Month: August 2019

Sharpening Part 7 – The Alchemy of Hard Steel 鋼の錬金術

An Alchemist and his assistants working late at night in his workshop.

Behold, I have created the smith that bloweth the coals in the fire, and that bringeth forth an instrument for his work.

Isaiah 54:16 KJV

In the previous post we looked at some of the supernatural aspects of making and forging steel. In this post we will examine some alchemical aspects of woodworking blades, in the particular the iron and steel used to make them and the related chemistry of sharpness and sharpening.

This post could be very technical, but your humble servant has simplified the description of chemical processes to make it easier for the non-technical Gentle Reader to follow. Please bear with me.

The Alchemy of Mutating Iron to Steel

When carbon is combined with iron in the right proportion, steel is formed. This mutation is easily accomplished nowadays, but for most of human history it was a fiendishly difficult, chancy, expensive process. No wonder those who could accomplish the deed were attributed with magical powers.

But just mixing chemicals does not yield a useful cutting tool. No, the blacksmith must make the steel hard enough to hold a cutting edge, but tough enough to endure actual work. The catalyst for this mutation is heat. The ability to create a fire hot enough to melt iron was, until fairly recently on the scale of human history, the biggest hurdle to producing quality steel consistently.

If steel is heated to within a specific range of temperatures (difficult to measure by eye) and then suddenly cooled, crystalline structures containing small, very hard and relatively brittle crystals called carbides form within a softer matrix of iron. These hard carbides supported in this rigid crystalline structure are what do the serious job of cutting, not the softer matrix.

At the extreme cutting edge, this structure might be compared to a modern circular saw blade comprised of a relatively soft body to which is attached very hard tungsten carbide cutting tips.

A steel blade dulls when the crystalline structure either shatters, or the pressure and friction of cutting wears away or cracks the softer supporting matrix, allowing the carbides to be torn from the matrix leaving behind gaps of soft, blunt metal. The larger the carbide clumps are and the greater the distance between them, the more easily they are shattered and torn away, and the duller a blade becomes with each crystal’s failure.

In a low-quality blade, and given the same amount of carbon in a fixed volume of steel, the crystals will form into relatively large and isolated clumps separated by wide rivers and lakes of softer metal, as seen from the viewpoint of a carbide. The steel will crack along these weaker pathways when stressed, and when cutting, the softer material in these lakes and rivers will erode first, leaving the desireable carbide clumps unsupported and more vulnerable to failure.

A photograph of Shirogami No.2 high-carbon steel following heat treatment and tempering. In this case, the temperatures used were less than ideal resulting in the irregular crystalline structure shown. The black material is carbon, the grey material is converted steel, and the whitish areas are soft, unconverted iron, points of natural weakness and paths of failure in the steel blade, not acceptable in a high-quality hand-forged blade.
The same steel shown above but following quenching and tempering using proper temperatures. The converted steel crystals are small and more evenly distributed. Islands of unconverted carbon and lakes of soft unconverted iron do not remain. This is a sample of ideal high-carbon steel, and is typical of the crystalline structure of the blades of our chisels, planes and kiridashi.

In a high-quality steel blade, by comparison, and given the same amount of carbon in a fixed volume of steel, the crystalline clumps are comparatively smaller and distributed more evenly throughout the matrix making it more resistant to erosion, and the carbide crystals more resistant to damage. Such steel is called “fine grained,” and has been highly prized since ancient times for its relative toughness and ability to become very sharp and stay sharp for a long time. This is the steel preferred by woodworking professionals in Japan and is the only kind found in our tools. Without exception.

Sadly, this crystalline structure is not visible to the naked eye, and anyone who says differently is trying to sell Beloved Customer something brown and smelly, probably with a side dish of flies.

Impurities and Alloys

Other than excellent and abundant water, endless forests, mountains overgrown with wonderful trees, and diligent people, the islands of Japan are poor in most of the natural resources critical to industrialization, including iron ore, coal, and petroleum. Prior to the mass importation of such resources after 1854, the best source of iron in Japan had been black sand (satetsu 砂鉄) found in rivers. The article at the following link details some of these traditional Japanese production methods: A Story of a Few Steels

Regardless of their source, all iron ores naturally contain impurities such as phosphorus, sulfur, or silicon to one degree or another. When these impurities exceed acceptable limits, they can weaken the steel, make it brittle or tend to warp badly, or make heat treating results inconsistent. They are often expensive to remove.

