San-mai cladding line / centering of the core steel

[esoo]

So that knife_science guy on IG (whose name I can't check as I asked a critical question of his work and he blocked me), keeps going on about a centering the core in billet, which got me thinking about the cladding line on san-mai.

On some san-mai (say Yoshikane), the cladding line is really even and straight. On other san-mai, the cladding line is wild and crazy. As a non-knife maker, I get how this can happen - it depends a lot on how the billet is drawn out to shape and other factors that us non-knife makers may not appreciate or have to deal with. To me, if the core is there to support the knife edge, I really don't see any issue with either way.

But here is the question - can the cladding line help indicate if the core is centered in the blade? I know there are many cases it may not, but I curious about the case I bring up below.

So here is a picture from that guy's instagram (in fact it was this commenting on this one that got me blocked). If you look at the red circled area, the cladding line is low on one side and high on the other. To me, in my non-knife makers mind, this implies that the core has been pushed over there.

I'm truly curious to know if this may be the case, or I'm just assuming things that are plain wrong (which wouldn't be the first time)

 

[Corradobrit1]

I tend to think if the cladding line is very straight and even it's prelaminated and there hasn't been a lot of hammer work. In the example you showed I have a feeling that is down to poor technique, and maybe some heavy handedness.

Apart from losing some comic relief that guy has done you a favour. You might have fallen prey to his cultish vibe.

 

[esoo]

I would tend to agree with the prelaminated comment, but it could be roll forged.

And yeah, it could be just heavy handedness on the the one side with the hammer in that spot, but I curious about how the end result speaks to cladding/core centeredness.

I'd rather have the comic relief. Doubt he would've turned me to his cult - his vibe isn't my thing.

 

[MSicardCutlery]

Yes. If the core is even, the height of the cladding will be even -even if it isn't the same height on both sides. Dips and waves that are not symmetrical indicate that the blank was warped when it was ground, though the edge and spine may be straight nevertheless. The blank may have also warped during grinding, which happens a lot with san-mai, especially stainless san-mai. In many cases you can manage to get a straight edge but the spine may not be so cooperative.

 

[esoo]

Again, my Canadian brethren comes to tell me stuff that wasn't on my mind - I hadn't thought of warpage during grinding (or at all), even though I've had blades that obviously showed grind issues due to warpage.

Yes. If the core is even, the height of the cladding will be even -even if it isn't the same height on both sides.

Yeah the height of the cladding line could vary due to the grind even if it is very straight due to how thin the grind is on that side of the blade. I notice this alot as I evaluate blades for how they may be for a lefty.

 

[MSicardCutlery]

Yeah, and the height of the cladding on a given side is not necessarily an indicator of whether the blade is a left or right hand grind either. Make the angle acute enough or steep enough and you can totally compensate for the grind asymmetry.

 

[brimmergj]

So that knife_science guy on IG (whose name I can't check as I asked a critical question of his work and he blocked me), keeps going on about a centering the core in billet, which got me thinking about the cladding line on san-mai.

On some san-mai (say Yoshikane), the cladding line is really even and straight. On other san-mai, the cladding line is wild and crazy. As a non-knife maker, I get how this can happen - it depends a lot on how the billet is drawn out to shape and other factors that us non-knife makers may not appreciate or have to deal with. To me, if the core is there to support the knife edge, I really don't see any issue with either way.

But here is the question - can the cladding line help indicate if the core is centered in the blade? I know there are many cases it may not, but I curious about the case I bring up below.

So here is a picture from that guy's instagram (in fact it was this commenting on this one that got me blocked). If you look at the red circled area, the cladding line is low on one side and high on the other. To me, in my non-knife makers mind, this implies that the core has been pushed over there.

View attachment 261506

I'm truly curious to know if this may be the case, or I'm just assuming things that are plain wrong (which wouldn't be the first time)

Where did the core steel go towards the tip on the right image? Looks a bit off-center and just shows cladding. Maybe I'm wrong, maybe I just handle "the science"

 

[esoo]

Where did the core steel go towards the tip on the right image? Looks a bit off-center and just shows cladding. Maybe I'm wrong, maybe I just handle "the science"

I would say the tip as the same thing as the red circle area - if you look at the right image, the cladding is down to the edge, but the in the left side it's all core.

 

[KenjiF]

Looks like in that case, it's not that the steel isn't centered on the whole knife it looks like it was hammered or warped as @MSicardCutlery said on that one spot. You can see it corresponds high on one side and low on the other. The only issue with higher cladding I have found is that if you get a big chip it will usually chip up to the cladding line. I'm sure it does have an effect but I can only guess how the ratio of steel and iron effects the performance of a knife... I'm guessing more steel and the knife is less flexible and harder to bend (more brittle). Am I close @MSicardCutlery?

As long as the cladding isn't hanging over the edge I haven't seen any performance difference between high and low cladding after accounting for grind and thickness.

 

[brimmergj]

I would say the tip as the same thing as the red circle area - if you look at the right image, the cladding is down to the edge, but the in the left side it's all core.

