime, I'll try and give a nutshell synopsis of how it works.

The purpose of any machine (stringing) is to apply a set reference tension to a string attached to the tensioning mechanism. The method of holding the string to the mechanism varies, and the application of the force (that creates the tension) to the string varies, but the result is the same . . . at some point in time after the start of the process the set tension is reached and the operator clamps the string.

For a spring lockout device, the tensioning head rides on a rail, to which is attached a linear gear track. Engaging the gear track is a small circular gear with hand crank to multiply the force applied by your hand and move the whole assembly (tensioning head) away from the turntable. The upper part of the head contains the string gripper and a mechanical comparison device (trigger mechanism) that looks at the tension on the string and the reference tension dialed in on the biasing spring. As the crank is manually turned the tension on the string increases until the two tensions are equal, then the trigger mechanism releases the catch assembly which ultimately (in a few milliseconds) locks the whole tensioning head to the rail prohibiting any further movement forwards or backwards. After the fixed string clamp has been moved and reattached inside the racquet frame, the release lever is manually rotated to unlock the tensioning head from the rail, allowing you to move the tensioning head toward the turntable, remove the string from the gripper and get ready for the next string to be tensioned.

As you can see, once the set tension has been reached, no further pulling (increasing tension) of the string can occur.

Hope that helps.

 

[wonder_wall]

As my reply to hangzou stated, I did the tests with my Gamma crank machine that showed, in no uncertain terms, that the split second that the machine locks out, the tension drops.

I don't think anyone's disputing that. The point here is that the same thing will happen with the drop weight when sufficiently off horizontal, even though you claim the dropper is "pulling" while the crank is "not pulling."

The point is to establish to what extent that claim has any meaning. I argue when significantly off horizontal, it has little meaning and the dropper behavior similar to the lockout.

Can you give us an estimate of how much tension loss you saw over how much time?

 

[Newberry]

Just image you pull a rubber band with your hands to centain distance, do you feel that you are pulling the band all the time to keep that distance? Sure, if you cut the rubber band, nothing will happen to you hands...

Heh, again we see things differently I guess!

Pulling a rubberband with your hands is working like a dropweight, you hands are dynamic, the muscles in your arms apply force to oppose the tension in the rubberband, just like the weight opposes the tension in the string. If the tension on the band increases, your hands move together, if it decreases your hands move apart (provided you are pulling with the same force). You are using energy to oppose this force, and eventually your arms will tire (gravity doesn't tire of pulling the dropweight thankfully) and the rubberband will return to its relaxed state because your hands move.

Bottom line- your hands "pull" to counter the band's "pull". The energy of your arm is transferred to the rubberband. That's why you eventually tire.

A lockout example would be pulling the rubberband, then hooking both ends to metal hooks in a brick wall. Is the brick pulling? No because no force is being applied by the brick to oppose the contraction of the rubberband. If the rubberband stretches, the brick does not move, it is not affected, it is static. All energy is stored in the rubberband.

Bottom line- all potential energy is stored in the rubberband. The brick never gets tired.

On a lockout machine, energy is used to turn the crank to a desired tension. That energy is transferred into the string. Once the machine locks, all the energy is now stored in the string. The machine is not pulling. That is why only the string moves if it is cut.

A lockout machine uses no energy to hold tension.

A dropweight uses energy (gravity converted through leverage) to hold tension.

Do you feel that your racquet is pulling on its strings to keep them under tension?

A good discussion!

 

[Jerry Seinfeld]

Let’s keep this real simple. Set tension on a Babolat Sensor, a LF and a regular drop weight all to 60 pounds. Put the string in the tensioner on the Sensor and hit the button. It applies 60 pounds to the string and stops. It moves a little bit more, it is still 60 pounds. One more time, and it is still 60 pounds.

Put the string into the tensioner of the LF and let the arm come down. It stops 45 degrees below horizontal. It is 60 pounds. It drops 5 more degrees, it is still 60 pounds. It drops one last time 5 more degrees and it is still 60 pounds.