Nagasaki Bay, the only Japanese port open to Western traders between 1639 and 1854, with primarily only Dutch ships permitted entrance.

There are three approaches commonly used to minimize the negative effects of these difficult-to-remove impurities. The first is simple avoidance of the problem by employing iron ore and scrap metal free of excess amounts of these contaminants. Such ore and scrap are available, but they are not found everywhere and are relatively expensive. For centuries, the purest iron ore has been mined in Sweden.

The second approach is to add purer iron or carefully sorted and tested scrap steel to the melting pot thereby reducing the percentages of the harmful contaminants, a technique called “ solution by dilution.”

Nakaya Takijiro’s saw forge, originally made for forging swords

The third fix is to add chemicals such as chrome, molybdenum, nickel, tungsten, vanadium and even lead to the pot forming steel “alloys” to help overcome the detrimental effects of natural impurities, specifically those related to brittleness, warping and unpredictable heat treatment. Some additives will make the steel more resistant to abrasion and corrosion, or even easier to cast, drop-forge, or machine.

Some steel alloys have serious advantages over plain high-carbon steel in mass-production, for example reducing material costs by allowing the use of cheaper lower-grade iron ore and scrap metal, or improved working and heat-treating characteristics making it possible to achieve higher productivity with fewer rejects even when worked by low-skill workers.

But the addition of these chemicals is not all blue bunnies and fairy farts because edged tools made from high-alloy steels typically have some disadvantages too. For instance, additives like chrome, nickel, molybdenum, vanadium and especially tungsten are costly. And due to the crystalline structure that develops in many high-alloy steels, products simply cannot be made as sharp as plain high-carbon steel, and are more difficult and time-consuming to sharpen by hand.

Some manufacturers cite the higher costs of high-alloy steels to justify higher prices for their products. However, what they never say out-loud is that labor costs are much much less when using high-alloy steel because skilled workers are not necessary. And because high-alloy steels produce fewer rejects, quality control is easier, overall productivity is higher, warranty problems are fewer, and profitability is increased. Indeed, without high-alloy steels, manufacturers would need to train and hire actual skilled workers and professionals instead of uneducated seasonal workers thereby destroying the Wally World mass-production model that is the foundation of modern society. Egads! Walmart’s shelves would be bare!

Our blacksmiths are not part of the Wally World production model, but make only professional-grade tools for craftsmen that value ease of sharpening, edge retention, and cutting performance above corporate profits. They charge more for plain high-carbon steel blades than for high-alloy steel products because labor and reject costs are higher.

So if a manufacturer brags about the excellence of the high-alloy steels they are using, rest assured increased profits are their motivation, not improved cutting performance. Caveat emptor, old son.

Blacksmith

Japanese Steels

The best plane and chisel blades are made from plain, high-purity, high-carbon steel. In Japan, the very best such steel is made by Hitachi Metals mostly using Swedish pig iron and carefully tested industrial scrap (vs used rebar and old car bumpers), and is designated Shirogamiko No.1 (白紙鋼 1 号 White-label steel No. 1). They also make a steel designated Shirogami No.2 steel containing less carbon. Another excellent steel for plane and chisel blades is designated Aogamiko No.1 steel (青紙鋼 Blue-label steel).

Aogami steel, like Shirogami steel, is made from extremely pure iron, but a bit of chrome and tungsten are added to make Aogami steel easier to heat treat with less warping. Aogami can be made very sharp, but it is not quite as easy or pleasant to sharpen as Shirogami. Some of the plain high-carbon Swedish steels are also excellent.

If worked expertly, either of these steels consistently produce the highest quality “fine-grained” steel blades.

Let’s compare the sharpening characteristics of these two steels. To begin with Shirogami steel is easy, indeed pleasant, to sharpen. It rides stones nicely and abrades quickly in a controlled manner.

Aogami steel, by comparison, is neither difficult nor unpleasant to sharpen, but it is different from Shirogami steel in subtle ways. It takes a few more strokes to sharpen, and feels “stickier” on the stones, but it will still produce fine-grain steel blades and performs well.

