K90 dissection-

[pyrokid]

So, I have this K90 I bought from somebody who told me it was "structurally sound."
However, after I played some with it, I noticed it had about 1/5 the feel of my other K90s, so I started checking for cracks, and I found some. (they were painted over to disguise them.)
I decided to hit with it some anyway, but it broke after about an hour. So I started cutting it up.

I'll have pics up in a bit, but just so you all know, the entire racket is filled with foam, the PWS adds about 2.5 grams to the 9 o clock, and the majority of the weight is in the bridge/lower hoop. I do not actually believe it it polarized after looking at the cross sections.

 

[zapvor]

that is way too cool. cant wait for pics. sorry to hear about you being scammed though

 

[pyrokid]

that is way too cool. cant wait for pics. sorry to hear about you being scammed though

Pics should be up in a few minutes.
If anyone wants me to saw through and other parts, I can try and do so. I believe I got all the major parts though.

 

[corners]

Remember that polarization is a relative term. It can be quantified as the ratio of static weight to recoil weight. So you don't have to cut it up to figure that out. The K90 is more polarized than many traditional player's sticks, such as the PS85, since it has a higher swingweight and still has the same headlight balance. But in comparison to other modern sticks, you're right, it isn't very polarized.

Looking forward to the pics. Please see if you can get one showing the braided construction, both inside and outside. Does it have two layers of braiding? The outside all black (graphite/graphite braid), the inside black and yellow (graphite/kevlar).

Actually, since we've seen pics of "naked" K90s without their paint, we know the outer braid is all black, all graphite. So a pic of the inside of the frame will show if it's double braided with the inner layer graphite/kevlar.

 

[Larrysümmers]

Did you at least get your cash back?

 

[pyrokid]

Did you at least get your cash back?

nope, I didn't pay much at all to start with, and I didn't think it would be possible to return a cracked frame.
I did buy it with the knowledge that it was a bit beaten up (actually, up isn't the word to use, it was beaten ON.) but I took it anyway because I got it cheap.
He did say it was structurally sound, though.

 

[pyrokid]

Here's a pic of the PWS, and I know it's hard to tell, but the PWS is actually made of solid graphite. You can't see the foam well in this shot, but it is there.

Here's the handle, if you look closely you can see where the two halves of the throat were joined. At least in real life, you can. I understand my terrible photography might make it... hard.

Here's the five o'clock area.

near the twelve...

 

[pyrokid]

Right next to the throat. As you can see, it's starting to thicken.

This is where I thought it got interesting... The foam's gone. That grey stuff is actually either some kind of filler, or another type of graphite, and it goes throughout the whole bridge, most likely for weight. (this is why I said it wasn't polarized)

Another shot of the throat stuff. It looks like some type of caulk, actually.

Here's the pieces of the racket that cracked during play. ( I know, it's a pretty massive breakdown.) You can see the true color of the foam, and some kevlar. However, something makes me think that the kevlar doesn't make up 20% of the weight...

 

[pyrokid]

And, finally, a picture of the beam on the throat.


By the way, I was sanding some of these pieces down while cutting them so I could have a look at the braided graphite, so that's why some spots are bare.

If people have some other requests, I'll try as best as I can to get them.

 

[corners]

Hey Pyrokid,

Thanks for taking the time to do all that cutting and snapping of pics. I wonder if the stuff in the throat isn't silicone caulk.

Do you have the capability to cut a piece in half lengthwise? Take a look at this pic of a KPS88 sawed lengthwise:

http://i41.tinypic.com/97604g.jpg

That was posted on the boards last year, but I can't find the actual post it was in. You can see that sawed like this, with the foam removed, you can clearly see the inner graphite/kevlar braid.

 

[pyrokid]

Hey Pyrokid,

Thanks for taking the time to do all that cutting and snapping of pics. I wonder if the stuff in the throat isn't silicone caulk.

Do you have the capability to cut a piece in half lengthwise? Take a look at this pic of a KPS88 sawed lengthwise:

http://i41.tinypic.com/97604g.jpg

That was posted on the boards last year, but I can't find the actual post it was in. You can see that sawed like this, with the foam removed, you can clearly see the inner graphite/kevlar braid.

Sure, I'll give it a shot after school.

 

[mltaylor]

Thanks for the pics Pyrokid.

I know this is off topic a bit, but would anyone know the advantages/disadvantages to having a thinner throat bridge than the rest of the head of the racquet?

In some popular mids like the K90/Head Prestige they have TB's the same size but the Dunlop AG 100/4D has a thinner one. I know the K90 feels much more solid than my AG 100 but that's probably just the weight.

Thanks.

 

[travlerajm]

As long as adequate structural rigidity is preserved, it is advantageous to have minimal amount of weight in the throat bridge and lower half of the hoop while maximizing the mass in the top half of the hoop.

