Constant pull vs Lockout
- Thread starter Irvin
- Start date
Rabbit
G.O.A.T.
Only there is no tension spring. There's a disc and two pads which "lock" it.
When a lockout locks, is it still pulling??
Yes and no.
Yes
When a lockout locks, the effect is the same as clamping.
It continues to pull the string but NOT to reference tension or near the reference tension.
A lockout ignores the additional string stretch that continue to occur after lockout/clamping.
It ignores tension loss due to string stretch. However, it is still pulling in the sense that it prevents the tension to drop to zero (0).
In this sense, you can also say that clamping continue to pull because it prevents the string tension from dropping to zero.
This so called 'pull' however, does not have anything to do with the 'reference tension'.
No
When a lockout locks, it stops pulling the string to reference tension.
In contrast, an eCP will continue to monitor the tension loss (due to string stretch) and automatically pull the string to reference tension or near reference tension.
An eCP will continue to do this until you clamp.
Note:
I use a dropweight.
I don't clamp while the bar is still dropping.
I only clamp when the bar remains at horizontal for 10 seconds.
Most of the string stretch occurs during the first few seconds of pulling tension.
Yes and no.
Yes
When a lockout locks, the effect is the same as clamping.
It continues to pull the string but NOT to reference tension or near the reference tension.
A lockout ignores the additional string stretch that continue to occur after lockout/clamping.
It ignores tension loss due to string stretch. However, it is still pulling in the sense that it prevents the tension to drop to zero (0).
In this sense, you can also say that clamping continue to pull because it prevents the string tension from dropping to zero.
This so called 'pull' however, does not have anything to do with the 'reference tension'.
No
When a lockout locks, it stops pulling the string to reference tension.
In contrast, an eCP will continue to monitor the tension loss (due to string stretch) and automatically pull the string to reference tension or near reference tension.
An eCP will continue to do this until you clamp.
Note:
I use a dropweight.
I don't clamp while the bar is still dropping.
I only clamp when the bar remains at horizontal for 10 seconds.
Most of the string stretch occurs during the first few seconds of pulling tension.
Rabbit
G.O.A.T.
Only if the bar is still dropping, how can it remain horizontal?
Irvin
Talk Tennis Guru
@ricardo I don’t think you understand how a lockout works.
First tension is set on the dial which compresses a tension spring that applies pressure on an arm connected to the gripper assembly.
Second as you rotate the crank tension on a string builds up and rotates the gripper assembly clockwise (CW.) At the same time the arm moves off its stop CW, compressing the tension spring more.
Third as the whole tension assembly moves away from the racket and tension reaches a set point the catch on the back releases a brake lever than actuated the brake. The brake holds a gear riding on the arm teeth from moving.
But that arm on the back of the gripper is still off it’s stop. The tension spring is still pushing on the arm which is trying to turn the gripper assembly CCW which is pulling on the string.
First tension is set on the dial which compresses a tension spring that applies pressure on an arm connected to the gripper assembly.
Second as you rotate the crank tension on a string builds up and rotates the gripper assembly clockwise (CW.) At the same time the arm moves off its stop CW, compressing the tension spring more.
Third as the whole tension assembly moves away from the racket and tension reaches a set point the catch on the back releases a brake lever than actuated the brake. The brake holds a gear riding on the arm teeth from moving.
But that arm on the back of the gripper is still off it’s stop. The tension spring is still pushing on the arm which is trying to turn the gripper assembly CCW which is pulling on the string.
Excellent question.
When the bar is still dropping (below horizontal), I lift the bar up past horizontal and let the bar drop again slowly.
I keep adjusting until the bar stops at/near horizontal.
When the bar stops at/near horizontal, I wait for 10 seconds.
If there is no additional bar drop after waiting for 10 seconds, I then clamp.
If I string Monogut ZX (or other stretchy string), I wait for 20 seconds before clamping.
If I string thick poly, I may wait for 3 seconds before clamping.
When I first began stringing, I was too impatient that I clamp even when the bar is still dropping below horizontal.