Inexperienced people lacking advanced sharpening skills typically can’t tell the difference between blades made from Shirogami, Aogami or Swedish steel and steels of lesser quality. But due to the difficulty of forging and heat treating Shirogami or other plain high-carbon steels, a blacksmith that routinely uses them will simply be more skilled and have better QC procedures than those whose skills limit them to using only less-sensitive high-alloy steels.

Professional Japanese woodworkers insist on chisel blades made from Shirogami No.1 steel. Some prefer Aogami No.1 for plane blades believing the edge holds up a bit better. At C&S Tools our plane blacksmith prefers to use Aogami because it is easier to work and more productive (especially in the case of carving chisels), but for a little extra they are happy to forge blades from Shirogami Steel.

I own and use Japanese planes made from Shirogami, Aogami, Aogami Super, Swedish steel, and a British steel called “Inukubi,” which translates to “dog neck,” a commercial steel imported to Japan from England (Andrews Steel) in the late 1800’s. Of these, Shirogami No.1 steel is my favorite. It’s a matter of personal taste.

Beware of a plane or chisel blacksmith that refuses to use plain high-carbon steel and tries to charge you more for blades made from Aogami or Aogami Super steel.

The Challenges of Working Plain High-Carbon Steel

What makes plain high-carbon steel so difficult to work, you ask? Your humble servant has never even forged a check much less a tool blade, but I will share with you what the blacksmiths I use and swordsmiths I know have told me in response to this question.

First, plain high-carbon steel is much more difficult to successfully heat treat because the range of allowable temperatures for forging and heat-treating is narrow. Heat it too hot and it will “burn” and be ruined. Quench it at too high or too low a temperature and it will not achieve the desired crystalline structure and/or hardness. Miss the appropriate range of temperatures and the blade may even crack, ruining it. Yikes! Please see the numbers and photos in the article linked to above.

Second, even if the temperatures are nuts-on, plain high-carbon steel has a nasty habit of warping and cracking during heat treating resulting in more rejects than alloy steels with additives such as chrome, tungsten or molybdenum. Strange as it may seem, when the crystalline structures that make steel useful form during quenching, they increase the blade’s volume. This change produces differential expansion causing the metal to warp, a troublesome characteristic that can be more or less controlled, or at least compensated for, by a skillful blacksmith, but it takes real skill, extra work, and a bit of luck. Not just any old Barney can do it consistently, so when working plain high-carbon steel, a blacksmith needs to know his stuff and pay close attention.

Other than wastage due to rejects, it doesn’t cost more to forge and heat-treat a blade made from plain high-carbon steel, but it takes serious skills and dedication to quality control to make a living working it for 5+ decades.

Let me give you an example of skill and experience as it relates to warpage management of plain high-carbon steel.

The photo below is of a swordsmith the instant before he quenches a glowing hot sword blade made of tamahagane, a traditional type of plain high-carbon steel made from iron sand, in a water trough. Notice the condition of his smithy: he is working in the middle of the night, the time when the best magicians and alchemists have always done the most difficult jobs because temperatures are easier to judge without inconsistent sunlight confusing things. His posture and facial expression are tense because he is about to roll the bones and, in the blink of an eye, either succeed in the most risky part of making a sword, or fail wasting weeks or months of work and thousands of dollars worth of materials. Notice how straight the glowing blade is before the plunge.

A Japanese swordsmith with a blade made from high-carbon Tamahagane steel poised for quenching. The blade is straight at this point in the process. He has invested months of work into this blade to this point and a misjudgment or even bad luck in the next second can waste it all. Not a job for the inexperienced or timid.

Note that the quantity of crystalline carbides formed in a Japanese sword during the quench is greatest nearest the hard cutting edge, and cause that area of the blade to expand and warp the most. The swordsmith therefore forges the blade straight before quenching it in expectation of it warping to the intended curvature when the crystalline structures at the cutting edge form, as seen in the photo below. This curvature is an intentional design feature that takes years of experience to achieve in a controlled manner.

Related image
After quenching, the resulting warpage is dramatic. The swordsmith must plan for this distortion and shape the blade accordingly prior to the quench if he is to avoid unfortunate results. Tool blacksmiths are faced with the same challenges on a smaller scale but more frequently. Notice the mud applied to the blade before quenching intended to control the formation of crystalline structures and achieve differential hardness. The patterns the swordsmith made in applying this insulating mixture heavily influence the limits of differential heating in the blade as well as the appearance of the “hamon” pattern that develops.