Put the string in the tensioner of the regular drop weight and let the arm come down. It stops 45 degrees below horizontal exactly like the LF. Is it 60 pounds? NO it is not. It is about 43 pounds. Gravity takes hold and Barry’s constant pull goes into effect and the arm drops 5 more degrees. Is it 60 pounds now? NO. Is it even holding constant at 43 pounds? NO. It is now about 38 pounds. Gravity does its thing one more time and “constantly pulls” the arm down 5 more degrees. Is it now 60 pounds? NO. 43? 38? NO. It is now about 33 pounds. Almost half the set tension. It is mathematical fact and not fuzzy physics. Folks, it’s going in the wrong direction.

In the first two examples, no matter what the tensioner does, no matter what the machine does, no matter what the string does, no matter what the stringer does, the first two examples automatically achieve the selected tension and it is automatically maintained at all times. The more the third example automatically pulls, the farther away you will be from the tension you want. How much simpler can this be explained. What is the point of constant pull on a Klippermate if the constant pulling takes you away from where you want to be.

This thread has lots going on. From where I sit it appears that fwtennis started the thread to pose a question about the truest definition of constant pull. For the most part there are two camps. The first camp defines a "constant pull machine" according to the strictest laws of physics and gravity. The second camps says in the stringing industry the term means something else, it means pulling to a set tension and maintaining that tension.

The original question basically asks, "should those in the second camp create a new name for what is meant when they say 'constant pull?'"

It is obvious from the content of this thread alone that the term does not have a universally accepted definition. Perhaps like many words and terms in the English language it has multiple definitions. The trouble with this is that it is confusing and can be misleading. So, ultimately I would conclude that the second camp needs to create a new term to use when they are referring to their perception of "constant pull."

From where I sit, I would place myself solidly and without question in the second camp. I think fwtennis hits the salient points perfectly when describing his interpretation of "constant pull" as it relates to the action performed by constant pull machines. Thanks for the spirited thread.

 

[wonder_wall]

Pulling a rubberband with your hands is working like a dropweight, you hands are dynamic, the muscles in your arms apply force to oppose the tension in the rubberband, just like the weight opposes the tension in the string. If the tension on the band increases, your hands move together, if it decreases your hands move apart (provided you are pulling with the same force). You are using energy to oppose this force, and eventually your arms will tire (gravity doesn't tire of pulling the dropweight thankfully) and the rubberband will return to its relaxed state because your hands move.

I guess if we bury two five foot two by fours deep in the dirt and then put two stiff rubber bands around them and the rubber bands are not moving one iota, it must be because the sticks are dynamic like a drop weight machine, flexing their little fiber muscles and getting tired all the time.

Jerry, I guess Newberry here represents the truest laws of physics in their purest sense, talking about dynamic sticks in the ground that are using muscles to push against rubber bands, right?

 

[Newberry]

I guess if we bury two five foot two by fours deep in the dirt and then put two stiff rubber bands around them and the rubber bands are not moving one iota, it must be because the sticks are dynamic like a drop weight machine, flexing their little fiber muscles and getting tired all the time.

Jerry, I guess Newberry here represents the truest laws of physics in their purest sense, talking about dynamic sticks in the ground that are using muscles to push against rubber bands, right?

Wouldn't you have to say the "sticks" are static? Like a lockout machine?


Your "sticks" example is basically the same as my example of a rubberband connected to two brick walls (lockout) not pulling with your hands (dropweight).

I'm just trying to explain to hangzhou why I feel that a lockout machine does not "pull".

 

[hangzhou]

Dave:

Thanks for your reply.

With due respect, your test approach is great but incomplete. Mechanical devices always have space/gap in between, which is called tolerance for assembling them together. Some are large, some are very small/tight. When you lock the crank head on gamma machine, there will be some slack/space in the locking device. Just like you push brake pad, the brake pad wouldn't touch rotor immediately. That's why you see you calibrator reading drop immediately and drop a lot, no surprise for me at all. Been there, done that. Different machine will have different drops depend on its tolerance. What's important is what will happen after that, i.e. all party are engaged, the lock mechanism is in place and working. Does the string have tension and who asserts this tension onto the string?