In other words, the more polarized the hoop, the better. If the hoop has more or less uniform mass density (as most racquets do), then there is a steep gradient in the power potential, with the bottom of the hoop having much more lively response than the top. This is clearly shown by the power maps available on the TW University site.

However, when the top half of the hoop has significantly more mass than the bottom half of the hoop, the slope of the power potential gradient is reduced. This reduction in the slope is more exaggerated for flexier racquets than stiffer ones.

By reducing the slope of the power potential gradient, the power level of the stringbed is more uniform, so depth control is greatly improved.

I believe this is one reason why many pros prefer to use "pro stock" frames that start with a SW of 280, then weight them up with multiple layers of lead under the bumper.

And it is why my favorite midplus frames are my highly customized cutdown POG LBs. After cutting down to 26.7", they start out with SW in the 270s. But I have them leaded to about 365 SW, with none of the hoop weight below 3 and 9.

This makes the hoop of these racquets more polarized. The more polarized the hoop, the closer to the throat the counterweight must be placed to achieve the same weight, balance, and SW. Placing the counterweight closer to the bridge increases the dynamic stiffness. Thus, if two frames have the same weight, balance, and SW, the frame with the more polarized hoop will play stiffer and hit a flatter, crisper ball, but it will have a more uniform stringbed response too.

My cutdown POG LB with polarized hoop (and coutnerweight near top of handle) plays crisp, similar to a leaded frame with 67 RA, even though it is actually a flexible frame.

 

[zapvor]

very interesting. thanks for the pics

 

[sureshs]

That grey stuff is actually either some kind of filler, or another type of graphite, and it goes throughout the whole bridge, most likely for weight.

Anyone know what it is?

 

[corners]

Isn't the bridge of the frame supposed to heavily determine feel? Maybe the material in there is to filter out certain vibrations for to enhance/dampen vibrations rather than for structural or weight purposes.

 

[The_Question]

Very interesting, but at the same time, it made me sick to my stomach...watching a racquet getting guttered up...

 

[Fed Kennedy]

Good pics pyro.
Does anyone know if the 6.1 wilson 95s have the same foam filling going through the frame? Just curious.

 

[WORLDWITHINAWORLD]

Merit Of Cut- Offs

As long as adequate structural rigidity is preserved, it is advantageous to have minimal amount of weight in the throat bridge and lower half of the hoop while maximizing the mass in the top half of the hoop.

In other words, the more polarized the hoop, the better. If the hoop has more or less uniform mass density (as most racquets do), then there is a steep gradient in the power potential, with the bottom of the hoop having much more lively response than the top. This is clearly shown by the power maps available on the TW University site.

However, when the top half of the hoop has significantly more mass than the bottom half of the hoop, the slope of the power potential gradient is reduced. This reduction in the slope is more exaggerated for flexier racquets than stiffer ones.

By reducing the slope of the power potential gradient, the power level of the stringbed is more uniform, so depth control is greatly improved.

I believe this is one reason why many pros prefer to use "pro stock" frames that start with a SW of 280, then weight them up with multiple layers of lead under the bumper.

And it is why my favorite midplus frames are my highly customized cutdown POG LBs. After cutting down to 26.7", they start out with SW in the 270s. But I have them leaded to about 365 SW, with none of the hoop weight below 3 and 9.

This makes the hoop of these racquets more polarized. The more polarized the hoop, the closer to the throat the counterweight must be placed to achieve the same weight, balance, and SW. Placing the counterweight closer to the bridge increases the dynamic stiffness. Thus, if two frames have the same weight, balance, and SW, the frame with the more polarized hoop will play stiffer and hit a flatter, crisper ball, but it will have a more uniform stringbed response too.

My cutdown POG LB with polarized hoop (and coutnerweight near top of handle) plays crisp, similar to a leaded frame with 67 RA, even though it is actually a flexible frame.

I AGREE,AND NOTE THAT EVERY TIME THAT I HAVE CUT A FRAME HANDLE DOWN 3/4 INCH OR 1 INCH ; THAT THE FRAME SEEMS ,TO ME, TO DO EVERYTHING BETTER. FASTER AT NET,BETTER SERVING, BETTER GROUNDIES, JUST BETTER OVERALL. I DIDN'T KNOW WHY. I WILL HAVE TO READ MORE ABOUT THE POLARIZATION PRINCIPAL, THANK YOU.

 

[edman9898]

I will man up and say that I sold this racquet to Pyrokid about 3 or 4 weeks ago. It was beat up but it did not have ANY cracks nor had any been painted over. The racquet had NEVER been thrown or hit on the ground intentionally one time, EVER! If it had cracks, I would happily have taken it back, but I was not told of anything. I actually played this racquet up until the week I sold it, with no issues whatsoever. I do not have one negative feedback, so people reading this please do not let it persuade you in dealings with me.

