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Adjusting sori after HT?


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Given this situation I would just make a new blade, not much more effort than re-doing the heat treat. Otherwise, I think that, no matter what, you will have to redo the heat treat.

Edited by B. Norris

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The Japanese use a block of hot copper to do this. They place the mune

on the block and hammer carefully on the ha.

No idea how far you can change the sori that way,

I've never tried it...

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I myself have had ZERO success in trying to get more sori after hardening. It is either there or it's not. You can flatten one out a little bit without too much trouble (hammer the shinogi-ji some, carefully), but getting more has never happened successfully for me.

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Yup, read the book too but didn't have much success when I tried it either. I think I can afford to sacrifice a few millimeters of blade width on the stones to add some grace to my curve.

 

...well I guess thats one way to adjust sori it then. :P

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You MIGHT be able to get more sori by putting the blade in 3 point bending, and tempering while the blade is held by the fixture. THis has worked with landing gear (300M) and other aerospace components.....but the fixture will have to be pretty stout.....

D. Scott MacKenzie, PhD

Heat Treating (Aluminum and Steel)

Quenching (Water, Polymer, Oil, Salt and Mar-Tempering)

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You MIGHT be able to get more sori by putting the blade in 3 point bending, and tempering while the blade is held by the fixture. THis has worked with landing gear (300M) and other aerospace components.....but the fixture will have to be pretty stout.....

 

Scott, I suspect that you also had fairly uniform structure in the piece to be bent. The martensitic edge is already under some serious forces from the collapse of the pearlitic structure from martensite. It's arguable whether those are the compression forces internally above the hardening line or resistance to expansion along the edge. Changing sori is not like changing a warp. Trying to get more sori into a blade is going to be a frustrating experience for whoever tries it.

 

Better to go for the most sori possible and relax the blade back to where you wanted it. Even that is frought with problems.

There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves. Will Rogers

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The Japanese use a block of hot copper to do this. They place the mune

on the block and hammer carefully on the ha.

No idea how far you can change the sori that way,

I've never tried it...

 

From what I understand the tapping on the Ha is to make better contact with the Copper mass so the heat will transfer as fast as possible. The goal is to create an intense localized heat on the spine. Then the Blade is queanched. The localized contraction would induce more curvature. This technique is for Tamahagane blades. Steel made from sand has different behavior than modern steels. Often these techniques do not adapt very well to commercially made steels. Also the designs were often abit different. Modern steel lets you get away with shapes that are not as easily done Tamahagane. Thinner spines and higher Ha. This is a recipe for a fragile sword with Tamahagane. I think that many older swords during the quench were proportioned and clayed to make roughly 80 percent pearlite/ferrite mix with 20 percent martensite edge. The volume of soft steel in the spine allows for great pull on the relativly smaller volume of martensite. Today I see swords here in the west that approach 50/50. So much martensite distributed so high on the blade would not be very responsive to the old copper block treatment.

Just some opinions I stopped making swords years ago, but I still study technique and design of Japanese swords both old and new.

Personally I would make a new sword versus attempting to induce more curvature.

2cents for free,

patrick

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From what I understand the tapping on the Ha is to make better contact with the Copper mass so the heat will transfer as fast as possible. The goal is to create an intense localized heat on the spine. Then the Blade is queanched. The localized contraction would induce more curvature. This technique is for Tamahagane blades. Steel made from sand has different behavior than modern steels. Often these techniques do not adapt very well to commercially made steels. Also the designs were often abit different. Modern steel lets you get away with shapes that are not as easily done Tamahagane. Thinner spines and higher Ha. This is a recipe for a fragile sword with Tamahagane. I think that many older swords during the quench were proportioned and clayed to make roughly 80 percent pearlite/ferrite mix with 20 percent martensite edge. The volume of soft steel in the spine allows for great pull on the relativly smaller volume of martensite. Today I see swords here in the west that approach 50/50. So much martensite distributed so high on the blade would not be very responsive to the old copper block treatment.