What's critical is the final read out for the tension calibrator after enough time, say 2, 3 minutes. If the read out is zero, then your claim is correct, and you win. However, I wouldn't use racket strung by lock out machines...

If the read out is higher than zero, I guess that number will be small. That means there is still some tension in the string. Why small? Because the spring in the calibrator has mush high elasticity. Then my claim is correct and you lose. Good thing is everyone can keep using lock out machines.

If you have time, please do us a favor of finishing this test and let us know the final read out.

SW stringer:
>>As you can see, once the set tension has been reached, no further pulling (increasing tension) of the string can occur. <<
From your statement, I got impression that you don't have full or correct understanding of what happens after locking out.

I agree with you on no further increasing tension pulling. But I believe there is reduced/dropped tension/pulling on the string. The locking mechanism locks up the crank head. Now there is no movement for the string, but it was stretched longer. So the string wants to go back to its original length. It will pull the crank head back and because the crank head is locked so the locking mechanism will assert count force to balance the string. Yes, the count force or tension will be less than the reference tension.

Newberry:

If you continuely pull the rubber band until you cann't pull anymore, then it's similar to drop weight machine. But if you only pull to certain distance, that's lock out machine.

>>On a lockout machine, energy is used to turn the crank to a desired tension. That energy is transferred into the string. Once the machine locks, all the energy is now stored in the string. The machine is not pulling. That is why only the string moves if it is cut.<<
The machine is pulling or the crank head is pulling the string to prevent the string going back to its originally length. The pulling force will be smaller than reference tension due to slack or tolerance in the locking mechanism. Because of the pulling force, the string will not go back to its original length, thus energy is stored in the stretched string.

Now for everyone, do you agree there is tension on the string after crank head locks?

If you answer is yes, then you can continue use your crank machine and you have to agree with me that the crank head is pulling the string constantly at less tension(smaller than reference tension).

If you answer is no,then you should throw your lock out machine into garbage can since the final strung rackets will have no tension at all for each string.

 

[Steve Huff]

WW. That's exactly what you do. The first time you drive a particular car, you push on the brake and access whether it will stop in time, stop in the middle of the road, or possibly keep going. After you touch the brake once, you surmised that it will stop you. If you hear a little grinding and don't feel much slowing down, there's a chance you hit the car ahead of you, or go right through the intersection. When the brake didn't work--I TRIED AGAIN. I refine my technique (just as I would with the dropweight). If you kept driving my car through the intersection time after time, I'd quit letting you drive my car. Likewise, if a stringer kept letting my racket string up differently becaue he often let the weight arm go past horizontal, I'd quit letting you string my racket and get someone who knew something about them.

 

[barry]

Let’s keep this real simple. Set tension on a Babolat Sensor, a LF and a regular drop weight all to 60 pounds. Put the string in the tensioner on the Sensor and hit the button. It applies 60 pounds to the string and stops. It moves a little bit more, it is still 60 pounds. One more time, and it is still 60 pounds.

Put the string into the tensioner of the LF and let the arm come down. It stops 45 degrees below horizontal. It is 60 pounds. It drops 5 more degrees, it is still 60 pounds. It drops one last time 5 more degrees and it is still 60 pounds.

Put the string in the tensioner of the regular drop weight and let the arm come down. It stops 45 degrees below horizontal exactly like the LF. Is it 60 pounds? NO it is not. It is about 43 pounds. Gravity takes hold and Barry’s constant pull goes into effect and the arm drops 5 more degrees. Is it 60 pounds now? NO. Is it even holding constant at 43 pounds? NO. It is now about 38 pounds. Gravity does its thing one more time and “constantly pulls” the arm down 5 more degrees. Is it now 60 pounds? NO. 43? 38? NO. It is now about 33 pounds. Almost half the set tension. It is mathematical fact and not fuzzy physics. Folks, it’s going in the wrong direction.

