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PostPosted: 08 Oct 2014, 06:44 
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This is a nebulous yet ubiquitous term that's annoyed me for a while because blades don't flex. To prove this to yourself do the following simple experiment: push down with ~10lb of force each on a rubber and a blade, then compare how much each deflect. The discrepancy is quite large: rubbers move around a lot, and blades hardly at all; a very poor signal to noise ratio if we're looking for signal from the blade. This is would be the best case scenario since on closed-face loops where this flex is supposed to manifest most of the force is parallel (and not into) to the blade and into the rubber instead.

One possibility or at least contributing factor is that fast (technically: elastic) blades are stiff as a matter of how physical materials work, so laymen will tend to choose "flexible" as the antonym to "stiff" (instead of less-stiff) simply as a matter of semantic description. However this seems a bit unsatisfying so let's provide blade reviewers with benefit of the doubt that they do feel something other then general lack of stiffness (ie slowness), and search for what is actually "flexing" in those always mentioned loop strokes. The experiment above on the relative movement of rubber vs blade provides a hint. The other hint comes from the observation that in fancy blade reviews "flex" is usually associated with "catapult" as if it's the flex which provides the elasticity, or something that needs to be "activated" on high speed loops. These terms all seem technical nonsense, but let's see if we can make physical sense out of it.

First, let's look a bit at what happens to pips in a spin stroke (fig 2):
Image

The cylindrical shape deforms and rebounds. On loop/drives with very high speed of contact there's a distinct "bite" feel as the rubber's pips nears their limits of mechanical deformation against the sponge (ie "bottoming out" but not quite). It's not like hitting a wall but rather more & more nonlinearity compared to the norm on faster and faster contact. This "bite" of rubber deformation gradually nearing its stops (and the whole bat moves around more than usual in your hand) can easily be felt as a sort of "flexing catapult". Higher level players who tend to swing hard should all have felt this, and for everyone else just try it yourself but swing like you mean it.

But then the question is if it's a function of the rubber why do slow (ie thin) blades supposedly "flex" more. I believe there are two main factors involved:

1. This bite is more clearly felt on wood blades which tend to transmit more of the sensation (dampens less) than composites, which is why wood blades of equivalent elasticity (ie speed) to a composite are said to "flex" more, even if the resulting shot is the same. This is also better felt on thinner less stiff blades which tend to transmit this sensation more, thus the "flexible" looping blade.

2. Another factor comes from observing how blade speed relates to skill level. Generally speaking a 20% faster blade still means ~20% more precision/timing is necessary to land that 20% faster shot. Since humans can't simply dial up more precision/skill on demand (if only!), they tend to slow down the stroke to regain the same timing/control they're used to. This means less contact speed on the rubber which is what invokes this phenomenon in the first place.

The other interesting observation is that it does take a good fast swing to "activate" this physical sensation, more so than intermediate players using a composite can generally pull off. So it's left as an exercise to the reader what less than high level blade reviewers are talking about when speaking of flex.

Mystery solved? IMO yes.


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PostPosted: 08 Oct 2014, 07:44 
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I don't know about your blades but mine flex with finger pressure a lot!. You can see it, you can feel it and it's definitely real. My blades bend quite a lot more than is possible from the rubber. The rubber is stuck to wood so it can't move much. The blade on the other hand can bend as far as it wants depending on how fast its accelerated and how hard is the impact until it snaps.

Of course its not going to snap until its bent more than 10mm and no one can swing that fast. Weight of the rubber is a major factor in how much the blade flexs, not much happens with ox on one side.

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PostPosted: 08 Oct 2014, 07:55 
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I have a Yinhe W6 on my desk right now (a "flexy" blade) with Med rubber mounted on one side. I'm pressing on the center while holding the edges and there's no visible bend to the blade surface while the rubber deforms significantly.

