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PostPosted: 27 Oct 2014, 01:54 
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The blade i got (the fake NCT) was pretty bad... Almost unusable.

Iskandar, I'd recommend the one you think to have best build quality, because after buying a lot of fakes, I realised that fake manufacturers don't necessarily try to copy the original so much as use the name of it to get more sales.


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PostPosted: 27 Oct 2014, 04:12 
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ZED wrote:
The blade i got (the fake NCT) was pretty bad... Almost unusable.

Iskandar, I'd recommend the one you think to have best build quality, because after buying a lot of fakes, I realised that fake manufacturers don't necessarily try to copy the original so much as use the name of it to get more sales.


Can you take a side shot of the layers and give approx total thickness?

This place likely makes those HRT copies of the stiga hardwoods and the reviews make it to seem they're faster than the stigas (6.2mm vs 5.8mm with thicker outers) but not "unusable" per se. I think the 5-ply versions might make ok substitute for the 7ply stiga. IMO still too fast for amateurs but then again people buy composite blades all the time.


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PostPosted: 27 Oct 2014, 11:52 
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There are some "side shots" on the web pages, but they're far from ideal (the ones posted on Eacheng's stores are a lot better). If I actually buy one (or more) of these things I'll definitely get the macro lens and digital calipers out. The "Korbel" has a thick core/thin face plies construction so at least we know it isn't cheap mass-produced bass plywood.

Why, one wonders, would a 6.2mm blade be faster than a 5.8mm blade? I guess we're assuming identical materials, of course...

Iskandar


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PostPosted: 27 Oct 2014, 12:03 
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ZED wrote:
The blade i got (the fake NCT) was pretty bad... Almost unusable.

Iskandar, I'd recommend the one you think to have best build quality, because after buying a lot of fakes, I realised that fake manufacturers don't necessarily try to copy the original so much as use the name of it to get more sales.


ROFL.. They've had 97 orders for that "Viscaria". Looking at the reviews, there's one that says it's plays very well. Most of the others give it five stars, but a lot of people will do that just because it arrived in three weeks. There are some I can't read (because they're in Russian).

So.. "Korbel" or "Primorac"? The "Primorac" is slightly cheaper and "slightly slower" :lol: based on the real Butterfly items. I'll bet build quality's identical since they probably came out of the same factory.

Iskandar


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PostPosted: 27 Oct 2014, 16:56 
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There's a side view here:

http://www.aliexpress.com/item/Free-shi ... 53259.html

They claim the thickness is 5.5mm.

Gosh, these things are everywhere. Try a search for "Butterfly Korbel" or "Butterfly Primorac" on AliExpress and see how many hits you get. Some people are selling them for a great deal more than $12.

Iskandar


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PostPosted: 27 Oct 2014, 19:32 
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iskandar taib wrote:
There are some "side shots" on the web pages, but they're far from ideal (the ones posted on Eacheng's stores are a lot better). If I actually buy one (or more) of these things I'll definitely get the macro lens and digital calipers out. The "Korbel" has a thick core/thin face plies construction so at least we know it isn't cheap mass-produced bass plywood.

Why, one wonders, would a 6.2mm blade be faster than a 5.8mm blade? I guess we're assuming identical materials, of course...

Iskandar


All things equal it's:

6.2^3/5.8^3
Ans = 1.221493296

~20% faster.

Side photos look ok, but thickness specs for these things are a crapshoot. Blades are hard to get wrong so it should be fine, and if really 5.5mm then probably the first true chinese ALL blade I've seen.


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PostPosted: 27 Oct 2014, 20:33 
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Yeah, but what's behind the correspondence between speed increase and increased thickness, where does the formula come from? Is there some principle of physics behind it? Would something twice as thick really be 8 times (800%) faster, and does this relationship extend to infinite thickness? And when you say 20% faster, what exactly does that mean?

I have a Chinese blade that's (eyeballing it) about 5.0mm thick - it's a Palio A08. Eacheng says 5.3mm, I'll get out the calipers tomorrow. Dark face, probably meranti or might be some other wood. By your calculations it should be a true ALL to ALL-. It didn't feel terribly slow when I tried it last, maybe I'll rubber it up again and give it another go.

http://www.aliexpress.com/item/Free-Shi ... 70496.html

I've got a "Primorac" on order - when it arrives (probably in three or four weeks) I'll post photos and measurements.

Iskandar


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PostPosted: 27 Oct 2014, 20:46 
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iskandar taib wrote:
Yeah, but what's behind the correspondence between speed increase and increased thickness, where does the formula come from? Would something twice as thick really be 8 times faster, and does this formula extend to infinite thickness? And when you say 20% faster, what exactly does that mean?

Iskandar


It's a general accurate empirically tested relationship. There are probably specific models for specific plates but the differences are going to be minor.

The metric is in relative stiffness, which also tends to correspond to various elasticity modulus. That more or less means you can hit 20% less hard for same exit speed. That may or may not be desirable in the game.


