# Time to make a knife?



## oivind_dahle (May 26, 2011)

I wonder how long time it takes to make a knife?

The reason Im asking is that Im planning my next purchase and came across this yanagiba (that I want bad...)
http://www.sushitrainer.com/japaneseknives/nenohimaru.php

And here I found:
The reason it takes 180 days for blades, is because at least 120 days are required to let the steel sit and stabilize aging.

So bladesmiths of the forum: How long does it take to make a knife? Should it at least be in your hands at least 120 days?

Inputs please.... How long do you wait to deliver to customer? Or is this just ******** from NENOHIMARU ????


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## Potato42 (May 26, 2011)

It seems to be an urban legend that steel somehow has changing properties after it sits a bit. I've read that some Japanese chefs use two sets of knives and allow one set to sit for a day or so after sharpening...

If I wanted a straight answer about steel the first place I'd turn is Larrin/Devin Thomas.


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## watercrawl (May 26, 2011)

Whether the resting period that Nenohi says is required is BS or not I can't comment on. 

As a complete newbie doing stock removal knife making, I'll provide my input:

30 minutes to cut out and shape a blade blank
Don't have a heat treat oven, but I've heard it takes a couple of hours
3 hours to grind a blade to shape
1 hour to drill, shape, and peen the bolsters in place
30 minutes to cut out the scales and drill the necessary holes
30 minutes to mix the epoxy and put the scales onto the knife.
1 hour to shape the handle once the epoxy is dry
2 hours to damn near infinity to finish everything off. I swear I have to force myself to send out knives once they're done as I keep finding little things I want to tweak, resand, etc. 

So...10 or so hours including time to heat treat. It's obviously not done in one day though.


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## Potato42 (May 26, 2011)

watercrawl said:


> It's obviously not done in one day though.


 
Unless you're Hoss, and you decide you want to make an edged implement to use that evening. I think he might have super powers...


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## rockbox (May 26, 2011)

Potato42 said:


> It seems to be an urban legend that steel somehow has changing properties after it sits a bit. I've read that some Japanese chefs use two sets of knives and allow one set to sit for a day or so after sharpening...
> 
> If I wanted a straight answer about steel the first place I'd turn is Larrin/Devin Thomas.


 
I don't think it is BS. I had this conversation with Devin about this when I was at his shop. Complete austenite to martensite transformation can take a long time, but this can be sped up with Cryo treating the blade. Since Japanese makers are very traditional, they don't use cryo treatment and need to wait a long period of time for the steel to settle.

Edit:

I think this is the reason Bill Burk sticks his blades overnight in the freezer between quenches.


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## Potato42 (May 26, 2011)

Yeah urban legend was probably the wrong choice of words. I don't know why you'd need to let blades sit after sharpening though.


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## JohnnyChance (May 27, 2011)

Potato42 said:


> Yeah urban legend was probably the wrong choice of words. I don't know why you'd need to let blades sit after sharpening though.


 
As an excuse to significant others why one need knives of the same size or type. "Baby, OF COURSE I need two 270mm gyutos! If I sharpen this one today, I cant use it until the day after tomorrow!"


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## oivind_dahle (May 27, 2011)

I didnt know Burke put the knives in the freezer. Ill ask him why 


I was hoping some of our smiths answered this too


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## rockbox (May 27, 2011)

Potato42 said:


> Yeah urban legend was probably the wrong choice of words. I don't know why you'd need to let blades sit after sharpening though.


 
No reason after sharpening, but plenty of reasons after heat treat.


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## DevinT (May 28, 2011)

It is about transforming the retained austenite into martensite. 

Time, subzero quenching, and artificial aging are all used to make the transformation. Austenite is a smaller phase then martensite. If the blade is straight and has retained austenite that then transforms to fresh martensite the blade will move or become crooked.

Thanks Sean for the compliment. I'm probably faster than most. It's only taken me 33 years.

Hoss


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## tk59 (May 28, 2011)

There are a lot of these kinetically controlled processes. An extreme example is diamond spontaneously converts to graphite but it's so slow it basically doesn't matter. As for letting a freshly sharpened knife sit for a few days... Maybe they are looking to have some sort of patina begin to form so it is less reactive when they do get around to using it. Total speculation...


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## oivind_dahle (May 28, 2011)

Thanks for info .)


