The physics of a dropweight tensioner

[jim e]

But imagine this situation:
we are both on an ATP-tournament, you with your lock-out, me with my Stringway (imagine ). And "a" player asks us to string his racquet, and he brings a string that we both do not know. And he asks: string my racquet at 25kg, mains and crosses. Which stringing machine will give the result that matches the expactations from that player?

This answer is depends! Although I use an electronic CP I could still use a LO, but either way you should know how to compensate going in either direction LO to CP or CP to LO. You may also be a sloppy stringer as technique does play into this situation, its not just the machine, as that is only a % of the situation.

You were not very specific with your question. If you are stringing ATP you better be asking the proper questions and not just say you have a stringway machine as that does not cut it. You did not say if the players racquets was last strung with LO or CP. If you string other players racquets you should ask this very important question if they are new for you! Stringers need to go in both directions not just CP to LO, but go LO to CP as well.
As you may know TW uses LO machines for their racquets they sell.

There should still be no issue with either machine as you could use the USRSA machine type calculator.
The USRSA calculator takes this into consideration:
Different string materials and constructions, and different racquet head sizes, will require different amounts of compensation to match the stringbed stiffness produced by a constant-pull machine to that produced by a lockout machine. For racquets with smaller heads and/or with lower elongation strings, use tensions toward the minimum shown on calculator going from LO to CP. For racquets with larger heads and/or with higher elongation strings, use tensions toward the maximum shown on calculator going from LO to CP. It is only a small % min. to max. and head size and string type gets you very close to desired tension needed.

Once you know string type, and you do not need to know 1000's of strings as has been mentioned in posts above, as strings can be placed in groups as certain types have greater elongation and others less, you can look at strings to determine the type of string, as most can determine if a poly, sg, multi. or gut by looking at it, also most have writing on them as well, but older poly strings have less elasticity, where nat. gut has more elasticity and others in between, and I started stringing in 1968 (CP machine as well) , strung my share of racquets and so far when players had a LO machine stringer previously string theirs I have successfully strung their racquets with a CP machine without 1 issue yet. Enough said for me on this. Have fun with your issues stringing.

BTW. even if we both used same machine, we would get a different result, as I do not wait a long period of time between reached tension on machine to clamping, as once the machine beeps, I clamp off, as this is done that way by slam stringers as well. You can view slam stringers string on some internet sites, and they are fast stringers, and they do not count a certain # of seconds delay between clamping as you do, and the pro's seem to do well with it.If you are trying to improve your game with equip. it may be better served with improving your playing technique instead.

 

[eelhc]

Food for thought: I would say, the "standard" for stringing are the high-end stringing-machines and procedures used at the ATP-tour. My stand: a drop-weight, and especially an automatic drop-weight can produce results closer to this "standard" as a lock-out. And yes, there are ways to "work-around" the draw-backs of a LO, but why should you? Take a machine that gives you those results WITHOUT needing work-arounds.

Love to see a reaction on this one...

I would say that we disagree on the Standard then. What you consider to be the standard are the machines used for a select group of ~200 or so (I am including the WTA) elite athletes. They do get their racquets restrung often but that's a tiny, tiny fraction of tennis players in the world.

What I consider to be the standard are the machines that are more commonly used across a broad spectrum of players at all levels. The Ektelon/Neos machines have been in production the longest and have sold countless machines.

Among the more serious home stringers (not professional), lockouts are the most common machine. A lot of folks start out with a dropweight, but move to a lockout once they start having to do some volume. Locally, they are mostly parents of high school players who were going broke paying for stringing. Also, The 2 local pro shops have lockouts (NEOS, Gamma) and the local big box sporting goods store has a Lockout (Gamma). The pro shop in the next town over has an electronic (Gamma) and a pro shop a little further away has an electronic (Babolat). A kid who strings for the local D1 college team and runs a craigslist business has a Neos in his dorm room.

Tennis Warehouse strings all of their customers racquets with a Neos 1000. The racquet/string reviewed they provide on their website and youtube are all strung with the Neos The playtesters comments and impressions of the equipment correlate directly to a lockout.

I prefer my definition of "the Standard". But again, it doesn't matter so long as one strings at the tension for the desired playability and when stringing for other players who have had their racquets strung on a different machine type, adjust the set reference tension accordingly (true whether going from a dropweight to a crank or visa versa).

I find your issue with lockouts unsubstantiated because there's no scientific basis for it. Again, same amount of material that is worked (formed or stretched) in the same manner that fills the same space... will have no difference.

Agree. Fact is, that if using the same "reference tension", there is difference in "material that fills the same space" when you compare a lock-out and a drop-weight

Now we're getting some place... the set reference tension is just a number. On a lockout, it has to be set higher to get the same amount of material to fill the same space for the same result given it's worked (pulled) the same way. Then only real difference is how the tension is locked. Even on a CP machine, once the string is clamped off, the tension is locked between the clamp and the far grommet. But regardless of what machine is used, the string will continue to relax and lose tension until it is cut out.

The fact the the set reference tension is higher on a lockout to get the end result of the material (string) as same as a dropweight is not a deficiency. It's different that's all.

