Pre-stretch setting on a Star 5...

[TopspinRules]

Hi all,

Thanks again for the guidance on tools and such to go w/ my Star 5 a few weeks ago, very helpful (and I did end up buying a Babolat starting clamp). I've done about 5 rackets at this point (all w/ Technifibre NRG2 strings), with the pre-stretch setting at 10%. The resulting stringbed feels a bit tighter than the results from a local pro-shop using a Sensor (don't know what setting they use for pre-stretch or if they do so by hand).

I've read the debates around hand pre-stretching vs. machine-based pre-stretching, but I've always been a technology guy (given I'm an IT professional in my day job) so I'm going the machine route. So I wanted to get an opinion from folks on what pre-stretch setting most were using with their Babolat Stringing machines? The Star 5 allows for increments of 5% (up to 20%). Most of the threads here and elsewhere I've read appear to be overwhelmingly slanted towards a 10% pre-stretch setting, but wanted to query the group here. Thanks in advance for the feedback.

 

[TopspinRules]

Hmmm, no feedback. How about pre-stretch settings for folks using any stringing machine with pre-stretch capability?

 

[Gaines Hillix]

I'm not a big believer in pre-stretching. In my mind, all it does is increase the string bed stiffness which some people interpret as reducing initial tension loss. If someone insists(very rarely), I do it, but otherwise I only do it on strings that have very high coil memory like LUX ALU Power or on NG and I do it off the machine.

 

[Greg Raven]

I have mine set at 5 percent, but I live (and play) at about 2900 feet above sea level, so the slightly firmer stringbed helps to compensate for the ball's tendency to fly, without forcing everyone to request a different tension.

 

[Old_Crow]

I only use 5% on the macine and only on gut or a really soft multi when someone requests it.

 

[TopspinRules]

Thanks for the feedback everyone. I also only pre-stretch for gut and soft multis (like the NRG2 I swear by). I guess in theory, pre-stretching should only be necessary with crank-type stringing machines since they stop once it initially hits the reference tension. I'll try it at 5% pre-stretch and then no pre-stretch to assess the results. Thanks again everyone!

 

[profitennis]

hello
what is the machine technicaly making? how is it prestretching?
because at my machine i do not see a difference when i have no or 10% prestretch?
can i test it somehow? because not possible with the normal tension calibrator or?
thanks

 

[abllee2198]

2007 US OPEN Prestretching

At the US Open, the machines have optional prestretch but we continue to do manual prestretch. On occasion, we get a player request for machine prestretch, but majority were done manually.

All manual prestretches were performed with a single loop around one of two safety poles.

Topspinrules: Your experience that the Star 5 strings tighter is my experience as well. Both my machines are calibrated, but the Star 5 consistently strings a tighter stringbed (perhaps 2 pounds). This comes about because the drawback is much less on the Star 5, than Sensor.

A..Lee
Wilson/**** Stringer

 

[Mike Cottrill]

hello
what is the machine technicaly making? how is it prestretching?
because at my machine i do not see a difference when i have no or 10% prestretch?
can i test it somehow? because not possible with the normal tension calibrator or?
thanks

The cheapest way would be to use a digital scale. There a few digital fish scales out there some folks use that have a higher end range. They are not the fastest scales, but they can give you an idea.

 

[Greg Raven]

hello
what is the machine technicaly making? how is it prestretching?
because at my machine i do not see a difference when i have no or 10% prestretch?
can i test it somehow? because not possible with the normal tension calibrator or?
thanks

If you mean, how do you tell during the pull, you can watch either the movement of the tension head, or some reference point on a relatively stretchy string. The tension head will move to its extreme (pre-stretching) position, then back toward the racquet a bit, then away from the racquet to the reference tension.

If you mean, how do you tell after the racquet is strung, you need to get something like an ERT 700 to measure the stringbed stiffness.

 

[profitennis]

this means, the machine should stop pulling after prestrech and then start again?
my machine is not stoping-hmm, means this my machine is damaged?

 

[Mike Cottrill]

this means, the machine should stop pulling after prestrech and then start again?
my machine is not stoping-hmm, means this my machine is damaged?

Not stop pulling just not pulling as hard. The machine should continue to pull until you tell it stop. Think of it like pulling a rubber band between your hands stretching it to 12” then lighten the pull of your hands until it reaches 10”. However, if you are pre-stretching a poly or Kevlar you’re not going to see much movement of the tension head during the pre stretch. This would be like stretching a piece of rope with the same force used to stretch the rubber band. You will not see the rope stretch like the rubber band. If your machine is not doing this, then it appears something is not working right. Does this help?

