The Ancient Art of Hand Forging

Those who hammer their guns into plows, will plow for those who do not. 

Thomas Jefferson

Hand forging is an ancient blacksmithing technique that, from the viewpoint of cutting tool performance, has been almost entirely replaced in modern times, but never surpassed. Understanding a little bit about this technique and its history is helpful in understanding what a good blade should be.

Before motor-powered machinery and gas-fired forges, steel was very expensive. It took a lot of expertise, fuel, manpower and endless hammering over long periods of time to turn rocks into useable pieces of steel, an economical reality that shaped civilization for millenia. International economics aside, all steel was of necessity hand-forged back then.

This is not an efficient process compared to drop forging or press shaping. It consumes more time and fuel, and requires more labor, skill and experience. It is contrary to modern mass-production methodology. It’s a job for a trained blacksmith who demands a fair wage, not a seasonal factory worker in Bümfüq Guangzhou intent on earning enough cash to put a new corrugated sheetmetal roof on his family hovel in the countryside.

In the final analysis, hand-forging is both unprofitable for corporations and too expensive for consumers who actively value low cost and appearance above performance. No wonder it’s as Dead as Disco.

You may recall people talking about how they prefer to use hand-forged antique chisels and planes because they are superior. Those old tools certainly don’t look superior to modern tools, and they aren’t cheap. But are they superior? And if so, why?

The essence of hand forging is using hammer, tongs, anvil and forge (charcoal/gas fired) to violently shape the metal during a series of heating and cooling cycles. The combination of hammer impacts and repeated heat cycles (heating, cooling, reheating) breaks the relatively isolated, large clumps of carbide crystals into uncountable small crystals, distributing them more evenly throughout the steel’s matrix, producing the sharper, more durable, and most desirable “fine-grained” steel.

The properties of this steel are what make it valuable.

A “Tatara” furnace in Japan used to create a “bloom” of “Tamahagane” steel from “satetsu” which translates to “sand iron.” This is the traditional steel that was used throughout Japanese history prior to the importation of Western steel from England in the 1860’s
A clump of Tamahagane (“Jewel Steel”) as it is sold from the bloom furnace. It contains lots of voids and impurities that make this material entirely unusable in modern tool-manufacturing processes.
Related image
A clump of Tamahagane early in the forging process. Most of this material will be lost as waste before a useful piece of steel is born.
After the Blacksmith hammers the raw clumps of Tamahagane hundreds of times, he then forms it into numerous small flat steel patties, which he breaks into the pieces shown in this photo in preparation for forge-welding them into a single larger piece of steel that he can then forge into a blade.

Let’s examine some of these coveted properties. The first is is that it is tougher than steel of lesser quality, meaning it is less likely to fracture due to crystalline defects. In the case of swords or knives it means the blade can cut and chop without breaking when subjected to stresses that would destroy a blade made of lower-quality steel.

The second and third ways fine-grained steel is superior is related to the first. The consistent crystalline structure with its finer carbide crystals distributed more uniformly throughout the matrix results in a cutting edge that can be made sharper, and that will retain that sharpness longer than steel of lesser quality. Of course, realizing this performance depends on the quality of the materials employed, and the skill and diligence of the blacksmith.

Many antique tools were made during a time when steel was expensive, and hand-forging was the only way to shape it. In fact, in the case of critical tools such as swords, this process included forging and reforging clumps of impure iron, folding and refolding the resulting mass into itself hundreds of times to remove impurities and adjust the carbon content, typically resulting in the a loss of 75+% of the original material’s mass. That’s a lot of material and manpower tossed onto the ash pile.

I call these tools critical not just because of their important functions but because of the implied warranty that went with them. For instance, if such a blade failed in battle, the blacksmith’s implied warranty went beyond financial compensation and involved the loss of his body parts at the hands of his vindictive customer’s surviving family members. How’s that for an “extended warranty?”

But any decent steel cutting tool was time consuming and expensive to produce. Until quite recently, blacksmiths did not have tools such as infrared temperature gauges, oxygen sensors, or hardness testers. All they had were their hands and Mark 1 Eyeball, so it took many years of training under a master for a blacksmith to learn how to make a good blade and survive.