I don't argue the superiority of machine types any more. it's been beat to death. But I do argue that it's easier and faster to get consistent results with a crank lockout vs a dropweight. Just watching some of the guys on youtube with their Gamma X-2 machines... The bar drops anywhere from once to four/five times - it's like each pull is random. Since you've studied physical chemistry, you can't deny the fact that the material has been worked /formed differently vs a crank lockout, automatic dropweight or an electronic CP. With a manual dropweight, it's important to nail the tension in one or two drops for consistent results IMO.

But imagine this situation:
we are both on an ATP-tournament, you with your lock-out, me with my Stringway (imagine ). And "a" player asks us to string his racquet, and he brings a string that we both do not know. And he asks: string my racquet at 25kg, mains and crosses. Which stringing machine will give the result that matches the expactations from that player?

I do not have a stringing business and do not take money for stringing (just do it for family and friends).

I can try to imagine that situation which will never happen or actually live/experience a situation that happens all the time - a local player asks to me to restring their racquet(s). I always ask but there is 90%+ likelihood that it was previously strung on a crank lockout. Just recently, a friend purchased a racquet from TW and realized that he had it strung too high. He asked me to restring it at a lower tension with the same string. TW uses a Neos 1000 and I have a Neos 1500 (same tensioner). tension differential correlates perfect.

 

[MathieuR]

@eelhc, thanks for your elaborate posting. This deserves an elaborate answer, but I don't have the time right now. Will come

Just a first reaction on 2 points:

I would say that we disagree on the Standard then. What you consider to be the standard are the machines used for a select group of ~200 or so (I am including the WTA) elite athletes. They do get their racquets restrung often but that's a tiny, tiny fraction of tennis players in the world.

Agree to disagree. "the standard" for me is: "best possible technique and procedures". That it is only used for the top is not really relevant. The standard stands .

What I consider to be the standard are the machines that are more commonly used across a broad spectrum of players at all levels. The Ektelon/Neos machines have been in production the longest and have sold countless machines.

The world is bigger as the US. In Europe lock-outs are a minority under the stringing-devices. Here in the Netherlands I have never seen a lock-out in a shop (no drop-weights either, only high-end eCP)

 

[eelhc]

@eelhc, thanks for your elaborate posting. This deserves an elaborate answer, but I don't have the time right now. Will come

Just a first reaction on 2 points:

Agree to disagree. "the standard" for me is: "best possible technique and procedures". That it is only used for the top is not really relevant. The standard stands .

The world is bigger as the US. In Europe lock-outs are a minority under the stringing-devices. Here in the Netherlands I have never seen a lock-out in a shop (no drop-weights either, only high-end eCP)

My stringing world is within ~30mi/50km radius of my home. Almost all stringers fall in this category. Not sure if you travel or string for players who are not local but the world is not as big as you state wrt to stringing.

Also, just because there aren't as many lockouts in Europe or the Netherlands, there's no reason to disparage that machine type. There are other ways to spur discourse without agitation. Maybe you're more American than Dutch.

With a lockout tensioner, one can produce just as consistent results as an eCP (again the material science)... but high end electronics have better turntable/clamps/etc vs lockouts just like lockouts tend to have better turntable/clamps/etc vs manual dropweights. You can't seriously be comparing a Gamma X-2 to a high end electronic and claiming that it meets the same "standard"... let's not be be silly.

I find your logic/posts confusing/incongruous... on the above post you say the "standard" is "best possible technique and procedures"... ATP tour. But you also have posts here on re-using natural gut. You do realize that most ATP players have their strings cut out and re-strung fresh for each match regardless of whether they used it or not...

 

[Technatic]

IMO

Stringers lose confidence in Lock outs as soon as they start to check their string beds with a sbs tester. It seems impossible for a stringer to compensate for the very different stretch behavior of modern strings, when a lock out is used.

If a stringers uses the same kind of strings all the time the lock out tensioner can be ok.


But this is actually the same discussion as :”what is more important consistent or accurate stringing”

I think that as soon as you string on stiffness consistent is not good enough.

 

[MathieuR]

Also, just because there aren't as many lockouts in Europe or the Netherlands, there's no reason to disparage that machine type. There are other ways to spur discourse without agitation.

Again, my "provocation" was meant to spur some reaction, not meaning to insult people or methods.

Not sure if you travel or string for players who are not local but the world is not as big as you state wrt to stringing

No, I don't travel as a stringer. But I do know what's going on in the Netherlands. I do think the world is as big as I state. There are apparently ~50million people playing tennis worldwide, 1million in the Netherlands. All these people need their racquets to be strung.

But you also have posts here on re-using natural gut.

1: this is an experiment 2: only for personal use 3: gut can have three lives ( apparently )

You do realize that most ATP players have their strings cut out and re-strung fresh for each match regardless of whether they used it or not...

Yeah, what a waste. I personally think that if they would use prestretched strings, they can ánd play longer with one stringbed, ánd if not used direct, also use them after a few days.

It seems impossible for a stringer to compensate for the very different stretch behavior of modern strings, when a lock out is used.

I think the only realistic option is to pre-stretch the strings when you use these on a lock-out.

Yesterday I strung my frame with Klip gut in the mains, Kirschbaum max.power in the crosses. As I found last time that the SBS went down quickly, I now machine-pre-stretched the gut with +9kg, and the crosses with +20kg. I could simply do this by adding and removing an extra weight on the arm (and remove it to get the reference tension, then clamp).
@eelhc: how would you do this on a lock-out?

