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San-mai manipulation (off center core)


J.Leon_Szesny

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I've been making some san-mai kitchen knives and the core keeps going off center.

Material butter iron and shirogami 2.

Method, hand hammering.

I start out with the core being centered, even measured it but...

 

So I tried to see what happens, if I only forge on the side that has more iron, thinking if I displace it more than the anvil would the thinner side, I could thin it and the core would be centered.

That thinking seemed very incorrect, it made it so much worse.

 

So I'll try the opposite now.

 

Anyone know for certain how to beat the sides so the core keeps being in center?

 

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I'm not sure you're going to get a simple answer beyond:  work both sides equally. and check your progress regularly and often.

 

This is harder than it seems due to the materials and methods we are using, especially if only doing hand hammering, which I think you only do.  Here's a few things that we need to consider:

- The side of the blade contacting the anvil will cool faster than the side you are hammering, and this starts as soon as your piece contacts the anvil and gets cooler the longer you hammer on that side.  And as you know, cooler steel won't deform as much as hotter steel.   Don't forget that time is an important constant to keep in mind (strike while the iron is hot) and in order to get exactly equal effects on the steel with each hammer blow for an entire heat, each blow will have to get progressively stronger to move the steel as much as the previous blow.

- The depth of forging you get with each blow goes depends on the force of the blow (lighter blows tend to move material on the surface whereas heavier blows will move deeper material).  So unless you are a machine, most likely some blows are harder and some not as hard, so now you've got that variable to try to adapt to.

 

If I were to design a machine to make this easy, it would be something like a hammer or press where you hold the billet in the center of the dies and they hit the billet equally from both sides at a time.  Or just get a rolling mill.

design.jpg

 

Edited by billyO
RIP Bear....be free!

 

as always

peace and love

billyO

 

 

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@billyO

I tried to thin the side out that had more iron by laying the thinner side on the anvil and only forging on the side with more iron.

 

In theory, that should prevent the thinner side on the anvil from getting thinner faster than the side I'm hammering on

But in practice

The exact opposite happened,

Twice!

 

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On 4/9/2023 at 12:34 AM, Alan Longmire said:

Billy covered it, to prevent one side from getting too thin you have to alternate sides every heat and count your hammer blows.  If it were easy, everyone would do it.

So basically once it goes off center, it's just game over?

 

I refuse to believe that it can't be manipulated somehow, to nudge it back.

If you can hammer it off center, then it should also be possible to hammer it back, center.

Right? Has to be.

 

Edited by J.Leon_Szesny
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5 hours ago, Alan Longmire said:

Well, you can grind off the excess on the thicker side.  If it's a little off center it might be fixable, but there is a point of no return.  

No need my beautiful bearded fellow!

Haha,

Feast thy eyes!

On a forge corrected sanmai core! :D

 

It works after all

But this is just a theory,

Now I need to further proof it. Prob by Intentionally off centering a core and beating it into the center

 

IMG_20230414_204307.jpg

IMG_20230414_204312.jpg

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20 hours ago, J.Leon_Szesny said:

It works after all

But this is just a theory,

Now I need to further proof it.

Congrats!  Of course it can be done, it's just not easy. 

One other thing I forgot to mention in my above post that you will need to consider when planning this is that the 2 different steels can/will move differently at the same heat.   I'm sure you could figure out all the parameters and the correct 'recipe' with enough time and experimentation.  Good luck.

RIP Bear....be free!

 

as always

peace and love

billyO

 

 

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  • 3 weeks later...

This is after this fact but for anyone new to forging reading this  it is the one of the first lessons of forging …… Ying/Yang….. what you do to one side needs to be done to the other BEFORE you turn it 90 degrees…… cold forging copper will highlight how good your forging chops are…..keeping a square bar from turning into a trapezoid is the challenge….it is not only the heat differential from the anvil sucking heat but the about the ratio of surface area of your hammer head to the surface area of the anvil in contact with the blade… forging copper or silver cold makes the amount a penetration even more critical so it will highlight any mistakes you make much quicker than hot forging will….

I learned this from Albert Paley giving  a lecture on forging basics in a jewelry class when he taught at the School for American Craftsman ….one of the best forging lessons i’ve learned…..

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