That's what I was figuring. Very hard to see as he cropped the tip out of view

 

[MSicardCutlery]

The only issue with higher cladding I have found is that if you get a big chip it will usually chip up to the cladding line. I'm sure it does have an effect but I can only guess how the ratio of steel and iron effects the performance of a knife... I'm guessing more steel and the knife is less flexible and harder to bend (more brittle). Am I close @MSicardCutlery?

Well, flex before failure is usually more determined by the thickness of the steel, less the hardness (core vs cladding) but it does contribute. Being harder to bend doesn't exactly make a knife more brittle when it comes to just straight flex. San mai does make cores much harder to crack if you bend a blade, but that has less to do with the thickness of the cladding than the diffusion boundary and carbon migration. Once the discussion turns to the mechanisms of failure things get pretty complicated quickly.

I think for the most part having a lower cladding line is beneficial because it reduces the effort required to thin a blade. IMO, tougher steels or more obtuse geometry are the way to go to limit chipping. The difference in toughness between 52100 or AEB-L and the white or blue steels at the same hardness is nearly or better than 2:1 almost universally.

 

[DevinT]

Yes, the cladding will tell you a lot. Sometimes the core is compressed and sometimes it gets a little off center, it doesn’t take much to look more exaggerated than it is.

Hoss

 

[Blank Blades.]

I don't mind some waviness to the cladding personally. Obviously provided the core is exposed the whole way.

And also that their isn't some kind of really extreme spot where one side has like no cladding, and the other goes almost to the edge.

 

[cotedupy]

So that knife_science guy on IG (whose name I can't check as I asked a critical question of his work and he blocked me), keeps going on about a centering the core in billet, which got me thinking about the cladding line on san-mai.

On some san-mai (say Yoshikane), the cladding line is really even and straight. On other san-mai, the cladding line is wild and crazy. As a non-knife maker, I get how this can happen - it depends a lot on how the billet is drawn out to shape and other factors that us non-knife makers may not appreciate or have to deal with. To me, if the core is there to support the knife edge, I really don't see any issue with either way.

But here is the question - can the cladding line help indicate if the core is centered in the blade? I know there are many cases it may not, but I curious about the case I bring up below.

So here is a picture from that guy's instagram (in fact it was this commenting on this one that got me blocked). If you look at the red circled area, the cladding line is low on one side and high on the other. To me, in my non-knife makers mind, this implies that the core has been pushed over there.

View attachment 261506

I'm truly curious to know if this may be the case, or I'm just assuming things that are plain wrong (which wouldn't be the first time)

Your thinking here is definitely along the right lines - the way that the lamination line mirrors across the two sides of the knife is because of the way it's been forged. In this instance with perhaps a slightly heavy hand. That doesn't necessarily imply or result in the core being off centre, though it can do...

You could forge a blank leaving a warp in it and then grind it even. Which would result in the mirroring of the lamination line being different from the heel to the tip of the knife. In your pic above the mirroring holds very well, up until about the point where the profile upsweep starts going to the tip. In the final 1/3rd or 1/4 it's not such a good reflection side-to-side.

If that knife has a true 50:50 grind all the way along - then the core steel is off centre up toward the tip. But I think what's actually happened if you look at the kuruochi, is that it's been ground more at the tip on the RHS of the knife (left in your pic), than it has on the other.

 

[ehhh]

In practice, has anyone ever sharpened a blade to the point where the core steel is so far off that the edge is cladding?

I have a couple knives where the cladding is very close to the edge in spots, but I'm hoping that won't be an issue as I thin the blade.

 

[Benuser]

In practice, has anyone ever sharpened a blade to the point where the core steel is so far off that the edge is cladding?

I have a couple knives where the cladding is very close to the edge in spots, but I'm hoping that won't be an issue as I thin the blade.

Have seen it happen with a stainless cladded. Not only the edge won't hold, but the blade behind the edge had become far to thick and cutting felt damped by the soft stainless. Free the core steel as you sharpen a pencil: remove the wood.

 

[cotedupy]

In practice, has anyone ever sharpened a blade to the point where the core steel is so far off that the edge is cladding?

I have a couple knives where the cladding is very close to the edge in spots, but I'm hoping that won't be an issue as I thin the blade.

Not on my own knives, but I've certainly seen it happen on others quite a lot. But as you say - if thinned properly this is very unlikely to cause as issue.

Also remember - it's likely that as you move up a forged san mai knife that the core steel will become thicker, because some of the taper from spine to edge is forged in. So unevenness / waviness in the lamination line will also get less pronounced as you continue to sharpen a knife over time.

 

[OkayMode]

I’ve been umming and ahhing about this very issue with my latest project knife over the last week.

Far more time has been spent (by me at least, not sure about the previous owner) thinning the left side of the blade compared to the right, and yet the cladding still almost reaches the edge in places whereas on the other side there’s a lot of core steel exposed in places after much less work.

 

[MSicardCutlery]

I’ve been umming and ahhing about this very issue with my latest project knife over the last week.