 

[eelhc]

Yesterday I strung my frame with Klip gut in the mains, Kirschbaum max.power in the crosses. As I found last time that the SBS went down quickly, I now machine-pre-stretched the gut with +9kg, and the crosses with +20kg. I could simply do this by adding and removing an extra weight on the arm (and remove it to get the reference tension, then clamp).
@eelhc: how would you do this on a lock-out?

I wouldn't attempt that on a lockout or a dropweight. That pre-stretching is not consistent. What you are pre-stretching is the section of string from the far grommet through the near grommet to the tensioner. Because the mains and crosses vary in length, you will never get a truly consistent pre-stretch. Some sections of the string would have been subjected more cycles of pre-stretch than others. Again, think back to your material science. Do you really think that working arbitrary sections of the string results in the same material characteristics?

There was a post here earlier (Ricardo?) who used a drop weight to pre-stretch the entire length of string prior to weaving and tensioning (tying the string to a far wall and using a dropweight to pull the entire length of main or cross. Again, given the material science, to me... this is the preferred method and one doesn't need a dropweight... Just a couple of pulleys and a bucked filled with weights will do. You would be better off tying a section of string ~20 ft away from your stringway and pulling tension with your machine for the entire length to pre-stretch BEFORE you start stringing. Me... I just manually use YULitle's method and tug on the string wrapped around a post.

You seem somewhat obsessed with taking all the initial tension loss out of strings. Did it occur to you that some players may prefer this portion of the string life cycle? and perhaps other players don't care because they string one in a while and can wait for the string bed to settle?

 

[Technatic]

Perhaps this information explains some more about the importance of Constant Pull.

In 1988 Rucanor sold 500 of these systems to shopkeepers. They called it a Tennis-Computer and it was an advisor and a stiffness tester.

The tennis player was invited to come to the shop and get their advise and has his racquet tested.

The “computer” advised a stringing stiffness on one side and the right string (out of 9) on the other side. When the stiffness was too high or too low compared to the advise the player needed a new string.

The stringer had to string the racquet on the right stiffness then. So Rucanor supplied a calculation disc to translate the stiffness to the right stringing tensions for that racquet.

In those days there were still many Lock outs in Dutch shops, and they had a big problems to obtain the right desired stiffness.

Because Rucanor was big in strings then many shops replaced their Lock outs by electronic Electronic CP machines.

These graphs show the tension on a lock out with different multi-filament strings. As you can see the final tension and the speed of stretching is very different.

Because of the huge difference in elongation of monos the difference can be much bigger with them.

 

[Irvin]

i wonder what that graph would look like if the stringer pulled tension a second time at the 6 second point? Would that be the same as eliminating the first six seconds of each graph?

 

[MathieuR]

What you are pre-stretching is the section of string from the far grommet through the near grommet to the tensioner. Because the mains and crosses vary in length, you will never get a truly consistent pre-stretch.

? ; I did the pre-stretch of course for every L/X-string.

Some sections of the string would have been subjected more cycles of pre-stretch than others

I don't think that is a bad thing on a cp-drop-weight. It would be on a lock-out though!

I just manually use YULitle's method and tug on the string wrapped around a post.

If you pull that way, you will be able to pull ~20kg, that's effectively 10kg. That's "nothing".

You seem somewhat obsessed with taking all the initial tension loss out of strings.

Obsessed? I'm in an "experimental phase". I only do this for my own racquets. Goal is to get a stringbed I like that is stable for a longer period of play.

Did it occur to you that some players may prefer this portion of the string life cycle?

If you can affort to restring with gut every 9 games, yes, be my guest. Cause I think this is the max. period that the string is in "this portion of the life cycle"

 

[MathieuR]

i wonder what that graph would look like if the stringer pulled tension a second time at the 6 second point? Would that be the same as eliminating the first six seconds of each graph?

As I see it, the string looses tension 6kg's (Nylon 1.8). In the first 6 seconds, the average tension is 28kg (not 31kg). So if the string is re-tensioned at 31kg, it still has to loose the creep from "31->28kg" . My rough estimate . So the tension-loss will be less, but still 3kg's I think.

Another pull, 1.5kg, yet another 0.75, and the 5th pull you will have 0.37kg. So it will take you 5-6 pulls on a lock-out to get the result what a drop-weight has standard in a controlled way.

 

[Irvin]

As I see it, the string looses tension 6kg's (Nylon 1.8). In the first 6 seconds, the average tension is 28kg (not 31kg). So if the string is re-tensioned at 31kg, it still has to loose the creep from "31->28kg" . My rough estimate . So the tension-loss will be less, but still 3kg's I think.

Another pull, 1.5kg, yet another 0.75, and the 5th pull you will have 0.37kg. So it will take you 5-6 pulls on a lock-out to get the result what a drop-weight has standard in a controlled way.

So not matter how long the string is stretched it will still drop to 28 no matter how (what tensioner LO, eCP, DW, or whatever.) now I see you have no idea of what your talking about.

 

[Technatic]

i wonder what that graph would look like if the stringer pulled tension a second time at the 6 second point? Would that be the same as eliminating the first six seconds of each graph?

If a string is tensioned for the second time the stringer only has to develop the remaining elongation that is left in the string.