Now I learned my lesson.
Thank you Master...
Irvin
Talk Tennis Guru
You’re welcome grasshopper.
The problem here is that Irvin is applying a scientific definition to the words "constantpull" rather than accounting for the common use of the words as used in regards to stringing machines.
In non technical speak a crank/lockout pulls until the spring trips the mechanism and then it HOLDS the string at that point. Yes it is still technically pulling, but with less and less force as the string stretches.
a "constant pull" machine pulls at the desired tension, or rather applies a constant amount of force, until released. (yes I know it's not absolutely constant as it pulls, stops, and pulls more when it senses the tension drop)
so while a lockout constantly pulls (scientifically speaking), it is not a "constant pull" machine.
In non technical speak a crank/lockout pulls until the spring trips the mechanism and then it HOLDS the string at that point. Yes it is still technically pulling, but with less and less force as the string stretches.
a "constant pull" machine pulls at the desired tension, or rather applies a constant amount of force, until released. (yes I know it's not absolutely constant as it pulls, stops, and pulls more when it senses the tension drop)
so while a lockout constantly pulls (scientifically speaking), it is not a "constant pull" machine.
Imago
Hall of Fame
And, mutatis mutandis, if the string is constantly stretching why the bar stands horizontal?
Another excellent question.
Yes. The string will constantly stretch but not at the same rate.
Most of the stretch occurs within a few seconds after pulling tension.
After that, the stretch becomes slower.
After some bar adjustments (lifting the bar up and letting it drop slowly),
the bar will eventually stop dropping (below horizontal) for a given time (1 sec, 3 sec 10 sec).
If the bar remains at horizontal for 10 seconds, I clamp.
The string, as you mentioned, will continue to stretch but at a much slower rate.
The string will stretch again significantly during the first minute/hour of hitting.
After that, it will stabilize again.
Experiment:
I did an experiment to determine additional stretch after the 10 seconds wait.
I left the bar on horizontal (no clamping).
1st 24 hours
the bar dropped requiring adjustment
2nd 24 hours
the bar dropped again but not as much. Adjusted it
3rd 24 hours
No bar drop at all.
I did not experiment beyond 3 days.
I assume that if I left the bar pulling for 1 month, it would drop.
How much drop? I don't have a clue.
Irvin
Talk Tennis Guru
If you put a string in the gripper and pull on it the arm going from the gripper to the tension spring moves off the stop and compresses the spring. The string pushes the arm which pulls the string. That’s not science that’s common sense.
EDIT: If I blow up a balloon, rest it on a table and press down on it the balloon pushes back. Same thing except in the case of the balloon there is no leverage action like with the arm connected to the gripper / tension spring in the LO.
If a LO pulls after lockout and an eCP constantly pulls, just not at a constant tension, what’s the difference? Correct me if I am wrong but an eCP (at least mine) pulls as the motor runs, then stops and holds the string until a load cell recognizes a specific tension drop, then the eCP pulls again. So if an eCP pulls and holds why is it called a constant pull and a LO that never stops pulling isn’t?
Last edited:
You are right again Master.
However, I am still confused.
So it pulls. But does it continously pull to reference tension like the eCP?
Does it even know the reference tension to pull to?
Irvin
Talk Tennis Guru
No that is impossible. Well not impossible, you could install a load cell between the tension spring and the gripper arm to measure the pushing force in the arm. Then compute the force into tension applied on the string. If you want 60# and you have 57# turn the tension dial up to 63#.
When Brett was @Gamma Tech he said the tension should be checked outside the frame and it should be the peak tension not the rested tension (after tension drops.) Now what if you used the resting tension and not the peak? (That will lead to different tension for different string but some people do it.) You set the dial to 60 and the LO pulls to something above that point and locks out. But when the tension drops you will have what you really wanted to begin with. Or on the other hand you set it up like Brett used to say and you like the tension you get from the LO when you set the tension to 63# even though you know it will drop to 60#. What’s the difference?