In the first two examples, no matter what the tensioner does, no matter what the machine does, no matter what the string does, no matter what the stringer does, the first two examples automatically achieve the selected tension and it is automatically maintained at all times. The more the third example automatically pulls, the farther away you will be from the tension you want. How much simpler can this be explained. What is the point of constant pull on a Klippermate if the constant pulling takes you away from where you want to be.

Not sure you have a clear understanding of how a drop weight systems works. Here is the way my tension head works and recommended usage http://www.eagnas.com/lilylee/griprach.html. Horizontal is the key, once the bar is horizontal, you have a true counterweight (equal balance). If you use a drop weight system PROPERLY, you achieve the desired weight once the bar is horizontal, clamp off the string, and move on to the next string. Weight is defined as the force with which a body is attracted to Earth or another celestial body, equal to the product of the object's mass and the acceleration of gravity

Concerning your LF example. Not owning one I can't test, but are you saying you set the weight at 60 pounds, and you drop the weight, you get 60 pounds, but no matter how many times you continue to pump the machine, it never changes? If so, you are describing a lock out machine. Maybe that is why LF uses the term “True constant pull” verses constant pull on their web site. A drop weight machine, has no internal mechanism to restrict tension only gravity, unless it is broken. Also you have to deactivate the tension head before the tension is released. A lock out machine you do not, once locked that is all you get.

 

[Newberry]

This info from silent partners website FAQ may help:

http://www.sptennis.com/stringer.asp#Swing
Number eleven at the bottom:


11) What's the difference between an "instant off" and a "constant pull" machine?

A string that is pulled to a reference tension such as 60 lb. and is then clamped will immediately start to lose tension as it stretches. Instant off machines pull the string to the reference tension and then immediately stop pulling. Constant pull machines pull the string to the reference tension and then continue pulling at that tension until the string is clamped and the tensioner is disengaged. Because constant pull machine "take-up the slack" in the string for a longer period of time than instant off machines, they usually yield string jobs that are about 10% higher in tension than instant off machine. This is not a trivial difference and good professional stringers will usually ask their customers about the type of machine that was used for their previous string job. The main type of instant off machines are those that employ a spring and brake tensioning mechanism (that's because tensioning stops and the brake is engaged the moment the reference tension is reached). Electric machines as well as drop weight machines usually provide constant pull. This is because the motor of an electric machine and the lever of a drop weight machine continue to pull on the string for as long as it takes to clamp the string and disengage the tensioning mechanism. Note that electric machine that use a pre-loaded spring (see FAQ 4) are instant off rather than constant pull.



They reference an "instant off" machine AKA "lockout" machine. Instant off- the machine pulls until it is locked, then pulls no more.

 

[David Pavlich]

This info from silent partners website FAQ may help:

http://www.sptennis.com/stringer.asp#Swing
Number eleven at the bottom:


11) What's the difference between an "instant off" and a "constant pull" machine?

A string that is pulled to a reference tension such as 60 lb. and is then clamped will immediately start to lose tension as it stretches. Instant off machines pull the string to the reference tension and then immediately stop pulling. Constant pull machines pull the string to the reference tension and then continue pulling at that tension until the string is clamped and the tensioner is disengaged. Because constant pull machine "take-up the slack" in the string for a longer period of time than instant off machines, they usually yield string jobs that are about 10% higher in tension than instant off machine. This is not a trivial difference and good professional stringers will usually ask their customers about the type of machine that was used for their previous string job. The main type of instant off machines are those that employ a spring and brake tensioning mechanism (that's because tensioning stops and the brake is engaged the moment the reference tension is reached). Electric machines as well as drop weight machines usually provide constant pull. This is because the motor of an electric machine and the lever of a drop weight machine continue to pull on the string for as long as it takes to clamp the string and disengage the tensioning mechanism. Note that electric machine that use a pre-loaded spring (see FAQ 4) are instant off rather than constant pull.