The graphs show that if a Lock out stringer wants to obtain maximum accuracy with a certain string, he has to adjust his speed of pulling.

When he strings a slow string he has to turn so slowly that all the elongation is out of the string at the moment that the system locks.

So with the upper string the final tension would be about 6 kg higher if he would have made his pull in about 8 seconds.

OF course pulling again would result in less loss also.


For your information 2 more graphs:

The upper one shows the tension of a CP dropweight, the lower one of quite a good electronic machine.

I do not think that electronic machines can beat this kind of DW.

As you can see the accuracy should be in the repull, which is "piece of cake" for the DW while it is very difficult not to overshoot the tension with the electronic machine.

 

[Irvin]

If a string is tensioned for the second time the stringer only has to develop the remaining elongation that is left in the string.

The graphs show that if a Lock out stringer wants to obtain maximum accuracy with a certain string, he has to adjust his speed ...

You must be looking at a different graph Technatic. What i see is the LO always pulls to the same tension before LO and after about 6 seconds most of relaxaction is gone.

EDIT: You would also like people to think the LO is inferior to your automatic DW (you do still own Stringway don't you?) so fewer people would buy the LO machine and your (Stringway) sales would go up. Granted I personally dont use a LO any longer but i think they can produce excellent results consistently.

 

[eelhc]

All machines are lockouts. Once the string is clamped, the section is string between the clamp and far grommet is in fact "locked out".

What the dropweight proponents are arguing is that tension is pulled and held longer to take the INITIAL stretch out. But in reality, the string between the clamp and the far grommet and in fact the entire string bed will continue to stretch and lose tension. On the next pull, some of this tension is regained slightly though there is some friction in the grommets.

But in the end, what matters is the amount of material that is filling the space. Doesn't matter what machine is used. If one starts with the same length of string, end ends up with the same amount left after tying off and cutting, the resulting string bed will be the same unless the string has been worked differently.

I think these guys have started with a conclusion that dropweights are superior and coming up with arguments to substantiate that conclusion. Normally I wouldn't waste my time but as this forum is a resource to many would be stringers, its important to get the facts and science correct.

 

[Technatic]

You must be looking at a different graph Technatic. What i see is the LO always pulls to the same tension before LO and after about 6 seconds most of relaxaction is gone.

That is exactly what I am saying and that is why the stringer should pull so slow that the system does not lock before all the elongation has been developed.

EDIT: You would also like people to think the LO is inferior to your automatic DW (you do still own Stringway don't you?) so fewer people would buy the LO machine and your (Stringway) sales would go up. Granted I personally dont use a LO any longer but i think they can produce excellent results consistently.

Come on Irvin don’t you think that always the same commercial suspiciousness starts to become boring?

All machines are lockouts. Once the string is clamped, the section is string between the clamp and far grommet is in fact "locked out".

What the dropweight proponents are arguing is that tension is pulled and held longer to take the INITIAL stretch out. But in reality, the string between the clamp and the far grommet and in fact the entire string bed will continue to stretch and lose tension. On the next pull, some of this tension is regained slightly though there is some friction in the grommet

I am quite sure that this is not true, we can see that very clearly when we do the string tests to measure the elongation character of strings.

A string stops stretching when all the remaining elongation is pulled out of the string.

For a fast string this takes 4 seconds and for a slow one more than 10.

 

[Irvin]

That is exactly what I am saying and that is why the stringer should pull so slow that the system does not lock before all the elongation has been developed.

No matter how fast or slow the stringer pulls the string it will lock out at the same tension. In the examples your show in the LO graph each pull took almost exactly the same time just over 2 sec so what is so hard about being consistent. Once you have used a LO for a short period of time I would think the time of each pull would be extremely close. The string will stretch after lockout and may fall from 60 to 55 on a free string as opposed to 60 to 54 or 56 dependent on the length of pull but they will be consistent time after time.

 

[Imago]

All machines are lockouts. Once the string is clamped, the section is string between the clamp and far grommet is in fact "locked out".

Ergo, do not use stringers who will string your racket for less than 1 hour.

 

[Technatic]

No matter how fast or slow the stringer pulls the string it will lock out at the same tension.

Every string needs a certain time to stretch, so stretches in a certain speed.
There are very fast and very slow strings depending on the friction in the material or between the filaments.

In the graphs, the speed of pulling was faster that the strings can follow. So after locking the string was still stretching, and that is why the tension drops.

So when the tensioner locks after all the elongation is developed in the string the string will not lose any tension after that.

 

[Technatic]

Ergo, do not use stringers who will string your racket for less than 1 hour.

I agree fully that it is not smart to tell your customer how fast you did it.

Because: "A fast stringer is a soft stringer".

But it can be done very well in half an houre.

 

[MathieuR]

So not matter how long the string is stretched it will still drop to 28 no matter how (what tensioner LO, eCP, DW, or whatever.) now I see you have no idea of what your talking about.