The other factor I considered was that reviewers are referring to the very slight bending at the neck of the blade where the wood is the thinnest. However this makes little sense given:

1. This can only happen for SH grip if the user doesn't grip the face much (PH is largely gripped on the edges and surface), yet I've never seen blade flex referred to as a SH only phenomenon even though this discrepancy would be very obvious. Eg. Penholder: "hey, how come I've never felt any flex?". Even for SH, those who use a loose grip and pinch the blade wouldn't get the flex; again a large distinction unheard of from those who are supposed connoisseurs. More importantly does that mean whatever flex does for handle-death-grippers doesn't happen for everyone else?

2. If this were the significant factor, then there's plenty of money to be made in offering fast but "flexible" blades which are weak at the neck. In fact yasaka did this with their gimmick "3D" models, and it didn't sell well at all. Funnily enough you can get 3d models in penhold.


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PostPosted: 08 Oct 2014, 09:12 
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I have an 88 gram stiga all round classic and a donic allplay 85 gram. The stiga all round flexs more than the donic and can take a lower throw rubber e.g. Something like a stiga magna TC that works well on the stiga but didn't work well on the donic requiring a better technique.
A 7 ply xiom solo 88 gram that I recently gave away flexed more easily than a 90 gram stiga clipper and required a higher skill to use the clipper. Solo had an aged max T05 whilst the clipper had a new 5Q VIP. This was confirmed by a talented youth in the club. He has stuck with the clipper that the coach recommended but played better in the short time he used the solo.
A 89 gram innerforce ZLC is the one blade that I have that's prone to catapulting and takes a lot of concentration to keep landing balls on the table with a max T05. A heavier 94 gram IF ZLC is more stable and does not seem to catapult to the same extent. The lighter blade is faster in the right hands. The heavier blade is limited as to what thickness / weight rubbers since I now prefer a setup that's under 185 grams.
So that's my understanding of flex and catapult.

P.s. Fast flexible blade - xiom v1 ?


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PostPosted: 08 Oct 2014, 12:18 
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Unless you hold the edges of your blade while playing I'd suggest pressing the blade while holding the handle on a flat surface :). Xiom v1 isn't flexible. The Stiga allround and donic allplay are moderately flexible. Still a long way from a true flexible blade. Some W6s are flexible but still its no 5.0mm Stiga Alser or OSP expert.

The bend isn't only at the neck, it should bend across the length of the blade if its built correctly. I saw a guy show me a 1970s stiga offensive and it could bend like a banana, a work of flexible art. Those things loop like you are playing with a sheet of rubber not wood. You never forget how it feels, almost impossible to miss.

A good 5.0-5.3mm will give you a very pronounced KICK through your hand on contact with the ball. Its something so obvious you can't mistake it. The stiga allround and donic allplay don't do that because they don't have that same hardness/spring in the wood you need to get the wood to flick back.The black limba on the osp works well and so does koto. But you dont get the effect with soft absorbent wood. You also don't feel it well with a very soft handle.

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PostPosted: 08 Oct 2014, 12:55 
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> The bend isn't only at the neck, it should bend across the length of the blade if its built correctly
> Unless you hold the edges of your blade while playing I'd suggest pressing the blade while holding the handle on a flat surface

If you do this with the neck in play it bends a little, if you hold the edges or any other way with the neck out of the picture it doesn't bend much at all. Logically, what does that tell you about which part is bending?

Many players pinch the blade face with soft grip on the handle (ie. no neck bending) and seem to loop the same as griping only the handle. Penholders seem to loop just fine with some of the best topspinners in the world. What does that imply about the contribution of that bending at the neck?

Perhaps the most convincing evidence is whether it's possible to hold the blade so hard in the hand (that's how we play TT) that the neck can be flexed in any meaningful way. It's certainly possible to push and deform the rubber while holding racket, but there's a reason a vice is needed to demonstrate even the neck bend.

It's also worth re-iterating that as a matter of geometry when closing the blade face very little impact is aligned into the blade during a loop. The majority is pushing sideways into the rubber. The rubber is literally the vast majority of a loop by definition; otherwise the ball cannot spin so much.


