constant pull phraseology

[hangzhou]

SW stringer:

I already looked that patent and looked again after your new post. You raised a new topic, which was created my statement. I will address that later. But please answer my simple question just like Mr. Newberry did.

Mr. Newberry:

Good you agree there is tension on the string so that lock out machine is valid string machine. Now the difference is that you don't buy in that crank head is constantly pulling the string because crank head is stationed or no movement due to locking.

If you want open a locked door, you will pull the door handler. You are pulling the door handler, but the door never open or move for you because it's locked. Can you say that you never pulled or pulling the door during your try?

Pulling or pushing is an action between objects, they will not depend whether movement will be created.

 

[Newberry]

SW stringer:

I already looked that patent and looked again after your new post. You raised a new topic, which was created my statement. I will address that later. But please answer my simple question just like Mr. Newberry did.

Mr. Newberry:

Good you agree there is tension on the string so that lock out machine is valid string machine. Now the difference is that you don't buy in that crank head is constantly pulling the string because crank head is stationed or no movement due to locking.

If you want open a locked door, you will pull the door handler. You are pulling the door handler, but the door never open or move for you because it's locked. Can you say that you never pulled or pulling the door during your try?

Pulling or pushing is an action between objects, they will not depend whether movement will be created.

Again, you are ignoring the definition of the word "pull" which is "applying force to move something". You are pulling on the door, but the door is not pulling back. Your are trying to move the door but the door is not trying to pull you through it.

In your scenario, you must imagine yourself as the string, and the door as the machine. You pull (as the tensioned string pulls) and the door resists, but doesn't pull back. You simply do not have enough "pull" to resist the tendency of the door to stay at rest (objects at rest tend to stay at rest). If you had the strength, you would rip the door off its hinges, but at no time does the door (machine) do any pulling.

Here's a simple question- In your opinion what would happen if you pulled a string to tension on a lockout machine, the machine locks out, and you let it set for 10 seconds.
You release the lock, and re-pull the same strand.
Will the machine lockout at:
A. a point closer to the racquet
B. the exact same point as the first pull
C. a point further from the racquet

 

[hangzhou]

Then again, you are misunderstanding of the word "pull". "pull" is "applying force to move something", but that doesn't mean something will move, it can be stationed or no movement at all.

The gravity is pulling the apple hang on tree, but the apple will not drop. The pulling exists all the time, that's Newton's third law. Check this pls: http://en.wikipedia.org/wiki/Newton's_law

My answer to you question is "C", there will be certain creeping, which would make the string longer than before, thus the machine will lockout at a point further from the racquet.

 

[Newberry]

Then again, you are misunderstanding of the word "pull". "pull" is "applying force to move something", but that doesn't mean something will move, it can be stationed or no movement at all.

The gravity is pulling the apple hang on tree, but the apple will not drop. The pulling exists all the time, that's Newton's third law. Check this pls: http://en.wikipedia.org/wiki/Newton's_law

My answer to you question is "C", there will be certain creeping, which would make the string longer than before, thus the machine will lockout at a point further from the racquet.

So is the tree exerting force pulling "up" on the apple? By your definition it is. In that example, gravity represents tension in the string and the tree represents the locked out head of the machine.

We agree that there is tension, but in a lockout, it is located in the string, not the machine. In a dropweight the weight is being pulled by gravity (just like your apple).

In your examples you always have something pulling but the stationary objects you refer to (like the door above, or the tree in this post) are what represent the machine in these examples. The door doesn't pull, and neither does the tree.

I agree on your answer to the question that the machine will lockout at a further distance from the racquet. I believe that the act of cranking the head IS pulling, but once the machine locks out it is NO LONGER pulling.

If the machine were pulling after lockout the first time, the second pull would result in the head locking in the same location.

In your thinking, why does the second pull result in a different (longer)location if the machine was pulling all along the first time?

Thanks for the reply

 

[SW Stringer]

Newton's first Law of Motion states: "An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force."

The point of contention in this thread being debated by Newberry and hangzhou hinges on the semantical difference of opinion on what the verb "pulling" means.

One, it could simple mean exerting a force upon an object, and if this force is counterbalanced with an equal and opposite force then the object will stay at rest if initially at rest or will continue to move at the same speed as before the forces were applied.

Or, two, pulling could mean the application of unbalance forces, so that the object of the unbalanced forces causes the object to move if stationary initially or move with more or less speed than before the unbalance forces were applied.

If you can both agree to either definition then I think the problem can be resolved.

My $0.02, I think pulling is exerting a force on an object whether the object moves or not. You can pull on a door knob as hard as you want, (assuming the latch is set in the striker plate and up to the point of ripping the knob or the door off it's hinges or the plate off the door frame - i.e. everything is still stationary), and the doorknob MUST be exerting an equal yet opposite force - meeting the criteria of Newtons first law.

As far as the crank lockout machine is concerned, when tensioning a string, the string is initially clamped between two points, one fixed in a clamp at the edge of a racquet frame and the other end clamped, but moveable in the string jaws of the tensioning head. As the crank is turned the tension in the string starts to rise as the string is being stretched and the tensioning head continues to move along the track until the very instant in time that the "trigger mechanism" senses the tension in the string to be equal to the "bias spring" whereupon the "latch" is released "locking" the tension head in position. At that instant in time the tension head is pulling (exerting a force) equal to the reference tension set in the "bias spring", the string is pulling back just as hard, the opposite end of the string is also pulling with that same force against the edge of the racquet grommet and the racquet is also pulling with the same force against the string . . . because the system is now stationary and all forces must be balanced according to Newtons first law.

But that's not all. There's more. The strings are not "perfect springs", ie they won't return to their original length if the tension is released due to the fact that the polymer chains in the string formulation begin to slip or "creep" thus reducing the stored tension is the fixed length of string. So seconds later the string is pulling with a force that is less than at the "latch" point, but since the whole system is still stationary the string jaws and the racquet must also pulling with the same reduced force as the string . . . and once again Newtons first law is satisfied. This analysis applies to nylon and polyester strings constructed with polymer chains, but whatever tension loss model that applies to kevlar, natural gut, etc., would also obey Newtons first law.

This dropoff in tension has already been verified by David or Steve with their crank machine. I have no reason to doubt the veracity of their post.

I would also refer the interested parties to the book "The Physics and Technology of Tennis" which has several chapters that discuss the properties of strings and describes different tests that were applied.

 

[David Pavlich]

Test results:

To preface this, I set the test up as best I could to simulate a frame being strung. The most important part is the length of string, which was close to everyday stringing. Prince sygut w/duraflex 16. Could have used something more elastic, but since this is an old standard and the best selling string worldwide, it made sense. Fresh string for each pull. I used my old Klipper.

The arc of the arm starts at the top...0 degrees.

The first test was at horizontal...90 degrees. I watched the gauge for 2 minutes, not enough time to make a sandwich, but enough time to eat a chocolate chip cookie. There was no movement of the gauge. The arm dropped about 1 degree.

The second test was at 45 degrees. I attempted 38 degrees but another of those pesky physical laws got in the way; for every action, there's an equal but opposite reaction. The string pulls back at the same rate which caused the arm to spring back and want to flip backwards past 0 degrees...not good for the health of the machine. However, it allowed the test at 45 degrees. What happened was no surprise. As the string stretched during the two minute time period, it allowed the arm to drop which meant that the arm was headed toward optimum pulling which is at 90 degrees (horizontal). The gauge showed a GAIN of 1/2 lb.

The third test was at 135 degrees; 45 degrees beyond horizontal. The gauge again showed no movement nor did the arm move any further. This tells me that the lesser pulling at this angle isn't enough to effect the Prince string, at least according to the Gamma gauge.

A couple of observations. First, since this gauge is a simple Gamma spring gauge, I couldn't tell any deviations in tiny increments like a digital gauge may have been able to detect, with the exception of the 45 degree test. That was obvious even with the Gamma gauge.

Second, because this was a straight pull on the string and not a piece of string going through a grommet, the test may have been different, although I doubt it.

Third, I have forgotten how much of a pain in the neck stringing with a Klipper is!

So...I'll get back on message, Wonderwall...my apologies.

Draw your own conclusions. It wasn't a real scientific test. I through it together rather quickly. But the results were still revealing. I still say, with the backing of Silent Partner, that a drop weight machine IS constant pull. My simple test proves that. Further, it refutes the claim that at severe angles, the drop weight would act like a crank machine. If you wish, do your own test. Use your own string. I did this to satisfy by sight what I already knew.

Thank you for your attention. Good night.

David

 

[Newberry]

the doorknob MUST be exerting an equal yet opposite force - meeting the criteria of Newtons first law.

I appreciate your input SW Stringer and you make valid points, but a doorknob cannot "exert".

Definition of exert:
to exercise; to use; to make an effort

I don't think a door can do that, it requires effort.

Definition of effort:
The use of physical or mental energy to do something; exertion.

I do believe the door (and the tension head) can resist pull, but they don't exert. Pulling requires effort, effort requires energy. Once the operator quits cranking, no more energy is going into the machine. A dropweight IS using energy (gravity).

Its all about our own learned definitions I suppose! We all have different takes on the meaning. I can certainly live with that, and agree to disagree, but my whole argument was with hangzhou's statement:

hanzhou states: "My point is that on lock out machines, the string is pulled all the time just like regular drop weight machines."

I just don't agree with that. There are two different things happening. If that statement was true, then both types of machine would produce the same stringjob, and they clearly don't.

Do you feel that a locked machine is still "pulling"?

Genuinely interested in everyone's opinion here

 

[David Pavlich]

Newberry asked: >>Do you feel that a locked machine is still "pulling"? <<

No. It's static. The tension imparted to the string is stored in the string once the head is locked, minus the tension creep. The tension head is stationary once locked, therefore it CANNOT be pulling. Once the tension head is locked, the only force is the string pulling on the tension head, not vice versa.

Another way to explain this is that the locking mechanism only allows the head to pull to a certain point. Once the preset tension is reached, IT STOPS PULLING. Very, very simple.

David

 

[hangzhou]

Newberry asked: >>Do you feel that a locked machine is still "pulling"? <<

No. It's static. The tension imparted to the string is stored in the string once the head is locked, minus the tension creep. The tension head is stationary once locked, therefore it CANNOT be pulling. Once the tension head is locked, the only force is the string pulling on the tension head, not vice versa.