Well, no reason to get rude No, you misread, misinterpretate my poste. First pull on the lock-out: locks at 31, drops to 25. second pull: locks at 31, drops to 28. Third pull, locks at 31, drops to 29.5. Fourth pull, locks at 31, drops to 30.25. Fifth pull, locks at 31, drops to 30.625.
Of course this was my estimate, and I can be wrong. Basic requirement would be you crank in 2 second to 31kg every pull.
On a constant-pull machine, be it eCP or (automatic) drop-weight, there will be a constant pulling force of 31kg. If you would wait long enough, ALL creep at that tension will be gone. Of course we can not wait forever, so we settle at a waiting time of say 6 seconds. "A lot" of the creep at that reference tension will be gone by then. Not all, as rightfully repeatedly stated. As soon as you clamp, the creep will continue, and the tension in the string will go down, independant if you used a LO or a CP. But the LO-string already starts "creeping down" at 26kg, in stead of 31. And yes, you can compensate this with the work-around method: just start at a higher "reference tension" (wasn't reference tension intended to be the tension to be reached for the to be strung string?)

No matter how fast or slow the stringer pulls the string it will lock out at the same tension.

Yeah, right. BUT: if you crank infinitely fast or infinitely slow, difference is huge. And every stringer will be "somewhere" in the middle.

 

[MathieuR]

What the dropweight proponents are arguing is that tension is pulled and held longer to take the INITIAL stretch out. But in reality, the string between the clamp and the far grommet and in fact the entire string bed will continue to stretch and lose tension. On the next pull, some of this tension is regained slightly though there is some friction in the grommets.

That "initial" stretch can be huge. And you will loose it on a CP. Big advantage I would say, as this happens under controlled conditions.

But in the end, what matters is the amount of material that is filling the space.

Agree. But with a LO there are far more uncertanties to get to this "same amount of material"

I think these guys have started with a conclusion that dropweights are superior

"these guys" are here to learn, and hope to be better stringers, with better, controlled results.

its important to get the facts and science correct.

agree 100%

 

[eelhc]

Ergo, do not use stringers who will string your racket for less than 1 hour.

Well I guess this guy won't be stringing for you then...

What is that... Like a little over 16 minutes? Probably under 20 including cutting the old string bed out.


.. and for you Stringway fans... Here's a guy (Jet method?).. Under 20 minutes too.

I don't like the way he pulls his center mains.

Well I'm out again... this is just nonsense all over again. Enjoy your stringing...

 

[jim e]

Ergo, do not use stringers who will string your racket for less than 1 hour.

I guess all the slam stringers are no good for you, as they have ability to string about 50 racquets/ day and have the last racquet as accurate as the first.
That type of stringing although is fast seems to work well for the pro's , but you must be in a league all your own.
BTW, string a racquet over an hour and you fail the USRSA exam, I guess you know something they don't, yet the USRSA gives credibility to the craft. Maybe you should enlighten them.

If you must find a stringer that strings a racquet in over an hour, best bet is to go to big box store where someone just gives a 2 min. instruction to a clerk on stringing and have that clerk string yours and enjoy!

TW should have a section for unconventional stringers so posts like this, and the stringers who untie knots, and like reused string better than new, and as such, can try and outdo each other with such "different" or non traditional views than the normal traditional standard or care of stringing.

 

[ElMagoElGato]

If you pull the string until it doesn't stretch any more, it won't stretch any more. It's simple. It'll keep the tension better. But I guess stringing isn't all about maintaining the tension.

I've had my string pre-stretched only once before. It kept higher tension and lasted longer than usual. But it was a trampoline from the start and uncontrollable. I'll never pre-stretch again.

 

[ricardo]

If you pull the string until it doesn't stretch any more, it won't stretch any more. It's simple. It'll keep the tension better. But I guess stringing isn't all about maintaining the tension.

I've had my string pre-stretched only once before. It kept higher tension and lasted longer than usual. But it was a trampoline from the start and uncontrollable. I'll never pre-stretch again.

You are confusing cause and effect.

The only thing pre-stretching does is to improve tension maintenance. That's all.
It does not make any string play better or worse.
The only thing that can do that is tension.
Tension too low and it plays mushy.
Tension too high and it plays boardy.
Tension right and it plays well.

However, tension changes, either fast or slowly.
When the tension changes, the way it plays also change,
from good to bad, or from bad to good or from bad to worse.

When you find the right tension, make sure that tension remains the same until it breaks.
Pre-stretching is one way of making tension almost constant.

 

[MathieuR]

There should still be no issue with either machine as you could use the USRSA machine type calculator.
The USRSA calculator takes this into consideration:
Different string materials and constructions, and different racquet head sizes, will require different amounts of compensation to match the stringbed stiffness produced by a constant-pull machine to that produced by a lockout machine. For racquets with smaller heads and/or with lower elongation strings, use tensions toward the minimum shown on calculator going from LO to CP. For racquets with larger heads and/or with higher elongation strings, use tensions toward the maximum shown on calculator going from LO to CP. It is only a small % min. to max. and head size and string type gets you very close to desired tension needed.

Is this a "public domain" calculator, or do you have to be a member. Tried to find it, no success.
There are however still 2 factors that you can not "translate" with the calculator: the pulling-time on a CP, and the cranking speed on a lock-out. Cranking speed on a lock-out is a huge "uncertanty".
Pulling time on a drop-weight is clear for most stringers: as long as the bar sinks, keep pulling. Simpel as that.

Now we're getting some place... the set reference tension is just a number.

Isn't the reference tension originally meant to be the tension of the string IN the frame.

