The Japanese Gennou & Handle Part 5 – Kigoroshi

The difference between something good and something great is attention to detail.

Charles R. Swindoll
A Japanese shipwright using a hammer to perform “kigoroshi” on the edges of planks for a traditional boat. The planks are joined using long nails “toenailed” from the upper plank into the lower plank. The pilot holes for these nails are made using a “tsubanomi.” When the boat’s hull is later wetted the fibers crushed during kigoroshi will swell back to near their original size filling gaps and tightly locking the planks together, even when the planks are once again dry.

In previous articles in this series about the Japanese hammer known as the gennou, we examined the background, history and general varieties commonly available nowadays. In this article, we will expand our analysis of the gennou to include a function not well known outside Japan. We hope our Beloved Customers and Gentle Readers find it amusing.

Kigoroshi 木殺し

As mentioned in Part 4 of this series, the standard ryoguchi gennou hammer has a flat striking face on one end and a domed striking face on the opposite end. The flat face is well suited to striking chisels, driving nails and the ceremonial wacking of thumbs, while the domed striking face excels at setting nails below the surface of a wooden board, just as Western hammers are. It can also be used for a task called “kigoroshi.” Indeed, this is a technique that can be employed with any hammer having a domed face, although the domed face on many Western claw hammers may be too drastic in some cases. It is a technique worth knowing.

The term Kigoroshi (木殺し)translates to “wood killing” meaning to use a hammer to temporarily crush wood cells. It is achieved by judiciously striking the wood with the hammer or gennou’s domed face. Easy peezy.

When a piece of wood is subjected to successful kigoroshi, the wood cells are deformed reducing their internal volume, but if the pressure is later relieved and some moisture added, over time the cells of many (but not all) species of wood will swell back to near their original volume.

So how is kigoroshi used? For instance, in the case of a mortise and tenon joint, the tenon is cut oversized, and then struck with the convex face of a gennou to deform the wood cells to the point the tenon will fit into the mortise. With time, the tenon absorbs moisture from its surroundings and naturally tries to swell back close to its original size locking it tightly into the mortise. I’m sure you can see the possibilities.

In this short video, the carpenter is performing kigoroshi with the convex face of his gennou to the shoulders of an Akita Sugi (Cryptomeria japonica) beam to enable it to fit inside a housed dovetail mortise. The shoulders will later swell back to close their original dimension closing any minor gaps and perhaps locking the beam tightly into the mortise hole.

Another application of kigoroshi is seen in traditional Japanese boat building where the edge joints between planks forming the hull are hammered, effectively making the planks narrower. After the planks are attached to the ship’s ribs, their crushed cells gradually swell and attempt to return to their original volume, tightly pressing the planks against each other and closing any gaps to create a waterproof joint. In this way, a joint that might otherwise loosen with time and changes in moisture content can be made to remain tight and waterproof. This boat building technique is not unique to Japan, of course.

A Japanese shipwright performing kigoroshi on the edges of planking prior to joining them together.

One more example. When making a rectangular wooden cask or bathtub from hinoki-wood boards (not staves) in the Japanese style, grooves are cut in the bottom board to receive tongues from the vertical side boards. If these tongues are planed oversize and then their sides are pounded judiciously with a hammer with a slightly rounded face like that of a ryouguchi gennou to reduce their thickness to fit into the groove, when assembled and then wet with water the crushed wood cells in the tongue will rebound and will expand to close its original thickness not only locking the tongue and groove tightly together, but also creating a watertight connection. If done properly, the joint will remain tight even after all the boards are no longer wet, same as the ship’s planking mentioned above.

Many people’s understanding of kigoroshi is too shallow to use the technique effectively and consistently without some practical experience. The opinions of inexperienced people therefore should be scrupulously ignored, but the Beloved Customer of C&S Tools are expected to meet a higher standard of woodworking, so I share this advanced technique with you.

There are a few points you should be aware of before attempting kigoroshi in a professional situation, in other words, a situation where cost, schedule, or reputation are at risk.

