main support deforming under load

Discussion in 'Badminton Stringing Techniques & Tools' started by konstancij, Jan 12, 2021.

  1. s_mair

    s_mair Regular Member

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    Very interesting insight. For some reason, I have always preferred a slightly(!) stretched frame to a round'ish one, only going by gut feeling. In general, I hate the feeling of the frame being loose or having play in any of the supports during the process.
     
  2. Mark A

    Mark A Regular Member

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    I always went by the relative tightness of the supports at the end of the job - if the 12/6 needed the same effort to release as the shoulders, I considered that correct.
     
  3. kwun

    kwun Administrator

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    step back a little and think about the larger picture.

    Is it a good thing to not have any compression on 6/12 o'clock? if we make the end posts completely rigid, ie. no compression at all, it means we are stopping nearly ~1000lbs of forces that is trying to compress the racket at bay. However, think about the other direction. when we pull the crosses, we are not doing that. same ~1000lbs of forces is now more freely to compress the racket frame sideway. is that imbalance a good thing? I don't know.

    ideally, we should hold the whole frame rigid, let all the forces be held first, and then have the whole racket head be compressed by all strings at the same time.
     
  4. s_mair

    s_mair Regular Member

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    Well, the supports are there to take that load, aren’t they? And they can only do that if they are in contact with the frame. The effective load on the frame in the end will be the same in both cases. The only difference is that the frame gets supported by the... well... supports in all six contact points - mostly in the beginning of the job.

    The more you get towards the end, the more load should be taken away from the supports again once the rackets gets closer towards the initial shape.
    I don’t see a benefit in having play or movement in any of the supports. The only times I had issues with deformed frames was when I switched machines and had the supports tightened too loosely in the beginning. Even going +2 lbs. on the crosses couldn’t compensate the loose main supports and resulted in round frames, so that was an impressive lesson for me.
     
  5. konstancij

    konstancij Regular Member

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    indeed if systrm is rigid, all load resides on main supports.
    a sad story of a racket gone during lockdown... on a verge of valantine day. I was stringing a 5u nanoflare700 with victor vbs-1, with my metal rod between main supports when heared a cracking sound. I was pulling last main string at the moment. Later, finished the job, i found a clear sign of damage on internal surface at 12 oclock. However, racket dimentions and stringbed sound are perfect.
    And who to blame?: my stock load spreaders, ofcourse, are not up to the task, as the racket is damaged between central mains only. I always was suspicious about these 5-tooth pieces, to me it is clerly a gimmick. Time to change. I am not sure about yonex Hpiece, but babolat piece indeed spreads 50/50 between two points, plus the are more advanced systems victor and gamma/alpha.
     

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  6. s_mair

    s_mair Regular Member

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    Those 5 tooth load spreaders are so common, I don’t think they are to blame for that tragic loss. Thinking about it, maybe it was a combination of the spreader and that metal rod. Although I can’t figure out a theory why yet.

    Have you tried re-tightening the main supports after the first two resp. four mains without using the rod?
     
  7. konstancij

    konstancij Regular Member

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    No, did not retighten this time, but I will, I have one lining n7ii for stringing, that is not mine. I will string it "classially" and look for freeplay.

    However, for my rackets, I want to continue searching for working "rigid" setup. I believe this is giving best result with no black magic necessary.
     
  8. flyingcords

    flyingcords Regular Member

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    I think what happened with your rigid/tight/main-support/rod system is an excessive compression at 12 o'clock due too no movement and elasticity at all, as if the frame was compressed against a wall made of titanium ;) You achieved what you were looking for in terms of no frame deformation but with an unexpected side-effect (or should we say main-effect ?)
     
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  9. s_mair

    s_mair Regular Member

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    My thoughts exactly. The rod somehow prevented the outer teeth from actually distributing the load to the frame and instead seemed to be focusing it right between the two centre mains. I would be careful with that rod solution in the future after this incident. This is too much of a coincidence if you ask me.
     
    #29 s_mair, Feb 14, 2021
    Last edited: Feb 16, 2021
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  10. konstancij

    konstancij Regular Member

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    hi, if anybody interesded, a little update on this topic. A week ago, I tried yonex load spreader, but it has surrended after just several mains were pulled. So not good. May be I've got a copy, not the real yonex part...
    So I decided to 3d print the load spreaders, you can see the picture. This version is not perfect yet, as there is problem to fix clamps on last crosses (used flying clamps), but the load is hold without problem and final dimentions of stringed racket are perfect. Now i need to make my rod less obtruseve/convinient.
     

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  11. s_mair

    s_mair Regular Member

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    The reason the H-piece broke is the same why the frame cracked right at the top. The rod is focussing all the load right in the centre and doesn’t allow the spreader to actually do its work. So in fact you are creating an even more dangerous situation for the frame with that rod instead of fixing the initial one.

    Have you tried the re-tightening thing after the first mains?

