Yonex grommet design.

#1
Below is a photo of the center of the bumper on a V Core Pro 97. A customer who has no prior history of shearing strings came in with a break of the center 2 mains (Biphase 16). I am wondering what the intended purpose of the 3 ridges between the mains is (under the string loops). Has anyone else seen unexpected breakage?

BTW, I took a rat tail file and removed them before re-stringing.

 

Irvin

Talk Tennis Guru
#3
Below is a photo of the center of the bumper on a V Core Pro 97. A customer who has no prior history of shearing strings came in with a break of the center 2 mains (Biphase 16). I am wondering what the intended purpose of the 3 ridges between the mains is (under the string loops). Has anyone else seen unexpected breakage?

BTW, I took a rat tail file and removed them before re-stringing.

My guess would be it lowers the friction between the string and grommet.
 

MAX PLY

Hall of Fame
#4
Where exactly did the break occur and after how many hours of play? Bi-phase is pretty soft (my personal string) and I break it quickly and usually one of center two mains. I would be surprised if those ridges would cause premature breakage.
 
#5
If the picture shown is accurate, then the ribs are actually there to offer more surface area to distribute the string's downward force against the grommet across more area. This would increase friction and spread stress of tension across the string.
 
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#6
They look like pressure relief carve outs. String pressure would cause the plastic grommet to flex downwards thereby increasing contact with the frame. This would theoretically decrease pressure in the area since there is more contact area. Whether it works or not is a guess. You would need some small strain/pressure gauges to measure if the difference is perceptible. Whether they contribute to shear is unknown since we do not know where the string broke.

So I am now waiting for images. :unsure:
 
#8
The string broke at the top of the frame where 1LM and 1RM diverge. No images available. Sorry.
no issues I can think of, stringing yonex sticks often, like you descrived on first post

in your picture though,, i would try greasing the ports, and/or adding a power pad in that location, to round-off the turn a bit more, looks a bit sharp/worn to me..
 

am1899

Hall of Fame
#9
If the picture shown is accurate, then the ribs are actually there to offer more surface area to distribute the string's downward force against the grommet across more area. This would increase friction and spread stress of tension across the string.
That would be my assessment as well.

in your picture though,, i would try greasing the ports, and/or adding a power pad in that location, to round-off the turn a bit more, looks a bit sharp/worn to me..
Would be inclined to agree with this also. If it were me, I’d probably tube the offending grommet, or replace the grommet set entirely. (OP, any idea how many times had this frame been restrung before this happened)?
 
#10
(OP, any idea how many times had this frame been restrung before this happened)?
I'm pretty sure it was the 2nd stringing. Will ask when the customer picks up.

I'm realizing now that I should have looked at the loops of string between 2H & 3H for signs of damage. Did not think of it at the time. Missed opportunity.
 
#12
The other, IMO more likely, explanation is that the player shanked a ball near the grommet which caused the breakage. You do have a couple of options, you could tube the suspect grommets or you could use power pads up there to lessen the angle and bypass any potential sharp edges. You could also use a scrap piece of string and "burn" the grommets a bit to smooth out any sharp edges. That was what used to happen with wood rackets when they were new to smooth out any edges in the grommets.
 

MAX PLY

Hall of Fame
#13
^^^ Agree with Rabbit, I think based on the break description, it was a Shankosaurus intervention. I think we would have heard about lots of string breakage problems if it were the Yonex system.
 

Irvin

Talk Tennis Guru
#14
@10shoe I would have placed a small piece of tubing between the 2 grommets to isolate the ridges from the grommets. If the string broke again it was a grommet problem and they should be replaced. If the string string didn't break it MAY BE a problem with the ridges. It could have also have been a twisted string where a kink was pulled until it snapped. X_One is bad for twisted because of the way it is wrapped. But since you filed off the ridges all this is a moot point.

Because it is only the second time the racket had been strung I think there is a freak issue with the grommets but I have a hard time imagining that is possible. Do you remember if the break occurred on a bend (top of grommet, below the grommet (shear,) or between the grommet (rib problem?)
 
#15
I'm pretty sure it was the 2nd stringing. Will ask when the customer picks up.

I'm realizing now that I should have looked at the loops of string between 2H & 3H for signs of damage. Did not think of it at the time. Missed opportunity.
that's hard todo, how often do you inspect each and every port on the racquet,,, that thoroughly??? I don't/wouldnt, I look racquet over and only big obvious issues get my attention initially,,
this issue could be user error "shankarooni", most likely,, but a reminder for yourself is needed now for that racket, on that spot!!..
from the picture, I cant tell if its too early to replace the entire grommet kit.. workarounds as listed above would be my suggestion at this time, imo..
 