Mirdad
Semi-Pro
Why the hostility? Take a chill pill dude! I never said I was an expert. Why the severe over reaction? Do you work for Prince? I merely asked the TW guy why they used a LO machine versus an ECP since I thought the ECP would of been much faster. I was surprised that the TW representative said the ECP was more accurate but less speedy than the LO. I stand behind my comment as that's the God's honest truth...that is what the guy said. So you attack me for that? Get a life! And no, the guy did not rush me off the phone. The mistake I made was forgetting to ask him to be more specific on the degree of inaccuracy that he experienced using a LO versus the ECP. Again, I never said that a ECP was more accurate than a LO.......the TW is the one who said that. Full disclosure: From my research, I'm still seriously thinking of buying a LO and not a ECP. So stick that where the sun don't shine pal......LOL!
A lockout doesn't pull after lockout, it holds. Both are applying a force, but there is a difference.
On the lockout the force applied drops as the string stretches.
A true constant pull would apply a constant amount of force regardless of the string stretching.
ECP machines may not be true constant pull like a Swingway dropweight is, but they do their best to imitate it. (There may actually be true ECP machines I don't know how they work internally.)
Imago
Hall of Fame
What if you pull the crank very slowly, esp., in the last stage. Will the LO be more accurate?
Mirdad
Semi-Pro
Good question IMago, but I'm too much of a rookie to answer your question so I will defer to Irvin or another more experienced poster.
Imago
Hall of Fame
Given the rush most pro stringers are clamping the string with after the tension is pulled, it makes no sense to buy an ECP...
MathieuR
Hall of Fame
That's why I claimed in another thread ages ago, that a (Stringway) dropweight is the only "real" CP.
MathieuR
Hall of Fame
Their "defense" will be: we do this in a rythm, so results are consistent.
But I agree: clamping "on the beep" on an eCP comes close to using it as a LO
MathieuR
Hall of Fame
In my example your "pulling LO" has to move at least 1.25mm with an average pulling force of 23.75kg.
Labor = force * distance
= 237,5 * 0.00125 = 0.297 Nm (= watt)
Where is this stored energy to perform this labor?
OccasionalStringer
Rookie
I have an old Tecnifibre Major SP44. The tension head seems to operate in servo mode, i.e. continuously adjusting tension, the shafts moving the tension head are in constant motion, rotating back and forth.
MathieuR
Hall of Fame
If this means the tensionhead is also moving back and forth, that would mean its overpulling/correcting/overpulling/etc. ≠ CP
OccasionalStringer
Rookie
Yes, it is or course continuously adjusting tension, i.e. reacting to string stretch and no electronic control system is perfect, there is always some over/undershoot or oscillation around the set reference.
But regarding stringway, the claim of accurate tension at every angle is only true in theory when string comes exactly horizontally to tension head and more importantly, tension head makes 90 degree angle with weight bar. Neither of these are true in the real implementation and thus the tension depends on weight bar angle. This has been discussed several times on these forums.
And when the string stretches the bar angle changes and also the tension changes, so no constant pull.
So the the question is what is the allowed range for tension variation to define a machine a constant pull machine, so far no limit has been presented.
Karma Tennis
Legend
IME, the faster the crank and then clamp off, the closer to Ref. Tension one will achieve.
The important thing with a LO is that the cranking is performed as evenly as possible. Do not change the speed of cranking during the string pull. Do not change the speed of cranking from one string pull to the next.
Imago
Hall of Fame
Thanks. Care to explain why? My understanding is that the more time it takes to reach the LO point, the less string tension is lost, because until then, the tensioner is acting so to say in a CP mode. On the other hand, until you reach some critical tension (the yield point), there is no stretching (plastic deformation) of the string, so we can go this part of the way as fast as possible.
Karma Tennis
Legend
I wrote "IME", NOT "IMO"!
I don't know why. Frankly, I don't care either. I've strung plenty of my racquets at various tensions with various stiff Poly strings. And in pretty much all cases, I get closer to Ref tension, or more precisely, closer to my desired SBS, if I crank quickly at a consistent pace to the LO point. YMMV.
