Sharpening Part 9 – Hard Steel & Soft Iron 鍛接

A piece of hot high-carbon steel, which will become the cutting edge, has been placed on the orange-hot low-carbon steel body of a knife as part of the “forge-welding” process. An acidic flux powder has been placed in-between and on the metals in preparation for laminating them together into a single blade.

Men are like steel. When they lose their temper, they lose their worth.

Chuck Norris

While Beloved Customers are of course familiar with the features of the high-quality woodworking blades we purvey, some Gentle Readers may have little knowledge of the important details of Japanese woodworking tools. So in this article we will try to remedy that by examining some simple historical points common to woodworking blades around the world, as well as some details that make Japanese blades unique.

Your humble servant believes an understanding of these basic facts will aid Beloved Customer’s sharpening efforts, or will at least tickle Gentle Reader’s interest in Japanese blades. Please comment and let me know your thoughts.

Laminated Bi-Metal Construction

As discussed in previous posts in this series, before technological advances in the 1850’s steel was difficult to make and expensive. Consequently, it was standard practice not only in Japan but everywhere, including Europe and the United States, to reduce production costs by minimizing the amount of precious steel used to make axe, scythe, plane and chisel etc. blades. This was achieved by laminating smallish pieces of high-carbon steel to softer and much cheaper wrought-iron bodies through a process called “forge welding.”

Most chisel and plane blade blacksmiths in Japan continue to employ this lamination technique even today, not because of some navel-gazing infatuation with the archaic, but because it has serious advantages.

The best Japanese plane and chisel blades are generally comprised of a layer of very hard high-carbon steel called “hagane” (鋼) in Japanese, forge-welded to a softer low-carbon/no-carbon iron body called “jigane” (地金). We discussed both of these metals in the previous two posts in the series here and here.

Here is the key point to understand: When a blade made from a lamination of high-carbon and low/carbon steel is quenched, the sudden temperature change causes the high-carbon steel layer to become hard, even brittle, while the softer low/no carbon layer is unaffected and remains soft.

A 30mm Hidarino Ichihiro Atsunomi, approximately 12″ OAL.

Why go to so much trouble? One advantage of this construction is that it allows the cutting edge to be made much harder than is possible in the case of an non-laminated blade therefore staying sharper longer in use than softer blade. But why does lamination make this possible? Consider the absolute fact that a chisel blade made of uniform material heat treated to a uniform hardness of, say, HRC65 might cut very well, and stay sharp a long time, it will always break in use. Not just chip, but actually break in half. The softer low/no carbon jigane layer supports and protects the hard high-carbon layer preventing it from rupturing. Such durability is one hell of an advantage.

Another benefit of laminated construction is ease of sharpening. Remember, the harder a piece of steel is, and the larger the its area, the more work it takes to abrade it. But in the case of a laminated blade, the amount of hard-steel exposed at the bevel the user must abrade is just the relatively thin strip of shiny metal seen in the chisel photos above and below. Please also recall that the darker low/no carbon layer jigane is dead soft and melts away on the sharpening stones without much effort.

So the laminated construction of hard hagane to soft jigane produces a blade that is tough but at the same time hard, one that will become very sharp and stay sharp a relatively long time thereby improving work quality and productivity while at the same time reducing the time spent sharpening.

BTW, this is not a technique that was invented in Japan, it’s just the Japanese blacksmiths that continue to employ this ancient and clearly superior technique, at least, that is, for a little while longer. A word to the wise.

A 42mm Hidarino Ichihiro Oiirenomi

Laminated Blades in the West

If you have examined antique plane blades with wooden bodies you may have noticed many have blades stamped ” Warranted Cast Steel”

Despite being designated “cast steel” in England and America in past centuries, unlike Conan’s Daddy’s sword, or the orc blades made in the bowels of Isengard, plane, chisel and saw blades with this mark were not “cast” by pouring molten metal into a mold to form a blade. Rather the process to make the steel involved melting iron ore in a crucible and pouring it into molds “casting” a strip, bar, or ingot of high-carbon steel which is then forged to make the blade, hence the name.