I guess all the slam stringers are no good for you, as they have ability to string about 50 racquets/ day and have the last racquet as accurate as the first.
That type of stringing although is fast seems to work well for the pro's , but you must be in a league all your own.

I know first hand, that a stringer at the AO is given 30 minutes to complete a racquet. There they will focus on quality.

And by the way, on a CP there is a way to be fast, AND have longer pulling times: while pulling a string, weave a string ahead. So, pull, weave the second string ahead (one is already prewoven). Clamp, pull "first string strung ahead" (second string is now first string strung ahead), weave a (new) second string ahead, etc.

TW should have a section for unconventional stringers so posts like this, and the stringers who untie knots, and like reused string better than new, and as such, can try and outdo each other with such "different" or non traditional views than the normal traditional standard or care of stringing

If you keep doing what you did, you will get what you got. No harm in experimenting, and reporting the results. If bad, reject, if promising, try it yourself.

 

[jim e]

Is this a "public domain" calculator, or do you have to be a member. Tried to find it, no success.

It is a member benefit, just like their online digest.

I know first hand, that a stringer at the AO is given 30 minutes to complete a racquet.

Ergo, do not use stringers who will string your racket for less than 1 hour.

So why do they only are given 30 min at AO, I guess they are all wrong??

If you keep doing what you did, you will get what you got. No harm in experimenting, and reporting the results. If bad, reject, if promising, try it yourself.

My results are consistent as that's what I strive for and my customers appreciate that as well.
Reusing strings throws any consistency out the window, as the strings characteristics, like elasticity, have changed resulting in a string that is not at all like a fresh set at all, and that result cannot be duplicated exactly again, as each reused string will have a different characteristic depending on string type and amount of usage. A fresh set of string strung the same way each time with proper technique can give consistent results. After all, how many pro players ask for used strings in their racquets, and just how many even have their stringers pull on the strings so much that it takes over an hour to string a racquet? I doubt there is even 1 yet the pros seem to hit well with what they use. Strings are manufactured with a certain amount of elasticity, and if you like to stretch the hell out of it and remove what elasticity is remaining and enjoy that, then that's your choice, happy hitting.

 

[onehandbh]

Interesting debate.

Poly strings probably lose a noticeable amount elasticity after a certain amount of pulling and usage.

While pulling a long time on a string may produce a more consistent and tighter stringbed at a given "stringing tension" set by the stringer, does it cause the string to lose too much of its elasticity and playing characteristics?

 

[Imago]

I wish there was a DT (SBS) calculator.

 

[Technatic]

I've had my string pre-stretched only once before. It kept higher tension and lasted longer than usual. But it was a trampoline from the start and uncontrollable. I'll never pre-stretch again.

Prestretching changes the stretch character of the string because you pull the remaining elongation out of a string at a higher tension than the stringing tension.

When you hit a ball with a non-prestretched string the string will stretch elastic plus remaining, so you feel the total elongation.

The remaining will not recover so the string loses a little tension with every stroke.

When you hit the ball with a prestretched string the string will feel much stiffer because the remaining elongation was already removed during stringing.

So:

- The string feels stiffer.

- All the elongation is elastic which will result in power.

- The string will not lose much tension.

I tested some strings this week and tested one string twice as you can see the elongation in the first pull is much bigger than in the second:

The elongation is measured from 20 >30 > 40 > 30 > 20 kg.

First pull: 1,0 > 3,1 > 2,6 > 1,8 %

Second pull: 0,4 > 1,6 > 0,9 > 0,2 %

As you can see the remaining elongation in the first pull was 1,8 % and in the second 0,2 %.

A string becomes a completely different string when you prestretch it.

And because monos have less elastic and much more remaining elongation they become quite “unplayable” after prestretching.

BUT: it depends strongly on how much extra prestretch tension you apply and if you prestretch a stretchy or stiff string.

 

[ElMagoElGato]

Prestretching changes the stretch character of the string because you pull the remaining elongation out of a string at a higher tension than the stringing tension.

When you hit a ball with a non-prestretched string the string will stretch elastic plus remaining, so you feel the total elongation.

The remaining will not recover so the string loses a little tension with every stroke.

When you hit the ball with a prestretched string the string will feel much stiffer because the remaining elongation was already removed during stringing.

So:

- The string feels stiffer.

- All the elongation is elastic which will result in power.

- The string will not lose much tension.

I tested some strings this week and tested one string twice as you can see the elongation in the first pull is much bigger than in the second:

The elongation is measured from 20 >30 > 40 > 30 > 20 kg.

First pull: 1,0 > 3,1 > 2,6 > 1,8 %

Second pull: 0,4 > 1,6 > 0,9 > 0,2 %

As you can see the remaining elongation in the first pull was 1,8 % and in the second 0,2 %.

A string becomes a completely different string when you prestretch it.

And because monos have less elastic and much more remaining elongation they become quite “unplayable” after prestretching.

BUT: it depends strongly on how much extra prestretch tension you apply and if you prestretch a stretchy or stiff string.

Thanks a lot. You explained my experience very logically. I'll restring mine when the remaining elongation is all gone, which will be quite often because I basically use poly. If one prefers not having the remaining elongation, it'll go totally different.

 

[ricardo]

A string becomes a completely different string when you prestretch it.

And because monos have less elastic and much more remaining elongation they become quite “unplayable” after prestretching.

