question concerning sori on tanto

samuraistuart

samuraistuart

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Dec 21, 2006
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One of these days I'm going to make a "traditional" Japanese tanto out of this .25" W2 that I've had for a year or so. I have an old tanto from Japan, it is absolutely beautiful, and I would like to copy it......mas o menos. My skill set, and equipment, is limited compared to most of you guys. However, one of these days I'm going to give it a go. Complete with sa'me (rayskin), the diamond pattern wrapped tsuka, an iron tsuba, copper fuchi and menuki, the wooden saya...the whole bit. This is a project at least a year away. I will not be doing the heat treat on this one, as I'm only set up for 1084 and shorter hunting type blades. I understand that katanas (much longer than the tanto) are forged with very little to zero sori (blade curve). They're forged practically straight, true? The sori comes during the quench. There is a video online, I'm sure you katana lovers have seen it, where a katana is quenched in a clear glass tank. Unbelievably, as soon as the blade is placed into the water, the tip of the katana actually bends DOWN....quite a bit, before it bends back UP into the classic curve of the katana. Weird!

So the question.....if I make this tanto (stock removal....W2....clay coated.....professionally heat treated), do I "machine" the blade straight, or with a slight upward curve already? Not being as long as a katana is, I'm not sure which way at all to procede. I've included a pic of the Japanese tanto for fellow Japanese blade fans.
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If the "professional heat treat" is to be a water quench, then leave it straight. If they are doing an oil quench in fast oil, grind in the sori desired.

It is often best to leave a little extra width to the blade to allow adjustment of the sori by grinding it to more or less curve after HT.
 
Ah, yes! Thanks, Stacy! I even forgot.....longer blades react differently to oil vs H20 quench. And the tip on "machining" extra width into the blade is well received and understood.

I've heard that a water quench will cause the curve up, but an oil quench does the opposite and curves down. I suppose on something shorter than the katana and waki, the oil quench is NOT going to cause a negative sori on the shorter tanto length blades.....correct? In other words......since this is a tanto sized blade.....the oil quench will not cause it to curve down on me? I'm like Sgt Shultz, "I know nothing, I see nothing, I was not even here!!!!!!"
 
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You are correct. In a short blade, the differential in contraction and expansion of the martensite and pearlite is insignificant. On a long enough blade, you can get some tip drop with an oil quench, but this is far less than the drop/rise in yaki-ire. OI adjust the sori if needed right after the interrupted quench, while the blade is still austenitic.

And the phrase you want to know is Shator didi...nadidi ( I saw nothing!) Look it up.
 
Shotor didi nadidi

I looked it up.....and that looks like a can of worms. You can ride a camel humpback, but not underground. You can't ride a camel humpback. You have seen the camel...but no you haven't. It also means...forget about what you think you've learned. Oh boy....what rabbit hole is this?

Very cool!
 
I've gotten a fair amount of negative sori on quasi-Japanese style blades around 12", forged from 5160 and quenched in canola. How much that's going to apply to your situation I can't say.
 
Shator didi, nadidi ( Farsi) - It means "You saw a camel? - you didn't see it!" It is exactly what Schultz meant when he said, "I saw nothing!" or " I know nothing!". It also can mean, "I don't know what you are talking about?"

If I handed you a piece of wood off my table at a show, and you asked what you owed me for the wood, I would say, "Shator didi, nadidi"....meaning "What wood?"
 
I say grind it curved for a different reason. You may run in to the same problem as me. I worked and worked and worked on one. Then it came time to heat treat. After all that work I just couldn't roll the dice in water... so I have a tanto as straight as an arrow.
 
I was getting "tip dip" on my Japanese inspired tanto/dirk blades while quenching in a vertical tank with HQ-K(roughly equivalent to P50). There are several ways of addressing that issue. Stacy mentioned a few. I switched to a horizontal tank and quench spine down. You can also leave some thickness on the edge at the last few inches of the tip. You will find that the negative sori mostly happens to blades with that shape and geometry... anything with a clip or false edge is usually safe.

I can't advise you on how to achieve a proper sori through water quenching, but I can share my experience in avoiding the wrong kind when quenching in oil.
 
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