Another way to explain this is that the locking mechanism only allows the head to pull to a certain point. Once the preset tension is reached, IT STOPS PULLING. Very, very simple.

David

You have stated "Once the tension head is locked, the only force is the string pulling on the tension head, not vice versa". That's totally wrong, it breaks Newton's third law.

If you agree the string is pulling the tension head, then tension head should be pulling the string same time with same acount of force at opposite direction.

If you don't believe the string is pulling the tension head, then the tension head will not pull the string. But the result is string will have no tension at all, that will beat the purpose of stringing racket.

Very very simple fact.

When you state your test on crank machine, you stated that the tension drop a lot first, but didn't watch out long enough to find the final reading. You should do this test again, then you will realize what will be the final true tension.

 

[hangzhou]

SW Stringer:

You haven't answered my question of whether there is tension in string on lock out machine. I don't want that be the stop for communication between us, so I will move forward to address your reply.

There should be tension in the string on lock out machine after crank head is locked, otherwise it will beat the purpose of stringing. The tension in the string will cause the string to pull the crank head, according to Newton's third law crank head should pull the string at opposite direction. That's simple, very simple fact although the pulling force should be smalled than reference tension due to backlash and string creeping.

I agree with you that all gear locking mechanism must have some gear backlash/back movement. That's how gears are deisgned to work,i.e. there must be some small space in between one face of two teeth. Otherwise gears will stuck together.

Now, when you look through this patent filed for helding device. It only states "freeze the crank wheel with friction". There are two types of friction, first one is kinetic friction(for our case, it's sliding friction) and second one is static friction. You could check here: http://en.wikipedia.org/wiki/Static_friction.

Now once the tension passes the reference tension, the locking mechanism will kick in to apply force to stop such motion between crank head and rail. Because there is relative motion, so the frition should be sliding friction first. That means there will be movement for the crank head, although it be might be very small depend on the power of locking system. Once the sliding friction pass tipping point as the locking system exerts more power, the movement will stop, thus there will be static friction between crank head and rail. This is the force to countbalance the pulling exerted by tensioned string. This static friction is the one who is contantly pulling the string. In simple way, we are saying that the crank head is pulling the string. The movement of crank head before the sliding friction turns into static friction is the major cause of tension drop as noticed by everyone as common knowledge of "5% to 10%". This contribution is very hard to estimated and varies with no pattern.

If you want study more of friction, there are tons of research thesis out there. Have fun...

 

[Newberry]

You have stated "Once the tension head is locked, the only force is the string pulling on the tension head, not vice versa". That's totally wrong, it breaks Newton's third law.

If you agree the string is pulling the tension head, then tension head should be pulling the string same time with same acount of force at opposite direction.

If you don't believe the string is pulling the tension head, then the tension head will not pull the string. But the result is string will have no tension at all, that will beat the purpose of stringing racket.

Very very simple fact.

When you state your test on crank machine, you stated that the tension drop a lot first, but didn't watch out long enough to find the final reading. You should do this test again, then you will realize what will be the final true tension.

It does not break Newton's third law which states:
For every action, there is an equal and opposite reaction
It does not state:
For every action, there is an equal and opposite action

Pulling is an action, you are using it as a verb-applying force to move something toward or with you
Pulling is not a reaction
Resistance IS a reaction

The action is the string trying to contract. The reaction is that the tension head, and the racquet resist the string's contraction. Resistance is the opposite reaction, not pulling.

resistance:
any mechanical force that tends to ****** or oppose motion

If it were pulling, when the string stretched, the head would move.

I'm still interested in your view of why a lockout machine will stop at a point further from the racquet on the second pull, if it were pulling the first time?

Thanks again for your reply.

 

[Newberry]

Newberry asked: >>Do you feel that a locked machine is still "pulling"? <<

No. It's static. The tension imparted to the string is stored in the string once the head is locked, minus the tension creep. The tension head is stationary once locked, therefore it CANNOT be pulling. Once the tension head is locked, the only force is the string pulling on the tension head, not vice versa.

Another way to explain this is that the locking mechanism only allows the head to pull to a certain point. Once the preset tension is reached, IT STOPS PULLING. Very, very simple.

David

I agree completely David, Thank you.

 

[David Pavlich]

You have stated "Once the tension head is locked, the only force is the string pulling on the tension head, not vice versa". That's totally wrong, it breaks Newton's third law.

If you agree the string is pulling the tension head, then tension head should be pulling the string same time with same acount of force at opposite direction.

If you don't believe the string is pulling the tension head, then the tension head will not pull the string. But the result is string will have no tension at all, that will beat the purpose of stringing racket.

Very very simple fact.

When you state your test on crank machine, you stated that the tension drop a lot first, but didn't watch out long enough to find the final reading. You should do this test again, then you will realize what will be the final true tension.

No, I shouldn't do the test again. If you string a racquet by pulling tension and watching it until the string settles, then it would take, oh, 2 days, 3, a week? Watching the string for 2 minutes was about 1 muinute and 55 seconds too long in the real world of stringing. But I watched for 2 minutes to satisfy even the most skeptical. It didn't work to your satisfaction.

Answer this: It's been pointed out as FACT, that a crank machine strings consistently lower than a drop weight. If what you say is true about the crank machine continuing to pull, how do you account for the fact that the stringbed stiffness is less on a crank strung frame than a CP strung frame?

You don't believe a stringing machine manufacturer, you're certainly not going to believe me. I surrender.

David

 

[wonder_wall]

..Test results...

Well, David, excellent post, I didn't know anyone asked you to do that test and I thank you, and I'm big enough to admit it if and when I'm wrong. And I admit that you've stated some things here I need to think about. I THINK EVERYONE CAN SEE WHY I SEEK A DEBATE WITH YOU SINCE YOU ARE AN HONORABLE AND REASONING OPPONENT, and if I'm wrong I want to find out!

But at this point, I still estimate a very small possibility of error, or to the extent I'm wrong, I think it's probably a definitional point about when a pull starts.

NEWBERRY

But first, let me say something regarding Newberry, since apparently David you've entered that discussion on one side, and I'm surprised you entered it since it would seem to be quite meaningless, and here's why:

Newberry has said that two human arms a fixed distance apart holding a string are "pull" but two sticks the exact same distance apart and the exact same thing happening on the string are not "pull."

For Newberry, THE FACT THAT THE SAME THING IS HAPPENING TO THE STRING IN THE MIDDLE IS A MATTER OF INCONSEQUENCE, ONE IS PULL, ONE IS NOT PULL.

Now, David, I think you'll have to agree that terms have meaning in a subject area due to their ability to refer to meaningful distinctions in that subject area. The subject area here is stringing, the subject is how different machines behave with regard to their effect on string.

By Newberry's logic your Babolat Sensor is not constant pull and a Wise machine is not constant pull either, because a machine that spends most of its time holding the string is not actually "pulling" or is pulling only relatively occasionally could not be described as constant pull by his standards.

"Constant pull" by his standard would have to be a machine that never disengages its motor from a string, never uses a brake, or perhaps action by a conscious entity.

THESE ARE WAYS OF VIEWING THINGS WHICH ELIMINATE OUR ABILITY TO TALK ABOUT MACHINES AND THEIR EFFECT ON STRING!

So, in this sense, David, you're actually arguing the case of meaninglessness and terms that HAVE A MEANING in the subject area of stringing you are arguing to be stripped of that meaning.

So, to eliminate Newberry's silliness, why don't we just say "constant force" is for us in the practice of stringing an interchangeable term with constant pull. In fact it is, because all we care about is the force on the string.

And if the stringing industry is guilty of a literary faux pas by not saying constant force stringing instead of constant pull stringing, who cares, this discussion is not about literary correctness.

With the term "constant force" Newberry would not have a point to make, literary or otherwise and he'd have to acknowledge that a same set of forces being applied to a string is the same thing for our discussion, whether he calls it "pull" or "not pull."

And maybe this solves some of the initial issue mentioned by the person who started this thread.

Now, if you agree with that David, then your Sensor is back to a "constant pull" machine since we are saying "constant pull" and "constant force" is the same thing for us, AND THAT'S BECAUSE WE ARE TALKING ABOUT WHAT THE STRING IS UNDERGOING OVER TIME, AND IT'S ALSO WHAT YOUR MACHINE IS DESIGNED TO DO, maintain a constant force on the string. We are not talking about unimportant implementation issues or the consciousness or agency that Newberry seems to want to irrelevantly discuss. We are discussing WHAT HAPPENS TO A STRING DIFFERENTLY IN DIFFERENT ARRANGEMENTS, a very simple matter, not consciousness.

MY POSITION

I AM ONLY MAKING A CLAIM HERE, but it is a very concrete claim and the other side is free to prove it wrong if it is wrong. It can be mathematically proven wrong if it is wrong. I admire your desire to try to directly defeat it.

My claim is based on proving to David ABSOLUTELY that the drop weight machine is not a constant pull ("constant force" interchangeable below) machine at off angles by establishing *SOME* LOCATION OF THE ARM WHERE THERE IS NO DIFFERENCE IN BEHAVIOR WITH A CRANK. I believe that if I can prove this to David, I win him over, to admit at the very least he has to restate or refine his position, because I have proven that both machines are having the same effect (over a given period of time) on the string.

So, I've taken the approach that I can actually prove a drop weight is not constant pull not by looking at my own definition, which is different from yours and I think a better definition, but by proving it doesn't even fit your own much more minimal definition of constant pull. I seek to prove the behavior in terms of TENSION LOSS HAPPENING ON THE STRING OVER TIME AT OFF ANGLES CAN BE SHOWN TO BE THE SAME OR WORSE than on a lockout.

If I can prove that, I think you have to accept that "constant pull" having meaning for what happens to string, you have to accept your definition does not include regular drop weights at off angles.

DAVID'S TEST RESULTS

I have alot of thanks for having a person to engage in this discussion energetic and reasonable enough to actually test out their theories. I do that myself all I can and I thank you for that. I think I picked my opponent well!

The test results are interesting, but I have at the very least some questions.

First, you didn't mention any of the tensions used.

