Sharpening Part 9 – Hard Steel & Soft Iron 鍛接

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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. An acidic flux powder has been placed in-between and on the metals in preparation for forge laminating them together into a single blade.

“It is our choices, Harry, that show what we truly are, far more than our abilities.” 

J.K. Rowling, Harry Potter and the Chamber of Secrets

If you are reading this, it’s safe to assume you are interested in sharpening woodworking blades. You may have little experience with Japanese tools, and even then you may not be aware of some of their important details. In this post 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.

I believe an understanding of these basic facts will you aid your sharpening efforts, or will at least tickle your 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 1800’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 costs by minimizing the amount of precious steel used to make axe, scythe, plane and chisel etc. blades 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 out of some navel-gazing preference for the archaic, but because it has serious advantages.

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

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 (ideally 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.

Why go to so much trouble? One advantage of this construction is that it allows the cutting edge to be made much harder, and therefore cut effectively longer than a blade of uniform hardness. For instance, a blade made entirely of steel hardened to HRC65 might cut very well, but it would break or shatter in use. And even if it did not break, it would be time consuming and irritating to sharpen such a wide expanse of hard steel. Remember, the harder a piece of steel is the more work it takes to abrade it.

A 42mm Hidarino Ichihiro Oiirenomi

By combining a thin layer of this very hard steel with a thicker layer of soft low-carbon steel or wrought iron the blade can be made thick, rigid, resistant to breaking, and will hold a sharp edge relatively longer while still being easy to sharpen. This once-common ancient structure is clearly superior to all other structural systems for planes and chisels at least.

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 by in 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 steel in a crucible and pouring it into molds “casting” a piece of high-carbon steel which is then forged to make the blade, hence the name.

This technology was widely used in the United States and Europe through the 1860’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 used 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. It is sad that this superior technology has been discarded and forgotten except in Japan, but wars and economics change everything while people remain the same.

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 was historically a simple flat plate in Western blades. This is also 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 the Japanese mind well.

Notice the lighter-colored hard steel lamination wrapped up the chisel’s sides in the four photographs above 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, carving chisels are not typically made this way.

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 my knowledge. We will look at this design detail more in the next post in this series.

The Point

What does any of this have to do with sharpening? Glad you asked. This design has some potential disadvantages that have been cleverly turned 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 64~65 HRc in hardness. The typical Western blade is made much softer at 50~55 HRc to avoid breakage. This extra hardness makes the blade 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. That would be bad.

The softer low-carbon/no-carbon steel or iron 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 is all one-piece of hard steel. Without the ura depression, you would need to abrade all that hard steel to initially flatten and regularly sharpen the blade, a necessity I guarantee would ruin your mellow mood without 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) around the ura. This is exceedingly good.

The ura depression makes it easier and quicker to not only sharpen the blade, but also to 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.

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

Links to Other Posts in the “Sharpening” Series

Sharpening Japanese Woodworking Tools Part 1

Sharpening Part 2 – The Journey

Sharpening Part 3 – Philosophy

Sharpening Part 4 – ‘Nando and the Sword Sharpener

Sharpening Part 5 – The Sharp Edge

Sharpening Part 6 – The Mystery of Steel

Sharpening Part 7 – The Alchemy of Hard Steel 鋼

Sharpening Part 8 – Soft Iron 地金

Sharpening Part 9 – Hard Steel & Soft Iron 鍛接

Sharpening Part 10 – The Ura 浦

Sharpening Part 11 – Supernatural Bevel Angles

Sharpening Part 12 – Skewampus Blades, Curved Cutting Edges, and Monkeyshines

Sharpening Part 13 – Nitty Gritty

Sharpening Part 14 – Natural Sharpening Stones

Sharpening Part 15 – The Most Important Stone

Sharpening Part 16 – Pixie Dust

Sharpening Part 17 – Gear

Sharpening Part 18 – The Nagura Stone

Sharpening Part 19 – Maintaining Sharpening Stones

Sharpening Part 20 – Flattening and Polishing the Ura

Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the question form located immediately below.

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 my previous ones on the subject of 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 dig into unartistic nitty gritty. I pray tender sensibilities are not offended. Many of my Gentle Readers already know most of what I will present in this post, but it is my fervent hope that one or two useful gems are hidden among the gritty.

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. 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 basics.

The Basics

A cutting tool is essentially a wedge, with two flat sides meeting at an angle. Applying force causes it to 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 cuts the intended material well 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.