If the swordsmith intended to make a straight sword blade, he would have a forged a reverse curvature into the blade to compensate for the warpage that occurs during quenching. Plane and chisel blades exhibit similar but less dramatic behavior due in part to the moderating effects of the low/no-carbon lamination.

「折れず、曲がらず、よく切れる」を追求し、極限まで鍛え上げられた凛とした姿に、千年を超える日本刀の歴史と、生きることのすべての力を注いだ刀鍛冶の姿が浮かび上がる。
A photo of both sides of a modern sword with the warpage being an intentional design feature

The thinner the piece of steel being heat-treated, the more unpredictable the warpage developed and more likely the blade will be to develop fatal cracks. Within limits, simple warpage can be corrected to a limited degree in thin blades during the first few seconds after quenching and/or tempering by bending and/or twisting the blade while it is still hot and malleable. These techniques do not work well in the case of thicker plane and chisel blades, however, so experienced blacksmiths don’t rely solely on corrective measures but anticipate warpage beforehand and create a curve or twist in the opposite direction when forging the blade to compensate. This takes skill and experience, and even then, some rejects are unavoidable.

Chemical alloys like chrome, molybdenum, and tungsten greatly reduce warping and the risk of cracking, so their benefits are huge.

None of this is mystical, but tools made from plain high-carbon steels such as Shirogami steel require more skill and experience than those possessed by factory workers, much less Chinese peasants, so mass-production is nearly impossible, labor costs are higher, profit margins are smaller, and advertising budgets are non-existent. No wonder such tools get little attention from the shills in the woodworking press.

While modern chemistry has unveiled the mystery of steel, it has only been during the last 70 years that metallurgical techniques were developed making it possible to understand the Mystery of Steel, and the tools to scientifically control the Alchemy of Steel are only a few decades old, a short period of time in human history.

The manufacture and working of steel are still magical processes that are the foundation of modern civilization. Be not deceived: while computer nerds and ijits with MBAs take all the credit, without the alchemy of steel and the skill to work it, human life on this planet would be short and brutal.

If you have good sharpening skills but haven’t yet tried chisel or plane blades made from Shirogami, Aogami or Asaab K-120 Swedish steel, you’re missing a treat.

In the next article in this magical series we will examine the genius of the soft iron component found in quality Japanese woodworking blades. Whether cat, bat or owl, please explain the details to your familiar to prepare them for the excitement to come!

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 everything I eat taste like mud.

Relevant Posts

The Story of a Few Steels

Sharpening Part 6 – The Mystery of Steel

“The most beautiful experience we can have is the mysterious. It is the fundamental emotion that stands at the cradle of true art and true science.” 

Albert Einstein, The World as I See It

The blades we are considering in this series of articles about sharpening are made from iron and steel, so it makes sense to examine these materials from the viewpoints of sharpness and sharpening. But let’s begin by consider some of the interesting supernatural and legendary aspects of working these materials first.

Steel Magic

Steel is a magical substance. Since ancient times, the blacksmiths that worked it were sometimes seen as gods, sometimes as wizards, and always as essential. Regardless of local traditions, the power blacksmiths possessed to combine and shape the elements of earth, wind, water, fire and even spirit into the tools and weapons of everyman’s trade was seen as magical.

Even the blacksmith’s forge and anvil were seen as magical in and of themselves, and rituals incorporating them were widely believed to keep evil at bay, provide good luck and blessings, and even to cure ailments.

There were several extremely famous magical blacksmiths back in the mists of time. Please allow your humble servant the honor of presenting two of them.

Vulcan the God

Related image
Vulcan (aka Hephaestus to the Greeks), Roman god of fire and blacksmithing. Archaic relief from Herculaneum (National Archaeological Museum, Naples).

The bas-relief stone carving in the photo above is of Vulcan, the Roman god of fire and blacksmithing, also known as Hephaestus to the Greeks. This carving was excavated at Herculaneum, located in the shadow of Mount Vesuvius near Pompeii. Herculaneum was an ancient Roman town destroyed by volcanic pyroclastic flows in 79 AD. The word “volcano” comes from the word Vulcan, so a stone carving of Vulcan retrieved from a town totally destroyed by Vulcan’s namesake is tragically ironic in the extreme.

Die Schmiede des Vulkan (The Forge of Vulcan) by Velázquez, Diego 1599–1660) Museo del Prado, Madrid, Spain.