They reference an "instant off" machine AKA "lockout" machine. Instant off- the machine pulls until it is locked, then pulls no more.

>>Electric machines as well as drop weight machines usually provide constant pull. This is because the motor of an electric machine and the lever of a drop weight machine continue to pull on the string for as long as it takes to clamp the string and disengage the tensioning mechanism.<< Copy and pasted for effect.

Uh-oh...Silent Partner agrees with me. I own an Aria and did own a DG eStringer. Good machines, both. Enough said?

Thanks for posting this, Mr. Newberry.

David

 

[David Pavlich]

I don't think anyone's disputing that. The point here is that the same thing will happen with the drop weight when sufficiently off horizontal, even though you claim the dropper is "pulling" while the crank is "not pulling."

The point is to establish to what extent that claim has any meaning. I argue when significantly off horizontal, it has little meaning and the dropper behavior similar to the lockout.

Can you give us an estimate of how much tension loss you saw over how much time?

This is a non-sequiter. If you aspire to good string jobs, then "significantly off horizontal" shouldn't even enter this conversation. It's poor stringing protocol. I could unclamp a previously tensioned string while my Sensor is pulling the next string to skew results. But why would I do that other than to make a specious argument?

I don't need to give an estimate concerning how much tension is lost when a crank locks...it's visible. And it is "common knowledge" that it is anywhere from 5% to 10% depending on all of the variables.

David

 

[wonder_wall]

This is a non-sequiter. If you aspire to good string jobs, then "significantly off horizontal" shouldn't even enter this conversation. It's poor stringing protocol. I could unclamp a previously tensioned string while my Sensor is pulling the next string to skew results. But why would I do that other than to make a specious argument?

I don't need to give an estimate concerning how much tension is lost when a crank locks...it's visible. And it is "common knowledge" that it is anywhere from 5% to 10% depending on all of the variables.

David

You're changing the subject.

David, IT IS YOUR CLAIM NOT MINE AND HAS NOTHING TO DO WITH STRINGING TECHNIQUE. Again, David said: "in the strictest terms, the drop weight is constantly pulling regardless of the angle of the arm."

If you want to relent on the point, you need to explain your new position rather than just changing the subject.

THIS IS THE POINT OF DEBATE BECAUSE APPARENTLY NEARLY EVERYONE ON YOUR SIDE OF THE ARGUMENT BELIEVES THIS AS WELL.

According to David's claim, there is a big difference between a drop weight which is losing close to 1 lb of tension per 1 mm of string stretch and a crank, because according to David's claim, the drop weight is "pullling" and the crank is "not pulling."

THERE ISN'T A DIFFERENCE IN BEHAVIOR AT A SUFFICIENTLY OFF ANGLE AND DAVID BROUGHT UP THE OFF ANGLES NOT ME. OTHERS HERE BELIEVE THE SAME AS DAVID, that it's constant pull just "because gravity" or "because weight" (a 5 pound weight pulling 60 lbs).

On the Wise site, you can see the Wise operating in lockout mode and it loses about 2 lb over 7 seconds, this is at 57 lbs, about 3 seconds for the first pound, and about 4 for the second and by the end of the 7 seconds, lots of slowing.

The drop weight at a sufficiently off angle WILL LOSE THE SAME AMOUNT OF TENSION OVER THE SAME PERIOD. That is my claim. IT IS THE POINT UNDER DISCUSSION. The drop weight is not constant pull at the off angles, David says it is I say it is not. I'VE ALREADY EXPLAINED THAT 3/4 LB IS LOST PER MM OF STRING CREEP UNDER A DROP WEIGHT AT 38 DEGREES OFF. I CAN PRODUCE LARGER AMOUNTS OF WEIGHT LOST BY CHANGING THE VARIABLES AS WELL!

THIS IS THE ITEM UNDER DISCUSSION, DAVID'S CLAIM AND THE CLAIM OF APPARENTLY EVERYONE ON HIS SIDE, THAT IT IS CONSTANT PULL BECAUSE GRAVITY EXISTS AND THAT "CONSTANT PULL" HAS NO WELL-DEFINED BEHAVIOR ASSOCIATED WITH IT.