Germ’s Eye View

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.

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 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 it is gone 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 cause trouble.

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 use reverse logic from our latin lover. Don’t rely on mahvelous appearance. Don’t rely on bar room tricks like shaving arm hair or 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 skills: Use your fingerprints to detect the presence and size of burrs. Use you 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

Links to Other Posts in the “Sharpening” Series

Sharpening Japanese Woodworking Tools Part 1

Sharpening Part 2 – The Journey

Sharpening Part 3 – Philosophy

Sharpening Part 4 – ‘Nando and the Sword Sharpener

Sharpening Part 5 – The Sharp Edge

Sharpening Part 6 – The Mystery of Steel

Sharpening Part 7 – The Alchemy of Hard Steel 鋼

Sharpening Part 8 – Soft Iron 地金

Sharpening Part 9 – Hard Steel & Soft Iron 鍛接

Sharpening Part 10 – The Ura 浦

Sharpening Part 11 – Supernatural Bevel Angles

Sharpening Part 12 – Skewampus Blades, Curved Cutting Edges, and Monkeyshines

Sharpening Part 13 – Nitty Gritty

Sharpening Part 14 – Natural Sharpening Stones

Sharpening Part 15 – The Most Important Stone

Sharpening Part 16 – Pixie Dust

Sharpening Part 17 – Gear

Sharpening Part 18 – The Nagura Stone

Sharpening Part 19 – Maintaining Sharpening Stones

Sharpening Part 20 – Flattening and Polishing the Ura

Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the question form located immediately below.

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
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Life is not a race. It’s a hard journey along many paths all leading to a single gateway.

What matters in this journey are the friends and family that travel with us, the kind deeds we do, the joy we share, the things we learn along the way, and the quality of our souls at the journey’s end. It’s no coincidence that these are all that will remain with us after we pass through the gateway.

Woodworking is both something we learn and a source of joy during this journey. For many it is a way to keep body and soul connected.

Travelers on the path to becoming excellent woodworkers learn early that dull tools will not and cannot make excellent wooden products regardless of the skill of the hand and eye that manipulates them.

Indeed, dull tools are not simply inefficient; I believe they are an impediment to good work 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.

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. It has always been the first and most important woodworking skill.

Anyone who aspires to become an accomplished woodworker and more than an artisan or machinist must obtain minimal sharpening skills. All other woodworking accomplishments flow from this bedrock skill. This attitude has thousands of years of history behind it.

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 artisans, I believe such individuals are less craftsmen and more machinery operators.

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 support the validity of this belief and the efficiency of the results. It is consistent with my work-driven philosophy about sharpening 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 requries composure. It requires meditative focus. And at the pinnacle, it requires one to feel with hands and hear with ears a place that cannot be seen, a place where destruction creates order. A place where nothing becomes something.

Some will disagree with my beliefs about free-hand sharpening, especially the machinist-types, those disinclined to remove their “training wheels,” 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, of course. No mystery there.

When accomplished woodworkers gather in the presence of edged tools, they will always be curious about the quality of other men’s tools. In Japan, it is considered rude to pick up another man’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 skill from his blades. Perhaps the condition of his tools can give a tiny glimpse into his character. Who can say?

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

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

Tianmen Gate, China. 999 steps in the stairway.

YMHOS

Links to Other Posts in the “Sharpening” Series

Sharpening Japanese Woodworking Tools Part 1

Sharpening Part 3 – Philosophy

Sharpening Part 4 – ‘Nando and the Sword Sharpener

Sharpening Part 5 – The Sharp Edge

Sharpening Part 6 – The Mystery of Steel

Sharpening Part 7 – The Alchemy of Hard Steel 鋼

Sharpening Part 8 – Soft Iron 地金

Sharpening Part 9 – Hard Steel & Soft Iron 鍛接

Sharpening Part 10 – The Ura 浦

Sharpening Part 11 – Supernatural Bevel Angles

Sharpening Part 12 – Skewampus Blades, Curved Cutting Edges, and Monkeyshines

Sharpening Part 13 – Nitty Gritty

Sharpening Part 14 – Natural Sharpening Stones

Sharpening Part 15 – The Most Important Stone

Sharpening Part 16 – Pixie Dust

Sharpening Part 17 – Gear

Sharpening Part 18 – The Nagura Stone

Sharpening Part 19 – Maintaining Sharpening Stones

Sharpening Part 20 – Flattening and Polishing the Ura

Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the questions form below.