> The stiga allround and donic allplay don't do that because they don't have that same hardness/spring in the wood you need to get the wood to flick back

Those are nearly the thinnest/softest/slowest blades on the market, slower than most def blades, meaning about every blade in practice has insignificant flex by this definition. If the flex referenced in blade reviews of commercial products have any concrete manifestation, this certainly isn't it.


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PostPosted: 08 Oct 2014, 13:35 
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You have to loop with an open face and forward swing to induce the blades flex. There isn't enough force on it otherwise, all part of the game and why there's an extra degree of difficulty using a bendy blade. Anyway its real so I'm not going to argue about it, you'll figure it out in your own time :). You'll be happy when you do if you are a looper. There's a huge difference in swing speeds between players too, my arm speed is possibly twice that of anyone else in my club so I doubt they get anywhere near the kick from the blade I feel although some of the better players have commented on feeling the kick when using my osp expert as a first impression. So they can feel something even if its a little bit only.

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Last edited by foam on 08 Oct 2014, 13:38, edited 1 time in total.

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PostPosted: 08 Oct 2014, 13:36 
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This is what I think is going on (a theory).

Clearly you feel vibrations in your hand when you hit the ball, so the blade moves and bends as a result of ball impact. The vibrations are occurring at several frequencies simultaneously since it is not a tuning fork or even a violin. With different materials in the blade and handle, and for that matter the shape and size of the head, the power contributed by various impact-evoked vibrations that you detect in your hand is different. So if you were to analyze all of the fluctuations in the blade and break them down by frequency -- to determine the power spectrum of the vibrations -- a relatively larger part of the variance is contributed by lower frequencies than by higher frequencies in blades that feel a bit more "flexible". Conversely, if those lower frequency components were relatively less important, the blade would feel more stiff. Blades filter the frequencies evoked by impact in many ways. Adding materials like arylate-carbon weave in some blades may reduce the low frequency vibrations but also some of the really high frequency vibrations, so the blade would feel stiff but soft. People are going to prefer some feel more than others, and also some materials are going to be faster. You can feel this because the ability of primate hands to sense vibration and texture is pretty exquisite. But my sense is that the impact that those factors have on how much spin you can impart on the ball are pretty minimal compared to the effect of the rubber -- the topsheet and sponge with all of the complexities of that.

I think this is pretty similar to what AgentHEX wrote minus the part about the influence of the rubber which I have to think about more but which reading quickly makes sense to me too.

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PostPosted: 08 Oct 2014, 13:58 
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foam wrote:
Unless you hold the edges of your blade while playing I'd suggest pressing the blade while holding the handle on a flat surface :). Xiom v1 isn't flexible. The Stiga allround and donic allplay are moderately flexible. Still a long way from a true flexible blade. Some W6s are flexible but still its no 5.0mm Stiga Alser or OSP expert.

The bend isn't only at the neck, it should bend across the length of the blade if its built correctly. I saw a guy show me a 1970s stiga offensive and it could bend like a banana, a work of flexible art. Those things loop like you are playing with a sheet of rubber not wood. You never forget how it feels, almost impossible to miss.

A good 5.0-5.3mm will give you a very pronounced KICK through your hand on contact with the ball. Its something so obvious you can't mistake it. The stiga allround and donic allplay don't do that because they don't have that same hardness/spring in the wood you need to get the wood to flick back.The black limba on the osp works well and so does koto. But you dont get the effect with soft absorbent wood. You also don't feel it well with a very soft handle.


OK, perhaps we can settle this with some photos. Perhaps someone can post a picture of a blade where the handle is being held tight on a flat surface and which is being bent by a force applied to the blade. So what blade would I need to perform this experiment? I see Stiga Alser and OSP Expert being mentioned, maybe I'll go get one and see if I can generate such photographs. I was going to get a Stiga Allround but it's supposedly only "moderately flexible".