The painting by Diego Velázquez above is from a scene in the Roman poet Ovid’s Metamorphoses where the god Apollo visits the god Vulcan in his forge to tell him that Venus, Vulcan’s wife, is being naughty with Mars, the god of war. Apollo is on the far left and can be recognized by his crown of laurel and shining aura. Vulcan stands next to Apollo with a shocked and incredulous expression on his less-than-beautiful face (nice abs, but the ‘stache needs a lot of work). Vulcan’s assistants have stopped their work on a plate armor project (decidedly 15th century in style) astounded by both the sudden appearance of Apollo and the news he delivers.

Obviously, Venus and Vulcan were not a happy couple. Legend says that whenever Venus was unfaithful, Vulcan grew angry and beat hammer on anvil so fiercely that sparks and smoke rose up from the top of Mount Etna on the island of Sicily, under which he had built a forge, creating a volcanic eruption. You could say he blew his top (ツ).

Perhaps Apollo is sharing this tidbit of news just to help out his old buddy Vulcan, or perhaps his reason for snitching is malicious. Whatever the reason, I think it’s safe to assume people loved drama in the 1600’s too. Nothing new under the sun.

Your humble servant’s point is that Vulcan (Hephaestus) was not only worshiped in ancient Greece but had a presence in popular culture that ranged from before an Etruscan tribe drained the swamps that became Rome in the 10th century BC, to as late as the 1600’s. And I won’t even get into Trekkie lore. Now that’s an influential craftsman.

Wayland the Smith

Wayland the Smith (Vølund Smed) 1873 sculpture. Stockholm Sweden.

Wayland the Smith was another famous blacksmith, metalworker, and magician. He was said to be a Lord of the Elvish folk who learned his trade from either giants or dwarves.

While not as old as Vulcan in human history, Wayland’s legend survives throughout Europe, and the products of his forge were central to heroic traditions of many peoples and kingdoms long before the days of the Viking longboats.

He is credited in Norse, Germanic, and Anglo-saxon legends and literature with forging magical objects of great renown, including rings of power (no, Professor Tolkien didn’t invent the concept), the impenetrable coat of ring mail worn by Beowulf during his epic battle with Grendel, the magical sword named Gram that Sigurd used to slay the dragon Fafnir, and even King Arthur’s sword Excalibur. Not just scribblers, but even Alfred the Great, king of the Anglo-Saxons (c.886~899AD) on the island that would later become England, wrote of him.

The chains on the legs of the statue above probably represent his maiming and imprisonment on an island at the pleasure of an evil Norse king upon whom he took a bizarre revenge involving unconventional drinking bowls and jewelry. Is Wayland’s slavery one of the reasons blacksmiths have wrapped chains around their anvils since ancient times, or is the purpose just to secure the anvil and mute the bright ringing song they sing? Another mystery…

Wayland’s influence in modern times is not insignificant. For example, Leonardo Da Vinci’s fascination with flying machines was probably stimulated by the legends of Wayland building and using a winged contraption to escape his slavery. And unlike Daedalus’s deadly device in Greek legend, Wayland’s glue didn’t melt.

File:Gowy-icaro-prado.jpg
Daedalus (the bald nekid guy) and his son Icarus (the falling nekid guy) using wings to escape the island of Crete, home of labyrinths and monsters. Against his father’s advice, legend holds that Icarus flew too near the son melting the wax securing the feathers that made the wings function. “Oops,” Murphy chortled in his glee.

The legends of Wayland the Smith were once deadly serious matters.

In a lighter vein, the writings of J.R.R. Tolkien, the author of the most popular works of written fiction in human history (no kidding), were influenced by these same legends.

The Blacksmith’s Shop

While some blacksmithing traditions such as those involving Vulcan and Wayland are decidedly pagan in origin, others fit well with Christianity. For example, the ring of the blacksmith’s hammer on his anvil was once believed to strengthen the chains that bind the devil in hell barring him and his demons from God-fearing folk’s hearths. In darker times in human history the blacksmith’s workshop was believed by many to be a safe haven from evil forces, one that Satan and his imps actively avoided.

File:Le Nain Brothers - Blacksmith at His Forge - WGA12575.jpg
The village smithy. Notice the horseshoe on the wall in the background, and its downward orientation. Due to the lack of char marks on the wall, we can tell this is not where the smith normally hangs horseshoes to cool. There is method to the madness.