First, please remember that if the flat face of the genno is used for kigoroshi, or the domed face is cocked so its corners dig in too far, or is used with too much force, the striking face’s perimeter edges may crush cells and sever fibers permanently so that they cannot return to anywhere near their original volume thereby defeating the purpose of kigoroshi and simply weakening the wood. That’s not good.

Second, be aware that if used in fine cabinetry and joinery work, kigoroshi can create unpredictable tolerance shifts at joints, making, for instance what should be a flush joint offset, so caution and experimentation may be necessary to avoid embarrassing snafus.

And third, kigorishi does not work well with some woods, especially hard, stiff woods, and can cause permanent damage in some cases. We will discuss this further below. But first, let’s examine the mechanics of kigoroshi.

Nuts and Bolts

Most commercial varieties of wood grow in climates with seasonal changes of winter and summer. A tree is essentially a big water pump that pulls (not pushes) water and some nutrients up from the ground through the pressure differential created by water evaporation at its leaves. The highest volume of water pumped, and cellular growth, occurs when the weather is warm, water is moving, and the sun is shining. Without water, sunlight, and functioning leaves, the pump stops. In the case of freezing weather, evergreen trees stop pumping water to prevent freezing and the resulting expansion that would destroy the tree.

During the colder months, beginning when leaves fall and the sun fades in Autumn, the pump as well as the tree’s growth slows and then stops. The pump starts up again during the spring thaw when water moves, the sun again shines, and leaves bud.

The stained cross-section of oak below is an excellent illustration of this point. The photo is bifurcated by a a nearly solid band of tight fibers bordered above and below by larger cells, some are rather large white voids. This nearly solid band of cells forms during late Autumn and early spring and is called “late wood” or “Autumn wood.” The areas of less density and larger voids is formed during warmer months of high-growth and is called “early Wood or “Spring wood.” These voids form branching and merging tubes leading from the tree’s roots to the tiny holes in the leaves where the water they carry evaporates powering the pump.

The difference in appearance between these bands of cells (aka growth rings”) can be seen on the surface of a board as its “grain.”

Every type of wood, indeed every piece of wood, is different and will react differently to kigoroshi attempts. Let’s review the physical properties of wood relevant to kigoroshi by examining a cross-section of a tree. For instance summer wood is carefully designed to transmit large amounts of water and nutrients, and so is comprised of large cells with thin walls. After the tree is felled and as the moisture content of the wood decreases, the cells shrink, the cell walls become thinner, harder, stronger and wrinkled and crinkled.

A cross-sectional slice of White Oak dyed red for clarity.

Winter wood in most commercial varieties is designed less to transmit water and nutrients and more to resist wind and winter storms. It is comprised of much smaller cells with thicker, stronger walls.

Effective kigoroshi temporarily squashes the cells of summer wood in what is called elastic deformation, meaning the deformation is temporary so that the cells rebounds to near their original volume when the moisture content is increased depending on the nature of the wood and the elapsed time.

The cell walls of winter wood, on the other hand, instead of squashing and then rebounding, are often shattered by kigoroshi in many cases and will rebound little. This is called plastic deformation.

Why does this matter? Consider a cube of quartersawn Douglas fir, a wood with very soft summer wood, and very strong winter wood. If we strike this cube perpendicular to the parallel rings, the larger, weaker cells of summer wood will squash down while the harder lines of winter wood will just be pressed closer together as the layer of summer wood squashes. An application of moisture to this block of wood will cause the summer wood to return to near its original volume and the cube of wood may retain any apparent damage.

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Doug Fir

Now what happens when we wack an identical cube in-line with the layer of harder winter wood? Some of the winter wood cells are squashed elastically and will rebound. But the rebound will be less and some of deformation will be permanent.

The oak, on the other hand is more dense and the cell walls are stiffer than a softwood like pine, so crushing the cells in kigoroshi will result in even less rebound, and may greatly weaken the wood permanently.