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PostPosted: 08 Oct 2014, 13:59 
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foam wrote:
You have to loop with an open face and forward swing to induce the blades flex. There isn't enough force on it otherwise, all part of the game and why there's an extra degree of difficulty using a bendy blade. Anyway its real so I'm not going to argue about it, you'll figure it out in your own time :). You'll be happy when you do if you are a looper.


I believe that's called a drive, and I already do it for higher or longer balls. :)

Slower blades with a greater margin for error make all fast spin strokes easier, but it's that faster swing which makes them powerful.

Quote:
There's a huge difference in swing speeds between players too, my arm speed is possibly twice that of anyone else in my club so I doubt they get anywhere near the kick from the blade I feel although some of the better players have commented on feeling the kick when using my osp expert as a first impression. So they can feel something even if its a little bit only.


I also happen to be a super-fast swinger (that came out wrong :)) so our experiences are probably similar on this. So I can confidently claim you're feeling the rubber bottoming out/bite (it gets harder the faster you swing as the material crunches together) and not the blade flex.

I recall we had this discussion about whether it's possible to generate high spin with a fast blade, so it makes sense that you said it wasn't possible. Recall my claim was that it's only near-impossible for club level players, but quite possible with enough skill. It's pretty hard to control the blade angle precisely enough when swinging fast (as you would need with a composite blade) because your muscles are either loose or oriented for the swing instead of control, so I get where you're coming from.


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PostPosted: 08 Oct 2014, 14:12 
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Baal wrote:
This is what I think is going on (a theory).

Clearly you feel vibrations in your hand when you hit the ball, so the blade moves and bends as a result of ball impact. The vibrations are occurring at several frequencies simultaneously since it is not a tuning fork or even a violin. With different materials in the blade and handle, and for that matter the shape and size of the head, the power contributed by various impact-evoked vibrations that you detect in your hand is different. So if you were to analyze all of the fluctuations in the blade and break them down by frequency -- to determine the power spectrum of the vibrations -- a relatively larger part of the variance is contributed by lower frequencies than by higher frequencies in blades that feel a bit more "flexible". Conversely, if those lower frequency components were relatively less important, the blade would feel more stiff. Blades filter the frequencies evoked by impact in many ways. Adding materials like arylate-carbon weave in some blades may reduce the low frequency vibrations but also some of the really high frequency vibrations, so the blade would feel stiff but soft. People are going to prefer some feel more than others, and also some materials are going to be faster. You can feel this because the ability of primate hands to sense vibration and texture is pretty exquisite. But my sense is that the impact that those factors have on how much spin you can impart on the ball are pretty minimal compared to the effect of the rubber -- the topsheet and sponge with all of the complexities of that.

I think this is pretty similar to what AgentHEX wrote minus the part about the influence of the rubber which I have to think about more but which reading quickly makes sense to me too.


In other words, it's not really flexing back and "storing energy" to be "released", it's simply vibrating when struck, which means really tiny, high frequency movements. I'm pretty much convinced this is what's being referred to as "flexy" - it's a feel, not the actual bending of the blade. Still, I'm curious to know what this really feels like, so I'm looking for a "genuinely flexy" blade, first, to see what this feel is like and second, to see if it'll actually bend. My thinnest blade here is a 5mm Palio 08 - it's the only one I can bend a little, and it bends at the neck, not along it's whole length.

Can't find the Stiga Alser blade on Stiga's website:

http://stigatabletennis.com/en/product-type/blades/

What series is it under? I looked up the OSP Expert:

http://ospblades.com/

Gee, that's WAY too much money. Anything cheaper that still flexes?

Iskandar


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PostPosted: 08 Oct 2014, 14:18 
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Baal wrote:
This is what I think is going on (a theory).