#16
The player who brought the racquet in has elbow issues and has no history of shearing in 11 yrs. Certainly it's possible it was plain and simple shearing. For my part, when I saw where the string broke, my first move was to check to see if there was a grommet problem. Even though I had strung the racquet it wasn't until that moment that I became aware of the 3 ridge design between the grommet holes.

As stated in the original post, I filed the ridges down. I'm sure they wouldn't cause problems for a player using poly but this player is using Biphase. It's been a couple decades since I can recall putting power pads on the top of a racquet. Too likely to expose a string loop to court abrasion IMO.
 
#17
@10shoe, I'm playing Yonex now. I haven't looked at the grommets. My three have been strung about 4 times each so far. I'm playing Gosen OGSM 18 in the mains. So far, nothing out of the ordinary. When next I string them, I'll take a look at the grommets and see if I'm "ridged". My money is on the shank. It happens to everyone. My best shank was with a Volkl Catapult 10 strung with Alpha Gut 2000 18. I had just strung it, took it out of the bag to warm up and first hit.....bingo bongo...shank-ti-fied! I put it back in the bag, got a C10 out and proceeded.
 

Irvin

Talk Tennis Guru
#18
The player who brought the racquet in has elbow issues and has no history of shearing in 11 yrs. Certainly it's possible it was plain and simple shearing.
I have strung a lot of X-One Biphase and have never seen a failure near a grommet. X-One is a soft string.
 

Irvin

Talk Tennis Guru
#20
Are you suggesting that soft strings are LESS susceptible to shearing?
Well that would depend on the string ZX by its stiffness rating is a soft string because it has little resistance to stretch. Kevlar on the other hand by its stiffness rating is a very stiff string but is one of the most playable strings you will ever string. Natural gut is not stiff either and is a soft string. I’ve seen ZX, gut, and poly shear but I’ve never seen a Kevlar string shear. So no I’m not saying soft strings are susceptible to shear. Most strings that is plyable does not shear easily but any string could shear.
 
#23
I have never seen a pig ride a bicycle. Pigs are smart.
I have never seen a cow dance. Cows eat grass.
I have never seen.... [Enter yours here]
 
#25
@10shoe - sorry for the late reply. I was looking at your image in post 1. Normally, I see channels forced into the plastic by the strings. Those channels are normally smooth and allow the string to curve from parallel to grommet to perpendicular. The ones shown appear to show some collateral damage as the string enters the hole. I am speculating that the string may be vibrating up there due to the raised ridges and that the excessive vibrations may be heating the string causing the break. Tubing would definitely help as this would restrict string vibrations in that area. Changing to a more durable string could also help if the client is willing. If the client comes back again, you should ask if they are hearing or feeling more vibration in the frame. Just a hypothesis, so feel free to ignore. My initial reaction was 'It is a shank', but now I am not so sure.
 
#27
@10shoe - sorry for the late reply. I was looking at your image in post 1. Normally, I see channels forced into the plastic by the strings. Those channels are normally smooth and allow the string to curve from parallel to grommet to perpendicular. The ones shown appear to show some collateral damage as the string enters the hole. I am speculating that the string may be vibrating up there due to the raised ridges and that the excessive vibrations may be heating the string causing the break. Tubing would definitely help as this would restrict string vibrations in that area. Changing to a more durable string could also help if the client is willing. If the client comes back again, you should ask if they are hearing or feeling more vibration in the frame. Just a hypothesis, so feel free to ignore. My initial reaction was 'It is a shank', but now I am not so sure.

Well, it's good to hear that at least one person thinks it's possibly not due to a shank.

Regarding your vibrations hypothesis: I suspect something much simpler. I recently had a set of natural gut break in a customer's racquet while it was sitting in my shop waiting to be picked up. I posted a thread about it. The cause was a fairly minute bit of wear through on the outside of the hoop where the grommet barrel meets the bumper. That was sufficient to kill a set of gut. So, what happens in cases like that is that a tensioned string leaning against a sharp edge causes one filament of the string to break. The next filament behind it snaps in to take it's place and in a cascading effect the string abruptly breaks. To me, these ridges on the Yonex seem sharp and I am suspicious of them.

I have 5 customers using this racquet. One recently had a pair strung with gut/poly hybrids. I will be looking forward to seeing how that holds up.
 
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