We are exploring the other side's version of "constant pull" to show in what ways it may be a completely meaningless idea. *THEIR* DEFINITION OF CONSTANT PULL IS MEANINGLESS, NOT MINE. THE PROPER DEFINITION HAS A VERY SIMPLE MEANING: PULL TO SET TENSION LIKE A CRANK, BUT KEEP THE TENSION THERE.

 

[barry]

You're changing the subject.

David, IT IS YOUR CLAIM NOT MINE AND HAS NOTHING TO DO WITH STRINGING TECHNIQUE. Again, David said: "in the strictest terms, the drop weight is constantly pulling regardless of the angle of the arm."

If you want to relent on the point, you need to explain your new position rather than just changing the subject.

THIS IS THE POINT OF DEBATE BECAUSE APPARENTLY NEARLY EVERYONE ON YOUR SIDE OF THE ARGUMENT BELIEVES THIS AS WELL.

According to David's claim, there is a big difference between a drop weight which is losing close to 1 lb of tension per 1 mm of string stretch and a crank, because according to David's claim, the drop weight is "pullling" and the crank is "not pulling."

THERE ISN'T A DIFFERENCE IN BEHAVIOR AT A SUFFICIENTLY OFF ANGLE AND DAVID BROUGHT UP THE OFF ANGLES NOT ME. OTHERS HERE BELIEVE THE SAME AS DAVID, that it's constant pull just "because gravity" or "because weight" (a 5 pound weight pulling 60 lbs).

On the Wise site, you can see the Wise operating in lockout mode and it loses about 2 lb over 7 seconds, this is at 57 lbs, about 3 seconds for the first pound, and about 4 for the second and by the end of the 7 seconds, lots of slowing.

The drop weight at a sufficiently off angle WILL LOSE THE SAME AMOUNT OF TENSION OVER THE SAME PERIOD. That is my claim. IT IS THE POINT UNDER DISCUSSION. The drop weight is not constant pull at the off angles, David says it is I say it is not. I'VE ALREADY EXPLAINED THAT 3/4 LB IS LOST PER MM OF STRING CREEP UNDER A DROP WEIGHT AT 38 DEGREES OFF. I CAN PRODUCE LARGER AMOUNTS OF WEIGHT LOST BY CHANGING THE VARIABLES AS WELL!

THIS IS THE ITEM UNDER DISCUSSION, DAVID'S CLAIM AND THE CLAIM OF APPARENTLY EVERYONE ON HIS SIDE, THAT IT IS CONSTANT PULL BECAUSE GRAVITY EXISTS AND THAT "CONSTANT PULL" HAS NO WELL-DEFINED BEHAVIOR ASSOCIATED WITH IT.

We are exploring the other side's version of "constant pull" to show in what ways it may be a completely meaningless idea. *THEIR* DEFINITION OF CONSTANT PULL IS MEANINGLESS, NOT MINE. THE PROPER DEFINITION HAS A VERY SIMPLE MEANING: PULL TO SET TENSION LIKE A CRANK, BUT KEEP THE TENSION THERE.

That is the point; you never use a drop weight machine in an off angle. Here is the way my machine works, and the proper way to string a frame.

http://www.eagnas.com/lilylee/griprach.html

As you can clearly see, holding the gripper and moving the drop weight to a horizontal position is pretty simple. It might move 1 degree more if the string stretches, but the weight is constant. One has to assume the reason the head dropped is because the string stretched, and if it had less tension the drop weight arm would not have moved.

 

[wonder_wall]

As you can clearly see, holding the gripper and moving the drop weight to a horizontal position is pretty simple..

Most drop weights out there are like Klippermates and do not have ratcheting grippers, so let's wait to get to how nice the ratcheting gripper is, that's not yet part of the discussion. This is just muddying the waters.