 

[Stan]

I believe in a manual prestretch. A machine prestretch is only going to increase the stringbed stiffness too much and lead to a stringbed that is not uniform. Here is why...

A manual prestretch reduces the initial tension loss. The string is pulled, and released. It relaxes and is then installed. No problems. In fact it helps reduce initial tension loss and coil memory.

When using a machine to perform a prestretch, the mains pull an extra x% (Whatever you set it at) and then they release before clamping. IMO this is fine. Not where the problem occurs. On the crosses, this is where you have a problem. Let's say you are stringing at 60 lbs with a 10% prestretch. The machine will pull to 66lbs and then release back to 60. However, due to the friction of the previously installed mains the crosses will not spring back down to 60 like the mains did. As you add more crosses you will change the amount of friction and you will get crosses that stay tighter and tighter. It won't be uniform. Some crosses will be 61, others 66 with all variations in between. This is why I do not advocate a machine prestretch.

Remember, for all your difficult tennis questions...Stan is the man!

 

[Greg Raven]

With or without prestretch -- machine or manual -- there will still be friction when pulling the crosses. I don't understand why manual prestretching in any way eliminates the variance due to this friction.

 

[Stan]

Greg,

You are missing the point. With a regular pull, the mains are being pulled at whatever weight set. In the case of the example, 60lbs. If you pull the mains with a machine prestretch of 10%, your machine is actually pulling at 66 lbs and then releasing down to 60. With the mains in place, the crosses retain more than the 60# they would get without the machine prestretch.

 

[jim e]

How much is also gained by machine prestretch, as was noted on the friction of crosses making the tension higher the you believe it is, and also, a portion of each string has an sort of prestretch, as the string from the frames edge to the tension clamp is being stretched when doing that string, as that part of the string goes to the next string, so a % of that string is already stretched. Seems no point to machine prestretch.

 

[Lindsay]

I used to use the feature on the STar 5. However, I was told by someone that you prestretch the string at 5% once, and you think that's all you're prestretching at. But when you prestretch 1 string, the space between the frame and the tension head is also pulled, and that's at least the length of 1 string if not 2, so you're going to pull that again on the next string, so really you're prestretching at 10% or more. Now I prestretch by hand. Takes longer, but its higher quality.

 

[Gaines Hillix]

Greg,

You are missing the point. With a regular pull, the mains are being pulled at whatever weight set. In the case of the example, 60lbs. If you pull the mains with a machine prestretch of 10%, your machine is actually pulling at 66 lbs and then releasing down to 60. With the mains in place, the crosses retain more than the 60# they would get without the machine prestretch.

Stan, you lost me on this . The crosses lose tension when pulled because of friction with the mains and the further down the string bed the more tension is lost as the stagger in the mains increases and the string bed stiffness increases. They aren't going to retain more than the 60# set tension. If you've ever used a stringmeter or similar device, the crosses have much less tension on them than the mains when the job is finished.

 

[gjoc]

Stan, you lost me on this . The crosses lose tension when pulled because of friction with the mains and the further down the string bed the more tension is lost as the stagger in the mains increases and the string bed stiffness increase. They aren't going to retain more than the 60# set tension. If you've ever used a stringmeter or similar device, the crosses have much less tension on them than the mains when the job is finished.

I think he’s saying that if you’re just pulling everything at 60 (non-prestretch mode, in other words), the crosses will have less than 60, because the friction will resist them being pulled through, as you said.

Now, if you machine prestretch at 10%, the machine will pull at 66, then release back to only pulling at 60, but the “friction effect” as described above will:

(1) keep the string from ever fully reaching the 66 you want it to reach temporarily (thus never being fully prestretched as much as you wanted it to be), for the same reason it won’t reach 60 in the non-prestretch case above; and,

(2) remain above the 60 you want it to ultimately end up at because friction going back the other way keeps it from fully drawing back the other way and releasing fully back down to 60, due to the same friction effect as above in reverse.

 

[gjoc]

I used to use the feature on the STar 5. However, I was told by someone that you prestretch the string at 5% once, and you think that's all you're prestretching at. But when you prestretch 1 string, the space between the frame and the tension head is also pulled, and that's at least the length of 1 string if not 2, so you're going to pull that again on the next string, so really you're prestretching at 10% or more. Now I prestretch by hand. Takes longer, but its higher quality.

Lindsay, it doesn’t work like that--prestretching 5% twice isn’t at all the same as prestretching 10% once. Prestretching 5% twice (or more) ultimately is essentially the same effect as prestretching 5% once.