The point is to be aware of the nature of the wood you plan to do kigoroshi to beforehand.

Kigoroshi for Gennou Tenons, and Chisel Handles

There are those who advocate using a hammer to perform kigoroshi on the tenon of gennou handles, the idea being that an oversized tenon can then be crushed a little allowing it to fit into the eye, and that the wood will rebound later locking it into the eye tightly. This sounds like a great idea, but it has problems that stem from the fact that gennou handles are typically made of dense hardwoods like white oak, and not softwoods like cedar.

We need the extra toughness and density that hardwoods provide when making a gennou handle because tenons cut in softer woods will loosen over time. Hard woods like white oak, for instance, do not submit well to kigoroshi because the more rigid cell walls are broken in plastic deformation instead of elastic deformation and won’t rebound enough. In other words, kigoroshi on hardwoods like oak, hickory or persimmon may decrease the cellular volume, but it will also physically weaken the wood. Why would you want to do that?

Instead of kigoroshi, a better solution is to use a good dense hardwood and to precisely cut the tenon just enough oversize so that a lot of force is required to insert it fully into the eye. In this way, you will have a tight tenon without compromising it’s cellular strength, a better long-term solution and a more craftsman-like technique.

Another option especially effective when making a gennou handle in humid months is to cut the tenon oversized and shrink it by removing water from the cells using gradual heat. Placing the handle in a more-or-less sealed container with a dry heat source such as an incandescent light bulb will do the job. Silica gel desiccant is another method, but slower. I do not recommend putting the handle in an oven of any kind to accomplish this, however. You have been warned.

Still others advocate performing kigoroshi on the ends of chisel handles to make the crown (hoop) fit better. They then say one must soak the end of the handle in water to make it swell back to shape and lock the crown in place. While popular, this is poppycock which wastes your time and weakens the handle. Please do not do this with C&S Tool’s chisels.

If the handle is in fact too big to accept the crown (unlikely if you purchased the chisel with a handle and crown already attached), please shave or file the end of the handle down to a dimension where it takes a number of hard hammer blows from a steel hammer to drive the crown onto the handle. The crown will thereby automatically perform all the kigoroshi necessary. This method is more professional and will provide better service.

Kigoroshi is a useful technique in some applications and with some types of wood. You may not need it but it’s worth understanding, especially if you have a gennou.

In the next post in this series we will examine the ancient ergonomic roots of the gennou handle we advocate and the unusual Japanese carpentry guild that codified them.

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.” We aren’t evil Google or incompetent facebook and so won’t sell, share, or profitably “misplace” your information. Cross my heart.

Previous Posts in The Japanese Gennou & Handle Series

Part 1 – Introduction

Part 2 – Ergonomics

Part 3 – What is a Gennou?

Part 4 – The Varieties of Gennou: Kataguchi, Ryoguchi & Daruma

The Japanese Gennou & Handle Part 4 – The Varieties of Gennou: Kataguchi, Ryoguchi & Daruma

It’s hubris to think that the way we see things is everything there is.

Lisa Randall

Varieties of Gennou: Ryouguchi Gennou

There are several types of gennou. The most popular is the standard, double-faced symmetrical gennou called the “ryouguchi gennou” 両口玄翁 pronounced ryou-guchi-gen-nouh. “Ryou” 両 translates to “both” and ”kuchi” 口 means mouth, so a ryoguchi gennou is one with a striking face on both ends. This category includes its stumpy brother the daruma gennou, which is a shorter, stubbier version of the ryouguchi gennou. One face of ryouguichi gennou hammer is flat, and the opposite face is domed. The flat face is used for striking chisels and nails, with the domed face is used for the last couple of hits on a nailhead to recess it below the wood’s surface. It can also be used for something called kigoroshi (“wood killing”木殺) which we will touch on in a future post.