Quality control was a big problem back then, but the blacksmiths in Scheffield, Philly, Solingen, Fukuoka and elsewhere still managed to make excellent blades of all varieties with fine-grain steel as the customer demanded. Most of those surviving blades are superior to what is manufactured in the West today. Certainly better than anything made in Chinese factories.

Drop-hammer forging parts in China

Unfortunately, it is impossible to judge a piece of steel’s crystalline structure with the naked eye, a fact mass producers exploit nowadays to make huge profits selling low-quality tools made from scrap at relatively high profits based solely on the tool’s appearance as it hangs on the hardware store wall encased in its impermeable armor of clear plastic. Lower-quality tools became widely acceptable once a generation or two of consumers that knew the value of cutting tools hand-forged from high-carbon steel left for the big lumberyard in the sky to be replaced by more urbanized generations that valued low cost and appearance more than performance.

Sadly, while the quality, consistency, and workability of steel as a material has greatly improved, the ancient technique of hand-forging has been abandoned throughout most of the world, skilled blacksmiths are almost extinct, and blade performance has suffered as a direct result.

Hand forging is still practiced by some blacksmiths in Japan, where the greater quality and performance this technique provides are still highly appreciated by craftsman obsessed with performance. Accordingly, our chisel and plane blades are made from modern high-quality high-purity steel produced by Hitachi metals instead of the much more expensive and difficult to work traditional Tamahagane. However, our blacksmiths hand-forge every single blade in their one-man forges through a minimum of three heats to form a fine-grain steel with the characteristics noted above that Japanese professional woodworkers demand.

鉋の製造工程
A composite photo of Nakano Takeo forging a plane blade.

YMHOS

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 located immediately below.

Sharpening Part 13 – Nitty Gritty

“The true mystery of the world is the visible, not the invisible.” 

Oscar Wilde

In this post we will dig into a few important nitty gritty points about sharpening stones everyone needs to know. Perhaps you already know all these points, but please ready your shovel because there may be at least one buried surprise.

A Flea’s-Eye View

When seen under high-magnification, the surface of a sharpening stone looks like millions of densely-packed stones embedded in a flat field. The smaller the stones, the finer the grit.

As the blade is pushed and pulled over these stones, they scratch and tear metal from the blade’s surface leaving behind scratches corresponding to the size of these small stones. This violence continues until the blade’s ura and bevel form a clean intersection of two planes.

A view of a blade sharpened with 1200 grit diamond plate showing the furrows left by individual pieces of grit

Seen under high-magnification, the cutting edge is jagged where these furrow-like scratches terminate at the cutting edge. To some degree, it may even look like a serrated sawblade. Some blades, like kitchen knives and swords, are used in a slicing motion to cut soft materials like meat and vegetables and enemy arms, and their performance benefits from a serrated cutting edge more than a highly-polished edge, and so do not need to be highly polished on fine-grit sharpening stones. 

Plane and chisel blades, however, are used to cut wood, a material typically harder than foodstuffs, in a straight-on direction, not in a slicing motion, for the most part. In this situation, a rough, serrated cutting edge is weaker than a highly polished edge because the jagged edges are projecting out into space like the teeth of a handsaw blade, and are relatively unsupported and more easily damaged than a highly-polished blade with smaller, more uniform scratches terminating more cleanly at the cutting edge. 

Therefore, in order to produce a sharp durable blade, we must make the microscopic cutting edge smoother and more uniform by using progressively finer grit stones to produce shallower and narrower scratches, and a thin, uniform cutting edge.

But how fine is fine enough? There is a curious phenomenon related to friction that is applicable to cutting edges, and is useful to understand. 

The Friction Paradox

Imagine a cube of heavy stone with its downward flat face resting on the level, flat surface of a larger slab of similar stone. Let’s say it takes some specific measure of force pushing horizontally on the stone cube to overcome the static force of friction between the two stone surfaces in order to make the cube start moving. 

If we gradually increase the degree of polish between the two contact surfaces and measure the force required to start the cube moving at each progressively higher level of polish, we will find the force decreases with each increment of increased polish, for a time. This is at least partially because the irregularities between the two surfaces (asperities) do not interlock as deeply when the surfaces become more polished. 