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PostPosted: 28 Oct 2014, 12:02 
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Who did the empirical measurements, and how was the quantification of effort vs. speed done? Is it published somewhere? I'm really curious about this because so much about table tennis equipment is very vaguely defined, and there are so many claims made, most of which seem to have as much validity as claims made for those magical water filters and "detox" treatments.

If the cube relationship is true then tiny differences in thickness will have profound impact on the speed of a blade. I can believe that the stiffness of beams would be proportional to the cube of the thickness, but how this translates to actual speed I can't imagine, since we've already determined that speed isn't caused by flex. Those Clipper blades must be absolute rockets.

Iskandar


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PostPosted: 28 Oct 2014, 12:36 
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This is one such (level of) theory:
http://en.wikipedia.org/wiki/Kirchhoff% ... verse_load

I've linked to the section with relevant derivation where X^3 relationship is clear. h is thickness and E is I think elasticity modulus and v some material attribute. This is a part of solid continuum mechanics which is one of many branches of physics which has been endlessly verified and refined through history. Eg this theory is from >100 years ago.

> I can believe that the stiffness of beams would be proportional to the cube of the thickness, but how this translates to actual speed I can't imagine, since we've already determined that speed isn't caused by flex.

Just because it's not "cause" by flex doesn't mean it isn't correlated. This isn't really related to anything I do but intuitively there appears some inverse relationship between this stiffness and a coefficient of restitution (where infinite stiffness corresponds to ideal restitution and zero stiffness to zero). By just looking at how much the ball bounces it seems to be in the middle of this where the relation is closest to linear. The "theory" of this is likely non-trivial unlike the idealized mechanics above and needs to be empirically determined to be exact but my naive guess shouldn't be off by too much, at least relatively speaking.

Btw you have the thickness of the Palio? I've found some of the chinese specs to be off.


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PostPosted: 28 Oct 2014, 15:02 
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&*%&^$^%$# batteries are dead. I'll have to dig up my vernier calipers, I think they're at home, or get more batteries. Eyeballing it with a ruler it does look like 5.3-5.4mm.

Modeling the blade as a deforming/oscillating flat plate would be OK if it were the only bending object in the system - in actuality the ball and the rubber would deform and bounce back far more than the blade does. So given the same rubber and the same wood, a blade twice as thick will NOT project the ball with 8 times the speed given the same amount of force applied.

Iskandar


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PostPosted: 28 Oct 2014, 15:18 
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iskandar taib wrote:
So given the same rubber and the same wood, a blade twice as thick will NOT project the ball with 8 times the speed given the same amount of force.

Iskandar


The overall COR is likely some multiplicative mash of ball & blade so both values need to be sane. Consider a ball bouncing off a suspended piece of paper, even with a rubber attached on top.

There's also more direct relationship around the middle of an inverse function (let Ball*Blade = X, and Y is COR):

http://www.wolframalpha.com/input/?i=-1 ... 1%29+%2B+1
Imagine a line tangential to that curve at X=1, its slope isn't too far from 1. It doesn't deviate too much from the function for some modest shift in Blade. So no 8 times more rigid isn't 8 times faster, but 20% more rigid is closer to 20% higher rebound (it may be 10%, 15% but close enough).


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PostPosted: 28 Oct 2014, 15:36 
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BTW, I took a look at JRSDallas's posts on wood properties:

http://mytabletennis.net/forum/forum_po ... ign#723964

And he assumes the blade rebound directly corresponds to frequency of first flex mode as if the blade "whips" the ball back out, which we know to be incorrect from empirical video & theoretical displacement models (rubber as spring). Though the way it looks like those equations work out it may coincidentally be an ok half-ass estimate akin to my "COR = -1/(Ball*Blade + 1) + 1".

I MSGed him and hopefully get a reply since he's ostensibly a legit physicist instead of me pretending to be. Though to be fair to me his meticulous calcs there are bit for naught.


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PostPosted: 28 Oct 2014, 17:33 
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Blade: Custom SoulSpin ALC blade
FH: Tibhar MX-P
BH: Xiom Omega V Pro
Have you notices the resemblance of some of the handles to other manufacturers...

The "viscaria" clone? is that implied by the handle? looks to me like thats the case. --- http://hzwes.en.alibaba.com/product/197 ... lenut.html

TBALC clone? --- http://hzwes.en.alibaba.com/product/197 ... lenut.html

TBS maybe? --- http://hzwes.en.alibaba.com/product/197 ... lenut.html

_________________
Custom SoulSpin Limba/ALC
FH: Tibhar Evo MX-P Max
BH: Xiom Omega V Pro Max


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PostPosted: 29 Oct 2014, 13:46 
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Palio A08: Half a dozen measurements taken around the edge of the blade varied between 5.38mm and 5.61mm (it looks like one side of the blade is slightly thicker than the other side). Average 5.49mm.

Just for the heck of it, another blade (Palio Chop No.1): 5.87mm - 6.11mm, average 5.96mm.

Iskandar


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