This most popular of gennou is symmetrical in all axis, an extremely stable shape making it well-suited for using at many different angles and at different swing velocities to make powerful hits where stability during the swing is important. And stability is often not just important but critical because a hammer that easily wiggles or twists out of alignment during the swing, or jinks upon impact, will make you look like a child.

Varieties of Gennou: Kataguchi Gennou

〔千吉〕片口玄能 小

Besides the ryoguchi, the other common variety of gennou is called a “kataguchi” 片口 or single-face gennou. “Kata” 片 in Japanese means “one” or “half” and “kuchi” 口 means “mouth” but for some reason unknown to me is used to mean “striking face” in the case of hammers. It has a slightly domed face on one end with the opposing end tapering to a small square face for setting nails. Besides setting nails, the tapered end is handy for “tapping-out” (uradashi) the hollow faces of Japanese plane blades. The domed face of the kataguchi gennou is shallow enough to be used for striking chisels, but is not as good for kigoroshi. Kataguchi genno include the yamakichi style common to Kyushu Island, the funate or Iwakuni style common to Western Honshu Island and Hokkaido way up north, and several variations thereof. 

The hammer pictured immediately below is the “Funate gennou” 船手 which translates to “boat hand” gennou. It is especially suited to driving nails, while it’s tapered tail can be used to make a starting hole for nails, a capability especially suited to ship building.

A funate-style gennou hammer with bubinga handle. The eye has a built-in forward cant. This style is popular in much of Western Japan, but not so much in Eastern Japan and Tokyo.
The face of the tapered end of the funate gennou, much smaller than the Yamakichi-style gennou pictured below. If this end is sharpened it can be used to start a hole for the diagonal nails used to join ship planking, perhaps why it’s name references ship building.

The gennou pictured immediately below is called the Yamakichi gennou 山吉, with Yamakichi meaning “lucky mountain.” This was the brandname of the blacksmith on Japan’s Kyushu Island who developed this style of hammer. It is a stubbier, heavier hybrid of the ryouguchi and funate styles, better suited to chisel work while still being well-suited to driving nails. I am told that Kosaburo received permission from Yamakichi and modified the design slightly to better meet the requests of his customers in the Tokyo area. If you can only have one hammer with you in the field or when doing installations at the Client’s home or facilities, the Yamakichi gennou is hard to beat. It’s unusual and sexy-looking.

A Yamakichi gennou by Hiroki with an American Osage Orange handle (thanks for the wood Matt!). This is the Kosaburo version of the Yamakichi style which originated on Kyushu Island. The face is not entirely flat, but is still flat enough for striking chisels without damaging them. The tapered end has a square face great for starting and setting nails. it also works well for “tapping-out” plane blades. Not quite as stable as the more symmetrical ryouguchi style, but it’s undeniably more versatile. If you need a gennou for driving nails, including finish nails, as well as striking chisels the yamakichi style gennou is hard to beat.
The tapered, square end of the Yamakichi gennou, perfect for starting and setting nails as well as tapping-out plane blades.
The butt of the osage orange handle. This shape, which we will explain in detail future posts, is a key factor in the handle design on which this series of articles is focused. Osage orange is a very tough, stringy wood used for fence posts, tool handles, musical instruments and bows for millenia. The color is a scary neon yellow when freshly cut, but when exposed to sunlight changes to this interesting color.

The Varieties of Gennou: Daruma Gennou

The daruma gennou (dah-ru-mah) 達磨玄翁 is a variation of the double-faced ryouguchi genno, but at the same weight, it is shorter and fatter. It is named after Bohdi Dharma, a Buddhist Monk who was the founder of the Zen (Chan) sect of Buddhism in China, as well as an important person in the history of the Shaolin Temple made famous in Hong Kong Kung Fu movies. You will remember seeing Shaolin Priests in Hong Kong movies dressed in saffron robes, and with rows of dots on their bald pates, jumping around thwarting evil warlords with long mustaches. 