    And knowing the machine, there’s another idea that has crossed my mind. Can you post a picture of a mounted racket that shows the distance between the main towers and the positions of the side supports? Or maybe even measure the distance between the main towers?
     
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  12. s_mair

    s_mair Regular Member

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    Just to make sure before I dive into some test here - this is a StringMaster Deluxe that you are using there, correct?
     
  13. konstancij

    konstancij Regular Member

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    to you questions, s_mair.
    1. no my machine is not delux, but 3700 pro - a badminton only version.
    2. i attached a picture of mounted racket, the racket is quite standart.

    As you see, my machine have 3 positions for mounting of plastic side-support things. I tried all 3, and there was no difference, to how the racket is compressed. Still same 4-6mm. Is it too close?

    I do like this machine, btw, really. I can string with it without any modifications. But, to me this project become a search how to modify it, to completely prevent racket deformation while pulling mains. And with my strong 3d printed supports, it is now possible.
     

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  14. speCulatius

    speCulatius Regular Member

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    That's a problem. The side supports can only take part of the load when the racket does deform.
     
  15. s_mair

    s_mair Regular Member

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    Thanks for the additional information. I have done some tests on my StringMaster Deluxe and now I really want to find the root cause for the issue. Bottom line: The supports on the Deluxe are rock solid, there is just minimal movement/deformation happening during the first main strings. Here are some pictures (click to enlarge):

    Distance between both main support bits without any tension applied, frame is not overstretched:
    upload_2021-2-28_13-56-27.png
    => 215 mm

    Same measurement after tensioning the first two mains with 24 lbs.:
    upload_2021-2-28_13-57-38.png
    => ~214 mm

    Same measurement after tenstioning the first 4 mains:
    upload_2021-2-28_13-58-35.png
    => still ~214 mm

    as predicted, a slight gap (<1 mm) is opening up between frame and support after the first two mains. However, I did not re-tighten the support at that point though:
    upload_2021-2-28_13-59-55.png

    Bottom line, I have no chance to cause a deformation in the range of those ~4 mm that you can seen on your machine. I've just tried it with a tennis racket and 60 lbs. tension and it ended up still in the range between 1-2 mm deformation. So either the mechanical construction in the main supports is significantly worse on the 3700 machine (which doesn't look like it on the pictures seen in the online shop), or there is something really fishy going on. Heck, I would even assume less deformation since the distance to the main towers is shorter on the 3700.

    So maybe it's best to get back to the start once again to figure out what's going on. Is it possible for you to make some videos or at least some detailed obervations regarding where exactly the deformation is happening? For example shooting videos (using a fixed camera position) from this perspective during the tensioning process:
    upload_2021-2-28_13-55-7.png

    Hopefully we can see from there which is the weak part in the chain. In my opinion, it's not normal and not acceptable that a machine at that price range and with that level of build quality causes that amount of deformation.

    One final thought: Are you sure that you have not maxed out the thread on one of the main support pieces inside the adjustment knobs?
     
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  16. konstancij

    konstancij Regular Member

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    thread is not maxed out, not even close, but the threaded rod is not very thick, it looks like M6 to me. Definately thinner than delux.
    In your tests, you have only 4 mains, this is about 20% of full load.
     
  17. speCulatius

    speCulatius Regular Member

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    Even a rather low quality M6 is build to hold more than twice the force of what you get when stringing 22 mains at 20 kp ("kg"; that's > 40 lbs) each. Even the eccentric force will not change much, especially since it's evenly distributed.

    True, but I doubt it will move much more - if at all. It already seems that way going from the first two to the first 4 mains.

    Why don't you follow the suggestion to upload a video?
     
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  18. Mark A

    Mark A Regular Member

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    That threaded rod was always a bad idea - it turns a six-point machine into a two-point machine.
     
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  19. s_mair

    s_mair Regular Member

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    So I’ve sacrificed that string set for the sake of science. As expected, there was no more movement until all the mains were in. It seems as if the first pulls take out the play between the components.

    I had another go in which I re-tightened the 6 o’clock support after the first two mains. And again, as expected, I ended up at exactly the start value of 215 mm after all the mains were in.

    Even an M6 steel rod will not show that amount of elastic deformation. The forces applied are too low for that.

    Question: After tensioning the first two and first 4 mains, how big is the gap that is opening up between the frame and the support piece or the load spreader respectively? You’ll have to look at that if you want to get closer to the root cause.

    And yeah... I feel like a video is becoming more and more mandatory. With the pictures and information so far the only thing that is clear is that the stabilising rod was causing more harm than good.

    Edit:
    Does your machine look like this?
    [​IMG]

    If yes, what is that screw/bolt doing there?
     
    #39 s_mair, Feb 28, 2021
    Last edited: Feb 28, 2021
  20. konstancij

    konstancij Regular Member

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    ok, i see. i will try to make a video, sure a lot of fun, the problem is luck of time to do it properly.
     

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