However, at some point, more polishing brings the surfaces of the two stones into such intimate contact that the molecular attraction between them, and therefore the force necessary to move the cube, actually increases. 

The Inflection Point

The same phenomenon occurs with tool blades. If you sharpen and polish your blades past a particular point, the friction and heat produced between blade and wood will increase, as will the energy that must be expended, while the resulting quality of the cut and durability of the cutting edge will not improve significantly. Of course, the time and money invested in stones spent sharpening past this point will be mostly wasted.

The inflection point where additional polishing yields increased friction with little improvement in cut quality will depend on your tool and the wood you are cutting, but you can gain a pretty good idea of where it is if you pay attention over time. While the sharpening stone manufacturers hate my saying it, in my well-informed opinion there is little practical gain, beyond self-satisfaction, to be had from sharpening chisels or planes past 6,000~8,000 grit, making this range of grit an inflection point in my mind. What about you?

Conclusion

I encourage you to conduct your own experiments to determine the inflection point in the case of your planes and wood you cut. Many who figure this out save themselves significant amounts of time and money sharpening over the long-term.

To those of our Gentle Readers that love sharpening more than woodworking, and enjoy putting money in the pockets of sharpening stone manufacturers more than keeping it for themselves, I apologize for pointing out the floater in the punch bowl. But you probably would have it noticed it eventually anyway, if only from the taste difference.

I will touch more on this important point in the next exciting installment in this scientificish adventure.

YMHOS

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.

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

Even monkeys fall from trees (猿も木から落ちる)

Japanese saying
A famous wood carving of 3 monkeys located at Nikko Toshogu Shrine post resconstruction that illustrates a famous saying originating in China that also works as a pun in the Japanese language. From right to left: See no evil; Speak no evil; Hear no evil (見ざる、聞かざる、言わざる).

Ideally, a tool blade will have absolutely uniform dimensions: the right thickness and taper, perfect cross-sections, uniform curvature, and straight edges and surfaces. However, professional grade Japanese tools are not made on CNC machines, but are hand forged, and have dimensional imperfections. Indeed, imperfections are part and parcel of all human endeavors. Most imperfections don’t matter; Sometimes they make the tool better; Other times they need to be remedied.

You, Gentle Reader, may not notice that the blade or cutting edge of one of your chisels or planes is “skewampus,” and consequently the cutting results are less than ideal. You may blame those poor results on your technique in using the tool or the irregular wood grain, when the real problem is the shape of the blade’s cross-section, or your unintentionally sharpening the blade with a skew. We will examine this problem in this post.

We will also look at the curved or “cambered” cutting edge profile in plane blades, the benefits and undesirable results it can produce, and how to incorporate this blade profile intelligently into your woodworking repertoire.

Many people, like monkeys in trees, learn bad habits from their friends and teachers. We hope this post will help you understand what is going on with your woodworking blades, and how to shape and sharpen them intelligently instead of just monkeying around. Please be sure to BYOB (bring your own bananas).

A serious craftsman doing Fine Woodworking in a Pixie-free workshop (notice the strategically-placed boots).

Dealing With Skewampus Blades

Skewampus is an interesting word I learned from my mother. I am told it is a combination of the word “Cattywampus” meaning “in disarray,” and “askew.” I think it is the perfect word for describing the ailments some blades suffer.

While less than ideal, it is not unusual for the thickness of a chisel blade’s cross section to vary slightly across its width, with one side being thicker than the other, forming an irregular quadrilateral cross section. This irregularity is found in plane blades too, but it is not typically a problem. Since there is more steel on the thicker side, the cutting edge will tend to develop a skew during sharpening.

Japanese plane and chisel blades are formed by laminating a layer of hard steel to a much softer body made of extremely low-carbon steel or iron. If the lamination exposed at the cutting edge is not uniform, the area of the blade with more hard steel touching the sharpening stone will abrade slower than areas with less exposed hard steel such that the cutting edge will tend to become skewed during sharpening. Perfection is not required, but the uniformity of the lamination is an important detail to observe when purchasing Japanese tools.

