Tension lost from pulling over the frame test setup

[BlxTennis]

So I want to know how much tension I am loosing from string rubbing on the frame when pulling tension. The set up is that I pull tension on both main, then clamp right main and back it up with a starting clamp. Re-pull tension on the left main and get reading on it. I did this once pulling from the throat. Then do this all again but pulling from the head. What I see is a difference of about 1.3lbs difference due to string pulling over the frame. But I would assumed on the next pull that 1.3lb would get it back on the next pull. Right?

1st 2 images show pulling from throat. The last 2 show pulling from head.

 

[David 110]

I pull the center mains from the top end to avoid tension loss caused by the strings crossing the frame. The technique also eliminates several string clamping steps which helps consistency as well. On crank machines it also eliminates interference between the crank handle/linear gripper and the racquet handle/frame.

https://www.youtube.com/watch?v=JHaUrtUqS_M

 

[BlxTennis]

I pull the center mains from the top end to avoid tension loss caused by the strings crossing the frame. The technique also eliminates several string clamping steps which helps consistency as well. On crank machines it also eliminates interference between the crank handle/linear gripper and the racquet handle/frame.

https://www.youtube.com/watch?v=JHaUrtUqS_M

I saw that video before but I am not too crazy of pulling 2 mains(double pulling?) over a grommet. After all, that's why I use the Yusuki method for starting main. In any case, when I do the next pull, in a way it's like pulling from the top again to try to gain that tension back and I do wiggle the strings on the next pull.

 

[Irvin]

To begin with the two center mains are both pulled in the same direction so the tension should be the same. Second it looks like you have an ML 100 I thought those were 360* rotation. If so and your string goes under the frame will there be any friction? Third a difference of just over a pound is not enough to cause concern IMHO.

 

[BlxTennis]

To begin with the two center mains are both pulled in the same direction so the tension should be the same. Second it looks like you have an ML 100 I thought those were 360* rotation. If so and your string goes under the frame will there be any friction? Third a difference of just over a pound is not enough to cause concern IMHO.

Thanks Irvin. I was more interested to find out how much tension is really loosing due to string over/under the frame. I have MS200 and it's not 360 rotation.

 

[Irvin]

Still with the frame (turntable) be mounted at a slant the racket is higher in the back so I would go under for less bend to create less friction and closer to reference tension. Again if it is just a pound or less I would not worry about it.

 

[bluegrass_stringer]

Still with the frame (turntable) be mounted at a slant the racket is higher in the back so I would go under for less bend to create less friction and closer to reference tension. Again if it is just a pound or less I would not worry about it.

Agreed...just crank up the tension a pound or two on that one

 

[OccasionalStringer]

The friction is not the only factor here. With this type of tension head the angle at which the string comes to tension head makes a big difference.

If the string comes at downward angle (above the horizontal level) to the tension head then the tension is higher compared to when the strings comes at horizontal level

And accordingly, when the string comes at upward angle (under the throat) then the tension is lower.

So going over the throat is way to go, then the higher tension from downward angle compensates some of the friction losses.

If you go under the throat the you have less tension due to string coming below the horizontal level and friction losses on top of that.

You can easily verify this with the scale

 

[BlxTennis]

The friction is not the only factor here. With this type of tension head the angle at which the string comes to tension head makes a big difference.

If the string comes at downward angle (above the horizontal level) to the tension head then the tension is higher compared to when the strings comes at horizontal level

And accordingly, when the string comes at upward angle (under the throat) then the tension is lower.

So going over the throat is way to go, then the higher tension from downward angle compensates some of the friction losses.

If you go under the throat the you have less tension due to string coming below the horizontal level and friction losses on top of that.

You can easily verify this with the scale

Thanks OCS. I think I consider going below at one point but it makes sense to go over the frame instead of under for this machine. The gripper is higher than the racquet. So if going under, there's a larger angle that the string bends around the frame. In any case, 1.3lbs is no big deal and it will be compensated on the next pull since this is a constant drop weight machine.

 

[Irvin]

... In any case, 1.3lbs is no big deal and it will be compensated on the next pull since this is a constant drop weight machine.

That what they want you to believe but from what I'm hearing in this thread is it not a consistent CP. If the angle changes going not the gripper the tension is off? Seems like it will always change depending on how you negotiate the throat and how long the string between the frame and the gripper is and the angle of the racket. But I would not worry about it. It probably would not even out on the next pull but when you pull the crosses.

 

[BlxTennis]

... If the angle changes going not the gripper the tension is off?

Irvin, how did you arrive to this assumption? The tension is off 1.3lbs is due to string run over the frame and being pulled by the tensioner. If the frame is not in the way, then we wouldn't have this problem. I assumed this situation applies to all strings that that string runs over the frame before being pulled unless someone can prove me wrong.

...But I would not worry about it....

You are correct. I am not worrying about it.

