The arbiter of success with regard to racket head shape is width divided by length - if the ratio before is the same as the ratio after, the racket is optimally strung. Matters not whether you add 10% for crosses or use the "square" method. (In fact, I've seen evidence that people who pre-weave might get a better result if they use square tensions - I think it's because the racket is under stress for a much shorter time, but it's only a theory).
Mark, your theory might have merits. If the machine's structure and shoulder supports aren't adequate, the frame do get shorten and wider with the extra time to weave the cross strings. Contrast that with a pre-weave frame, the stress duration is much shorter as you mentioned. On certain machine, it is very difficult to repeat the same result: namely, how much to tighten the shoulder supports knobs. To make matter worst, the shoulder supports are not optimized for badminton frames. Re-producing the same width/length ratio is very difficult in this case, if not impossible.
Whatever the case is, all I know is that when you're re-stringing apacs rackets (at least the Lethal 70 anyway), it's a good idea to string the mains tension at 2-3 pounds lower than the cross tension if you want to maintain the shape of the racket head. My Lethal 70 is still going well - currently strung at 3 pounds lower on the mains and head shape looks good. Just haven't been playing with it as much lately as I've been using the rather amazing 3U VT80. By the way, apparently Lin Dan's racket head is huge due to the distorted head, creating a larger sweet spot? Sounds exactly like what happened to my Lethal 70 when it was strung at 27x27.
on a 6pt machine as well? bummer. i just got 2 Apacs 900 Power earlier this week to string. if i had knew it earlier, i could've done the measurements. too late now as they both have been strung and one is back to the owner.
What tension did you string it at? I'm not sure what machine my friend was using, but I'll try to remember to ask him when we next meet. It was pretty obvious when I got the racket back at 27x27 with the distorted head shape - it looked so much bigger! Just compare it with any other isometric racket head and there is an obvious difference.
one of them were 24x24 and the other one 26x26. i didn't feel that it was deformed. but as it is the case that our eyes are not very accurate judge of shapes. at least my aging eyes are getting worse and worse at it!
Ah ah, the fanatic stringers will go one step furter by using a digital caliper of some sort to measure the before and after widt/length .
i wish my digital calipers goes that wide. i just use a ruler. within 1/16" is good enough for me. i don't think my brain can comprehend anything smaller than that anymore!
Oh aye - you can get a 300 mm digital vernier off eBay for peanuts these days (but it'll come from HK, usually).
Whether or not you need to lower the main string tension depends on the stringing machine you use to string the racquet with. On 6 point mount machines the additional four shoulder support arms will keep the racquet in shape and prevent distortion which normally happens when you string the main strings. The general rule that you must string the main strings at a lower tension does not always apply either. I have seen a lengthened and slightly squashed-inwards racquet which had its cross strings done at a tension too much higher than the main strings on a 2 point mount machine. However on further investigation the cross strings are only uniformly 2lb higher according to the stringer which is what Yonex recommended for the main to cross string ratio. On another racquet when I asked the stringer to try just 1lb lower on the main strings, the racquet frame came out strung the way it looked when it was unstrung. You have to remember that due to the fat, squarish shape of iso racquet frames, at most times when we assess the freshly strung frame, it is easier to detect a lengthened and squashed-inwards frame than a shortened and widened frame, even though the earlier lengthened frame actually looks exactly the same as an unstrung frame. You will realise this when you start measuring each racquet's frame you have the way that kwun did before and after stringing. Although if you string the same tension for the main and cross strings on a 2 point mount machine, it is possible to distort the racquet and lengthen the shape if you don't tension the cross strings at a correct ratio to the main string tension. This is because after already tensioning the main strings the frame will be slightly squashed-inwards at the sides due to the compression force (which only happens on woven and strung strings as the string is now pulling both ways on the frame inwards which is different compared to when you tension pull the string where the force is only going in one direction towards the tension pull head and not affecting both opposite sides of the frame). When you string the cross strings then you will need to counter this already expanded shape by giving the cross strings more compression force (thus stringing a slightly higher tension) to pull the shape back into the original. An analogy is how you would need more strength (or force exertion) to push a too-low hanging object upwards to meet the height mark then support it compared to just going in there and support the object at that height mark. And of course in the end, it will boil down to exactly what string machine your friend is using and how the problem you faced could be avoided and prepared for on your next string job.
Guess most of the "audience" who are knowledgeable and care enough to comment have spoken. Personally, I was stringing iso and oval frames with 1~2lbs differentials and sometimes experimented with reverse differentials (main lbs > cross lbs) for quite awhile before recently switching to same ratio stringing (after I got 4 of my favorite ISO racquet: YY AT900 Technique). I find the results very little difference between the two ways. Majority of the racquets I strung have held out well and maintained close to original shape. I suspect that 6pt support makes the point moot. As long as the mounting of the racquet is correctly done and supports sufficiently set, there shouldn't be too much variation from the original shape. I also agree that the duration of the racquet in stress is a significant factor. Since I started pre-weave my crosses after the 3rd cross from the top, it kept better shape than when I tension each cross; not to mention shorter stringing time with pre-weaving.
I saw the pictures are also shorter at main and fatter at cross. maybe Kwun can take another picture from similar grommet-to-grommet. The picture on the cross is not using similar grommet. at picture #4, the left grommet is slightly low compare to the picture #5, therefor the result of measurement almost the same, but if move the ruler on the similar position, the picture #4 would be shorter. but, I think the shorter or fatter is around 2mm only, which is still OK with me. and as per Pete LSD said ... as long as the racket shape is still the same, it is no issue whether to put more 2lbs on Cross or keep it similar. but, from the Victor catalog 2011 , it said : - 5 first top cross = main tension - 4 last bottom cross = main tension - other cross = main tension + 2lbs So, Victor has revealed their stringing pattern, .....
This is what I use when going over 30 lbs - makes a lot of sense. Looooong shipping delays (unless you're in HK, ofc).
Lately, I have been stringing the cross string very similar to Victor's instruction, but with a few twists: 1st 2 crosses from top @ 30 lbs next 2 crosses @ 31 lbs next 2 crosses @ 32 lbs and then back to 33 lbs for the remaining crosses