A string becomes a completely different string when you prestretch it.

I totally agree.
A pre-stretched string becomes stiffer and thinner and tension maintenance is significantly improved

And because monos have less elastic and much more remaining elongation they become quite “unplayable” after prestretching.

To me, pre-stretched co-polys are playable.
I pre-stretch co-polys at 80 lbs for 10 hours.
I string them at 30-40 lbs on the crosses.

 

[Technatic]

A string becomes a completely different string when you prestretch it.

I totally agree.
A pre-stretched string becomes stiffer and thinner and tension maintenance is significantly improved

And because monos have less elastic and much more remaining elongation they become quite “unplayable” after prestretching.

To me, pre-stretched co-polys are playable.
I pre-stretch co-polys at 80 lbs for 10 hours.
I string them at 30-40 lbs on the crosses.

This is exactly the trick!!
the stringer feels the sbs much more than the string, so just lower the sbs with a stiff string and it is playable.

But:
There is something in between what you did and not prestretching.

- It is not necessary to do it for 10 hrs because all the remaining elongation is out after 1 minute.
- you can tune the feeling by chosing the amount of prestretch, 30 % prestretch will feel stiffer than 20 %.
- And look at the elongation test list first because prestretching a S4 mono does not make sense.

http://www.stringway-nl.com/pdf/Stringtest2014-1 tot el-ENG.pdf

 

[ricardo]

- It is not necessary to do it for 10 hrs because all the remaining elongation is out after 1 minute.
- you can tune the feeling by chosing the amount of prestretch, 30 % prestretch will feel stiffer than 20 %.
- And look at the elongation test list first because prestretching a S4 mono does not make sense.

http://www.stringway-nl.com/pdf/Stringtest2014-1 tot el-ENG.pdf

To me, stretch and elongation are two different things.
Stretch is temporary, elongation is permanent.

When I stretch a 20ft long string for 1 minute, the string remains 20ft after I remove the tension.
There is no permanent elongation no matter how much the string stretched.

When I stretch a 20ft long string for more than 1 minute (up to 10 hours),
the string elongates permanently. It is no longer 20ft long. It is longer

When I pre-stretch I basically want to permanently deform a string.
My belief is that I need a permanent elongation to get a significantly improved tension maintenance,
not just getting rid of coil memory, which I don't really care about.

I have had 2 inches to 2 feet (out of 20ft) of permanent elongation.
To me, if there is no permanent elongation, tension maintenance is not improve.

Some co-polys (Volkl V-Star 18g), permanently elongates by 1 foot (out of 20ft).

BTW, I measure permanent elongation 24 hours after pre-stretching.
Some strings stretch by 3 ft (out of 20ft) while being pre-stretch. However, this stretch shrinks to about 6 inches after the pre-stretch.

 

[Technatic]

I am afraid we talk different things;

When the time is so long we call that creep.

At what tension do you tension the string?

The lower the tension the more elastic elongation and less remaining elongation.

This elongation test that we do does not take longer than 1,5 minute up and down.

First pull: 1,0 > 3,1 > 2,6 > 1,8 %


Second pull: 0,4 > 1,6 > 0,9 > 0,2 %


And the length after getting back to the beginning is very different and also the elongation when you repeat the test with the same piece of string.

And the test I very simple and accurate with the sensor directly on the string.

 

[teekaywhy]

There always seems to be questions regarding how accurate a dropweight tensioner is. In simple words, very accurate.
I will present here the physics governing a dropweight tensioner.

Here is a schematic of a string being tensioned by a dropweight machine:

We know from physics that, in order to rotate an object such as a rotational tensioner indicated in the schematic as a red wheel, you need to apply a torque.

torque = force x distance

Newton has figured out that force = Mass x acceleration. On earth, each object with a mass will exert a downward force equal to the product of its mass (M) and the earth's gravitational acceleration denoted as "g."
Therefore, the gravitational force (Fg) provided by a dropweight is M x g, as indicated with green letters on the schematic.
If we also know the distance (R) between the center of the Mass and the axis of the rotation for the tensioner, we can figure out the torque. Remember that torque = force x distance, therefore the torque exerted by the dropweight (on the right side of the schematic) is:
torque right side = M x g x R
This is why as you move the dropweight farther from the center, you pull a greater tension on the string.

When the string is being tensioned, the rotational tensioner does not move. That's because the torque exerted by the dropweight is balanced by the torque exerted on it by the string.
Again, the equation for torque does not change: torque = force x distance.
On the left side, the distance in question is the distance between the center of the rotational axis and where the string applies its force. In other words, the radius of the tension head is the distance (r) of interest. The force in this case is the "reference tension" imparted on the string.
When the tension head is at rest, it means the torque on the left side equals the torque on the right side, therefore we can set up an equation:
torque left side = torque right side, therefore
f x r = M x g x R

Play with that equation a little bit, you get:
f = (M g / r) R

Mass (M), gravitational acceleration (g), and the tensioner's radius (r) are all constant, i.e. they never change. Therefore, the reference tension is directly proportional to the distance (R). That's why a dropweight tensioner is simple and requires no calibration, and is impeccably accurate.