That’s why prestretching works--whatever stretch you get out of it when you prestretch it is that much less stretch available to come out of it later, once it’s on your racquet.

In any event, you’re doing it right, imo, since you’re doing it by hand.

 

[Stan]

I think he’s saying that if you’re just pulling everything at 60 (non-prestretch mode, in other words), the crosses will have less than 60, because the friction will resist them being pulled through, as you said.

Now, if you machine prestretch at 10%, the machine will pull at 66, then release back to only pulling at 60, but the “friction effect” as described above will:

(1) keep the string from ever fully reaching the 66 you want it to reach temporarily (thus never being fully prestretched as much as you wanted it to be), for the same reason it won’t reach 60 in the non-prestretch case above; and,

(2) remain above the 60 you want it to ultimately end up at because friction going back the other way keeps it from fully drawing back the other way and releasing fully back down to 60, due to the same friction effect as above in reverse.

gjoc is absolutely correct. He states it better than I. I will give it another shot.

When prestretching, the machine will pull the extra x%. In my example we used 10% or 6 lbs. With the machine pulling the mains at 10% and then releasing to reference tension, the string first reaches 66 and then goes down to 60 before clamping. On the crosses, due to friction it pulls at 66lbs. When the tension releases back to 60 the effect is not the same as the mains. Let's hypothesize the first cross actually gets to 65.5 on the first part of the pull. Because there is not as much friction but when released it can not drop back down to 60 because of the friction that does exist. Let's say it goes to 61. Now let's take the 10th cross string. Now there is additional friction because the stringbed is more complete. Let's project the initial pull goes to 64 and when released only pulls back to 63. What you are doing is creating a stringjob that is not uniform. The non-uniformity is exacerbated by the prestretch function.

Bottom line: Manual prestretching is superior to machine prestretching. A machine prestretch creates a stringbed that is much less uniform and consistent than a stringbed that is installed without a machine prestretch.

 

[Lindsay]

Lindsay, it doesn’t work like that--prestretching 5% twice isn’t at all the same as prestretching 10% once. Prestretching 5% twice (or more) ultimately is essentially the same effect as prestretching 5% once.

That’s why prestretching works--whatever stretch you get out of it when you prestretch it is that much less stretch available to come out of it later, once it’s on your racquet.

In any event, you’re doing it right, imo, since you’re doing it by hand.

You're more likely to break string the more you prestretch. I had this discussion with one of the most respected names in the stringing community. I thought just like you till I got the whole story of how its been tested, and now I prestretch by hand, which is better IMO.

 

[Greg Raven]

Greg,

You are missing the point. With a regular pull, the mains are being pulled at whatever weight set. In the case of the example, 60lbs. If you pull the mains with a machine prestretch of 10%, your machine is actually pulling at 66 lbs and then releasing down to 60. With the mains in place, the crosses retain more than the 60# they would get without the machine prestretch.

With the Star 5 prestretch, I believe that the machine pulls to the prestretch tension, then releases to below the reference tension, then re-pulls to the reference tension and holds.

I'd be astonished if any cross retained tension in excess of the pulling tension. If that were the case, you would not need clamps to hold the strings when installing the crosses.

I'd also be very surprised if you could pull a cross at 60 pounds (say), and have the tension on the entire cross be the same tension. I can understand the tension on the portion of the cross nearest the tension head being at or near the reference tension, but the tension on that portion of the cross farthest away from the tension head is almost certainly not going to be at the reference tension, due to friction between the cross and the mains.

Because of that, it would seem that there could well be some value in setting a machine prestretch, as the higher-tension initial pull could overcome friction enough to get the "far" end of the cross up to the reference tension, so that after the final pull the tension on the cross would be more even from end to end.

 

[Jerry Seinfeld]

I understand the root of Stan's post. When I got my Star 5, I tried using the machine prestretch and found the stringbed stiffness was reading several points higher than I got with a manual prestretch. I can not quantify what he is saying, but from my limited experience I would agree that for some reason, perhaps friction...perhaps something else, the machine prestretch creates a firmer stringbed. I choose not to use the prestretch function and still do my prestretching the old fashioned way, by hand. Stan's friction theory is one that could help explain what I have observed.

On the other hand I understand Greg's argument that a cross could not possibly hold a tension that is higher than being pulled. Interesting point and discussion. Wish there were some data to available to help understand what really happens when a machine prestretch is being used. Most importantly, I tend to wonder if a machine prestretch is consistent? Afterall, that is really the name of the game.