Clearly you feel vibrations in your hand when you hit the ball, so the blade moves and bends as a result of ball impact. The vibrations are occurring at several frequencies simultaneously since it is not a tuning fork or even a violin. With different materials in the blade and handle, and for that matter the shape and size of the head, the power contributed by various impact-evoked vibrations that you detect in your hand is different. So if you were to analyze all of the fluctuations in the blade and break them down by frequency -- to determine the power spectrum of the vibrations -- a relatively larger part of the variance is contributed by lower frequencies than by higher frequencies in blades that feel a bit more "flexible". Conversely, if those lower frequency components were relatively less important, the blade would feel more stiff. Blades filter the frequencies evoked by impact in many ways. Adding materials like arylate-carbon weave in some blades may reduce the low frequency vibrations but also some of the really high frequency vibrations, so the blade would feel stiff but soft. People are going to prefer some feel more than others, and also some materials are going to be faster. You can feel this because the ability of primate hands to sense vibration and texture is pretty exquisite. But my sense is that the impact that those factors have on how much spin you can impart on the ball are pretty minimal compared to the effect of the rubber -- the topsheet and sponge with all of the complexities of that.

I think this is pretty similar to what AgentHEX wrote minus the part about the influence of the rubber which I have to think about more but which reading quickly makes sense to me too.


There was a guy JRSDallas with I believe a srs bidness physics background who compiled a very readable report of theories relevant this to: http://mytabletennis.net/forum/forum_po ... ign#723973, specifically part 3 & 4.

None of it is scientifically novel, which is a good thing since it's pretty uncontentious. In short the frequencies are near directly correlation with the elasticity (ie speed) of the blade. Eg. more composite -> faster -> higher freq for each mode, though some dampening occurs so some freqs are attenuated (but not changed). Softer solid material does tend to be more "flexible" in a sense (that mechanical weakness is directly related to its slowness), but not in a way that can be felt in spin-shots for reasons stated.


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PostPosted: 08 Oct 2014, 14:27 
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iskandar taib wrote:
I'm pretty much convinced this is what's being referred to as "flexy" - it's a feel, not the actual bending of the blade.


For a while I thought it had to be the vibrations, too, even though I could never formulate any cohesive hypothesis of the specifics. Then I started hitting the ball much harder. Faster swingers (like foam, or high level players broadly) can definitely feel a flex-like sensation when the rubber pips buckle that doesn't come from the blade (but it does go through the blade with effects that I try to elucidate in the OP).

The slower (and more "flexible") the blade, the faster you can swing for a given skill level, so a positive feedback loop forms in the mind rationalizing the idea that the blade is accountable for this.


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PostPosted: 08 Oct 2014, 19:53 
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foam wrote:
Unless you hold the edges of your blade while playing I'd suggest pressing the blade while holding the handle on a flat surface :). Xiom v1 isn't flexible. The Stiga allround and donic allplay are moderately flexible. Still a long way from a true flexible blade. Some W6s are flexible but still its no 5.0mm Stiga Alser or OSP expert.


To put things in context of the blades that I have and have used the stiga all round classic was the most flexible and more so in the first one that I bought that only weighed 82 grams than the current 88 gram.

A description of the V1 from Xiom describes it as fast and speedy and thin at 5.4mm. One of the reviews refers to it as being flexible. I got the V1 off a club mate who sold it to me stating that it flexed too much when he was hitting hard with it. Personally I found that the flex in the blade made it an easy to use blade but for most it's too much on the fast side.
http://www.tabletennisdb.com/blade/xiom-v1.html

Catching up on the last few posts I've found that the Innerforce ZLC possibly vibrates too much particularly in the lighter 89 gram model and results in a blade that's prone to the catapult effect. Maybe there's too much going on with all the materials embedded into it. Comparing it with a xiom vega europe with it's jointless wood construction it seems to be more 'all together' although it has the downside of a blade that would be described as stiff. This stiffness results in having rubbers that are medium to medium high throw.


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PostPosted: 08 Oct 2014, 21:46 
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I always found it hard to believe that a tennis (!) racket would flex, until I saw some slow motion pictures (see below). Of course a table tennis blade isn't near a tennis racket and the impact of the balls aren't comparable...




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