Now you must be asking this question: what if the tension bar isn't exactly horizontal?
Here is another schematic to show you the error when the tension bar is not horizontal:

Remember again: torque = force x distance

Gravity "does not know" if the bar is horizontal, but gravity does know the true distance between the center axis of the tensioner and the center of Mass of the dropweight.
In other words, the torque for the right side should be replaced by this equation instead:
f x r = M x g x L, where L is the horizontal distance between the center of the tensioner to the dropweight.
We know from trigonometry how to related R to L, that if the tension bar is resting at an angle Q, then L = (cos Q) R.

Thus, to improve upon the original equation, the tension you're imparting on the string (f) at any angle is:
f = (M g / r) L , or
f = (M g / r) (cos Q) R

At Q = 0, cos Q = 1. Therefore, the number you see on the tension bar, if the bar is resting at exactly horizontal, is exactly the tension you're imparting on the string.
Cos 5 = cos (-5) = 0.996, i.e. if you set the mark at 60 lb, but the bar is either 5 degrees above or below horizontal, the actual tension is 59.8 lb.
Cos 10 = cos (-10) = 0.985, i.e. if you want 60 lb., you get 59 lb.
That's why the advice is that, if the bar is close enough to horizontal, your tension really is close enough to what you want.


Two additional questions you guys might be wondering:
1) I use the center of mass of the dropweight to calculate the distance, but the mass of a dropweight isn't at a point. It spans a distance of 3 inches. Does that introduce an error in my calculation?

The answer is no. This simplification does not introduce error.
If you don't want to take my words for it, I will prove it mathematically.
First let's clarify one thing. In everyday life, we use mass terms as force, i.e. 1 pound of force, etc., the reason is that when we say "1 pound of force," it is implicit that we mean 1 pound of mass multiplied by the gravitational acceleration. For instance, 1 kg of force really means 1 kg x 9.8 m/sec^2 = 10 Newtons.

Let's simply the equations and use M as force.
By definition, torque in integration form is:

Also, by definition, the point of Center of Mass (rCoM) is:

If you multiply the radius of Center of Mass by Total Mass, it's exactly torque.

2) The tension bar itself weights a few ounces, does that introduce an error?

In fact, it does, but the mass of the tension bar << mass of the dropweight, thus the effect is negligible.
Also keep in mind that the mass of the tension bar does not change, either. Thus, it is not a variable for your stringing machine. The error can simply be corrected in my equation by adding a small correction to the Mass, by taking into account the mass of not only the dropweight, but also the tension bar.

Conceptually correct and the math is pretty good.
Dropweight stringers are simply a mechanically advantaged ratchet that allows the translation of a Force Normal in the vertical into the horizontal via a ratchet mechanism. The proportional ratio of the radius (R in he diagram above) and the radius of the ratcheting mechanism (r above) describes the ratio in which the Force Normal is translated. This mechanical advantage is found is a lot of different devices all throughout history (closest cousin in modern times would be the bicycle sprocket system/chain).

Well done young man. Your trigonometry and understanding of statics/dynamics and Newtonian physics is spot on.
I'll just add that the Force Normal you describe can be treated as a point from the COM of the entire ratchet arm/dropweight System. Both are constant as you point out. The only that governs the actual Force Normal being translated is theta and R. Less to go wrong, fewer losses within the system due to mechanical inefficiencies. The only error is really human error.

 

[shamaho]

Ok, I'll make a fool of myself as I request help checking the numbers applying the formula: f = (M g / r) (cos Q) R

Im having "strange" results, and I don't quite know what I'm doign wrong, so I have following values:

M - Mass of DropWeight 2,971Kg
R - Distance of tensioner to drop weight 23,6 cm for a ref tension of 24Kg
r - radius of the tension head of 3 cm
Q - set at zero degrees (horizontal ?)

My result for f on above formula is: 228,58
Then I attempt a "Newton to Kg" (pardon my lack of knowledge) conversion by multiplying by 0,101971621 (newton to kilo?)
The result is 23,31 Kg, when it should be pulling 24 Kg no ?

Thanks in advance for your help.

 

[Irvin]

I would think (23.6/3) * 2.971 = 23.372 Kg. But that does ot include the weight of the bar the DW is attached to. That must account for some extra leverage.

EDIT: Also the center of mass of the DW should be used not the edge of the DW.

 

[shamaho]

EDIT: Also the center of mass of the DW should be used not the edge of the DW.

That I took into account and is reflected into the numbers.

and the weight of the bar is variable according to distance... that might account for the difference ? it does in fact get progressively lower with the DW closer to the center (inward)...

SO I guess I might just as well stick to the : COS (Q) part of the equation... to get theoretical value (which in reality is just an approximation)...

 

[Irvin]

the weight of the bar is variable according to distance.

The weight of the bar is the weight of the bar and it should never ever change.

 

[shamaho]

The weight of the bar is the weight of the bar and it should never ever change.

If I add the weight of the bar (422 g) to that of the DW, I still don't get 24 Kg , now I get higher than that 26,6 Kg (for an angle of zero).
So, what's is definitely wrong with my application of the formula ?

 

[Irvin]

If I add the weight of the bar (422 g) to that of the DW, I still don't get 24 Kg , now I get higher than that 26,6 Kg (for an angle of zero).
So, what's is definitely wrong with my application of the formula ?

All I can do is guess what you’re doing. If you want to see what the tension is get a gauge and test it.