machine pre-stretching on a cp lever-machine

[MathieuR]

the only reason I could think of to switch from my Stringway constant-pull lever-machine to an "electric" was the machine pre-stretching. Pre-stretching will help to deal with strings that loose tension quickly due to "creep" and "lasting-elongation" when tensioned. ( IMHO only elastic elongation is what you are looking for in a string)

But I found a simple solution: just add an extra weight on the lever, tension the string, remove the extra-weight, and bingo, you have accomplished a controlled machine-pre-stretch.

(I was also suggested to lightly push down the lever instead of using an extra weight. Can be done of course, but you won't have any controll on the extra weight)

 

[esgee48]

I just wait 20 - 30 seconds before clamping.

 

[MathieuR]

I just wait 20 - 30 seconds before clamping.

that's fine to get rid of the "creep" at reference tension. But machine-pre-stretch is intended to go "further".

I would like to get rid of the tension-loss that occurs the first hours of play ( especially for poly's)

 

[Imago]

I use my axe.

 

[Gamma Tech]

One of the easiest and quickest ways to crack a racquet, or break a string, is to push down on the bar of a drop weight machine.

 

[esgee48]

From my experience, if I wait 20-30 seconds before clamping instead of clamping within 5 seconds, then I have a stringbed that holds tension better. While waiting, I make sure the clamped string is straight. Takes longer to string, but I am not in a hurry. A LONG LONG time ago, I use to clamp within 5 seconds and my stringbeds lost more tension just settling in. YMMV. Pushing down means a variable tension increase for a variable amount of time. Even if you release the bar and it rises back up, how does that improve consistency since the prestretch is variable?

 

[MathieuR]

I use my axe.

You will be surprised how small the tension is you apply this way, especially if you pull on 2 strings simultaniously. My guestimate: 25kg max in total, so 12.5kg/string; that's nothing for pre-stretching

One of the easiest and quickest ways to crack a racquet, or break a string, is to push down on the bar of a drop weight machine.

I don't push the lever

Pushing down means a variable tension increase for a variable amount of time. Even if you release the bar and it rises back up, how does that improve consistency since the prestretch is variable?

Please read: I don't push the lever. I add an extra weight on the bar. So I know exactly how much extra pulling-force I use when pre-stretching. Then I remove the extra weight, and I tension with the reference-tension before clamping the string.

 

[MathieuR]

I experimented with a simple syn.gut. I used an extra weight, that gave an extra 20kg. So in total pre-stretching was done with 40, then back to 20 before clamping. I enden up with a much stiffer stringbed as "normal".
By experience I know I would have a DT of 35, now I found almost 40!
So, when I use this (excessive) pre-stretching, I will have to go down in reference-tension if I want to end with a DT of ~35. ( for this specific string that is)

 

[JBH]

Another advantage of an electronic copy head is variable pull speed. I always use slow. Pre-stretching, as has been discussed here pre-viously, will have inconsistent effects on different strings and with polys, only results in eliminating a portion of their play duration, since they die through deformation rather than fatigue.

 

[MathieuR]

every string, when tensioned has 2 "types" of elongation: elastic and non-elastic. The non-elastic elongation will "stay" if you relax the string.
So, while playing, more and more of the non-elastic/permanent elongation will lengthen the string (caused by the extra tension from the ball-impact), and therefore causing tension-loss.

 

[MathieuR]

and this permanent-elongation part is "neutralized" with the pre-stretching. But yes, you change the string-character by doing this. So most likely you will have to diminish the string-tension

 

[jim e]

Using a machine for pre stretch, like my electronic machine has different % increases for pre stretch, if that function is used, there would be no way to determine exactly how much friction effects the cross strings when pre stretched go back to reference tension, just how much does indeed go back to reference, as friction against the mains with the cross string will hold up some of that pre stretch and that can vary all along the cross string, and that would increase the tension of the cross string as well. It just introduces another variable in the stringing process. I only machine pre stretch when a customer asks for it, and that has not happened yet.

 

[MathieuR]

just how much does indeed go back to reference, as friction against the mains with the cross string will hold up some of that pre stretch and that can vary all along the cross string, and that would increase the tension of the cross string as well

No, cause after the pre-stretching you start pulling again with 0 force. So, I remove the extra weight, I raise the lever, relax the string, and then tension it using the reference-tension.
Note: this "problem" is non-existent when stringing the L-strings.