This became possible only when the technology required to reliably and fully melt steel to a liquid state on an industrial scale was developed. Such steel was also called “Crucible Steel” after the crucible container used to melt iron ore.

This technology was widely used in the United States and Europe through the 1870’s. In fact, one steel mill is said to have been producing crucible steel until the 1960’s. Toolmanblog has an interesting summary on cast steel.

With few exceptions, these plane blades have a thin piece of high-carbon steel forge-welded to a soft wrought iron body, very similar to Japanese plane blades. I have reused a couple of these antique blades to make Krenovian planes and testify of their excellent cutting ability.

Chisels were also once made in Europe using this same lamination technique, although fewer examples remain extant.

Axes, hatchets, and many farming implements were also mass-produced up until the 1920’s in the US using a variation of this same technique with a “bit” of steel forming the cutting edge laminated to or sandwiched inside a body of low-carbon steel or wrought iron. Axes are still made this way in Japan. It’s a proven technique with a lot of advantages, but it does require a skilled blacksmith to pull off successfully.

The point I am trying to make is that blades made using forge-welded laminated technology were the very best available in Europe and the United States for many centuries.

Here is a link to a blog post by Paul Sellers where he praises the old chisels and laments the new.

U-Channel Construction

A closeup of the 42mm Hidarino Ichihiro Oiirenomi showing the lamination line between the steel cutting layer and low-carbon steel body of the blade
The same 42mm Hidarino Ichihiro Oiirenomi. Notice the hard-steel lamination wrapped up the blade’s sides to add rigidity.
A 30mm Hidarino Ichihiro Atsunomi, approximately 12″ OAL. Notice the hard steel lamination forming the cutting edge at the bevel. This is a beautiful lamination.
A beautiful hand-filed shoulder detail typical of Yamazaki-san’s work

The shape of the hard steel cutting layer laminated to the softer low-carbon steel (or wrought iron) body of chisels was historically a simple flat plate in Western blades. This is still the case for Japanese plane blades, axes, and farming implements. But if you imagine Japanese blacksmiths would be satisfied with such a simple design for all applications, you don’t know them well.

If Beloved Customer will carefully consider the blades pictured in the four photographs above, you will notice the lighter-colored hard steel lamination wrapped up the chisel’s sides forming a “U channel” of hardened steel adding necessary rigidity and strength. This is a critical detail for Japanese chisels intended to be struck with a hammer. Interestingly, Japanese carving chisels are not typically made this way, and are consequently structurally weaker.

Plane blades are not subjected to the high loads chisels experience and so would not benefit from this structural detail.

The Ura

Japanese chisel and plane blades, among others, typically have a hollow-ground depression called the “Ura” (pronounced “ooh/rah”) which translates to “ocean” or “bay,” located at what is called the “flat” on Western blades. Notice the polished hard steel lamination extending from the cutting edge to several millimeters up the neck. The black area surrounded by the shiny lands is the same hard metal, but has been ground to form a hollow called the “ura.”

This clever and effective design detail is unique to Japanese tools to the best of your humble servant’s knowledge. We will look at this design detail more in the next article in this series.

The Point

What does any of this have to do with sharpening? Allow me to focus what we have discussed previously.

These design details cleverly turn potential disadvantages into distinct advantages you need to understand when sharpening Japanese woodworking blades.

For instance, the layer of high-carbon steel laminated into our chisels and planes is usually 65~66 HRc in hardness. Western blades are made of a single piece of steel heat-treated to approximately 50~55 HRc to make the tool softer/tougher thereby limiting breakage. The extra hardness of the Japanese blade helps it stay sharper longer, an important benefit if your time is worth anything. This is good.

But if the entire blade were made of a solid piece of this extra-hard steel, it would a royal pain in the tukus to sharpen, I guarantee you. It would also break. Oh my, that would be bad.