Far more time has been spent (by me at least, not sure about the previous owner) thinning the left side of the blade compared to the right, and yet the cladding still almost reaches the edge in places whereas on the other side there’s a lot of core steel exposed in places after much less work.

Yeah, and the height of the cladding on a given side is not necessarily an indicator of whether the blade is a left or right hand grind either. Make the angle acute enough or steep enough and you can totally compensate for the grind asymmetry.

If the centerline of the blade is further to one side than the other, and the shinogi angle on that side is correspondingly lower, the cladding can still be the same height on both sides despite the shallower angle on the one side and the steeper on the opposing side. The more asymmetrically ground the blade is, the lower of an angle the "inside" facing shinogi needs to be ground at to have an even cladding height as on the outer face. The relationship between asymmetry and grind geometry dictates the average cladding height. It's just a trigonometric relationship so everything should be proportional. (ie, 75:25 asymmetry, the shinogi on the inside will need to be at an angle that has it terminating (25/75=.3333) 33% higher than that of the shinogi on the right side to have an even cladding height). This is assuming an asymmetric grind with an otherwise centered core. If the core is out of center than you just add/subtract the corresponding ratio of its asymmetry to the value above. So you could have a core that extended 33% further towards the inner face and with a 25:75 grind, you could have a shinogi the same height on both sides and have a cladding line the same height on both sides.

In your case it is probable that the centerline is more out of center than the inner shinogi angle is low enough to compensate for. The greater surface area of the inner face is also likely what accounts for the greater effort to thin that side. This is assuming perfectly flat thinning though.

I hope this is helpful

 

[OkayMode]

If the centerline of the blade is further to one side than the other, and the shinogi angle on that side is correspondingly lower, the cladding can still be the same height on both sides despite the shallower angle on the one side and the steeper on the opposing side. The more asymmetrically ground the blade is, the lower of an angle the "inside" facing shinogi needs to be ground at to have an even cladding height as on the outer face. The relationship between asymmetry and grind geometry dictates the average cladding height. It's just a trigonometric relationship so everything should be proportional. (ie, 75:25 asymmetry, the shinogi on the inside will need to be at an angle that has it terminating (25/75=.3333) 33% higher than that of the shinogi on the right side to have an even cladding height). This is assuming an asymmetric grind with an otherwise centered core. If the core is out of center than you just add/subtract the corresponding ratio of its asymmetry to the value above. So you could have a core that extended 33% further towards the inner face and with a 25:75 grind, you could have a shinogi the same height on both sides and have a cladding line the same height on both sides.

In your case it is probable that the centerline is more out of center than the inner shinogi angle is low enough to compensate for. The greater surface area of the inner face is also likely what accounts for the greater effort to thin that side. This is assuming perfectly flat thinning though.

I hope this is helpful

Brain hurty.

That makes a lot of sense, thank you!

 

[MSicardCutlery]

Brain hurty.

Mine too.

And anytime!

 

[S_Webb]

From someone who has built a few of these types of core steel knives. mostly pattern welded / damascus outside with a core steel. the core is shifted either by hammering or warpage. Freehand hammering it is very easy to squish it off center. Just a guess due to the acute angle of kitchen knives. Guessing .005 to .01 off center. I was grinding a multi layered knife a while back and every pass would relieve some of the heat treat stress and it would curl more and more each pass across the grinder. Sense a hydraulic press during the forging process you will get less deformation of these layers. compared to a power hammer or by hand, getting the greatest amount of deformation.. Ir is a pain chasing the core attempting to keep the core centered. couple passes on the grinder and etch to check. I jacked one blade up entirely from not working it evenly on both sides. sense the anvil sucks the heat faster that the other compressing more. Building one I have discovered it is harder than you think. I am a rookie and still learning how the processes work.

 

[DevinT]

Rolling mill is best, power hammer is second best, and press is serviceable but not ideal.

Hoss

 

[HSC /// Knives]

rolling mill for the win

 

[chefcomesback]

Power hammer is all I use , sold rolling mill for not using it enough

 

[blokey]

As an end customer I like nice wavy line, as long as it doesn’t look like OP’s lol

 

[jnat0215]

I believe this is a mistake although the pattern could be manipulated to create shapes and patterns, the hagane left is too thin which is pretty hard to believe it is intentional.

 

[esoo]

This is what I love about this forum. I ask a question to self check an assumption. Get some very solid technical answers, basically proving I could be wrong for a variety of reasons. Included in those responses are some from a variety of well respected makers, highlighting that there are many ways to get to a fantastic end result.

 

[MSicardCutlery]

I use a press....it works ok but oh what I wouldn't give for a good rolling mill

 

[Blank Blades.]

This is what I love about this forum. I ask a question to self check an assumption. Get some very solid technical answers, basically proving I could be wrong for a variety of reasons. Included in those responses are some from a variety of well respected makers, highlighting that there are many ways to get to a fantastic end result.

Idk. I thought the general consensus was that it was slightly pushed off center a little bit.

So idk if they said you were wrong necessarily.