There are many legends about the Enlightened Dharma, but one story says that while meditating for nine years in a cave near the Shaolin Temple, his atrophied arms and legs fell off leaving just his trunk and head. Because of this legend, in Japan he is portrayed as an oval-shaped figure without any limbs, and with bushy eyebrows glaring out from inside a red hood. He has come to symbolize wisdom and victory through persistence and endurance. This image has deep roots in Japanese culture.

The daruma genno is named after him because, like the buddhist priest, it is short, stubby, and round. Religious matters aside, at any given weight, the daruma is not as physically stable as the standard genno due to its reduced Moment of Inertia. 

The Moment of Inertia refers to the tendency of a body to resist changes in position. Quoting from Wikipedia (which is no doubt a quote from some physics textbook): “It is the moment of inertia of the pole carried by a tight-rope walker that resists rotation and helps the walker maintain balance. In the same way the long axis of a dragster resists turning forces which helps to keep it moving in a straight line.” 

It is the increased Moment of Inertia that makes a steel I-beam so much stiffer and stronger than a plain steel rod of the same length and weight.

Like these three examples, the standard genno head has its mass spread out from the center, making it more resistant to movement than if the same mass were concentrated in a solid ball. 

The math for a rod about a center, which is a close approximation of a hammer head, is I= (1/12) x ML2, where I equals the Moment of Inertia, M equals the mass of the rod, and L equals the length of the rod. As you can see from the equation, the Moment of Inertia varies with the square of the object’s length, so that a ball has the lowest possible Moment of Inertia for a given mass, and is the easiest shape to get moving, while a hammer head with its mass moved away from the center will have a much higher Moment of Inertia, and will therefore be more resistant to changes in direction. 

For any given mass, the daruma gennou head has less length than the standard genno head, and therefore has a reduced Moment of Inertia, and so is less stable. 

Why is this important? Because you are not a machine, and when you swing a hammer several contradictory forces act on the hammer. Sometimes those forces are large and problematic and sometimes they are small and insignificant, but often some of those forces work to drive the hammer off course so it misses the target, and others tend to cause it to twist during the swing so that a line drawn through center of the hammer’s face and the center of its mass is not aligned with the target causing a glancing blow wasting time and energy. But since a longer hammer head has a higher Moment of Inertia, it will tend to not twist out of alignment as easily as the shorter daruma will during a swing, and is more likely to impart more of its energy into the chisel even if the hit ends up being a bit off-center.

In comparison to the shorter daruma, the longer standard ryouguchi gennou head, or even Yamakichi gennou, will tend to rebound straight back, instead of twisting, helping the user to maintain a steady rhythm thereby saving time. Of course, with practice, the daruma can perform just as well as the standard ryouguchi gennou head, but if you intend to make a lot of fast, hard strokes at various angles, which is common in carpentry and timber framing, a standard ryouguchi gennou with its higher stability is a superior choice. 

The daruma gennou has traditionally been the preferred primary hammer for two trades: Joiners (tategushi), who use the daruma to their advantage in a specific way, and sculptors, who don’t require stability but do appreciate a large face. Cabinetmakers, tategushi and tansu makers often have a heavy daruma on hand for assembly work because the high face area/weight ratio is convenient for knocking joints together.

I learned about daruma genno from a retired joiner in Tokyo who was kind enough to instruct me occasionally over a period of several years in the making of Japanese tategu, especially wooden doors, shoji, ranma, and free-standing screens (tsuitate). Nowadays, commercial joiners (tategushi) cut mortises mostly by machine, but traditionally, all joints were cut by hand, so the old boys were required to do very precise work, very quickly, frequently cutting hundreds of small mortises for a single screen or door. The daruma gennou exceeds at this precise, repetitive, speedy work where the chisel is almost always oriented vertically in the cut, the workpiece is almost always located at an unchanging height from joint to joint, and the hammer is not so much swung at the chisel as dropped on it to ensure a very predictable depth of cut with stability not being a significant problem making the daruma suited for very precise cuts in narrower workpieces such as door and furniture parts.