Just some opinions I stopped making swords years ago, but I still study technique and design of Japanese swords both old and new.

Personally I would make a new sword versus attempting to induce more curvature.

2cents for free,

patrick

 

That is some excellent insight, Patrick. Thank you. :)

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The Japanese use a block of hot copper to do this. They place the mune

on the block and hammer carefully on the ha.

No idea how far you can change the sori that way,

I've never tried it...

 

as howard and others have noted... I had no success NONE AT ALL with that method... I guess on our "modern" steels it just doesn't work...

 

daniel

 

redo the HT is what I would do...

FERRUM - Daniel Gentile

custom knives & forging classes

http://www.ferrum-d.com

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Patrick, that's an interesting thought that didn't occur to me. Realistically, steel is steel, but there are characteristics of tamahagane that do not match mill steels. However, I can rectify that oversight by making the attempt. I don't know when I'll get it done, but an experiment will be made. Now I have to find a copper block big enough...

There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves. Will Rogers

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Patrick, that's an interesting thought that didn't occur to me. Realistically, steel is steel, but there are characteristics of tamahagane that do not match mill steels. However, I can rectify that oversight by making the attempt. I don't know when I'll get it done, but an experiment will be made. Now I have to find a copper block big enough...

 

Louis Mills might have some insight on this. He is the one that explained to me in detail some of the differences in material responce between Tamahagane and mill steel.

patrick

 

Patrick, that's an interesting thought that didn't occur to me. Realistically, steel is steel, but there are characteristics of tamahagane that do not match mill steels. However, I can rectify that oversight by making the attempt. I don't know when I'll get it done, but an experiment will be made. Now I have to find a copper block big enough...

 

Just a thought, but a smaller piece of copper with a torch feeding it heat would do just aswell as long as the torch was not directly heating the blade.

patrick

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Louis' a good man, I sure wish he'd come out to play more. He knows as much as any about homemade steels in the US.

There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves. Will Rogers

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  • 2 weeks later...

Louis' a good man, I sure wish he'd come out to play more. He knows as much as any about homemade steels in the US.

Thank you for the compliments. Play time for me is very limited especially in the summer ( gardening, small farm chores etc etc) . I have had good luck increasing the sori of my blades. Decreasing the sori has been virtually impossible for me. To increase I put the blade edge in a tub of water( my quench tank ) leaving the back ridge exposed. I then heat the back ridge with a torch ( I know , not very traditional ) until some colors appear (yellow brown blue ) and then quench it immediately. I continue systematically up or down the blade ( depending on where I started from) at the spot I want the increased sori until I have what I want ( or as much as I can get). Keeping the edge in the water prevents the heat from destroying the hamon. This will also take out unwanted hard spots on the back ridge or shinogi area.

Hope this helps .

 

Louie ( Yasutomo )

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All those techniques (copper block, torch) are basically an identical phenomenon to what is commonly used in welding straightening and body work (how to flatten a steel panel or take the spring out of it).

The principle of it can be best illustrated by a simple experiment. Affix a little steel bar within the open branches of an U made of heavy steel (to obtain sort of a square with one branch thinner). Then heat up the thin branch, if properly done when it's cooled down the thin branch will have been broken in traction or the U will have been deformed inwardly.

That symbolizes what is happening within the blade (thick part is hard edge and shinogi, thin branch is the spine).

The exact principle of why it works has to do with expansion, stress and deformation and relative malleability at different temperatures. Bottom line it should work but is a tricky thing to get right. I have no experience myself with a blade and sori, but I've done the other ways (steel plate, and welded piece) many times. Same, it's tricky to get right but it works.

Edited by Michael
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there's a pic of jason dingledine adjusting sori with a copper block and tapping on the ha here:

http://www.tigerclawforge.net/about_my_work

Jake Cleland - Skye Knives

www.knifemaker.co.uk

"We can't solve problems by using the same kind of thinking we used when we created them."

"Everything should be made as simple as possible, but not simpler."

"Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe."

 

Albert Einstein

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