Below is a download link to a charming story about why blacksmiths ring their anvils and how to make sure a horseshoe brings you luck at work and at home. I encourage you to read it.

Legend of the Ringing AnvilDownload

The Japanese Smithy

If you have ever spent time in small one-man traditional smithies of the sort where our blacksmiths labor to produce the tools we provide to our Beloved Customers then you know the other-worldly atmosphere typical of such workplaces. Imagine wattle and daub walls and exposed , twisting, rough-hewn wooden roof beams blackened with 70+ years of soot, the compacted but lumpy dirt floor, the darkness of carefully-managed sunlight (the better to judge metal temperatures by eye), the bitter smells of charcoal fumes, straw ash, flux, hot steel and smoking oil; the roar of forced gas forges; the sounds of grinders and the dangerous leather belt systems that drive them; and finally the terrible racket and vibration of spring hammers and ringing anvils. A man that could work alone in a place like that 12 hours a day for 65 years is not afraid of your garden variety demon, no siree Bob.

It’s quite a sight to see a craftsman working in such an environment. They often start late in the morning to avoid noise complaints from the neighbors, and work until late at night doing heat treating when sunlight won’t interfere with the colors of the hot metal.

By noon their arms are black to the elbows and charcoal smudges are on their faces. The sight of a small, wizened 82 year-old man with strong sinewy arms scowling into the face of yellow-hot steel as he hammers the hell out of it is like a scene from Dante’s Inferno. Something of the ancient magic of Vulcan and Wayland can be felt in such places.

In the next post we will examine some alchemical aspects of the Mystery of Steel. Until then, I have the honor to remain,

YMHOS

Related image
Mr. Junichi Takagi, Japan’s last adze blacksmith, passed away April 2, 2019. A kind man, talented blacksmith and excellent sharpener. He will be missed especially since he had no apprentices and left no one to carry on his work.
Mr. Takagi working on his wet grinder in August 2018.
Mr. Nakajima’s Forge in Yoita, Nagaoka Japan. Unfortunately it was recently demolished following his retirement.
Nakaya Takijiro’s forge, originally made for swords, now dedicated to forging handsaws.

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 fresh boils burst forth on my nose daily.

Relevant Posts

The Story of a Few Steels

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.

Many Beloved Customers and Gentle Readers already know most of what is presented in this post, and of them your humble servant begs forgiveness, but it may be that one or two useful gems may be discovered among these scribbles by careful Gentle Readers.

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?

Being in the construction industry, your humble servant would like to begin building this discussion on a firm foundation anchored in bedrock. So let’s get to digging.

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°. Such an edge could be made 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.

In a woodworking tool his wedge is incorporated into a blade as a beveled edge. In an efficient tool this edge that will be thin enough to cut the intended material well, but at the same time resist dulling 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 design 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 you should be aware of is a cutting edge that is sharp only because it has a defect called a burr. Burrs by themselves can be sharp indeed, but they are thin, irregular, and fragile, and being relatively unsupported by the rest of the blade, 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 suddenly 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

A Cool Coat

A few weeks ago I posted an article about seismic dampers used on a high-rise building currently under construction near my office in Marunouchi Tokyo (a 3 minute walk from Tokyo Station). I pass this same jobsite on foot several times a week and take the occasional snapshot. I have other construction sites ongoing, but no high-rise buildings right now, and none that non-disclosure agreements will allow me to share with you. So this is a good opportunity to introduce you to some lesser-known details about major construction work in Tokyo as seen from the sidewalk without risk of offending any clients.

Please notice the gentleman in the orange uniform and big boots in the picture above. I have never met him before, but judging by the color of his uniform, he’s an employee with Obayashi Corporation, one of Japan’s largest and arguably most competent general contractors. I have done a lot of work with this company and respect it a great deal.

Sir Norman Foster, a famous British architect and the designer of Apple’s Campus 2 in Cupertino, California once said that Obayashi Corp is the world’s best general contractor. I tend to agree. And I say this as someone that used to work for two of Obayashi’s competitors in Japan, and who has also worked with many other contractors around the world. If you have visited the Boulder Dam near Las Vegas, Nevada recently, you probably drove over Obayashi’s bridge spanning the gorge.

