# Why is this guy hammering these Toishi?



## Eamon Burke (Jul 8, 2012)

[video=youtube;hSxk9fa92l0]http://www.youtube.com/watch?feature=endscreen&NR=1&v=hSxk9fa92l0[/video]

What gives?


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## sachem allison (Jul 8, 2012)

listening for cracks and flaws. The sound will change if there is a hidden crack.


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## GlassEye (Jul 8, 2012)

I will be disappointed if Maxim's next video does not have some stone hammering.

This is not something I will be trying at home.


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## markenki (Jul 8, 2012)

Is that what those hammers are for? Interesting.


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## Lucretia (Jul 8, 2012)

It's a pretty darn good way of finding defects. 

Back in the dark ages when I worked on the Atlas Centaur rocket program, the rocket had a nose cone (fairing) made out of fiberglass honeycomb sandwiched between solid sheets of fiberglass. The air in the honeycomb is at sea level/atmospheric pressure, and when the vehicle was launched, as it moved into space and external pressure approached a vacuum, the air in the honeycomb would push outward against the fiberglass skin. If there were large enough areas where the skin wasn't attached well to the honeycomb, the fairing would tear itself apart.

There was a lady with a well-trained ear that they used to fly from Houston to Cape Canaveral to do a "coin-tap" test--basically rap the entire fairing with a hammer and listen for voids where the skin wasn't attached to the core. Not high tech, but effective.


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## maxim (Jul 8, 2012)

Harder stones have different density and different sound when hammering on them, it is a way to test how hard/fine stone is.


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## brainsausage (Jul 8, 2012)

Lucretia said:


> It's a pretty darn good way of finding defects.
> 
> Back in the dark ages when I worked on the Atlas Centaur rocket program, the rocket had a nose cone (fairing) made out of fiberglass honeycomb sandwiched between solid sheets of fiberglass. The air in the honeycomb is at sea level/atmospheric pressure, and when the vehicle was launched, as it moved into space and external pressure approached a vacuum, the air in the honeycomb would push outward against the fiberglass skin. If there were large enough areas where the skin wasn't attached well to the honeycomb, the fairing would tear itself apart.
> 
> There was a lady with a well-trained ear that they used to fly from Houston to Cape Canaveral to do a "coin-tap" test--basically rap the entire fairing with a hammer and listen for voids where the skin wasn't attached to the core. Not high tech, but effective.



I love stories like this. Weird background stuff that you never realize is making an impact. No pun intended. Fun video too.


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## Cipcich (Jul 8, 2012)

Lucretia said:


> It's a pretty darn good way of finding defects.
> 
> Back in the dark ages when I worked on the Atlas Centaur rocket program, the rocket had a nose cone (fairing) made out of fiberglass honeycomb sandwiched between solid sheets of fiberglass. The air in the honeycomb is at sea level/atmospheric pressure, and when the vehicle was launched, as it moved into space and external pressure approached a vacuum, the air in the honeycomb would push outward against the fiberglass skin. If there were large enough areas where the skin wasn't attached well to the honeycomb, the fairing would tear itself apart.
> 
> There was a lady with a well-trained ear that they used to fly from Houston to Cape Canaveral to do a "coin-tap" test--basically rap the entire fairing with a hammer and listen for voids where the skin wasn't attached to the core. Not high tech, but effective.



A great story. I don't know what i could add. Maybe i'll start tapping on things/people listening for voids . . .


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## Eamon Burke (Jul 8, 2012)

I figured it was to find faults in the stone, but who cares? Thay doesn't denote performance, does it?


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## maxim (Jul 8, 2012)

It is not to find faults in the stone, its for finding out hardness of the stone


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## sachem allison (Jul 8, 2012)

sorry,my bad. when we work with stone, we always check for the soundness of the stone by tapping it with a hammer. just assumed he was doing the same thing . sorry for my misinformation.