The softer low-carbon/no-carbon steel or iron jigane body, however, is much softer and easily abraded making it possible to keep the hard steel layer thin, and therefore easily abraded, while protecting it from breaking. This is good.

Unlike the blade’s bevel, however, the ura (or “flat” as it is called in Western chisels) is all one-piece of hard steel. Without the hollow-ground ura depression, you would need to abrade all that hard steel at one time to initially flatten and regularly sharpen the blade, a necessity I guarantee would ruin your mellow mood even if you consumed massive quantities of controlled substances. But with the addition of the ura detail, we only need to abrade the perimeter planar lands (the shiny areas in the photos above) surrounding the ura. This is exceedingly good.

The ura depression makes it easier and quicker to not only sharpen the blade, but also to keep the “flat” planar (in a single plane). Without the ura, such a hard blade would be difficult to maintain planar and frustrating to sharpen. With the addition of the ura, the blade is genius.

An important skill to learn when sharpening Japanese blades is how to maintain the lamination and ura effectively. We will discuss this important subject more in future posts, including the final article in this series.

Conclusion

If you didn’t learn at least three new things from this post then you are either very smart or weren’t paying attention. ¯\_(ツ)_/¯

In the next installment in this bodice-ripping tale of romance and derring-do we will examine the hollow-ground “Ura” in more detail. It’s important enough to deserve a special post.

YMHOS

It is not my intention to be fulsome, but I confess that I covet your skull.”
Sir Arthur Conan Doyle, The Hound of the Baskervilles

If you have questions or would like to learn more about our tools, please click the “Pricelist” link here or at the top of the page and use the “Contact Us” form located immediately below.

Please share your insights and comments with everyone in the form located further below labeled “Leave a Reply.” We aren’t evil Google, fascist facebook, or thuggish Twitter and so won’t sell, share, or profitably “misplace” your information. If I lie may I cough up a hairball during every meal.

Sharpening Part 5 – The Sharp Edge

The gem cannot be polished without friction, nor man perfected without trials.” 

Confucius

This post may not be as entertaining as previous ones in this series about sharpening Japanese woodworking tool blades: No swords or artwork or handsome Hollywood philosophers, I’m sorry to say. But with this post we will roll up our sleeves and get some work done.

Your humble servant prostrates and begs forgiveness if Beloved Customer’s tender sensibilities are in any way offended. Many Beloved Customers and Gentle Readers already know most of what is presented in this post, but it is my fervent hope that one or two useful gems may be discovered.

You know the difference between the quality of work a sharp edge performs compared to that of a dull edge. Cuts are clean and finished surfaces are smooth, maybe even shimmering. Your tools are happy, singing and chirping as they cut away. But have you given thought to what a sharp edge really is?

Since the purpose of sharpening is to produce this condition in a blade, a clear understanding is useful, so we will consider the basics in this post.

We shall also examine the naughty cutting edge that seems sharp but suddenly and unexpectedly dulls after just a little use. Would it be useful to know how to detect such a cutting edge before it fails wasting your time and money?

Let’s begin with bedrock.

The Basics

A cutting tool is essentially a wedge, with two flat sides meeting at an angle. Applying force causes it to wedge apart and sever materials, be it wood, metal, meat or mushrooms.

The geometry of this wedge is critical to its performance. At one extreme, the angle could be 90°. It won’t be sharp, it will be hard to push, and it will crush and tear wood instead of cutting it cleanly, but it will be durable.

At the other extreme, the wedge might be made more acute, say 3°. It could be extremely sharp indeed, but it would be too fragile to cut anything but whip cream for long. The point is that the sharp edge is a compromise, acute enough to cut well, but not so acute that cutting pressure and friction will make it dent, roll, wear away, crack or chip easily.

The effective blade must have a bevel angle that will cut the intended material well, but at the same time supports the thin cutting edge from premature wear and damage for a relatively long time. The words “well” and “long” in the previous sentence are where the magic lies. We will examine these important points in future posts in this series.