For example, when cutting joints in shoji, the material remaining at the bottom of a mortise cut in a stile to receive a rail may be only be 1/4 millimeter thick, almost translucent, so if care is not taken, the chisel will cut all the way through ruining the stile. To avoid this, the joiner needs to be able to control the depth of cut very precisely, and rather than swinging the hammer, it is more-or-less allowed to drop imparting uniform impact forces than would be more difficult to achieve by swinging the hammer. The hammer should not rebound from the chisel but transfer all its energy for smooth, consistent cuts. When used properly, a daruma genno feels like it is sucked towards the chisel, and when it strikes, it feels like it sticks to the chisel for a fraction of second with little or no rebound providing excellent control and more precise control of the depth of cut. This technique takes lots of practice to master.

I have seen carpenters in Japan laugh at a fellow that brought a daruma gennou to a jobsite because the stumpy things are thought by many carpenters to appear clumsy. I must agree. Also, they assume that a fellow that uses a hammer with a face as big as a daruma does so because he has a hard time finding the end of his chisel with a standard hammer. They may have a point. 

For reasons unclear to me, Americans and Europeans have an illogical affinity for the daruma gennou. That said, when I need to cut a lot of small, precise mortises, I use a daruma. When I need to cut bigger or deeper mortises, or mortises at angles, however, I bring out a standard gennou of the appropriate weight for the relatively greater stability they provide. If you only have one gennou, the standard ryouguchi style head or even yamakichi style would be a good choice.

In the next chapter in this bodice-ripping yarn of romance and intrigue we will examine a more sinister application of the gennou hammer, namely kigoroshi, or “wood-killing.” Please use the bathroom before reading it to avoid embarrassing accidents.

YMHOS

Previous Posts in The Japanese Gennou & Handle Series

Part 1 – Introduction

Part 2 – Ergonomics

Part 3 – What is a Gennou?

Part 5 – Kigoroshi

Hammers to Use With Chisels Part 6 – Hammers & Health

I wanted a perfect ending. Now I’ve learned, the hard way, that some poems don’t rhyme, and some stories don’t have a clear beginning, middle, and end. Life is about not knowing, having to change, taking the moment and making the best of it, without knowing what’s going to happen next. Delicious Ambiguity.

Gilda Radner
A box-stock hardware store gennou hammer. Delicious Ambiguity. A good place to start.

In previous posts in this series about hammers to use with C&S Tools’s chisels, we looked at factors such as the type of hammer to use, the sort of face a hammer should have, how much it should weigh, and how to use hammers and chisel as a dance team effectively. In this final post we will look at how the hammers can impact our health.

Health Matters

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Swinging a hammer is a violent movement that places large, repetitive impact and vibration stresses on joints, tendons, nerves and muscles. These stresses can make our bodies stronger, or break them down. Carpel tunnel syndrome in office workers clicking away at computer keyboards gets all the attention, but hammers are much more likely to cause health problems. Before nailguns it was common for carpenters to have nerve damage in their hands and arms. Chopping dovetails with a pneumatic chisel is not an option, however.

When I was a young apprentice carpenter working in Las Vegas I wanted to be like the older more experienced carpenters on the jobsite that used shiny 32oz waffle-face Vaughn hammers to drive 16d nails through stacked 2×4’s in a single swing (this was before the advent of nailguns and LGS studs). I got where I could do that. I still own that hammer, although it is no longer smooth and shiny, and I have replaced the wooden handle 3 or 4 times.

I barely remember him, but he was a young man with lots of energy focused on gaining respect and being productive. Fortunately, I was blessed to work on crews led by older guys with no ego left, whose joints ached (like mine do now), and who just wanted to get as much good work done as efficiently as possible each day until beer-thirty. What I learned from them went beyond wacking nails, and more about actually building things. 