 

[Irvin]

Irvin, how did you arrive to this assumption? The tension is off 1.3lbs is due to string run over the frame and being pulled by the tensioner. If the frame is not in the way, then we wouldn't have this problem. I assumed this situation applies to all strings that that string runs over the frame before being pulled unless someone can prove me wrong...

I don't know that IS just an assumption on my part. Drop weight stringers work on leverage to pull tension. The shorter (or longer) the distance the from the griping point to the pivot point the greater the tension. Changing the angle changes the length.

 

[BlxTennis]

I don't know that IS just an assumption on my part. Drop weight stringers work on leverage to pull tension. The shorter (or longer) the distance the from the griping point to the pivot point the greater the tension. Changing the angle changes the length.

I see. That may be the case for most drop-weights but Stringway does it differently. Take a look at the comparison below.

 

[Irvin]

I see. That may be the case for most drop-weights but Stringway does it differently. Take a look at the comparison below.

Exactly my point. If you look at most drop weights (picture on the left) the radius of the pivot where the string connects is round so the radius is constant. But on the Stringway (right) if the angle of the string coming in changes you tension changes as you will have more or less leverage. Distance V not only changes as the weight is dropped but it changes with the angle of the string coming to it. Where as the on the normal drop weight distance R never changes but distance H does.

Again too small to worry about.

 

[BlxTennis]

...But on the Stringway (right) if the angle of the string coming in changes you tension changes as you will have more or less leverage. Distance V not only changes as the weight is dropped but it changes with the angle of the string coming to it. Where as the on the normal drop weight distance R never changes but distance H does.
...

Irvin, that's interesting observation. You may have a point. However, the distance difference is so small and the angle difference is also so small that it may not make a difference for the tension range we are dealing with. Take a look at the photos below.

 

[Irvin]

I think you're right. Looking at those pictures it's clear sheer is more string bend and pressure on the frame going under the frame. It is also easier to weave going over. Frames tend to develop cracks right where the frame hoop meets the yoke of the handle so I would go for the over.

 

[diredesire]

I think you're right. Looking at those pictures it's clear sheer is more string bend and pressure on the frame going under the frame. It is also easier to weave going over. Frames tend to develop cracks right where the frame hoop meets the yoke of the handle so I would go for the over.

I think a more interesting takeaway in the last photo is that there's only a .2lb difference with an exaggerated bend in one scenario. There's a consistent tension differential between head and throat pulling. Interesting.

@BlxTennis: Did you use the center two grommets for the head pull attempt? Could you try offsetting the pull by one so we're dealing with a rounded grommet? I'm also interested to see if you tried this with poly (or preferably Kevlar) if the results change at all. How are you controlling stretch and settling?

Thanks for performing this, very interesting stuff.

 

[BlxTennis]

I think a more interesting takeaway in the last photo is that there's only a .2lb difference with an exaggerated bend in one scenario. There's a consistent tension differential between head and throat pulling. Interesting.

@BlxTennis: Did you use the center two grommets for the head pull attempt? Could you try offsetting the pull by one so we're dealing with a rounded grommet? I'm also interested to see if you tried this with poly (or preferably Kevlar) if the results change at all. How are you controlling stretch and settling?

Thanks for performing this, very interesting stuff.

I am actually using Kevlar string 16g. "controlling stretch" of the string? Since it's a constant pull, I pretty much let the machine pull the the string and then walk off to get my camera. Tension doesn't fluctuate much reading from the scale. When I take the picture, I actually didn't clamp the string.

I am using the center 2 grommets. I can do an offset by one when I get a chance tomorrow or by the weekend.

 

[Irvin]

I am actually using Kevlar string 16g. "controlling stretch" of the string? Since it's a constant pull, I pretty much let the machine pull the the string and then walk off to get my camera. Tension doesn't fluctuate much reading from the scale. When I take the picture, I actually didn't clamp the string.

I am using the center 2 grommets. I can do an offset by one when I get a chance tomorrow or by the weekend.

In every picture you took I've seen so far your scale had reached the lock state if that makes any difference.

 

[BlxTennis]

In every picture you took I've seen so far your scale had reached the lock state if that makes any difference.

Irvin, you are correct and good observation. Since I don't clamp after letting the weight drop pulling tension on the string, scale will lock once the tension is stabled(51.xxx). It takes about 10 - 15sec then the scale auto locks. I was too lazy to look for the manual see if I can disable that auto lock feature on the scale. I may not even have that manual anymore.

 

[Irvin]

I think you just press the on/off button to release the lock.

 

[BlxTennis]

I think you just press the on/off button to release the lock.

Thanks Irvin. You are correct. Once scale is locked, press on/off button quickly unlocks it and it continues to monitor tension. I will do that next time.

 

[BlxTennis]

...Could you try offsetting the pull by one so we're dealing with a rounded grommet? ...

Below are pictures are done with one offset grommet. 1st one pulling from top, 2nd from bottom. Both I wait until scale locks, then turn off autolock and wait another ~10sec or so and take the picture.