Wood Shaving’s Eye View

Ideally, the extreme edge of the ideal metal tool’s extreme cutting should be perfectly smooth and only a single molecule thick. In the real world, cutting edges are rougher and wider, but still manage to cut pretty well.

Examine a sharp cutting edge under a microscope, and you will see imperfections. A dull blade will look even worse of course, showing dents, rips, and even cracks. 

knife edge_microscope800
The edge created by an 800 grit stone
Still sharp but starting to wear
A dulled and dented knife blade

Using a blade wears away and damages the cutting edge rounding and flattening it, destroying the geometry that makes it an effective wedge. Sharpening is the process of (1) restoring the intended wedge geometry; and (2) removing defects from the meeting of the wedge’s sides by abrading metal from one or both sides down past any damage, leaving a relatively clean, uniform wedge with minimal defects. This is the sharp edge. It is what the wood experiences. It requires effort to achieve, but it ain’t rocket surgery.

The most difficult part of achieving the two objectives listed above is making nothing from something, in a place that cannot be seen. Now that’s a Zen koan if I ever heard one.

Building confidence in one’s ability to achieve results at the microscopic level is not easy. The key is to understand the goal, and to consistently follow reliable procedures. I will describe those goals and procedures in future posts in this series.

Edge Failure

The ideal cutting edge is uniformly sharp, but few edges in the real world meet these severe criteria at the microscopic level where it matters most. A blade may be sharp in some places, and dull in others. Likewise, a blade may cut well for a while and then dull quickly and suddenly. We have all experienced these irritating failures.

One common cause of these inconsistencies and failures is that the edge is sharp only because it has a defect called a burr. Burrs by themselves can be sharp indeed, but they are thin, irregular, fragile and can bend, roll over, or break off at the root suddenly and unpredictably creating a nasty dull edge in an instant. A truly sharp edge will not just feel sharp, but will stay sharp for a relatively long time because it is properly shaped and well supported, instead of being only temporarily sharp because of an irregular and fragile burr.

I call burrs a “defect” because they are, but creating a burr is an important step in making a sharp edge. The trick is to continue to refine the wedge after the burr is created until the burr melts away on the stones and the edge is as perfect as we can reasonably expect to make it. Stop the refinement work too soon, or fail to do it completely, and all or part of that unreliable burr may survive to plop a floater into your punchbowl.

So how does one tell if an edge is properly sharp and free of deceptive burrs without using a scanning electron microscope?

Do you remember ‘Nando’s philosophy described in my previous post? One must reverse the latin lover’s logic. Don’t rely on mahvelous appearance. Don’t rely on bar room stunts like shaving arm hair or telemarketing tricks like cutting strips of paper. Develop skills and train your senses other than eyesight to detect the shape of steel at the microscopic level. This may sound strange but it is possible because your nerve endings are microscopic and can sense the difference between a burr and a truly sharp edge.

I will save the explanation of detailed techniques for a future post, but for now, here are two essential techniques for sensing things too small to see: Use your fingerprints and the exquisitely fine nerves connected to them to detect the presence and size of burrs; Use your fingernails to check the condition of the burr and determine when the blade is ready to move onto the next stone in the sharpening process. Please don’t cut yourself.

In the meantime, let’s have some pleasure before pain. Prepare to be amazed, Ladies and Germs, because in Part 6, coming soon, The Mystery of Steel will unfold before your very eyes! There will be marble relief carvings, bronze statues, oil paintings, gods and demons, death and destruction, and even a pagan soap opera about forbidden love. Oh my! We’re in negotiations for the movie rights now ♫꒰・‿・๑꒱ and need someone to play Vulcan. If anyone knows Spiderman’s agent, please have his people contact my people right away.

YMHOS

If you have questions or would like to learn more about our tools, please click the “Pricelist” link here or at the top of the page and use the “Contact Us” form located immediately below.

Please share your insights and comments with everyone in the form located further below labeled “Leave a Reply.” We aren’t evil Google, fascist facebook, or thuggish Twitter and so won’t sell, share, or profitably “misplace” your information. If I lie may all my donuts be infested with lawyers.