 

[hangzhou]

Funny thing is no one want answer this simple question: Do you believe there is tension on the string on lock out machine after the crank head is locked?

Mr. Newberry:

I am not surprised to your reference at all. The originator of this thread is trying to challenge this wrong notion used by many industry insiders or veterans. I bet you will find more of such misleading information from many "credible" sources.

Now if you believe install-off machine, i.e. lock out machine does not pull the string anymore, then you should agree that there is no tension on the string because the two ends of the string is held at crank head and racket(both sit there and don't move anymore). If there is no tension on string, what's the purpose of stringing racket using lock out machines?

More scientifically, you can use Mark's software to check the string bed stiffness for string bed strung by lock out machine. Or even use RDC machine to check whether there is tension on string. The anwser is yes. Yes, there is tension on the string. Now who creates this tension after locking out? It's the locking mechanism, who fixs the crank head to the fixed position to prevent string going back to its original length. The crank head is continuesly pulling the string in order to maintain the stretched distance. Is that hard to understand?

Dave, I am waiting for you test result if you have time.

The common knowledge of 5% or 10% tension lost from lock out machine are contributed or generated mainly by the break in gap of locking mechanism. That's a random variable, each lock out might have different break in space depend on the starting position. String creeping is a very slow and small yielding process, which shouldn't contribut much of the tension lost in short time.

 

[Newberry]

hangzhou,
Yes I do agree that there is tension on the string after a machine is locked out What we cannot seem to agree on is whether the machine is continuing to "pull" after it is locked out.

Definition of "pull" per wordreference.com:

pull
1 pull, pulling

the act of pulling; applying force to move something toward or with you; "the pull up the hill had him breathing harder"; "his strenuous pulling strained his back"


As defined, in order to "pull" the device must be applying force to move something. A locked lockout cannot move.
The lockout is clearly not "applying force to move something" as it cannot move itself therefore it is NOT pulling.
The string is doing its dangdest to return to its relaxed state, but the machine is exerting no force to counter the force of the string.

now the definition of lock:

1 lock

become rigid or immoveable; "The therapist noticed that the patient's knees tended to lock in this exercise"


Exactly what the lockout machine does (thus the name!) Nothing that is rigid or immoveable can possibly "pull".

Grasp the head of a "locked" lockout machine. Tug it, pull it, whatever you want. If it is locked out the tension on the string will not change. There is no possibility of motion, therefore no pull (as defined above).

Grasp the weight of a dropweight. Pull it down and the tension increases (you just increased its "pull") Pull it up and the string tension decreases (you just decreased its "pull"). There cannot be pull without the possibility of motion. A locked lockout does not have this possibility.

I do agree that a dropweight is only accurate at horizontal. If the weight drops below horizontal, the weight drops off, but that doesn't mean it isn't still pulling. If you allowed slack in the string the machine would continue to pull until the weight bottoms out. The potential for movement is why a dropweight "pulls", and the lack of that same potential is why the lockout cannot pull.

...wondering how I got into this discussion... I don't even have a string machine! :mrgreen:

 

[SW Stringer]

hangzhou says: " . . . The common knowledge of 5% or 10% tension lost from lock out machine are contributed or generated mainly by the break in gap of locking mechanism. That's a random variable, each lock out might have different break in space depend on the starting position. String creeping is a very slow and small yielding process, which shouldn't contribut much of the tension lost in short time."

hangzhou, if you'd take the time to look at the Held patent you'd see that the mechanism has "ZERO" break, or gear lash. The gear on the handle is held in close contact to the gear track by the counterforce in the string (ie the stretch in the string . . . the string is basically modelled as a spring) and the "catch" or locking mechanism "jams" or locks the crank wheel with friction, freezing the tensioning head assemble at the exact point it had reached on the track when the trigger mechanism released the "catch".

Until I found the Patent filing for the Held device, I thought there must be some gear backlash (or back movement) when the device latched, but the locking device is independent of the gear and gear track, it only "Freezes the crank wheel with friction". If you don't believe me just look up the patent and satisfy your own curiosity.