Second, one key thing here is that the "pull" starts as soon as the arm EVEN BEGINS to settle as far as I'm concerned. That's where the relevant starting position is. My hunch is you WAITED FOR THE ARM TO SETTLE which would take probably at the very least 3 or 4 seconds and until you had plenty of time to measure your "degree mark" and then had that cookie you mentioned. That would be rather late in the process since as someone else stated MOST OF THIS HAPPENS IN FIRST 7 SECONDS. I ALSO ARGUED ABOUT THE 7 SECOND MARK SAYING THERE WOULD BE VERY, VERY NOTICEABLE SLOWING IN STRING STRETCHING AFTER THAT. I'D ARGUE YOU MAY NOT HAVE BEEN THINKING ABOUT WHAT WAS HAPPENING IN THIS PERIOD BECAUSE YOU WERE STILL WAITING FOR THE MACHINE IN THAT TIME, in the stage where you were staring at it wondering what it was going to do next (that "fun" stage on the regular drop weight). *THAT* stage is where you see how the drop weight actually performs a pull and that is its actual pull in my book.

Probably the crank as well can be said to be constant pull with a string like baling wire or a string that has no stretch. If you do the experiment and wait until the Prince stuff is acting alot like that baling wire, the test in my book has little meaning.

Third point: to test the off angles and get a meaningful comparison with a crank, you'd have to have a much higher weight set so that the two machines can be meaningfully compared. Which is why I mentioned 70 lbs and 55 lbs actually pulled at 38 degrees off horizontal. I have a hunch you used 50 lbs and were then pulling only 35 lbs at your 45 degrees off. Hardly a test that's going to produce much stretch. But if you want to do that test, the relevant comparison to a crank is what happens when you set the crank for 35 lbs, not a higher weight. At 35 lbs on the crank, is there a noticeable drop off in tension on the crank (it would be much harder to see as well I'd gather)? If so, how much. I'd bet it would be less than a pound and also hardly observable with a typical tension meter.

We should strive to arrange the tests for the test equipment so that we can see consequences relevant to the claims.

Also, my 38 degree numbers would be relevant at what you are calling 128 degrees, not 38 degrees. These are numbers off horizontal and I was assuming DOWN from horizontal, though the discussion of above horizontal is a different and somewhat interesting discussion as well.

Offhand, I think PSG is sufficiently stretchy for the test, though I have some multifilament which I would have used. Both nylon though, I'm not sure but don't think there's that much difference.

I've used regular drop weights before and recall that the arm tends to move through an arc before settling, especially at odd angles, not true? It is this period we are talking about, NOT THE PERIOD AFTER THE ARM SETTLES when we're into Rich S's "days of stretching" scenario.

In practice therefore, your test would be quite hard to do in my opinion with accuracy, because the arm would be moving while you are trying to measure the starting angle in the first few seconds, no? "The pull" starts from the beginning of the arc where the machine is engaged with the string, not the end of it.

Lastly, I'd note that my point is proven to you if I can prove there is ANY WEIGHT on the drop weight machine that I can set it to where the behavior is the same as the crank, and that the comparison to the crank at the off angles then has to compare with the same LOWER WEIGHT actually being pulled by the drop weight at the off angle.

For instance, if at 38 degrees off horizontal and 70 lbs tension setting and 55lb comparison to crank doesn't work, I think I'll still be able to prove you wrong by simply changing the variables. E.g. 90 lbs tension setting (I think Klipper will go up that high), 38 degrees off horizontal, comparison to 70 lb at crank. Or maybe 90 lb tension setting, 45 deg off horizontal, 64 lb comparison to crank. But I'll only accept being wrong once all the variables are exhausted, because those are the conditions of your claim, that at off angles the drop weight is still constant pull.

So, I'm going to think about some of these issues further myself, but I still believe I am correct and am going to try to actually get a machine to experiment on, but would like your feedback on the above...

 

[jbs24]

Then again, you are misunderstanding of the word "pull". "pull" is "applying force to move something", but that doesn't mean something will move, it can be stationed or no movement at all.

My answer to you question is "C", there will be certain creeping, which would make the string longer than before, thus the machine will lockout at a point further from the racquet.

omg, if you don't understand this you shouldn't be stringing racquets. I would want my racket stringer to understand this most basic of concepts.

A constant pull machine pulls with CONSTANT TENSION, so if the string stretches, it will pull more to keep a constant tension on the string.
A lockout machine pulls with CONSTANT STRAIN, or constant length, so as the string relaxes, the total length of string remains the same because the lockout machine is locked and doesn't pull any further.

Why is the answer C? because a constant pull machine would reach point C all by itself, while a lockout machine would have to be pulled 2 or 3 times to reach the same length.

I shouldn't be so hard on those that don't understand this. It's a basic engineering concept of stress vs. strain that most engineers have trouble with at some time or another. So welcome to the club.

pop quiz:
Is a spring being compressed in a bench vise constant stress (tension) or strain?
Is a spring in your car strut, for example, (and being compressed by the weight of the car) constant stress or strain?

If you can answer these with confidence then you can string my racquets, unless you say that a drop-weight isn't a constant pull machine.

 

[Newberry]

Newberry has said that two human arms a fixed distance apart holding a string are "pull" but two sticks the exact same distance apart and the exact same thing happening on the string are not "pull."

For Newberry, THE FACT THAT THE SAME THING IS HAPPENING TO THE STRING IN THE MIDDLE IS A MATTER OF INCONSEQUENCE, ONE IS PULL, ONE IS NOT PULL.

Hi WW,
I am glad to see you agree that one is pull, and one is not. I have to disagree about them being the same though. The same thing is not happening. The string (I think we said rubber band) pulled by your hands will be longer, and thinner (and most importantly have a different final tension) than the one between the boards, because your hands move apart as it stretches. Minutely longer, and thinner, but measurably. That's why a lockout machine locks out at a longer distance on a second pull.

You are exactly right that, in the end, it doesn't matter at all. I (& probably 99% of the players here) am not going to notice the difference one bit. It does seem to matter enough that a lot of stringers will ask what type of machine was used to last string a racquet.

You are also right about what I would consider "constant pull". If I would have picked a term for the stringing society to use, I would have used "true tension". Like you say, CP electrics have pauses between adjustments, and really aren't "constant".

There seem to be three possibilities for Constant Pull:

1. If you are talking strictly about pulling with no pauses, then only a dropweight, one of the old spring-crank, or one of the old-style weighted stringers would be what I would call a "constant pull" if you use the definitions of the words "constant" and "pull".

2. If you want to talk "constant pull" as what I believe the manufacturers were trying to convey (dynamically maintaining a target weight) then the CP electrics and the LF dropweight fall into this category, whereas a standard dropweight does not due to tension falloff past horizontal.

3. If you want to talk "constant pull" as a machine that constantly pulls at the target weight without pause, then the only machine that comes to mind is the LF dropweight.

I do believe that a good stringer using a spring clutch dropweight can get very similar results as a CP electric, by continuing to adjusting the dropweight to horizontal after the initial string stretch.

I also believe that a good stringer using a lockout machine will produce the most consistent stringbed. Less variables produce tighter tolerences.

Sorry you feel my posts are "silly" WW. I would be hesitant to call anyones opinion silly, but some things are just easy to understand. For instance, the fact that a lockout and a dropweight produce different stringbeds. Thats easy to understand. To say they both work the same way, or that the same thing is happening to the string might be considered silly by some but I would call it illogical. You evidently agree with the fact that a lockout doesn't pull (which is what I was saying all along), so I fail to see why you would say that "the same thing is happing to the string in the middle" when the end results are different between a LO and a DW.

Lets keep this debate civil. Words like "silliness" don't belong here. Facts, & logical ideas do.

Edited for HTML tags (left out my brackets)

 

[SW Stringer]

Newberry says: " . . . but a doorknob cannot "exert".
Definition of exert:
to exercise; to use; to make an effort
I don't think a door can do that, it requires effort."
Newberry, in partial response I've taken a quote from The Physics Classroom: "According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body."

I'll stick with my verbage about the doorknow "exerting" a force.

Newberry then says: "Its all about our own learned definitions I suppose! We all have different takes on the meaning."

Yes, I agree. The concepts used in my explanations draw upon a background in Newtonian physics courses where terms such as, stress, strain, tension, force, friction, vectors have specific, unambiguous meanings. If you don't have some basic physics (or science) under your belt it makes it all the more difficult to have a meaningful discussion.

So, Newberry, did you take any Physics in high school or college?

hangzhou, same question, did you take any Physics in high school or college?

hangzhou says: " . . . very simple fact although the pulling force should be smalled than reference tension due to backlash and string creeping."

My understanding of the Held patent allows no gear backlash due to the method the crankwheel is frozen in place . . . independent of the gear track.

hangzhou also says: "I agree with you that all gear locking mechanism must have some gear backlash/back movement. That's how gears are deisgned to work,i.e. there must be some small space in between one face of two teeth."

I agree there is some space between one face of two teeth, but the gear mesh isn't changed when the wheel is frozen. The gear surfaces in contact when the "snatch" releases (freezing the crank wheel) remain in contact, immovable, fixed until the operator releases and only then will the backlash/back movement come into play. So, for the lockout manual crank machine, the only thing that can affect the tension in the string after lockout, is the string creep.

 

[jbs24]

For instance, if at 38 degrees off horizontal and 70 lbs tension setting and 55lb comparison to crank doesn't work, I think I'll still be able to prove you wrong by simply changing the variables. E.g. 90 lbs tension setting (I think Klipper will go up that high), 38 degrees off horizontal, comparison to 70 lb at crank. Or maybe 90 lb tension setting, 45 deg off horizontal, 64 lb comparison to crank. But I'll only accept being wrong once all the variables are exhausted, because those are the conditions of your claim, that at off angles the drop weight is still constant pull.

The only time a drop weight would act like a crank is if the bar is well below horizontal. You have to realize that the torque applied to the string depends on the length of the shadow below the arm, so the greatest tension by a few percent at most, is when the bar is horizontal.

Below horizontal, as the string stretches, the applied tension drops.
If you start above horizontal, as the string stretches, the tension should actually increase.
Any change would be very minute (a percent or even fractions of percent), depending on the amount of string stretch after the initial pull, but it would be the below horizontal case that would 'act' like a lockout.