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## Eamon Burke (Jul 8, 2012)

Right, but I mean, does this equate to a useful evaluation? Should I start whacking natural stones when I see them to see if they are dense or not?


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## sachem allison (Jul 8, 2012)

no whacking, just tapping gently.


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## Eamon Burke (Jul 8, 2012)

Lol I was kidding. But seriously, is this a way we can find out if a stone is a good fit for us without using it?


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## maxim (Jul 8, 2012)

Nehh i will not test them like that, you will need to know all sounds from different stones to know what is good and there are also feeling, how stone feels on the knife.
So it is very approximate guess how hard stone is. And like sachem allison says there may be some lines or cracks that can blok for some sounds.


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## Cutty Sharp (Jul 8, 2012)

I've no idea how long natural stones may take to wear down through sharpening use - if ever - but maybe someone experienced with this can get a feel for if there any inconsistencies within a stone, and thus judge quality based on how a stone wears? Certain stones might also have hidden cracks/lines inside and not seen on sides, and even be more liable to crack over time through use when given pressure or not supported well when sharpening? 

.. I'm just speculating, but interesting to think about. I've just got one nat stone and am wondering what to expect from it over time.


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## Tristan (Jul 8, 2012)

Cutty Sharp said:


> I've no idea how long natural stones may take to wear down through sharpening use - if ever - but maybe someone experienced with this can get a feel for if there any inconsistencies within a stone, and thus judge quality based on how a stone wears? Certain stones might also have hidden cracks/lines inside and not seen on sides, and even be more liable to crack over time through use when given pressure or not supported well when sharpening?
> 
> .. I'm just speculating, but interesting to think about. I've just got one nat stone and am wondering what to expect from it over time.



Yes, that is the question that is in my mind. When you use a stone over the years, will the figure change significantly? Does Renge or karasu figure change as you go a few mm deeper? And will this change the way a stone works?

How about non toxic surface lines, will they become more 'toxic' past the surface if their mineral composition changes?


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## mainaman (Jul 8, 2012)

sachem allison said:


> sorry,my bad. when we work with stone, we always check for the soundness of the stone by tapping it with a hammer. just assumed he was doing the same thing . sorry for my misinformation.


I believe the stones are tested for cracks when they are still slabs before cutting, the sound when tapping can give some idea of hardness.
One can't tell how good the stone is by tapping on it , one will have to put steel to the stone to determine the quality.


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## maxim (Jul 9, 2012)

You have no way of teling it really not for 100 % at least. You have to look on the sides and bottom of the stone if it is uniform, but also many lines or inclusions that is not toxic. So it can also be misleading. 
Karasu or range patterns do not add very much to the stone. But they look very cool  

General if you buy quality stones, they are very uniform hardnes true whole stone, so it will not change to much by performance.



Tristan said:


> Yes, that is the question that is in my mind. When you use a stone over the years, will the figure change significantly? Does Renge or karasu figure change as you go a few mm deeper? And will this change the way a stone works?
> 
> How about non toxic surface lines, will they become more 'toxic' past the surface if their mineral composition changes?


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## Cutty Sharp (Jul 9, 2012)

Though I know mining of natural stones has curtailed a lot these days, do you - Maxim or anyone else - know if new stones or, I guess, old ones are now tested in any other way? Easy to imagine tapping as one traditional way to assess quality. But these days, there must be some devices/technology (more advanced than the hammer) that they can use to give a good idea.


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## wsfarrell (Jul 9, 2012)

Though I'm not a dealer in stones, my thinking matches sachem's on this: he's testing for cracks. Notice he holds the stone at the very top, allowing maximum vibration. Then he taps down low, near what looks like a line, then higher, then back down low. If a crack went all the way through the stone, the vibrations and sound would be very different depending on where you tapped--as in finding studs or space shuttle defects. 

Seems to me the only real test for hardness/fineness is putting a blade on the stone.


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