Likewise, Western plane and chisel blades that are not uniformly heat-treated, and that exhibit differential hardening across the bevel’s width, will also tend to become skewed during sharpening as one side of the bevel abrades quicker than the other. This problem is more common than you might imagine, especially in the case of inexpensive tools where appearance and low price are given higher priority than quality.

Anyone that has experience bidding high-dollar construction projects will understand the statement “the most profitable job may be the one you lose.” Cheap tools are much the same way: that low-cost chisel or plane may look good on paper, but if you count your time worth anything, if you dislike headaches, and real-world performance matters to your bottom line, then such a tool is often disastrous. Caveat emptor, baby.

A chisel or plane blade that has an irregular cross section or a skewed cutting edge may not be a problem for many cutting operations. However, when cutting mortises, a chisel blade with a skewed cutting edge or irregular cross section will tend to drift to the side gouging the mortise’s walls and ruining tolerances. If you find that your mortise walls are gouged, or that tolerances are poor, check your chisel blade’s shape, and correct any deformities.

Like all human work spaces, Japan’s smithies are not immune from pixie infestation despite annual blessings by Shinto priests and periodic offerings of rice, salt and wine to the spirits. In a previous post we discussed supernatural predators, so I will refer you to it for antidotes to pernicious pixie pox. But the deformities we are examining in this post are more often the natural result of the human eye misjudging hammer blows or non-judicious use of grinder wheels rather than precocious pixies at play.

If your blade’s deformity is not excessive, you can compensate by applying a little extra pressure on the blade’s thicker side while sharpening it. 

It is interesting how a little off-center pressure on a blade being sharpened over many strokes can change its shape. Many people unintentionally deform their cutting edges by not paying attention to the amount and location of the pressure their fingers apply. A word to the wise.

Another potential solution is to skew the blade in relation to the direction of travel when sharpening the bevel. This works because the leading corner of a skewed blade is abraded quicker than the trailing corner. But once again, inattention causes many people to skew their blades when moving them around on their sharpening stones unintentionally creating, instead of intentionally correcting, skewed cutting edges. There is nothing wrong with skewing the blade when sharpening so long as you are aware of the distortion this practice can produce and compensate accordingly. Another word to the wise.

If these methods don’t compensate adequately, you may want to grind and lap a chisel blade to a more uniform cross-sectional shape. A chemical bluing solution used afterwards will help conceal the shiny metal exposed by this operation if your chisel objects to the shiny spots. Some of them can be quite vain, you know.

A chisel with a an adequately uniform lamination and cross-section, and nice polish.

Cutting Edge Profiles

Many people have access to electrical jointers and planers, but relatively few have industrial equipment with the capacity to dimension wide boards such as tabletops. And of course architectural beams and columns are typically too long or too heavy to dimension with most stationary electrical equipment.

The choices available to most people for dimensioning such materials therefore are either handheld electrical power planers and/or sanders, or axes, adzes and hand planes. Powerplaners, sanders, axes and adzes are beyond the scope of this article, but we will look at hand planes.

I need more than one plane? You can’t be serious!

Although the very idea gives some woodworkers vapors (I don’t mean gas), an efficient craftsman will have multiple planes with cutting edges honed to profiles matched to specific operations.

Everyone that dimensions larger pieces of lumber by hand needs a plane with a wide mouth and a curved or “cambered,” cutting edge called a “scrub plane” in the West, and “arashiko kanna” in Japan.

This variety of plane excels at hogging a lot of wood quickly when the craftsman needs to significantly reduce the thickness of his lumber.  If the blade is narrow and curvature is deep, this plane will hog wood quickly, but leave a deeply rippled surface, often with bad tearout.

One might also have a second arashiko, or jack plane with a wider blade with a shallower curvature for the next steps in the dimensioning process. Such a plane will not hog wood as quickly, but it will produce a surface that is closer to flat and smooth and with less tearout. You can see the advantage of having two arashiko planes, or a scrub plane and a jack plane, with different cutting edge profiles when dimensioning lumber.

Many Gentle Readers use electrical-powered planes to dimension lumber before turning it into furniture, doors, chairs, or sawdust, etc. and are aware that planers always leave tiny ripple-like scallop cuts on the wood’s surface, along with some tearout. This will not do as a final surface. A hand-plane finish is far superior, but it doesn’t make sense to remove any more than the bare minimum of wood necessary to remove the washboard.