I would never use a Klippermate or any other drop weight more than 15 degrees off-horizontal.

 

[David Pavlich]

Wonderwall: First, you must have carpal tunnel after that post!

As I said, I can't say that my test was as "scientific" as it could have been. First, the gauge is marked in 1lb increments and is not as sensitive as a digital scale. Second, The Klipper isn't the best machine to use, but it's the only drop weight that I own. The pulls were straight with nothing to interfere such as grommets and differing angles. I couldn't mount a frame and have room for the gauge at the same time. This would probably be the best way to do it, though.

I used 60lbs as the reference tension, by the way. And as I stated in the test, the 38 degree mark wouldn't work because the tension arm wanted to spring back. Perhaps a better machine might be more effective.

You analysis of a Sensor not being a CP machine, in the strictest sense, is correct. However, the hysterisis is such on the Sensor that the corrections happen at the tiniest deviation. It's the only way an electronic can work. There will always be an hysterisis setting. When the strain gauge reaches the reference tension, it stops pulling. Tension creep sets in and it pulls again to reference tension. I suppose that's part of the reason that the Sensor is so expensive; its hysterisis is tiny compared to other machines. I guess high class gizmos are expensive!

In the end, all of this is meaningless in the day to day stringing life. Regardless of the machine type, if a stringer follows the protocols, chances are there will be a consistent product at the end within the tolerances of the machine and its workings. And it's consistency that is the Holy Grail of a good stringer. Stringers, especially good stringers, tend to get caught up in the "paralysis by analysis" syndrome. It's not necessarily a bad thing, but it can gum up the works if you let it.

David

 

[Newberry]

Newberry says: " . . . but a doorknob cannot "exert".
Definition of exert:
to exercise; to use; to make an effort
I don't think a door can do that, it requires effort."
Newberry, in partial response I've taken a quote from The Physics Classroom: "According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body."

I'll stick with my verbage about the doorknow "exerting" a force.

Newberry then says: "Its all about our own learned definitions I suppose! We all have different takes on the meaning."

Yes, I agree. The concepts used in my explanations draw upon a background in Newtonian physics courses where terms such as, stress, strain, tension, force, friction, vectors have specific, unambiguous meanings. If you don't have some basic physics (or science) under your belt it makes it all the more difficult to have a meaningful discussion.

So, Newberry, did you take any Physics in high school or college?

[/B]

Nope no Physics in HS, but I am a Computer Aided Drafting & Design instructor & adjunct college professor with a degree in engineering specializing in drafting and design. I spend most of my day teaching 3D modeling & design of machine parts & architectural floor plans. My Father was a machinist for Univac & built (among many things) missile parts. I've been around technical terms all my life (ever do any structural steel calculations?).

I'm fairly comfortable talking about Physics, although it is certainly not my specialty.

If you want to say the doorknob exerts a force, that certainly won bother me. Ignore the given definition & base it on a quote, but does that force have the ability to move your hand towards the door? If not, its not pulling.

Remember here is the definition of Pull taken this time from Merriam-Webster dictionary online:
PULL:
1 a : to exert force upon so as to cause or tend to cause motion toward the force

Call your "force" what you will, but you can't call it pulling because it can't move your hand towards the door.

I appreciate your response & certainly don't mean to offend. We can talk physics & definitions all day (I guess we have!) but I still see no evidence that a locked out head is "pulling". If it pulled, it would move when the string stretches.

I hope I have enough education for us to have a meaningful discussion.

 

[Steve Huff]

Wonder Wall, You're right about the car. That was a lousy example I used. Oh well. You seem like a bright guy. Without all the semantics, I'm sure you know what is considered a constant pull and what is not considered a constant pull. I'm just saying that when used properly, it delivers a constant pull.

FW--a dropweight that falls to 45 degrees below horizontal is still a constant pull. It will never get to 35 pounds if it was originally set at 60. The 60 that was applied to the string simply wouldn't let it get that far down if done correctly. If not done correctly, ie too quickly with not enough slack taken up, then the string tension never made it to 60 pounds anyway, unless you just dropped the weight and the tension was reached momentarily before the friction could be overcome.

Hangzhou--when a lockout machine reaches the reference tension, it QUITS pulling, even before you clamp it off. As the string relaxes, the machine doesn't pull it back up to the reference tension. On a constant pull, when the string relaxes, the machine keeps pulling at the reference tension. Even when you clamp it, the machine is still pulling until you release the tension, lift the dropweight, etc. Of course, the clamp prevents the tension from reaching the string before the clamp, so it's irrelevant how long it keeps pulling after the string is clamped.

 

[hangzhou]

To everyone:

Please answer the following questions:
1. Do you agree there is tension in the string after locking on crank machines? Of course this tension will be less than the reference tension.
2. Do you agree that the string is pulling the crank head because of this tension in order to go back to its original length?
3. Do you agree that crank head will keep pulling the string on opposite direction according to Newton's third law?

Remember there are only two things holding the two end of string, one end is the clamp and another is the gripper on crank head.

Now, Mr. Newberry agrees with #1 and #2, but not #3. So does Mr. David. Seems both of you can not accept #3, this is physics 1,2,3 far few than physics 101.

According Newton's third law, if object A pulls object B, then object B will assert countbalance force to pull object A. If the string is pulling the crank head, then it's common knowledge that crank head is pulling the string also.

To Mr. Newberry:
SC Stringer explained these concepts much better than me. Pulling or pushing doen's associated to movement at all. Pulling, pushing are force interaction. If no movement then there is no work done, or no energy transfer. If you reserve the word of "pulling" for your own definition, then, I would say that the crank head is exerting a force to keep the string from going back to its original length, or holding the string... The key is not let the string go back to its original length, same as the level arm holding the string on drop weight machine.

To SC Stringer:
I have more than enough of physics and engineering education for this topic. I won't ask for you background and had believe that you do understand thing much deeper or better than others.
I guess our only difference is on what creates the tension lost on crank machine. Let me explain or elaborate my thoughts, let me know if you don't agree:
The manual crank will rotate the gear so that moves the crank head out away from racket to generate tension in the string. The true tension in the string will increase and reach to the setted reference tension. By then the locking mechanism will be triggered or kicked in. In plain english, it will exert force to pressure crankwheel contact the rail. This pressure will create sliding friction force first as there is small movement and eventually friction force will surpass the cranking force. Thus the crank head will eventually stop and operator will stop cranking. The friction force will become static friction force. But the important thing here is these sliding friction and static friction force are intended to stop the crank head moving away from racket. Under microscope, these contacting surface are not perfect planes, they have ups and downs, hills and valleys... The transition from sliding friction to static friction is a process of break some of these ups and downs, hills and valleys, and finally bite in or mate in.

After locking, the operator will release the crank or not rotate the crank anymore. There is no force to moving crank head outside, but the string has tension so it will pull the crank head back. This pull back motion is on opposite direction than the previous motion. Although these two planes are mated to prevent movement outside, but they are not mated to stop movement inward. That will lead the crank head move backward even there is sufficient pressure on the mating planes. Until enough ups/downs, hills/valleys being break away, then these two plane will mate and have sufficient sliding friction force to stop such movement and turn to static fricton force to balance the pulling exerted from string.

The backward movement, I called it as backlash, contribute the sudden tension drop witnessed by David's incomplete test. String creeping won't create such sudden drop, it's a slow process, takes minutes or hours.

Now if gear doesn't have gear backlash, i.e. gear's teeth are contact with each other on both surfaces. Then this backlash will not happen.

We agreed that gear has gear backlash. This gear backlash will allow the backlash created by sliding friction work.

As a conclusion, I believe the tension drop is caused by this backlash and string creeping, more specifically the sudden tension drop is caused by backlash, not string creeping.

David:

Since you have stated there is tension in the string, so the requested test is no longer needed. The less string bed stiffness on crank machine compare to CP machines is caused by the tension drop you have noticed during your incomplete test. The tension drop is generated by the backlash and string creeping as explained in my reply to SC Stringer. On CP machine, the tension head keeps pulling the string, thus eats up the string creeping. CP machine doesn't have backlash since the pulling motion is alway outward. Not like crank machine, move outward first, stop and then move inward and finally stops.

I do buying the claims from LF and some other stringing machine manufacturers, but I don't buying those with wrong claims. I have proved that LS is a constant pull machine theoretically and estimated the maximum tension deviation in another thread.

You should surrender, not to me, or others, but Mr. Newton and his three laws. Accetping his third law, you should have no difficulty of accepting the fact that crank head is pulling the string at lower/dropped tension.

Steve:

Please see my explaination to SC Stringer. Yes, the string will relax on lockout machine as for the backlash plus string creeping length. But not anymore afterward, thus the string has relaxed a little bit, but still stretched. The string will keep pulling back unless the crank head stops it by pulling...

jbs24:

Welcome to earth, Mr. Stranger from Mar. Welcome to club to dicuss Newton's laws, sliding friction, static friction and material creaping, and other basic engineering concepts. Welcome to club to study patent and their design and how these patents are working.

Pop quiz for you:
Will clay return to original shape after your finger pushes?

Have fun everyone...

 

[Newberry]

To everyone:

Please answer the following questions:
1. Do you agree there is tension in the string after locking on crank machines? Of course this tension will be less than the reference tension.
2. Do you agree that the string is pulling the crank head because of this tension in order to go back to its original length?
3. Do you agree that crank head will keep pulling the string on opposite direction according to Newton's third law?

Now, Mr. Newberry agrees with #1 and #2, but not #3. So does Mr. David. Seems both of you can not accept #3, this is physics 1,2,3 far few than physics 101.

According Newton's third law, if object A pulls object B, then object B will assert countbalance force to pull object A. If the string is pulling the crank head, then it's common knowledge that crank head is pulling the string also.

To Mr. Newberry:
SC Stringer explained these concepts much better than me. Pulling or pushing doen's associated to movement at all. Pulling, pushing are force interaction. If no movement then there is no work done, or no energy transfer. If you reserve the word of "pulling" for your own definition, then, I would say that the crank head is exerting a force to keep the string from going back to its original length, or holding the string... The key is not let the string go back to its original length, same as the level arm holding the string on drop weight machine.

Thanks for your reply hangzhou. I really don't know what else I can add. Again I did not have a specialized physics class in HS, but I did have lots of English classes, and we did learn to use the dictionary.

