New to stringning Some questions..

Just quick and dirty simplified thoughts:

around 4300mm string runs inside the frame. We choose an average tension of 24 lbs. We have 22 mains. Let's imagine we clamp each main 20mm away from the frame. 20mm sounds reasonable according to the pictures. If we just get 0.5 of the tension on this part according to the doublepull rule:

We tension 3860mm (4300mm - 22*20mm) with 100% of 24lbs and we tension 440mm (22*20mm) with 50% of 24lbs. So we tension inside the frame just = 0,94884% of 24lbs which equals 22,7722lbs, by ignoring string around the frame etc. Just having 2cm with got tensioned on every pull of the next main by 50%.

It could be a huge mistake by me, but according to the double pull rule that just around 50% of tension got pulled on the previous string segment it sounds like an equal amount which we always expected because of the friction by pulling the cross?

 

I literally have to sleep about this...

But you are on to something here, so much I can tell pre-sleep.

 

Sure. You also have slack at the crosses, but not by that huge amount. I never said, that the cross clamping don't have this, but the distance to the frame is around 0.5cm on my machine in average. Even on your starting routine you have around 8.5cm slack. That are 80% of all crosses. I will update this post with pictures me cross clamping.

Friction is still there, but as stated it is not constant and depending on texture and gauge of the string and massage maybe overcome it abit. Same for the ziggzagging the mains which depends by the thickness of the string. Would you mind to make a seperate thread and copy the last posts?

My intention is to find an explaination for square tension, because the friction and ziggzagging tells that the main tension increase, while cross string decrease. I just want to discuss that we never paid attention on the mains, which we always threat as perfectly tensioned and according to my previous post it sounds like an interesting topic.

I compared today a 3 weeks old square stringing job (played 8 hours) and it became very slightly more narrow than an unstrung frame. Right off the machine it was same as untensioned. With having the 10% discussion from Paul und Reinhold Messner of the Yonex stringing team in my mind I think we should talk about this (again).

 

great thinking to go by the ping frequency! I'll make some tests on the the next job and make a short video in case there is anything interesting happening.

I think your approach of calculating an estimation is correct. However, I think some of the assumptions in the equations are not.
First of all, the distance between clamp and frame are highly depending on the machine and clamps that are used. I've just checked my own video

and I would say that the distance only exceeds 10 mm to the frame on the first two strings when the clamps are too close to each other or the main supports(click to enlarge):


After that, the distance is hardly more that what you would achieve on the crosses:


Also, you will have the same thing happening on the crosses (in parts) since you cannot achieve a zero distance there. So overall, you would have to consider only the difference between the "lower tension parts" of both mains and crosses on the end calculation.

And to add one more thing, going with the numbers from the double pull tests (https://stringing.info/2018/03/29/nur-jede-zweite-saite-ziehen/), you'll only have a loss of around 16% when you do a double pull on the mains without pre-stretch and only 3,6% when adding pre-stretch. The loss on the crosses a lot more (~49% without PS, ~37% with PS) so that would shift the effect into the other direction.

Bottom line: I don't see that the clamping distance does play a major role in the whole complex equation. It adds certain nuances that might vary with different machines and clamps and that again emphasises that the "optimal ratio" is depending on the machine and stringer.

 

Did you have enough string at 11:47 to go up to B10 (and tie at B6)?

The missing cross on that pattern offends me.

 

Have you read the title of the video? Would have been an epic fail to add that string in B10.

 

You are right. The clamps and the frame also play a role. Furthermore the support dimensions, pattern, starting routine and the pattern of the racket. Maybe you didn't went square because of that you are able to clamp the mains closer with less loss? I remember pretty well our personal conversation about the hybrid of your client whose racket became shorter on square tension with a 4 knot job. We always said in the past "Depends on the side supports." Even if the support don't cause deformation, the difference of applied force of the string segments must be inbalance which maybe result in deformation over time? I also have the sinking issues of some frames in my mind which can be a result of imbalanced tensions?

Sure, but only on your current machine. I would expect that your mains will be tighter than mine. Maybe this result influence that some machines need the extra on cross. Not only because of friction, ziggzagging of the mains and the solid supports, also the clamping of the mains. This would lead why some stringers of the Yonex Stringing Team don't do square. Because their mains are tighter than usual machines like e.g. mine.

One point I noticed is that on your pattern is that not all mains are strung without friction. What also comes to my mind are the Babolat rackets with 20 mains or shifted mains and crosses like Oliver Microtec 08 which will result in less mains than cross for Babolat (also an exception) or an Oliver Microtec 09 which don't allow optimal cross clamping and has more friction in the middle for the cross and not a constant ziggzagging. Anyway, for me it was just a simplified quick and dirty thought and something which not involves all complex variables. To make it nearly complete let me also name thick frames with a thin profile like the Nanoflare 700, the different angles of the pulled segment which also result in more or less grommet friction. The height of tensioner (with or without rising on pull) also influence.