Anyway, please notice that this erstwhile young man is wearing what looks like a thick coat all puffed up like a marshmallow on a sunny day in mid-August in 37℃ (98°F) temperatures in the shade and 76% relative humidity? Is he loco, Cisco?

Setting aside the somewhat inelegant safety boots (something glittery by Jimmy Choo would suit better methinks) and rolled trouser cuffs that do not help the fashion statement his ensemble is making, you will notice a round white grill on his coat near his elbow. There is an identical grill on the opposite side of the coat you can’t see.

If you haven’t already guessed, the two round grills are actually battery-powered fans pulling outside air into the coat and pushing it out at his collar and wrists cooling our young contractor as he labors diligently in the heat.

Makita tool cordless fan jacket
A maintenance dude sporting a two-fan cool coat

These “fan coats” are very popular in Japan. They can make a big difference so long as one can perspire adequately. Indeed, these battery-powered garments are credited with saving many construction workers from heat stroke and even death in hot months.

They also come in kiddie sizes and many colors.

Makita makes a “Cordless Fan Jacket” that is sold on Amazon overseas for a lot more than it costs in Japan. Instead of two fans, it has a single fan at the back. I have not used the Makita product and can’t endorse it.

The Makita Cordless Fan Jacket. Notice the high, stiff collar directing moving air over his neck for better cooling, and the fan unit at his back. The cord is leading to the angle grinder he is using, not to the fan.

I hope the weather in your neck of the woods is always balmy with cool breezes in summer so a coat like this is never useful. In the meantime, I’m just waiting for someone to develop sexy-looking steel-toed boots with cooling fans. I wonder what Jimmy Choo will be offering later this year (ツ)

YMHOS

If you have questions or would like to learn more about our tools, please use the questions form located immediately below. Please share your insights and comments with everyone in the form located further below labeled “Leave a Reply.” Your information will remain confidential (we’re not evil Google or incompetent facebook).

The Varieties of Japanese Chisels Part 12 – The Usunomi Paring Chisel (薄鑿)

24mm Mentori Usunomi by Sukezane (Face View)

Our thoughts flow to our hands; our tools become as part of our bodies, the blade of our bodies.

Tsunekazu Nishioka, Temple Carpenter, Horyuji Temple Restoration, Nara Japan.

In the first post in this series, we examined the two main categories of Japanese chisels: the tatakinomi designed to be struck with hammer, and the tsukinomi used to pare wood without using a hammer. Beginning with this post we will shift our focus to several varieties of tsukinomi.

If you need to cut precise joints in wood, then you need both striking and paring chisels.

The most popular variety of tsukinomi is the mentori usunomi (面取り薄鑿）which translates to “beveled thin chisel.” The name is appropriate as the blade is long and thin and the neck gently tapered.

42mm Mentori Usunomi by Sukezane (Side View)
42mm Mentori Usunomi by Sukezane (Face View)
42mm Mentori Usunomi by Sukezane (Ura View)
24mm Mentori Usunomi by Sukezane (Ura View)

Description

Just as with oiirenomi, the blades of tsukinomi can be made with different profiles, such as the stiffer rectangular cross-section of the kakuuchi, or the more triangular cross-section of the shinogi usunomi.

The mentori usunomi has a streamlined cross-section similar to the mentori oiirenomi with two bevels ground into the right and left sides of the blade’s face, flowing over the shoulders and feathering into the neck.

An atsunomi or oiirenomi can pare joints, of course, but the steel crown and mushroomed wood fibers on the handle’s end make them uncomfortable for using hours on end.

In comparison, lacking the steel crown and mushroomed handle, the usunomi is more comfortable to use. More importantly, the blades and handles of these chisels are longer and lighter in weight providing superior angular control for precision paring operations.

Western paring chisels by comparison are even thinner and have longer blades than Japanese paring chisels. There can be no denying they do a fine job. But Japanese paring chisels like the usunomi have a few potential advantages worth considering.

The most significant advantage is that the steel cutting edges of Japanese paring chisels are much harder. The paring chisels our blacksmiths forge are around 65~66 HRc in hardness, whereas Western paring chisels are usually around 55 HRc. A Western style paring chisel with its thin blade of uniform steel hardened to 65 HRc would easily snap in half in practical use.