At first I wondered why the bosses would hire old farts when younger guys moved faster and got more work accomplished. What I learned, however, was that while the old guys did not appear to be as active as the younger carpenters, at the end of the day they had always accomplished more actual work, and with less rework. It was difficult for the young man I was back then to accept, but the bosses new their business, including two important points:

  1. “Fast” and “productive” are not the same thing (the tortoise and the hare principle, “Festina lente“);
  2. Rework takes more than twice the time and money to accomplish than doing the work right the first time.

These two principles are key to being a successful professional woodworker, so a forehead tattoo might help to remember. Just a suggestion….

None of those old boys I worked with used extra-long extra-heavy hammers because they knew that productive work required driving nails of different sizes in many different directions (not just straight down or straight forward) more accurately with fewer misses, something a heavy single-purpose framing hammer was not suited to. They knew how to avoid wasted motion and time. They knew about rhythm.

They were not what could be called kindly gentlemen, but looking back I prefer to imagine they were looking out for me when they said things like “bring us more 2×12’s, quick now dammit,” and “stop being a pain in the ass, kid.” Ah yes, good times.

They were prophets too when they warned me that the stresses I placed on my hands, arms, knees and back when I was young and dumb and full of something may not hurt at the time but would hurt every day many years later. It truly pains me to admit it, but those crusty old farts might have been right.

So in memory of those cranky carpenters who are sorting boards in the big lumberyard in the sky nowadays, let me summarize three pieces of profound wisdom they taught me. Do with them as you will. If you still have room, you might want to add them to that forehead tattoo you’ve got going (ツ)

First, strive to use your hammer efficiently with minimum force, minimum wasted motion, and minimum stress on joints and tendons. Or as they put it: “less swingin more hittin.”

Second, use an efficient hammer of the right type and weight that will get the job done without damaging your joints and tendons.

And third, stop being a pain in the ass.

Just be thankful that I am kinder than those crusty critters were and will tell you clearly in words what they communicated to me only with grunts and curses and boots while chewing on stogies and chortling as they watched me struggle with concrete form-work 16 feet in the air like the proverbial amorous monkey with his football. Yes, love was in the air…

Indeed, just to prove what a sweetheart I am, here are two more pieces of detailed advice specifically related to hammers: First, determine the style of hammer and weight that works best for you and the work situation. This will take experimentation.

Second, make handles for your hammers that suit your body and the combined natural frequency and the work you use them for instead of settling for the usual one-size-fits-nobody hammers hanging like noxious neon-colored plastic fruit on the walls of big-box retailers.

This last point will be the subject of another series of future articles.

That forehead tattoo is down past your chin by now, I suppose.

Series Summary

For such a simple subject this series has been rather long. Let me summarize what you should take away:

  1. Use a steel hammer to strike Japanese chisels instead of a mallet made of wood, rawhide, rubber, plastic or brass;
  2. Use a hammer with a flat, polished face to strike your C&S Tool’s chisels for greater efficiency and to increased lifespan;
  3. Through experimentation, determine and use the hammer weight(s) that best compliments the chisel’s weight and width, the hardness of the wood, and the natural frequency of your hand and arm;
  4. Make a handle for your hammer that follows sound ergonomic principles (versus marketing hype), fits your body, and helps you work with greater speed and precision;
  5. Less swingin more cuttin;
  6. Cut the wood with a sharp blade instead of beating it to slivers and prying it out with a sharpened screwdriver;
  7. Control your chisel’s depth of cut to prevent the cutting edge from binding in the wood, slowing the work down, and dulling the chisel;
  8. Do the “chisel cha-cha” but never the “chisel wiggle;” just don’t.
  9. Don’t use the chisel to lever out waste, but instead flick waste out of joints with a quick twist of your wrist without slowing down or setting aside chisel or hammer;
  10. Work to a rhythm to maintain your cutting pace and focus.