PULL:
1 a : to exert force upon so as to cause or tend to cause motion toward the force

If a lockout head were pulling, it would cause, or tend to cause motion toward the force, your force being in the direction that you say the head is pulling, opposite the force the string is pulling. That is to say according to you the head is pulling away from the racquet. How can you call this pulling with it does not satisfy the basic definition of the word?

I think what you (and SW stringer for that matter) are arguing is that a force is acting on the string, from the head in the opposite direction of the strings pull. I'll agree with that. When the string pulls at 60lbs, there is 60lbs of force being exerted on the head, which the head counters, BUT that force is always EXACTLY even, and without the possibility of motion, negating the possibility of using the term "pull" as it does not satisfy the known english language defintion of the word.

When your "force" drops to 58.3 pounds, so does the force in the head, when it drops to 58.298990 pounds, again so does the force in the head, never doing any actual "pulling" (no motion).

That is why there are different forces acting on a string in a LO machine versus a DW. The LO only has one force acting on it, that is the tension in the string. The DW has two forces, the tension in the string ALONG with gravity pulling the weight. The DW has the possiblility of motion, so it does satisfy the exact defintion of pull. It is "to exerting force upon the string so as to cause or tend to cause motion toward the force".

I think our whole debate was simply over your statement that the forces acting on a string in a lockout machine are the same as on a dropweight.
Do you still feel that way?

 

[David Pavlich]

To everyone:

Please answer the following questions:
1. Do you agree there is tension in the string after locking on crank machines? Of course this tension will be less than the reference tension.
2. Do you agree that the string is pulling the crank head because of this tension in order to go back to its original length?
3. Do you agree that crank head will keep pulling the string on opposite direction according to Newton's third law?

Remember there are only two things holding the two end of string, one end is the clamp and another is the gripper on crank head.

Now, Mr. Newberry agrees with #1 and #2, but not #3. So does Mr. David. Seems both of you can not accept #3, this is physics 1,2,3 far few than physics 101.

According Newton's third law, if object A pulls object B, then object B will assert countbalance force to pull object A. If the string is pulling the crank head, then it's common knowledge that crank head is pulling the string also.

To Mr. Newberry:
SC Stringer explained these concepts much better than me. Pulling or pushing doen's associated to movement at all. Pulling, pushing are force interaction. If no movement then there is no work done, or no energy transfer. If you reserve the word of "pulling" for your own definition, then, I would say that the crank head is exerting a force to keep the string from going back to its original length, or holding the string... The key is not let the string go back to its original length, same as the level arm holding the string on drop weight machine.

To SC Stringer:
I have more than enough of physics and engineering education for this topic. I won't ask for you background and had believe that you do understand thing much deeper or better than others.
I guess our only difference is on what creates the tension lost on crank machine. Let me explain or elaborate my thoughts, let me know if you don't agree:
The manual crank will rotate the gear so that moves the crank head out away from racket to generate tension in the string. The true tension in the string will increase and reach to the setted reference tension. By then the locking mechanism will be triggered or kicked in. In plain english, it will exert force to pressure crankwheel contact the rail. This pressure will create sliding friction force first as there is small movement and eventually friction force will surpass the cranking force. Thus the crank head will eventually stop and operator will stop cranking. The friction force will become static friction force. But the important thing here is these sliding friction and static friction force are intended to stop the crank head moving away from racket. Under microscope, these contacting surface are not perfect planes, they have ups and downs, hills and valleys... The transition from sliding friction to static friction is a process of break some of these ups and downs, hills and valleys, and finally bite in or mate in.

After locking, the operator will release the crank or not rotate the crank anymore. There is no force to moving crank head outside, but the string has tension so it will pull the crank head back. This pull back motion is on opposite direction than the previous motion. Although these two planes are mated to prevent movement outside, but they are not mated to stop movement inward. That will lead the crank head move backward even there is sufficient pressure on the mating planes. Until enough ups/downs, hills/valleys being break away, then these two plane will mate and have sufficient sliding friction force to stop such movement and turn to static fricton force to balance the pulling exerted from string.

The backward movement, I called it as backlash, contribute the sudden tension drop witnessed by David's incomplete test. String creeping won't create such sudden drop, it's a slow process, takes minutes or hours.

Now if gear doesn't have gear backlash, i.e. gear's teeth are contact with each other on both surfaces. Then this backlash will not happen.

We agreed that gear has gear backlash. This gear backlash will allow the backlash created by sliding friction work.

As a conclusion, I believe the tension drop is caused by this backlash and string creeping, more specifically the sudden tension drop is caused by backlash, not string creeping.

David:

Since you have stated there is tension in the string, so the requested test is no longer needed. The less string bed stiffness on crank machine compare to CP machines is caused by the tension drop you have noticed during your incomplete test. The tension drop is generated by the backlash and string creeping as explained in my reply to SC Stringer. On CP machine, the tension head keeps pulling the string, thus eats up the string creeping. CP machine doesn't have backlash since the pulling motion is alway outward. Not like crank machine, move outward first, stop and then move inward and finally stops.

I do buying the claims from LF and some other stringing machine manufacturers, but I don't buying those with wrong claims. I have proved that LS is a constant pull machine theoretically and estimated the maximum tension deviation in another thread.

You should surrender, not to me, or others, but Mr. Newton and his three laws. Accetping his third law, you should have no difficulty of accepting the fact that crank head is pulling the string at lower/dropped tension.

Steve:

Please see my explaination to SC Stringer. Yes, the string will relax on lockout machine as for the backlash plus string creeping length. But not anymore afterward, thus the string has relaxed a little bit, but still stretched. The string will keep pulling back unless the crank head stops it by pulling...

jbs24:

Welcome to earth, Mr. Stranger from Mar. Welcome to club to dicuss Newton's laws, sliding friction, static friction and material creaping, and other basic engineering concepts. Welcome to club to study patent and their design and how these patents are working.

Pop quiz for you:
Will clay return to original shape after your finger pushes?

Have fun everyone...

You need not ask me any more questions. As I stated, you don't believe a stringing machine manufacturer so if you follow the logic, you won't believe me.

David

 

[barry]

Wonder Wall, You're right about the car. That was a lousy example I used. Oh well. You seem like a bright guy. Without all the semantics, I'm sure you know what is considered a constant pull and what is not considered a constant pull. I'm just saying that when used properly, it delivers a constant pull.

FW--a dropweight that falls to 45 degrees below horizontal is still a constant pull. It will never get to 35 pounds if it was originally set at 60. The 60 that was applied to the string simply wouldn't let it get that far down if done correctly. If not done correctly, ie too quickly with not enough slack taken up, then the string tension never made it to 60 pounds anyway, unless you just dropped the weight and the tension was reached momentarily before the friction could be overcome.

Hangzhou--when a lockout machine reaches the reference tension, it QUITS pulling, even before you clamp it off. As the string relaxes, the machine doesn't pull it back up to the reference tension. On a constant pull, when the string relaxes, the machine keeps pulling at the reference tension. Even when you clamp it, the machine is still pulling until you release the tension, lift the dropweight, etc. Of course, the clamp prevents the tension from reaching the string before the clamp, so it's irrelevant how long it keeps pulling after the string is clamped.

Just curious, did you get your Wise 2086 back? Mine is working very well. I usually string with poly mains and synthetic crosses and turned on the pre-stretch 10% for one of the rackets. The string bed played tighter than just using the Constant Pull.
Do you ever use pre-stretch? And is tighter string normal?

Nice to have a constant pull backup (drop weight) with a constant pull electronic machine, the Wise has spoiled me!

 

[Steve Huff]

Barry, yes, I got it back. It's working great. It's pretty slow this time of year, so not nearly as many rackets being strung. Hope it picks up as the mixed, indoor season gets ready to start.

Hangzhou. Think of it this way. If you had a string hanging from above (say tied around a tree limb or something). It has a 60# weight tied to the end. As soon as it drops down where all the slack is gone, you place a table under it so that it can't drop any more. The force pulling the string down is now NOT pulling it any further(the table prevents it from continuing to pull), although the string is still being held by the 60# weight. This is your lockout. Remove that table. The string continues to stretch again. Now you've got a constant pull.

 

[SW Stringer]

To All: In threads of this sort which occur periodically, someone steps in to utter the truest words, in this case it was David Pavlich who said: " . . . In the end, all of this is meaningless in the day to day stringing life. Regardless of the machine type, if a stringer follows the protocols, chances are there will be a consistent product at the end within the tolerances of the machine and its workings. And it's consistency that is the Holy Grail of a good stringer. . . . "

I also believe the pursuit of knowledge and understanding is a good thing in itself and with more of the former and latter, one may be able to improve ones "stringing protocols" and get a more consistent product.

Another less "lofty" motivation for participating in the thread is the need to be right, correct, on the winning side . . . and yes, I'll even admit to it.


Newberry cites the dictionary as his source for the definition of "pull : to exert force upon so as to cause or tend to cause motion toward the force". The definition is a two part clause, the second part starts with the OR which I believe gives the FULL meaning of pull if you look up the meaning of the intransitive verb tend. It means : to exert an influence in a certain direction. So pull can have two (closely related) meanings, one that Newberry uses is to actually cause motion , the other is intent to cause motion, whether the motion actually occurs or not. And I will give an example of the use of the word pull (second meaning) for which everyone can relate.

A synonym for pull is tug. Virtually all of us have witnessed a tug of war or have even participated. Once the contest begins, when the judge sees the marker cross a predetermined line the contest is over. Each side PULLS or TUGS, or EXERTS with all their force and might to move the marker to their line. And here's the problem with Newberry's limited meaning of pull, when an impasse occurs, and the marker is no longer moving, are the participants not now pulling on the rope? Need I say more? OK, I will. Yes, they ARE indeed pulling, their every intent is to get that mark moving, and the second clause of Newberry's citing allows the use of the verb pull . . . ie, they are TENDING TO CAUSE MOTION . . .they are exerting an influence in their teams direction to cause motion . . . but during the impasse the other team is exerting an equal and opposite influence resulting in no movement.