Keep in mind. I am a member of that fanatical group that believes stretching many types of fresh Poly string too much ruins them from the get-go.
How long does the tension remain at/near the reference tension?
A string's performance depends on how stiff it is (http://twu.tennis-warehouse.com/learning_center/stringstiffness.php).
The only variable that you can control about a string's stiffness is tension.
The higher you tension, the stiffer the string becomes.
My goal is to ensure that the tension remains at/near the reference tension until I break my strings, usually at least a month.
I tension slowly. The dropweight bar should remain at horizontal for at least 10 seconds before I clamp.
I pre-stretch (https://tt.tennis-warehouse.com/index.php?threads/pre-stretching-using-a-dw-tensioner.554225/).
I re-tension (https://tt.tennis-warehouse.com/index.php?threads/how-to-re-tension-a-string.558504/#post-10154243).
So for me, accuracy is tension maintenance.
Accuracy is how long does the tension remain at or near the reference tension?
If one string job loses 50% tension after 24 hours of hitting and another string job loses only 10%,
then the 10% lose is more accurate.
A string's performance depends on how stiff it is (http://twu.tennis-warehouse.com/learning_center/stringstiffness.php).
The only variable that you can control about a string's stiffness is tension.
The higher you tension, the stiffer the string becomes.
My goal is to ensure that the tension remains at/near the reference tension until I break my strings, usually at least a month.
I tension slowly. The dropweight bar should remain at horizontal for at least 10 seconds before I clamp.
I pre-stretch (https://tt.tennis-warehouse.com/index.php?threads/pre-stretching-using-a-dw-tensioner.554225/).
I re-tension (https://tt.tennis-warehouse.com/index.php?threads/how-to-re-tension-a-string.558504/#post-10154243).
So for me, accuracy is tension maintenance.
Accuracy is how long does the tension remain at or near the reference tension?
If one string job loses 50% tension after 24 hours of hitting and another string job loses only 10%,
then the 10% lose is more accurate.
WYK
Legend
Their "defense" will be: we do this in a rythm, so results are consistent.
But I agree: clamping "on the beep" on an eCP comes close to using it as a LO
And yet the pros keep chugging along without any problems basically having what amounts to a lockout string job in every stick they use...
And @ricardo waiting 10 seconds after every pull? How long does it take to string an 18X20 racquet using this technique?
WYK
Legend
We'll have to agree on that. I prefer not to spend an extra 6+ minutes of every string job staring at a counterweight.
The main thing that affects your stringing results/predictability/quality is the person using the machine, not the machine itself.
d-quik
Legend
you are a 4.5 player right?
In other words if you string slowly with constant pull your stringbed feels significantly tighter afterwards. All the strings then have less stretchability left as they have been "over-stretched" ... unless you want them that way.
Another factor re the whole stringbed is that the strings on a typically oval racket are different lengths so the distance between the clamps varies a lot so the ratio of straight string v. string going out of and back into a grommet to the next straight string varies and friction affects this U-turn. It is all a very imperfect set up so it is amazing how accurately a good player in the zone can play.
Another factor re the whole stringbed is that the strings on a typically oval racket are different lengths so the distance between the clamps varies a lot so the ratio of straight string v. string going out of and back into a grommet to the next straight string varies and friction affects this U-turn. It is all a very imperfect set up so it is amazing how accurately a good player in the zone can play.
Last edited:
MathieuR
Hall of Fame
On a good eCP (or dropweight) the string is never overstretched. Ref.tension --> quantity of stretch, plus a little influence of the tensioning time.
The time-influence is very clear when you use a string like zyex; you then are better of prestretching that string (and the like)
Garro
Rookie
This idea seems to have been debunked by another user on these boards. At least with regard to eCP. I have linked to his post below.
Why constant pull when stringing fast?
In observing this discussion I am still left with the unanswered question.... Given proper and consistent technique.... If I am stringing poly and don't want to "deform/kill/pre-stretch" the string but do want a result close to the desired tension should I adjust my machine for a slow pull or...
tt.tennis-warehouse.com
Similar threads
