A Question On Cladding

[Anteater]

For knives comprised of one steel clad in another, what goes into the decision-making process behind how much of the core steel is exposed?

Obviously, there needs to be enough of the outter steel to justify its inclusion, but how does a knife maker decide just how much core to expose? Are there utilitarian reasons? Is it just aesthetic? Could you, for instance, have a knife where the only exposed core steel is at the bevel?

 

[tedg]

I bought a set of Japanese knives from Garret Wade about 25 years ago. They have the core showing only in the center. The three layers appear to be divided about equally. Don't know the brand, they are written in Japanese.

 

[RDalman]

Soft laminate is primarily utilitarian, to add straightenability. The forged proportions and dimensions are usually done to work well with the makers intended target dimensions. A very thin knife needs a thinner core in order to retain straightenability. The overall goal is probably usually to make a "good" working knife. How much core is exposed is secondary imo.

 

[Barmoley]

Thanks Robin. To add a little to the question, besides straightenability how do you choose which of the types of metal to use, stainless soft steel is understandable, but what about mild steel vs wrought iron vs “regular” iron.

 

[Dan P.]

Thanks Robin. To add a little to the question, besides straightenability how do you choose which of the types of metal to use, stainless soft steel is understandable, but what about mild steel vs wrought iron vs “regular” iron.

Given that mild steel, wrought iron and soft stainless will all have the same sort of degree of straightenability, I guess it comes down to consumer preference?

 

[Anteater]

Can y'all elaborate on "straightenability" a bit? What exactly are y'all referring to?

 

[Dan P.]

Soft cladding in sanmai makes straightening quenched blades much easier, should any warp or twist occur.

 

[Nemo]

Soft cladding in sanmai makes straightening quenched blades much easier, should any warp or twist occur.

Is this also a benefit of differential hardening a monosteel blade?

 

[Dan P.]

Is this also a benefit of differential hardening a monosteel blade?

I would say so, yes, but differential hardening can also be the cause of warpage, so I think it is rather a stylistic thing for the most part.

 

[Keith Sinclair]

Does anyone know how they get wavy patterns at the clad lines? Kind of cool like the Hamon line on a katana. Most clad carbon cores don't have it, but some do.

 

[Corradobrit1]

My guess its a function of repeated forging and hammering. Probably more obvious for blanks that are forged in house eg TF, rather than pre-clad.

 

[osakajoe]

For Japanese double bevel San mai Knives Hand forged out from pre-laminated bar stock, how much core comes out at at the edge is quite important.

If one side the core has been exposed a lot, you probably have thinned it too much and the opposite side may not for an edge due to not enough core for both sides. Thus you will have to grind your knife down in size and restart.

This is why the first step in grinding is to bring out the core just a little on each side without thinning it too much. From there it’s more grinding to put the grind on and eventually more thinning without exposing too much core.

If you ever see a double bevel San mai knife with a core quite exposed on one side, turn it over to inspect the reverse side. You will more than likely see very little core or sometimes even faults where no core has be exposed.

 

[Dan P.]

My guess its a function of repeated forging and hammering. Probably more obvious for blanks that are forged in house eg TF, rather than pre-clad.

Exactly. Also the more aggressive the dies used to forge, ie more acutely crowned or even fullers, will give more pronounced "topography".

 

[Keith Sinclair]

Thanks was wondering how they do that to a super thin edge like the AS core Ikazuchi.

Then there are Dave's spa treatment Hiromoto's the 240mm's had a good clad line to work with.

 

[Anteater]

Soft cladding in sanmai makes straightening quenched blades much easier, should any warp or twist occur.

I never realized this, which is why I was always slightly confused about San Mai blades where the outer steel wasn't stainless. I figured maybe even something like iron was less reactive than carbon steel. Is that the primary function of non SS cladding, then, to improve "straightenability?"