 

[Irvin]

Funny there is a higher tension on the bottom one. My conclusion is there is more tension lost through the bend in the grommet rather than the bend around the frame.

 

[BlxTennis]

So I was thinking that I would gain the tension lost on the next pull. I decided to do one more test see if that's the case. Picture 1, I pulled tension on the string with the scale over the frame while one of the main was "double pulled" & backed up with starting clamp(Yusuki starting). Scale shows 51.15lbs similar to before. Picture2, I clamped the string which is being tension with the scale while take out as much slack as possible, which I can see about 3-4mm drawback. After releasing the tension head, scale reads 36.1lbs. Before releasing tension head and before the clamp moved 1mm, it was still reading 51.15lbs. Picture3, I am pulling tension on the string which I just clamped and then release the clamp. It reads 46.18lbs. Hm...unless the scale is not accurate, I think I did everything right. Not what I expected. May be Irvin or someone else can repeat this experiment? So what does this mean to me? Not much, I don't think I will change the way I have been stringing since I found the tension which I like for my game.

Pic1:

Pic2:

Pic3:

 

[Irvin]

No need to repeat your test that's exactly what I'd expect but I will if you want. And I do think your scale is accurate. From what I've found you will always have drawback and when you pull tension on the next string it may look like you recover most if not all of it but it will not happen because of the surface friction in the grommets for the 180* turn. But it is possible with the over pull on a Babolat you may get a little closer.

EDIT: All in all a tension loss of 10% in a minute is not bad if you think about it. Think about what happens when you string with a crank. You pull tension and after it locks out the string starts loosing tension. To obtain the tension you like you just ask the stringer to string at a specific reference tension. No one really cares if it's pound, kilograms, or what the number is as long as it works.

 

[BlxTennis]

No need to repeat your test that's exactly what I'd expect but I will if you want. And I do think your scale is accurate. From what I've found you will always have drawback and when you pull tension on the next string it may look like you recover most if not all of it but it will not happen because of the surface friction in the grommets for the 180* turn. But it is possible with the over pull on a Babolat you may get a little closer.

Thanks Irvin. Now I know. I always thought when I set a certain tension, each pull of string will come close to the set tension. Looks like that's not the case. And this is why it's important to be consistent in our stringing to get a consistent string bed stiffness.

 

[Irvin]

Thanks Irvin. Now I know. I always thought when I set a certain tension, each pull of string will come close to the set tension. Looks like that's not the case. And this is why it's important to be consistent in our stringing to get a consistent string bed stiffness.

Absolutely accurate. Another thing, if you stop to help a customer for thirty minutes the previously strung string relaxes more stretches farther and offers less back pressure than any other. Now when you pull tension on the next string it will stretch farther because of the difference is back pressure. Stretching more means after some time it is tighter than the adjacent strings and according to the USRSA strings with different tension (like proportional stringing) do not even out in play.

 

[diredesire]

I am actually using Kevlar string 16g. "controlling stretch" of the string? Since it's a constant pull, I pretty much let the machine pull the the string and then walk off to get my camera. Tension doesn't fluctuate much reading from the scale. When I take the picture, I actually didn't clamp the string.

I am using the center 2 grommets. I can do an offset by one when I get a chance tomorrow or by the weekend.

Umm... are you sure? That certainly looks like a duraflex style string to me. That's a nylon core with aramid/kevlar wraps, but not 100% aramid/kevlar. I could be wrong, though

No need to repeat your test that's exactly what I'd expect but I will if you want. And I do think your scale is accurate. From what I've found you will always have drawback and when you pull tension on the next string it may look like you recover most if not all of it but it will not happen because of the surface friction in the grommets for the 180* turn. But it is possible with the over pull on a Babolat you may get a little closer.

EDIT: All in all a tension loss of 10% in a minute is not bad if you think about it. Think about what happens when you string with a crank. You pull tension and after it locks out the string starts loosing tension. To obtain the tension you like you just ask the stringer to string at a specific reference tension. No one really cares if it's pound, kilograms, or what the number is as long as it works.

Yep, the above analysis makes sense to me. I don't think it's an issue, though. It's just how stringing works, and it's WHY it's important to know the relationship between reference tension and actual tension (stringbed stiffness)

Thanks Irvin. Now I know. I always thought when I set a certain tension, each pull of string will come close to the set tension. Looks like that's not the case. And this is why it's important to be consistent in our stringing to get a consistent string bed stiffness.

Actually, each pull DOES come close at some point in the stringing process... what you end up with may be a bit further from the max tension the string sees, though. It's not a big deal, like everyone says: consistency is the goal.

 

[BlxTennis]

Umm... are you sure? That certainly looks like a duraflex style string to me. That's a nylon core with aramid/kevlar wraps, but not 100% aramid/kevlar. I could be wrong, though
...

You may be right. I don't know how you can tell but this is the string I was using for all these measurements.