This extra-hard lamination is hand-forged by our blacksmith from Hitachi Metal’s Yasugi Shirogami No.1 steel (aka “White Label Steel”), an exceptionally pure high-carbon steel that makes possible an edge that stays sharper longer, with the result that, given the same number of sharpening opportunities and time in a given workday, a professional-grade usunomi will help you do more hours of high-quality work than a softer blade.

For craftsmen that use their tools to feed their families this higher-level of performance is not something to be sniffed at.

The second advantage of the Japanese paring chisel is their hollow-ground ura which makes it easier to maintain a flat bearing surface, especially important in the case of the hard steel used in our chisels. If you haven’t used Japanese chisels, this claim may sound unlikely. But please recall that there are narrow lands surrounding the ura, all in the same plane, that create a flat bearing surface to guide the chisel.

Usage

This tool is well-suited to reaching into narrow mortises and other wood joints to clean and pare surfaces roughed out by axe, adze, saw and tatakinomi to precise tolerances.

It excels at trimming mortise side walls and end walls. And shaving tenon cheeks and shoulders to precise dimensions without causing spelching or cutting too deeply as shoulder planes are wont to do is a piece of cake.

In addition, the longer blade and flat face of the usunomi make it ideal for paring angles, such a 45° mitres, in combination with wooden guide blocks or jigs.

The usunomi may be struck with the heel of the hand, but never with a hammer or mallet. The slender neck, thin blade, and un-reinforced handle will simply not accept such abuse gracefully.

Chisels intended to be struck with a hammer typically perform best with a cutting edge bevel of 27~30°. Any shallower and the hard steel at the cutting edge may chip instantly dulling the tool. However, the cutting edges of usunomi along with other tsukinomi are not normally subjected to the high stresses chisels motivated with hammers must endure, so the cutting efficiency can be increased by lowering the angle to 24° or so without creating problems, depending of course, on nature of the wood you need to pare and the type of paring you intend. For instance, paring end the grain of maple may require a steeper angle than when paring the long grain of pine.

If you have used long-bladed Western chisels hard for a few years, you will have no doubt experienced your chisel’s flat becoming somewhat rounded over after many sharpenings. This occurs because, for various reasons, the center portion of the blade’s flat is abraded at a slower rate when being sharpened than the blade’s perimeter, resulting in distortion regardless of whether you keep your stones perfectly flat or not.

Obviously, a chisel with a flat that is banana-shaped lengthwise and crosswise is not ideal for paring flat surfaces, but there is a bigger problem. Namely, it is simply more difficult and time-consuming  to create a sharp edge on a blade with a curved flat than one with a true flat. A flat like this begs for amateurish tricks using rulers, etc.. of the sort professionals would be embarrassed to use. A friend once scathingly described these techniques as “training wheels.” Oh my.

The ura on the Japanese chisel is specifically designed to deal with this shortcoming, and it does a great job of it.

30mm Unsunomi by Nagamitsu – View of Mitsuura
30mm Unsunomi by Nagamitsu – View of Face
30mm Unsunomi by Nagamitsu – Closeup of Mitsuura

The 30mm usunomi in the photo above has an ura with three hollow-ground areas instead of one. This detail is called a ” mitsuura” ミツ浦 meaning ”triple ura.” It has the advantage of providing a larger bearing surface than the standard ura does, one that is helpful when used with wooden jigs for paring to precise angles, for instance. It also helps the ura index better when paring large surfaces, especially with chisel blades wider than 24mm.

Some people prefer chisels with the mitsuura detail for their appearance. I admit mitsuura look sexy, but I am not a fan of using this detail unless it is truly necessary because of the downsides I will not deal with in this already overlong post.

If I can liken the atsunomi to a shire horse, then the usunomi is a falcon. Both are beautiful powerful animals, but just as one wouldn’t use a draught horse to chase down a rabbit, or a peregrine to pull a plow, neither oiirenomi nor atsunomi are as effective as the usunomi for paring and cleaning joints.

A Shire Horse and His Little Friend. Stout, heavy and strong is good for some jobs, but…
Slim, light, fast and sharp is better for others.

The usunomi is one of those tools that is a pleasure to use.

Among woodworking tools, the usunomi is special: as it becomes part of your hand, you will discover that neither the blade nor your hand but your mind is shaping the wood.

YMHOS

If you have questions or would like to learn more about our tools, please click the see 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 by using 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 a shire horse polish his hooves on my back.