Great post. Never the less this method also ignore pulling angles of a whole string process. The more outside you pull mains, the more grommet friction can be there due the angle. Is also not a complete measurement which can be said for every main. It also ignore that the friction which increase when you go up to the top for the cross. The measurments just happend at a very low (nearly not requested) tension. How about serious ones? Is it linear like a percentage says? 16% of 9kg are 1,4kg. How about a 14-16kg, tension which got asked by pros?

Kudos to @Lukas Nguyen He proofed that the friction is not constant and became more to overcome at the top.

I think at the moment, that a more bulky constructions of the machine lead to some distance of main clamping than the cross, if it is nothing exotic racket. My aim is to find an explanation why square works even on cheap machines and why Yonex Stringers recommend 2lbs or even 10% on high end machines. My thought is that their mains are tighter by a small margin which can be a part of the puzzle to explain why they do so big extras on the cross. I also spotted at a video of Mark Lawrence that he don't clamp past the last main on the crosses.









I don't know where it leads, but I'm pretty unsatisfied with the explaination of "side supports built like a tank" to justify ratios or the stringer. If crosses are less (21) than mains (22) and we all agree that based on frictions the tension of the cross are lower, while on the other side the mains are nearly perfectly tensioned and only increase tension due the ziggzagging, why does square work? Not only right off the machine?

If the friction is lowest or constant of 6,7% (simplified I don't know each) The forces are will be unequal. At best and lowest there will be 22 x 9kg - 21x9kg(1-0,067) = 21,663kg squeezing the frame to make it round. To compensate it, without PS we need to add 1kg. Something which is close to the 10% rule. Let's take a pro tensions. Again, simplified no measurements. I know it will be not a good calculation. 22 x 14kg - 21x14kg(1-0,067) = 33,698kg. We need to add also something around 10% even round up on cross. I doubt that this imbalance got be taken by the frame completely or neutralized due strong supports. If it wouldn't be so complicated and time consuming I would make a simulation in COMSUL Multiphysics. And even then there will be something imcomplete. I just want to find two explainations. Why does square work and why pro stringers can add 10% on cross without deforming much? Even small parts can sum up.

 

God, I just love those super geeky discussions!

In retrospectice, that was indeed a perfect example that shows the importance of the side supports. Cause hands down, the reason those frames came out short was because I had the side supports far too loose. Since I got the hang of how much I need to tighten the one-wheel thingy, I never had an issue with round frames. So based on that experience, the support stability seems to be a top priority in the whole picture.

Only the last mains on both sides are tightened with the crosses being in. That would end up as a similar effect than double pulling the outer two mains. And besides, thanks to the rising popularity of hybrid setups, I've been doing a handful of 2-piece jobs recently (BGAB, NBG99/LN1, GT5/LN1) and all of them came out in shape as well with square tensions. So not even the different string gauges seem to have that much of an impact there.

That is indeed interesting to see. If that was done by all Yonex stringers, then this would add to the picture - but I have no clue if that is just a personal thing of Mark Lawrence right there.

The problem is that all simplyfied calculation approaches are failing because the whole system is super complex. For example, to calculate how much "total weight" is pulling on the frame from each side, you need to include the pulling angles between frame and string - cause as soon as the string is not in a perfect 90° angle to the frame, you will have two different force vectors that will be distributed inside the frame construction. And this again will depend on the construction of the frame which is a complete unknown factor. But given that square tensions seem to work on pretty much all racket constructions, this also doesn't seem to have an sort of significant impact there. A decent FEM simulation would be an interesting way to at least see what is going on inside the frame in terms of force distribution throughout the whole stringjob. What it couldn't really show is the impact of the human factor (workflow, clamping distance...) in the whole process though.

What I'm asking myself is how much the principle "never change a working system" plays a role in the +10% Yonex recommendation. I mean... apparently, they are not breaking a noticeable amount of frames on the machines, the rackets come out in a way that the pros like it and frankly, they don't give a wet fart about the head shape being 2 mm longer after several days or weeks. And if it works and the clients are happy, why even think about changing anything and raise unnecessary questions and discussions?

 

I'm not in the mood to change anything atm, but experiment and have thought experiments, but how many people here change rackets twice in a season, change strings or invent new hybrids, patterns? I always thought this is vital here? Every person with passion want to understand why he/she do something also people who want to learn. I still wanna learn and questioning why I do something like this or that or why. I'm not results-driven. But I can stop here if this is unnecessary.

 

I was speaking from the position of Yonex. They are doing well with their +10% role for years. Why even question it?

That we nerds keep testing, trying and tweaking to the end of our day hopefully won’t change. How boring would life be?

 

Here is the right spot to talk about my experiment with replacing grommets with badminton tubing Again. Sorry guys for insisting
https://www.badmintoncentral.com/forums/index.php?threads/grommet-friction.173607/#post-2594369
The thing about this experiment is how does less friction on those kind of grommets affect the result of a stringjob or the playability of the racquet. (I have experienced that the tubing is more slippery than normal grommets, so it does change a little the tension when applied and the tension after the racquet has been played.) of course it's a bit challenging to string with tubing, because it doesn't stay easily in place, so you have to cut the right lenght of tubing to prevent cutting of the string during tensioning.