I think we've beat that dead horse enough, but I do look forward to your thoughtful and witty reply Newberry.

hangzhou says: "I guess our only difference is on what creates the tension lost on crank machine." Yes, I agree.Then hangzhou says: "The manual crank will rotate the gear so that moves the crank head out away from racket to generate tension in the string. The true tension in the string will increase and reach to the setted reference tension. By then the locking mechanism will be triggered or kicked in." Yes, I'm with you up to here.

hangzhou continues: "In plain english, it will exert force to pressure crankwheel contact the rail." Here's where I don't agree. The patent disclosure describes edge of disc 62 being pinched or locked between the frame 50 and the brake wedge 110 by the action of rotating lever 104 mounted to frame 50 on with threaded nut 116 to shaft 108, the pivot point. As the lever rotates (due to compressed torsion spring 106) after being released by the trigger mechanism the pitch of the threaded nut 116 drives washer 114 against brake wedge 110 thus pinching (with friction) the disc 62 between the frame 50 and the brake wedge 110. See figure 3 in the claims. This is what "freezes" the crank assembly. It's the same action as a disc brake - the rotor (disc with gear welded in center and crank handle bolted to it) is pinched between the two brake pads of the stator (frame 50 and brake wedge 110) by the compressive action of rotating lever 104, nut 116, shaft 108 and washer 114. The braking action occurs in milliseconds and does not change the loading or position of the gear on the rack, it simply freezes the position. Bear in mind the designer had to take into account the coefficient of friction of steel on steel, the contact area, the required spring force of torsion spring 106, and the design goal of tensioning string up to 90 pounds of tension. The mechanism will probably hold well over 120 pounds of force to give adequite margin for manufacturing tolerances of the critical parts.

For this reason I don't believe there to be any gear backlash, mechanical drawback, or whatever to add to the string tension dropoff due to string creep. If I've missed something on figure 3 please point it out.

Figure 30.8 in Chapter 30 of the Physics and Technology of Tennis which shows the Static Tensio Loss vs time of various string formulations pretty much says it all.

 

[jbs24]

Pop quiz for you:
Will clay return to original shape after your finger pushes?

Depends on the clay and the amount of plastic vs. elastic behavior. Perfectly plastic clay will just mush on contact and not recover any shape when you remove your finger. Perfectly elastic would mean it's like a rubber ball and recovers all its shape. Most clays are plastic, but have some small amount of elasticity due to water content, temperature, etc.

You may be quoting physics, but that doesn't mean you're quoting/applying it correctly.

 

[Newberry]

I think we've beat that dead horse enough, but I do look forward to your thoughtful and witty reply Newberry.

I don't know about witty, but I'll try to be thoughtful in simply saying that I agree, I've beat that horse until I can't lift my arms and I'm tired!

I will add that tug-of-war has the possibility of motion, which is why it is pulling .

I've said all I can say, and more than I intended or needed to say for that matter. I certainly don't want to develop a bad relationship with the folks on the forum as I'm hoping to purchase a stringer (it will be a dropweight!) in the New Year, and I will be needing everyone's advice (including you SW, and maybe even WW) and help in producing the best results I can with the equipment available to me.

As long as there are no "hurt" feelings, and everone has been forced to think "outside the box" a bit, I'd call this thread a useful one, despite our inability to agree on a four letter word.

Anyone who feels they just can't rest, could post a poll in machine forum asking "Does a LO machine pull" and see what the rest of the community thinks.

As for me, I look forward to sharing ideas about stringing & tennis in general here on the forum. Maybe we should spend more time discussing the things we can agree on, rather than the things we can't (although I have learned a lot during this thread).

Cheers,
Wayne

 

[hangzhou]

Barry, yes, I got it back. It's working great. It's pretty slow this time of year, so not nearly as many rackets being strung. Hope it picks up as the mixed, indoor season gets ready to start.

Hangzhou. Think of it this way. If you had a string hanging from above (say tied around a tree limb or something). It has a 60# weight tied to the end. As soon as it drops down where all the slack is gone, you place a table under it so that it can't drop any more. The force pulling the string down is now NOT pulling it any further(the table prevents it from continuing to pull), although the string is still being held by the 60# weight. This is your lockout. Remove that table. The string continues to stretch again. Now you've got a constant pull.

Your case is more complicated than it looks like.

Let me explain the case on lock out machine first. We should agree there is tension in the string after lock out. This is sole purpose of stringing. Now once there is tension in the string, the string will try go back to its original length all the time unless something is holding or pulling it back. On one end of the string is the clamp. The other end is crank head. These two things are pulling to keep string elongated. Release any one of them, string will go back to original length.

If someone claim that the crank head is not pulling string, then he must agree that the clamp is not pulling the string neither. With these two thing not pulling. Which parts are keeping the string stretched so that there is tension inside the string?

Let's take a look at your case, let's assume the string has elasticity of E1 and table is a perfect elasitc object with elasticity of E2. The weight of iron is W. The elongation of string will be W/E1 before table contact the iron. When the table just contact the iron, there is no deformation thus no force between the iron and table. If you keep moving table upward for a distance D, there will be deformation on the table and the elongation on string will be redcued. Let's assume the deformation on table is DT, and reduction of elongation of string be DS. Then we should have D=DT+DS. Then the actual elongation of string will be W/E1-DS. Now let's look at the iron only, it has string pulling upward with force of (W/E1-DS)*E1 and table pushing upward of DT*E2. These two force should equal to the weight of iron W, i.e. W=(W/E1-DS)*E1+DT*E2.

Now we have two equations:
D=DT+DS
W=(W/E1-DS)*E1+DT*E2
We know W, E1, E2, and D. We should be able to calculate DT and DS. After knowing DT, DS, we then would know the actual force between string, iron, and table, i.e. (W/E1-DS)*E1 AND DT*E2.

This is a gradual process, as D increases, and DT increase, while DS decreases. Eventually (W/E1-DS) will be zero, i.e. the string don't pull the iron anymore. There is no tension in the string anymore.

For lock out machine, D is the combination of mechanical drawback, backlash, and string creeping length(SC Stringer don't agree with on this part, I will adress this later). This value is relative small so that there is still tension on string. I want experimental proof, that's the reason why I have asked David to complete his test and let us know the final calibrator read out to prove there is tension in the string. That's fine with me since we have common knowledge that there is tension in the string.

You conclusion of the table will fully support the iron, this assume D is larger enough to make string tensionless. This doesn't happen on lock out machine, since D, i.e. the combination of mechanical drawback, backlash, string creeping is relative small.

 

[hangzhou]

hangzhou says: "I guess our only difference is on what creates the tension lost on crank machine." Yes, I agree.Then hangzhou says: "The manual crank will rotate the gear so that moves the crank head out away from racket to generate tension in the string. The true tension in the string will increase and reach to the setted reference tension. By then the locking mechanism will be triggered or kicked in." Yes, I'm with you up to here.

hangzhou continues: "In plain english, it will exert force to pressure crankwheel contact the rail." Here's where I don't agree. The patent disclosure describes edge of disc 62 being pinched or locked between the frame 50 and the brake wedge 110 by the action of rotating lever 104 mounted to frame 50 on with threaded nut 116 to shaft 108, the pivot point. As the lever rotates (due to compressed torsion spring 106) after being released by the trigger mechanism the pitch of the threaded nut 116 drives washer 114 against brake wedge 110 thus pinching (with friction) the disc 62 between the frame 50 and the brake wedge 110. See figure 3 in the claims. This is what "freezes" the crank assembly. It's the same action as a disc brake - the rotor (disc with gear welded in center and crank handle bolted to it) is pinched between the two brake pads of the stator (frame 50 and brake wedge 110) by the compressive action of rotating lever 104, nut 116, shaft 108 and washer 114. The braking action occurs in milliseconds and does not change the loading or position of the gear on the rack, it simply freezes the position. Bear in mind the designer had to take into account the coefficient of friction of steel on steel, the contact area, the required spring force of torsion spring 106, and the design goal of tensioning string up to 90 pounds of tension. The mechanism will probably hold well over 120 pounds of force to give adequite margin for manufacturing tolerances of the critical parts.

For this reason I don't believe there to be any gear backlash, mechanical drawback, or whatever to add to the string tension dropoff due to string creep. If I've missed something on figure 3 please point it out.

Figure 30.8 in Chapter 30 of the Physics and Technology of Tennis which shows the Static Tensio Loss vs time of various string formulations pretty much says it all.

SC Stringer:
I rushed of my wording last night. You description of the part of how lockout mechanism works is more complete and accurate.

I believe our disagreement has less relevancy to this thread, thus better to discuss in other ways if you don't mind so that we don't waste other's time.

Let me state my logic, reasoning and conclusion for open discussion:
1. There are always gear backlash, mechanical drawback, and string creeping all the time. The higher tolerance, the less backlash, drawback. The elastic string, the less creeping.
2. The higher design/manufacturing tolerance, the higher total cost for making machines.
3. The higher friction between brake pads and stator, the stronger spring is required, thus more money. The higher friction will make brake worn fast and has less life time.
4. Mechanical machine design is a compromising to balance the cost and results.
5. Any device using friction force to stop movement, no matter how larger and how fast the pressure will be, there is always small movement. That's because there is relative motion and the sliding friction starts first and eventually turns into static sliding friction.
6. The lock out mechanism has two phases, the first one is to stop the motion outward, which is generated by operator by rotating the crank and gear. The second is stop the motion inward, i.e. pulling by string.
7. The first phase of motion is stopped by sliding friction and then static friction. That make the brake pads mated. But they are mated only for the motion outward, not inward. When the second phase kicks in, i.e. operator stops rotating crank, the inward motion has no initial resistence, i.e. the brake pads are not mated for that motion. You would see very small movement as generate sliding friction. That will eventually stop.
8. David's incomplete test has shown sudden tension drop. This sudden drop cann't be explained by string creeping which is a slow process.
9. All patents describe how things or machines will work in theory. Unless you have detailed design and manufacture drawings with tolerance information, then you can discuss the possbile gear backlash, mechanical drawback. The best and quickest way of testing these things is by real testing or measurement.
10. Don't have the book you are talking about, so no comments on that figure 30.8.

To all:
I had stated my thoughts in previous posts, many of you don't agree or accept. I have tried my best, spending time of reading every responses, and writing up my responses in order to correct these misleading information or concepts. I guess it's time to call it off. Enough is enough. For those of you don't agree or accept. Let's agree of disgree. Have fun...