Pyrokid - If you did believe it was cracked, you should have contacted me. However, thanks for not putting my name out there without contacting me. That shows integrity on your part.

 

[pyrokid]

I will man up and say that I sold this racquet to Pyrokid about 3 or 4 weeks ago. It was beat up but it did not have ANY cracks nor had any been painted over. The racquet had NEVER been thrown or hit on the ground intentionally one time, EVER! If it had cracks, I would happily have taken it back, but I was not told of anything. I actually played this racquet up until the week I sold it, with no issues whatsoever. I do not have one negative feedback, so people reading this please do not let it persuade you in dealings with me.

Pyrokid - If you did believe it was cracked, you should have contacted me. However, thanks for not putting my name out there without contacting me. That shows integrity on your part.

NONONONONONOnonono it wasn't you, don't worry. I bought about six of these at the same time, yours wasn't the bad one. Yours was great.

On an unrelated note, here's a cross section I did after school. I can't find my regular camera though, so it's a phone pic... Sorry. You can still see the Kevlar weaving. It looks exactly like the one of the KPS88.

 

[edman9898]

Phew, good. I truly felt bad for you, but knew that the racquet was fine when I shipped it (although it is ugly) It does show what kind of person you are though by not posting his name.

 

[pyrokid]

Phew, good. I truly felt bad for you, but knew that the racquet was fine when I shipped it (although it is ugly) It does show what kind of person you are though by not posting his name.

Well I'm currently Emailing back and forth to try and see if he knows about the crack. It's looking like he didn't, and he's offering me a refund, even though the racket is now in pieces, so I truly believe it was an accident.

If he didn't offer a refund or at least apologize, though, I probably would have to post his name, just to make sure other people were warned.

 

[corners]

On an unrelated note, here's a cross section I did after school. I can't find my regular camera though, so it's a phone pic... Sorry. You can still see the Kevlar weaving. It looks exactly like the one of the KPS88.

Thanks a bunch Pyrokid.

 

[faultfoot]

NONONONONONOnonono it wasn't you, don't worry. I bought about six of these at the same time, yours wasn't the bad one. Yours was great.

On an unrelated note, here's a cross section I did after school. I can't find my regular camera though, so it's a phone pic... Sorry. You can still see the Kevlar weaving. It looks exactly like the one of the KPS88.

Just amazing stuff. Thanks for taking the time and effort to share with all of us. Really great!

 

[pyrokid]

Just amazing stuff. Thanks for taking the time and effort to share with all of us. Really great!

No problem, if I'm going to see it myself, might as well share it.

Also, I peeled off that layer with the graphite/kevlar weaving, and it's the only one. Underneath it's just graphite.

 

[corners]

No problem, if I'm going to see it myself, might as well share it.

Also, I peeled off that layer with the graphite/kevlar weaving, and it's the only one. Underneath it's just graphite.

Hey Pyrokid, When you find your camera would you mind posting some more pics of that? I'm curious exactly what this double braiding actually means. Is it two layers of braiding, both of equal thickness, or what....?

I suppose since the outer layer is probably bonded very tight to the paint that you can't really peel that out and compare thickness with the inner braid, but some kind of comparison pics, or whatever you can manage, would be very cool.

Thanks again.

 

[pyrokid]

Hey Pyrokid, When you find your camera would you mind posting some more pics of that? I'm curious exactly what this double braiding actually means. Is it two layers of braiding, both of equal thickness, or what....?

I suppose since the outer layer is probably bonded very tight to the paint that you can't really peel that out and compare thickness with the inner braid, but some kind of comparison pics, or whatever you can manage, would be very cool.

Thanks again.

The racket is actually about 12 or so layers thick, with all of the layers being double braided.

 

[paul_tennis]

Cool pictures of the K90!

 

[Don't Let It Bounce]

I will man up and say that I sold this racquet to Pyrokid about 3 or 4 weeks ago. It was beat up but it did not have ANY cracks nor had any been painted over. The racquet had NEVER been thrown or hit on the ground intentionally one time, EVER! If it had cracks, I would happily have taken it back, but I was not told of anything. I actually played this racquet up until the week I sold it, with no issues whatsoever. I do not have one negative feedback, so people reading this please do not let it persuade you in dealings with me.

Pyrokid - If you did believe it was cracked, you should have contacted me. However, thanks for not putting my name out there without contacting me. That shows integrity on your part.

And, though it turned out to have been someone else's K90, this post shows integrity on yours.

 

[BagelMe]

DAM!

I should do this to one of my broken N90's ....lolll

 

[5gpc9]

Now I knew what the inside of my racquet,K90 looks like. GREAT sharing !!!Thanks for your picutres,