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## SpikeC (May 28, 2011)

DevinT said:


> It is about transforming the retained austenite into martensite.
> 
> Time, subzero quenching, and artificial aging are all used to make the transformation. Austenite is a smaller phase then martensite. If the blade is straight and has retained austenite that then transforms to fresh martensite the blade will move or become crooked.
> 
> ...


 
So what are the ramifications of this for the O1 blades that I'm making? I HT at 1500º, then temper at 350º for an hour, generally twice. Is the O1 going to change over time? The first blade that I did I HTed after grinding and it warped, after it was completed I took the handle back off and tempered again with the blade clamped to a heavy file and it is now almost straight. All together that blade was tempered 4 times. 
What I am now wondering is what am I going to have 3 months from now?


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## DevinT (May 28, 2011)

Lower austinetizing temperatures, faster heating rates, less soak times, subzero quenching, longer tempering cycles, faster quench rates can all reduce retained austenite.

I recomend that you grind less before HT. Quench from 1475f after soaking for 5 min. Quench in heated oil. Temper immediatly following the quench. 2x for 2 hrs each time. It is also good to go as cold as possible after the quench. You can go into the freezer directly after the oil quench for an hour. Of course it is best to do a full sub zero quench in liquid nitrogen or dry ice with acetone. 

Hoss


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## SpikeC (May 28, 2011)

I have stopped doing any grinding prior to HT on this last blade. I also did about 5 min. on the soak, but the temp was a bit higher. I'm confused about your comment regarding post quench, however. Tempering immediately after quench is what I'm doing, but where does the freezer fit in this sequence? 
Dry ice and acetone, eh? That must get the temp down pretty good! 
(When I was in the Army hospital in Japan after surgery, my temp went up to 106 and they packed me in ice and alcohol. Chills ya right down, boy howdy!)


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## rockbox (May 28, 2011)

dry ice and acetone makes liquid hydrogen.


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## DevinT (May 29, 2011)

Continous cool down is what you want. Then temper.

Hoss


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## tk59 (May 29, 2011)

rockbox said:


> dry ice and acetone makes liquid hydrogen.


 
Huh? Did I miss something?


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## rockbox (May 29, 2011)

tk59 said:


> Huh? Did I miss something?


 

Oops! I meant liquid nitrogen.


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## rockbox (May 29, 2011)

rockbox said:


> Oops! I meant liquid nitrogen.



I was wrong about that too. LOL,
Edit:

I guess its time for me to take a chemistry class again. Its been 20 years.


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## SpikeC (May 29, 2011)

I was wondering how to get that cold without liquid nitrogen, cool trick! I can't wait to start on the next one now, with a cryogenic treated blade!


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## l r harner (May 29, 2011)

LN = -300f ish 
dry ice and accatone is about -100f 

some have thought about seening what liquid He would do as its -400f


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## SpikeC (May 29, 2011)

I found this on "simply tool steel .com". Would this apply to O1?

It is recommended that one thermal temper cycle is performed on the tool before a cryogenic treatment is performed. Since the newly hardened and quenched tool is brittle, tempering prior to cryogenic treatment will reduce the chance of cracking due to stress induced during the process. At least one thermal tempering cycle should follow the cryogenic treatment in order to temper the newly formed martensite resulting from the cryogenic treatment.


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## DevinT (May 30, 2011)

Spike,

It doesn't do much good to cryo after tempering. Tempering before cryo stablizes the retained austenite and it will not convert to fresh martensite after that. 

The greatest benifit comes from a continuous cool down. Time and tempering cause the austenite to stablize. The steel needs to be subzero quenched within 5 min after the oil quench to get the most benifit.

Hoss


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## SpikeC (May 30, 2011)

Thanks, Hoss. I don't yet have access to liquid nitrogen figured out, but I see that the acetone/dry ice slurry provides about 50% of the benefit, which is still significant as far as toughness is concerned.


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## DevinT (May 30, 2011)

You will get the full benifit from the dry ice and acetone if you get the knife in there fast enough. With in about 2-3 minutes.

Hoss


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## SpikeC (May 30, 2011)

Thanks, I can do that!


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## SpikeC (Jun 8, 2011)

How long should the blade soak in the cryo bath?


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## SpikeC (Aug 17, 2011)

30 minutes, he said later!


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## Eamon Burke (Aug 17, 2011)

this thread rocks. :headbang:


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## SpikeC (Aug 17, 2011)

I'm getting ready to HT a blade, and I couldn't find this post. I had to look though a bunch of stuff to find it again because I didn't bother to write down the info!


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