 

[jbs24]

Now once there is tension in the string, the string will try go back to its original length all the time unless something is holding or pulling it back. On one end of the string is the clamp. The other end is crank head. These two things are pulling to keep string elongated. Release any one of them, string will go back to original length.

This is absolutely untrue and is the whole reason why lockouts and CP machines are different. As the string stretches under tension, on a lockout, that tension is gone and tension can only be raised by pulling further. If you were to release tension, the elastic part of the string would recover most of its length, but it WOULD NOT GO BACK TO ITS ORIGINAL LENGTH. If strings were perfectly elastic, there would be virtually no difference between a CP and LO machine.

Nice equations and all, but why do you even include deformation of the table to complicate things?

 

[SW Stringer]

hangzhou says: "8. David's incomplete test has shown sudden tension drop. This sudden drop cann't be explained by string creeping which is a slow process."

hangzhou, the chart I referenced from The Physics and Technology of Tennis, is a chart of static tension loss on various strings, plotted on the same graph. The strings under test were tensioned to 62 pounds, held there for 10 seconds at 62 pounds, and then clamped off. The measurements of the tension decay starts with the clamp off. All string materials showed an exponential decay, dropping very quickly and then leveling off. Most of the tension drop off ocurred in the first 100 seconds. Due to the scale of the drawing it's hard to see what ocurred in the first few seconds, but that's where the negative slope of the curves is the greatest.

From my analysis of the machine design and the string testing done in the above mentioned reference, I'm convinced the sudden drop-off is due ONLY to string creep, whose decay curve is exponential.

Here's a simple test that anyone with a Wise head could do. Set machine in lockout mode. Lay a wristwatch/chronograph in stopwatch mode running next to display. Aim video camera at display and running stopwatch. Draw tension on test string to reference. Record for 10 to 20 seconds. Play back in frame by frame mode (usually 1/30th second intervals), and record tension drop-off, or better yet make AVI file so anyone on web can replay.

Same thing could be done with a fish scale, stopwatch, and any brand crank lock-out machine. Gamma Tech - you want to volunteer?

Any volunteers out there who'd like to run the test? Most of the digital cameras these days have an AVI mode for recording a few minutes of video. That would be more than sufficient for this test.

I've got neither a Wise head nor a crank lockout machine at my disposal to do the test, but hey, if someone wants to ship me one I'd be glad to do it!

 

[jbs24]

The backward movement, I called it as backlash, contribute the sudden tension drop witnessed by David's incomplete test. String creeping won't create such sudden drop, it's a slow process, takes minutes or hours.

After further review, Hangzhou is full of hot air. It intrigues me how someone can quote facts and make an intelligent-sounding argument the same time as making a bogus argument.

String creep is immediate. I can prestretch a string and make a 30' length about 3 inches longer by pulling on it once with 60 lbs of tension. That's about 3 seconds of pull time. This test also ignores clamp movement.

Gear 'backlash' is negligible in comparison to clamp movement and string creep. String clamps cause way more tension loss than any gear backlash would. You're talking about movement on a microscopic level. Clamp movement is visible with the eye.

Btw, creep is dependent on tension, time, temperature and other factors. In a crank machine, tension is slowly dropping, so that the creep rate drops as well, this is why the curve is exponential and will approach some equilibrium tension. It will never reach zero tension, or if it did, it wouldn't make a good tennis string.

 

[fwtennis]

It’s disappointing when people who seem to be educated engineers are mocked for trying to be helpful explaining that the some of the conclusions based on casual observation are not exactly correct.

Give the guy a break. Hangzhou is responding with sound engineering principles to a specific observational point of another poster. There are countless variables that come into play. It unfair to say he is “full of hot air” when you toss in another variable such as clamp movement, which by itself is infinitely variable since every stringing machine in use is going to be slightly different. It seems like every time the guy tries to help explain something specific, somebody new comes along and says “oh yeah.. but what about this or what about that”?

Besides, I think you may be misreading him. He states that “backlash” contributes to the loss and continued to say that it is very minimal. He did not say it was the sole CAUSE of the tension loss. It is just another one of those pesky variables. Plus, as you point out the experiment he was referencing, the string was never clamped off so clamp movement can, in Hangzhou’s explanation, can be ruled out. It was not part of the question nor was at least a dozen other variables that I can think of. It does not make his answer any less accurate. It only makes the observation/question incomplete.

Anecdotal hyperbole is not a good substitute for engineering principles and practices.

Happy Holidays Everybody!

 

[SW Stringer]

David said earlier in this thread: " . . . 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."

hangzhou claims most of this immediate tension drop is due to the mechanical limitations (gear backlash, drawback, etc) of the crank lockout machine.

I claim it's most (90% or better) if not all from creep (molecular level chain slipping and reallignment) in the string.

In further support of my claim, I've found another chart in the Physics and Technology of Tennis, by Howard Brody, Rod Cross and Crawford Lindsey, published by Raquet Tech Publishing, and also available at Tennis Warehouse. The Chart shows Creep Tension loss immediately after clamping off after reaching reference tension. In this case the reference tension was 55 pounds. I did my best to estimate the data points from the graph:

Time(seconds) Tension(pounds)
0 55
1 51.1
2 48
3 46.6
4 45.1
10 44
60 40.4

This test exactly duplicates what a pull & brake machine does, was performed by Dr. Carl Love and cited by Crawford Lindsey in Chapter 33 (String Tension - Factors in Tension and Tension Loss) of the above mention book.

I highly recommend this book, it's chocked full of data, scientific setup and testing, and thoughtful analysis of what it means on all phases of tennis - it really is too much to assimilate at one time. I didn't even recall reading Chapter 33.

Anyway, as can be seen from the table, tension dropoff is immediate and precipitous, exactly what David observed in his test.

 

[Steve Huff]

Hangzhou, in your equation, D remains constant after the lockout machine mechanisism is triggered. However, elongagation (or relaxation) of the string continues. Tension continues to decrease as the string relaxes.

With a constant pull, elongagation continues, D INCREASES (as the string relaxes), TENSION remains constant.

So, you can clearly see that there is a difference in the way they work:
Lockout Constant Pull
1. String length Constant String length increases
2. Tension Decreases Tension remains constant
(as string relaxes) (as string relaxes, tension head pulls)

If you have a rope up the side of a hill, and you are using it to go up the hill, there is a difference between having it tied around a stationary object (say a tree) and having something (say a tractor) pull the rope up. If it's tied to a tree, you (the weight) are applying a force downward. The tree applies an equal force upward. But, it's not PULLING you upward. But, when it's attached to a tractor that PULLS you upward, it is applying more than an equal force because it is moving you.

 

[hangzhou]

SC Stringer:

I will agree with you that the creeping makes up the majority of tension lost based on these data. I don't know that strings are so plastic and couldn't hold tension well. No wonder my game hasn't improved. What is the testing string, and how about natural gut?

Gear backlash, drawback should has much short duration, say less than tenth of second. That will be hard or impossible to measure or record using regular camera/scale unless using industry high speed camera or highly sensible scale. However it will impossible to say that there will be no drawback or backlash for ordinary lockout machines.

Now there is interesting point I want ask you. Normally people clamp off after 1 or 2 seconds on lock out machines, with your data, then the tension drop will be more than 10%. This is different than common knowledge of 5 to 10% difference than CP machines. Why? What will be the cause? Has the book address this issue or subject?

 

[hangzhou]

Steve:"in your equation, D remains constant after the lockout machine mechanisism is triggered. However, elongagation (or relaxation) of the string continues. Tension continues to decrease as the string relaxes."

Agree.

Steve: "With a constant pull, elongagation continues, D INCREASES (as the string relaxes), TENSION remains constant."

D should decrease, i.e. in negative numbers... the tension head will move outward to compensate string creeping.

Steve: "So, you can clearly see that there is a difference in the way they work:
Lockout Constant Pull
1. String length Constant String length increases
2. Tension Decreases Tension remains constant
(as string relaxes) (as string relaxes, tension head pulls)"

Agree. When you compare CP machines to drop weight machines (excluding LF machines), the second point doesn't hold. When the weight arm was above horizontal, as string creeps or elongates, the tension will increase. When the weight arm was below horizontal, the tension will decrease instead. So these three types of machine behavior differently.

Steve:"If you have a rope up the side of a hill, and you are using it to go up the hill, there is a difference between having it tied around a stationary object (say a tree) and having something (say a tractor) pull the rope up. If it's tied to a tree, you (the weight) are applying a force downward. The tree applies an equal force upward. But, it's not PULLING you upward. But, when it's attached to a tractor that PULLS you upward, it is applying more than an equal force because it is moving you."

There is difference in this case, it is who did the work of pulling or who output the energy for such movement. Tractor will do the work/output energy in one case, while human being will be the one in other case.

However, pulling is same as pushing, they are only interacting forces between objects. They are independant of movement, energy transfer. SC stringer has better explaination on this subject, pls check his reply to Newberry.

 

[hangzhou]

I think our whole debate was simply over your statement that the forces acting on a string in a lockout machine are the same as on a dropweight.
Do you still feel that way?

Well, many people believed that drop weight machines are CP machines, I don't agree with that.

Many people believed there is no tension in the string on lock out machine, I disagree with that.

In my reply to Steve, I have point out these three types of machine works differently.

Sorry I didn't see your question until now...

 

[hangzhou]

fwtennis:

I believe jbs24 has very good background, however he didn't read everything carefully or correctly. I took a sarcastic approach of responding his post, that didn't work well I guess.

jbs24:

If you have better approach to explain or model steve's case, pls show us.
If you found more "hot air", pls let us know... TIA.

 

[SW Stringer]

SC Stringer:

I will agree with you that the creeping makes up the majority of tension lost based on these data. I don't know that strings are so plastic and couldn't hold tension well. No wonder my game hasn't improved. What is the testing string, and how about natural gut?

Gear backlash, drawback should has much short duration, say less than tenth of second. That will be hard or impossible to measure or record using regular camera/scale unless using industry high speed camera or highly sensible scale. However it will impossible to say that there will be no drawback or backlash for ordinary lockout machines.