Other Relevant Posts

The Story of a Few Steels

Sharpening Part 2 – The Journey

You don’t have a soul, Doctor. You are a soul. You have a body, temporarily.” 

Walter M. Miller Jr., A Canticle for Leibowitz

Life is neither a dead-end course nor a race, but a hard journey along many paths all leading to a single gateway. What matters are the friends and family that journey with us, the kind deeds we do, the joy we share, the things we experience and learn along the way, and most importantly, the quality of our souls at the journey’s end, for these are all that will pass through that last gateway into eternity with us; Nothing else matters a hill of beans.

Woodworking can be a wonderful diversion and even a source of joy during this journey, one that can make our lives and the lives of those around us more pleasant. For many it is a way to keep body and soul connected. For those that rely on their tools to feed their families, the efficiency of that work, and the joy they find in doing it are not trivial matters.

Thoughtful woodworkers on this path learn early that dull tools are an impediment to making excellent wooden products regardless of the skill of the hand and eye that manipulates them, because, being an extension of the user’s mind and hands, a dull tool will often darken the mind and leaden the hand of even an accomplished woodworker.

Sharpening has always been the most important woodworking skill. It is no coincidence that for millennia the first thing apprentices were taught once they were permitted to handle valuable tools was how to sharpen them properly.

In our time the prevalence of machinery with built-in precision and blades driven by motors and sharpened by others has made it possible for those lacking even basic sharpening skills to represent themselves as craftsmen. Although they may be skilled, I believe such individuals are less craftsmen in wood and more machinery operators.

Those thoughtful souls who aspire to become accomplished woodworkers, and not just machine operators, need minimal sharpening skills. Untold thousands of years of human history verify the truth that all other woodworking accomplishments flow from this bedrock skill.

I believe, perhaps because the men I learned from and respected also believed, that free-hand sharpening is the way a skilled craftsman maintains his tools. My experience and observations over many years have confirmed the efficiency of this technique. It is consistent with my work-driven philosophy about sharpening which I will explain in more detail in the next post in this series.

Sharpening a blade free-hand is a zen-like activity. It requires observation. It requires muscle memory. It requires consistency. It requires composure. It requires meditative focus. And at the pinnacle, it requires one to feel and hear work being done in a place one cannot see, a place where destruction creates order; where nothing becomes something.

Some will disagree with my beliefs about free-hand sharpening, especially the machinist-types, the scribblers and gurus promising instant results in a few hours for the price of a book, DVD, or class, and the purveyors of sharpening jigs disinclined to work without “training wheels.” No mystery there. So I won’t even try to please everyone, just professional woodworkers.

When professional woodworkers gather in the presence of edged tools, they often talk about sharpening techniques and rare stones, and they are always curious about the quality of other men’s tools. In Japan, it is considered rude to pick up another’s tools and examine the edges, or even to look at them too hard, but the desire is always there nonetheless because it is human nature to compare oneself to one’s peers. 

Indeed, much can be learned about a man’s quality standards and his skills from his blades. Perhaps the condition of one’s tools gives a tiny glimpse into the owner’s character.

What do your tools say about you? Some are terrible gossips, you know. (ツ)

The journey will continue in Part 3 with wisdom from a celebrity and pictures of pretty swords.

Allow me to end this article with a quote from the best-selling book of fiction in human history:

End? No, the journey doesn't end here. Death is just another path. One that we all must take. J.R.R. Tolkien, The Return of the King

YMHOS

Tianmen Gate, China. 999 steps to the natural gateway above.

If you have questions or would like to learn more about our tools, please click the “Pricelist” link here or at the top of the page and use the “Contact Us” form located immediately below.

Please share your insights and comments with everyone in the form located further below labeled “Leave a Reply.” We aren’t evil Google, fascist facebook, or thuggish Twitter and so won’t sell, share, or profitably “misplace” your information. If I lie may I never finish the journey.