A finish plane is the perfect tool for this job on condition that it is sharp, set to a fine cut, the chipbreaker is tuned and set properly, the blade profile is appropriate for the width of the wood to be finished, and the wood does not have too many large knots. In one or two passes such a plane can easily remove the ripples and leave the wood clean and shiny without changing its dimensions much at all.

Assuming the wood is cooperative and one knows how to sharpen and setup their plane properly, blade profile frequently remains a key factor many fail to grasp. Obviously, the curved cutting edge of a scrub plane cannot produce the perfectly flat surfaces required for joining two pieces of wood together. On the other hand, the corners of a perfectly straight blade will leave clearly visible steps or unsightly tracks on the surface of a board wider than the blade, which is not a problem when rough dimensioning a board, but is painful to see if the board’s surface is to be left with just a planed finish.

So how do we solve this conundrum? When finish planing, the professional approach is to use two planes each with a different cutting edge profile. The first type of finish plane has a perfectly straight cutting edge used to plane pieces narrower than the blade’s width. Since the blade’s corners are not riding on the wood while cutting it, they won’t leave tracks and ridges.

The second type of finish plane found in the professional’s toolkit has a curved cutting edge, or more correctly, curved just at the corners to prevent it from leaving tracks and ridges when planing boards wider than the blade. Nearly all the edge is left straight, but creating this tiny amount of curvature at the right and left corners causes it to smoothly disappear into the plane’s mouth so no tracks are made and any ridges are nearly impossible to see or feel. In other words, the corners of the cutting edge never touch the surface of the board, and so don’t leave discernible tracks or ridges. The finer the cut made the smaller any ridges created will be. Indeed, where a high-quality surface is required, the final cut with the finish plane will produce shavings thin enough to see one’s fingerprints through.

You may want to reread the previous two paragraphs to make sure you understand what these two cutting edge profiles are and what they can accomplish before you read further.

Naturally, a professional doing high-quality work needs at least two finish planes, one with a straight cutting edge used to produce flat, precisely-dimensioned surfaces on wood narrower than the blade’s width, and another finish plane with a cutting edge very slightly curved at the corners used to finish wider surfaces.

There are those that advocate using a curved blade, sometimes dramatically “cambered” as some call them, for all applications. Those who teach this sloppy technique twist themselves into knots justifying tricks to approximate flat surfaces using such blades. I have no doubt this is an ancient technique, but I think it is a sad practice that sprung from the carelessness of some craftsmen in flattening their sharpening stones, and with time this bad habit became a tradition in some quarters. I strongly suspect fans of this strange way of doing business habitually sand all visible surfaces anyway so tracks and ridges are not a problem for them. But the fact remains that perfectly flat, track/ridge-free surfaces work best for joinery.

Tradition and “monkey see monkey do” are a useful place to start, but as his skill level increases, the thoughtful and efficient craftsman will eventually seek to confirm the validity of the traditions he has been taught. I urge you to get started early.

Sadly, too many people never notice the strange instruction label pasted to their boot’s sole, nor that smelly stuff sloshing around inside.(ツ)

monkey-see-monkey-do
Mommy monkey teaching baby monkey bad habits. When will they ever learn?

Conclusion

As we come to the end of this post, my advice to you, Gentle Reader, is to learn two bedrock basic skills to perfection. First, learn how to keep your sharpening stones flat; And second, learn how to sharpen your blades to have a straight cutting edge. Everything else will flow naturally from these skills. Your blades deserve it. We will talk more about these subjects in the future.

In this post, we have discussed 12 serious points about plane and chisel blades and how to use and improve them all but a few woodworkers in the West are unaware of, or ignore, but which are common knowledge among professional Japanese woodworkers in advanced trades. While condensed, it is enough information to fill a book, but we are giving it to you for the price of bananas (BYOB, remember?). We hope you picked up on each point, and test those that are new to you.

The next installment in this simian soap opera of sharpening will focus less on monkeyshines, and more on stones and techniques. Please stay tuned.

YMHOS

I can’t wait to read the next post!!

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 located immediately below.