Now there is interesting point I want ask you. Normally people clamp off after 1 or 2 seconds on lock out machines, with your data, then the tension drop will be more than 10%. This is different than common knowledge of 5 to 10% difference than CP machines. Why? What will be the cause? Has the book address this issue or subject?

The testing only showed a "standard" nylon. The same test for natural gut wasn't performed. I'd like to see that one too.

Gear backlash doesn't come in to play in my estimation since the mechanical system is still under the same tension as before the brake was set. Backlash in the gear system would come into play were you to reverse directions, and load the opposite side of the gear teeth. That won't happen. The only device with any slop would be the fixed clamps drawback which will vary by machine but should be constant on the same machine. But then again the static test from the book just looked at string creep after pulling to reference tension.

If there were any mechanical drawback I agree it would take sampling the strain gauge at a higher rate than once per second to catch that.

The chart shows the individual strings drop in tension, whereas the standard 5% to 10% difference between CP and Lockout machines is in the total stringbed stiffness. A string pulled using CP machine will still drop it's tension, but depending on how long it was left at tension, string elongation comes into play which mitigates somewhat the individual strings tension loss.

Yes, the book looks at many different factors affecting string tension loss, but doesn't examine types of machines in any detail. That would be a much appreciated addition to any further revisions of the book.

 

[Steve Huff]

Hangzhou, I didn't say the STRING had no tension in a lockout machine. The tension has already been applied. Take a bungee cord. Stretch it from one fixed object to another. The cord still has tension on it, but neither fixed object is still pulling it apart. If you left it sitting this way for a while, over time, the fibers will relax and the cord will lose a little tension. Same with the string on the lockout. On a CP, every time the cord lost a little tension, it would pull it back up to that tension.

As for a dropweight, it still depends on using it properly. When I was using mine, I let it come to a rest slightly above horizontal. As the string relaxed, it crept down to horizontal until it wasn't moving any more (they do come to a point where you cannot see it moving anymore--this is when you clamp). Granted, if it kept dropping, it wouldn't pull at quite the same tension. This is why proper technique is even more important with this type of machine. But still, if use PROPERLY, it is a constant pull machine. Hangzhou, you do make some interesting points though. You need to string more because I'm sure you are a perfectionist, and we need more stringers that are.

 

[jbs24]

My apologies for any misdirected sarcasm, i'm happy to contribute to this discussion.

My beliefs:
A drop-weight used correctly is a constant pull machine.
String creep causes only 5-10 degrees of drop-arm drop.
A CP machine is different from a LO in the few seconds between tensioning and clamping.

I did some crude tests on my dropweight. With a 24" length of 17-gauge string, the dropweight, set at 60lbs. rotates about 120 degrees around a drum of 2.5" diameter. This means a string stretch of about 2.6 inches. Please follow the diagrams and thought experiment below for a bit:

This is a length of string, L1
-----------------------------------------------
This is the length a string stretches under tension, L(elastic)
---- OR EEEE
This is the length a string 'creeps' under tension, over time, L(creep)
--> OR CC>
The total length changes over time, but is always
L1+L(elastic)+L(creep)
-----------------------------------------------EEEECC>

Tension, T, is always proportional to the elastic portion, or L(elastic) times the string stiffness or modulus, E
or Tension = L(elastic) x E.

In a constant pull machine, tension, and hence L(elastic), is constant, and L(creep) is taken up by the machine, keeping L(elastic) consant. So T = constant = L(elastic) x E

In a lockout, total length, L(total) is always constant, so
L(total) = constant = L1+L(elastic)+L(creep).
As L(creep) increases, L(elastic) must decrease, and so tension drops. It's a complicated equation as L(creep) is tension and time dependent, but the rate of tension drop is proportional to the rate of creep increase.
The THOUGHT experiment for the lockout is:
A) Put a constant tension on a string of length L1. It will stretch L(elastic) for a total length of L1+L(elastic).
B) Over time L(creep) will be added to this so total length is
L1+L(elastic)+L(creep)
C) Reduce the string length to the same length as is step A and that is how a lockout machine works.
The new tension will be {L(elastic)-L(creep)} / E.
With respect to L(elastic), if it creeped 10%, tension will drop about 9%. If it creeped 50%, tension will drop 33%. 100% creep with respect to L(elastic), 50% tension drop. Get it?

According to the Technology of Tennis data presented earlier, with an initial pull of 55lbs., 7 lbs. are lost in the first 2 seconds, with 8 more pounds lost over the next minute. If it takes you about 2 seconds to clamp off (which is fast), you lost 7 lbs. using a LO versus a CP. You still will lose 8 pounds at the 1-minute mark with the CP, but you're not losing 15lbs. over a minute. This is the difference between the CP and LO machines, so this 7lbs is about 12% of the original tension which is why LO machines are said to string about 10% lower. This will vary with how quickly you can clamp off---if you could clamp off a LO or CP instantaneously, they will in theory be the same, however you will see 15lbs of tension loss on the racquet since all of the creep will occur on the racquet.

Back to my drop weight. My L(elastic) value was about 2.6". If tension in a lockout were to drop 20%, this is about 0.52" of creep in the dropweight. This converts to about a 24-degree change in drop-arm angle. I would say that we never see this much drop because by the time we let go of the arm (which we never DROP, we always let down slowly), close to 50% of the string creep has occurred. Plus, we learn quickly and know to feed more string into the gripper and let the arm drop to slightly above horizontal. The other 50% of creep is another 0.26" or about 10-degrees. But this 10 degrees isn't much. If you start with the arm 10 degrees above horizontal and it slowly drops to horizontal, you calculate cos(10) - cos(0), to see that this is only a 2% change in tension (actually an increase in tension), or about 1 pound when stringing at 55lbs. If you started at horizontal and it dropped 10 degrees, it would be a 1 pound reduction in tension. Not so much when compared with frictional losses at grommets, clamping losses, and tie-off losses. However if you're anal, you can easily get this 1 pound back by ratcheting the arm back up 10 degrees to level. So phew, there, that's why i think a drop weight is a CP machine.

 

[hangzhou]

Constant pulll should be a feature or character of string machines,regardless of operator. When the operator is included in, then equivalently a very smart or intelligent controller is added to observe and correct these tension deviations(such as string creep, weight arm level).

The claim of drop weight is a CP machine speaks of:
drop weight machine + experienced operator = CP machine.

When you take out the experienced operator, then you should have:
drop weight machine < CP machine.

If you insist that, same thing can be claimed for lock out machines if operator recrank after noticing any string creeping. Thus they should be viewed as CP machine also.

There are siginicant different results for lock out machines, drop weight machines and CP machine, that is whether the machine can maintain the final tension at certain range, say 59.5 to 60.5 lbs, regardless of operator's skill, the type of string, weight arm level angle. For lock out machines, and drop weight machines, there is no such guaranty. Thus it's reasonable to see the price different among them.

 

[jbs24]

If you insist that, same thing can be claimed for lock out machines if operator recrank after noticing any string creeping. Thus they should be viewed as CP machine also.

How do you notice string creep on a lockout?
When doesn't string creep happen?
How come it's well known by all good stringers that CP machines result in tighter stringbeds compared with lockouts?
you should go to grand slam stringers . com and see what pro stringers think of your theories. I've given more than my two cents.

In order for a lockout to give you CP results, you need to double or triple-pull strings. This is not a time saver for a professional stringer, they just bump up the tension on the lockout.

 

[hangzhou]

It would be hard to notice string creep, but this can be accomplished by wait sufficient long time until string gets enough or majority of creeping.

Only these is no tension then string creep will stop.

Yes, everyone agree and this is the fact that CP machine result in tighter stringbeds. However it's debatable that drop weight machines will always produce tighter stringbeds regardless of operators and stringing protocals.

You have touched another big point here, i.e. speed. Lock out machines and electronic CP machines are fastest, thus they are preferred choices for professional stringers.

The second important point or key is accuracy, electronic CP machines and LF machines deliver much better results in this area. For every pull, they can assure you that the tension will be in designed range, say 59.5 lbs to 60.5 lbs regardless of operator's skill and the type of string.

The last point is consistancy, electronic CP machines, LF machines, and lock out machines can deliver consistant results for same setup, i.e. same racket, same string, and same time duration before clamp off. Regular drop weight machines probably could deliver close result only when the weight arm settles close to horizontal for every pull plus string creeping, which is very hard and time consuming.

Finally, I would say, to be a true CP machine, you have to have a device or mechanism on the machine (not operator's skills) so that final pulling tension will remain at certain range regardless of machine setup, racket setup and the type of string(for creeping). This is why true CP machines cost more moeny.

 

[Gaines Hillix]

It would be hard to notice string creep, but this can be accomplished by wait sufficient long time until string gets enough or majority of creeping.

Only these is no tension then string creep will stop.

hangzhou, IMO, it isn't practical to use this technique and it's not repeatable, which is the key to consistency for a string job. Creep never stops. The rate at which the string creeps is reduced with time but it never stops, so this assumption really is not true.

Yes, everyone agree and this is the fact that CP machine result in tighter stringbeds. However it's debatable that drop weight machines will always produce tighter stringbeds regardless of operators and stringing protocals.

You have touched another big point here, i.e. speed. Lock out machines and electronic CP machines are fastest, thus they are preferred choices for professional stringers.

The second important point or key is accuracy, electronic CP machines and LF machines deliver much better results in this area. For every pull, they can assure you that the tension will be in designed range, say 59.5 lbs to 60.5 lbs regardless of operator's skill and the type of string.

The last point is consistancy, electronic CP machines, LF machines, and lock out machines can deliver consistant results for same setup, i.e. same racket, same string, and same time duration before clamp off. Regular drop weight machines probably could deliver close result only when the weight arm settles close to horizontal for every pull plus string creeping, which is very hard and time consuming.

Finally, I would say, to be a true CP machine, you have to have a device or mechanism on the machine (not operator's skills) so that final pulling tension will remain at certain range regardless of machine setup, racket setup and the type of string(for creeping). This is why true CP machines cost more moeny.

Your observations are good. Consistency is the key and manufacturers put a lot of effort into making the tensioning accurate and repeatable and not as subject to variations that can be introduced by the stringer. However, on any machine proper setup and stringing technique are still needed. AFAIK, no one has found a way to take the stringer out of the equation.

BTW, flying clamps are another variable on many drop weight machines.