 

[XooMG]

I never realized this, which is why I was always slightly confused about San Mai blades where the outer steel wasn't stainless. I figured maybe even something like iron was less reactive than carbon steel. Is that the primary function of non SS cladding, then, to improve "straightenability?"

Easier to straighten, squish, grind, and polish; traditionally cheaper. Less catastrophic failure under some hardening regimes but that's not necessarily a serious concern.

 

[Keith Sinclair]

So the wavy lines are formed on a edge while red hot? Also when most of the edge is already ground is blade reheated using a type of drawing peen to create waves in the cladding?

Just trying to picture how it is done, seems like an extra step in the forging process. I guess as with any thing once a system is set up with experience it can be done rather quickly.

 

[Dan P.]

So the wavy lines are formed on a edge while red hot? Also when most of the edge is already ground is blade reheated using a type of drawing peen to create waves in the cladding?

Just trying to picture how it is done, seems like an extra step in the forging process. I guess as with any thing once a system is set up with experience it can be done rather quickly.

No, it gets that way during normal forging.
One might intuit that if the laminate is made completely flat after deformation by crowned dies during forging, then the core alignment will likewise return to being completely straight, but this not the case.
That said, the wavy lines of the cladding will represent perhaps a mere fraction of a millimetre of deviance from true. Cut obliquely during grinding they become more noticeable.

 

[Keith Sinclair]

Thanks Dan makes sense that it is made more noticeable during grinding process.

When Dave thinned those Hiromoto's it accented the wavy line more.

 

[Anteater]

While we're on cladding, how flush is the border between the cladding and core steels supposed to be? Is it supposed to be completely smoothed or is a slight ridge common?

 

[Corradobrit1]

Should be contiguous with no perceptible transition (except visually) if grind is done right.

 

[Anteater]

Hmm. I wonder if that's part of why when I did the Sharpie trick for sharpening it seemed to "stain" the border even with acetone and a rub down with Barkeeper's Friend.

The slightly brighter area along the cladding/core border is a perceptible ridge. The darker part behind that is seemingly from the Sharpie.

Edit: perceptible in that I can feel it with my thumb. It's not extreme, but it's there.

 

[Anteater]

Forgot the image.

 

[RDalman]

Slight ridge is probably common. Will depend on the producers finishing route, for example heavy buffing, sandblasting or etching in phosphorous for contrast. Will be smooth if stone of sandpaper finished.

 

[Dan P.]

Should be contiguous with no perceptible transition (except visually) if grind is done right.

If there is a ridge it is probably not so much the grinding as subsequent abrasion, especially where soft backed wheels (glazing wheels, polishing mops and/or felts) were used. The abrade the soft cladding faster than the core, and being soft (“soft” is not necessarily that soft) they can sort of dig into the cladding.

 

[John N]

I think the best way to visualise or demonstrate the 'wavy' - take 3 layers of playdoh, or what ever pliable medium, join them together, then whack them with a rolling pin on both sides - a bit aggressively at first, then chill with it, until its near enough flat, but still a bit whacked. Then slice it with a knife to make an 'edge bevel'. The middle bit has been shoved into the cladding by the process (or the cladding has been shoved into the middle bit).

As Dan says, any perceptible ridge is from etch or mechanical abrasion acting a bit different on the different materials.

 

[Keith Sinclair]

Since this thread went & checked out my carbon core blades. Even ones that seem to have a straighter clad line are somewhat uneven. Often the tip has more exposure where the grind is thinner.

Most have a ghost line just above patina core steel. When wheels are used to mist bottom half the stainless core wears a little thinner just above the clad line.

 

[Anteater]

That makes sense. Also, I got the darkening clad line thing worked out. Rust erasers took it right off and I think it was actually a dark patina rather than sharpie residue. It seems like I just took so long to actually sharpen the blade that it started patina-ing quite noticeably.

 

[Chef Doom]

I met on maker that told me he decided a long time ago by coin toss.