YMHOS

Other Posts in this Series “Hammers to Use With Our Chisels”

Part 1 – Hammer Varieties

Part 2 – Hammer Faces

Part 3 – Hammer Weight

Part 4 – The Chisel Cha-Cha

Part 5 – Rhythm & Song

Part 6 – Hammers & Health

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.” We aren’t evil Google or incompetent facebook and so won’t sell, share, or profitably “misplace” your information. May the fleas of a thousand camels infest my crotch if I lie.

Hammers to Use With Chisels Part 5 – Rhythm & Song

This life’s hard, but it’s harder if you’re stupid.

George V. Higgins, The Friends of Eddie Coyle
A specialized chisel used for cutting precise acoustic hollows into the underside of a thick wooden gameboard called a “goban” used to play the Japanese game of “Igo.” This carefully designed hole is intended to tune the clicking sound the white and black stones used in the game make when they are are placed on the board, a sound considered critically important to the quality of the game. The chisel is designed to produce a cleanly radiused internal corner where the walls meet, precise work that requires a delicate dance by chisel and hammer, especially in a production situation. Don’t ever let anyone tell you that using chisels is not elegant and artistic.

In previous posts in this series about the characteristics of the hammers our Beloved Customers should use with C&S Tools chisels, we looked at factors such as the type of hammer to use, the sort of face a hammer should have and how much it should weigh. We even examined ways to use our chisels and hammers more effectively when cutting mortises, and how to avoid the dreaded chisel wiggle. It was a footloose post.

In this post we will delve a little deeper into how to use hammers and chisels as a dance team.

The photos above and below are of gameboards, and while gameboards are not really the subject of this post, these photos illustrate an aspect of precise work with chisel and hammer intended not to create a shape to please the eye, but an artistic sound to improve concentration. Perhaps you never have thought about using a chisel to make beautiful sounds, but many of our Beloved Customers that make musical instruments professionally are focused like a laser on this very objective. I hope you will find this little article amusing.

A masterpiece goban made in 1910 from a single block of wood. Overall height: 29cm (11.4″); 45.2×42.4cm (17.8″square) x thickness: 16.1cm (6.3″). This is the old style goban and a little smaller than modern models.

Natural Frequency

Much hammer and chisel work is very repetitive with motions repeated thousands of times in a single day, each motion consuming time and energy, hopefully with precision and speed. Are time, energy, precision, and speed important to you? I propose that “Sure and steady wins the race,” sooner and more efficiently than a 2lb steel woodpecker on meth.

If you have studied pendulums and harmonic motion in physics classes you understand that every moving object from watch balances, to buildings, to mountain ranges (yes, mountains wiggle) have a natural “frequency” that defines the vibration of that object when subjected to specific forces. This reliable characteristic is why a mechanical clock can keep accurate time. Like the pendulum in a grandfather clock, within a certain range of energy input, the longer and heavier an object is, the longer it’s natural frequency is likely to be. In the case of hammer work this means that a man with a long, heavy arm and hammer combination will naturally swing a hammer cyclically slower than a man with a shorter lighter arm/hammer combination. That does not mean one is better than the other, it just means that an arm/hammer combination will work most effectively if the assembly’s natural frequency is worked with instead of fought against.

There are several ways to reliably adjust this natural frequency, for instance changing the weight of the hammer/chisel combination, or changing the length of the hammer handle. The closer the hammer weight is to the ideal for a particular arm/chisel/wood combination the easier it becomes for us to consistently adjust the assembly’s frequency and rhythm of the cutting process while controlling the impact force and thereby the depth of cut.

Rhythm

So let’s say we have the hammer/chisel/wood/arm combination (or saw/wood/arm combination) where we need it to be and we start cutting wood in a repetitive motion. If we keep this motion consistent, like a clock pendulum, we will develop what in music is called “rhythm,” a phenomenon deeply rooted in the human beast. Rhythm is critical to cutting speed and precision. Anything that breaks that rhythm other than the job being completed is counterproductive.

Rhythm has psychological benefits too because it helps us to maintain focus and thereby accomplish more work quicker and more consistently without losing focus.

But how does one maintain rhythm when cutting mortises? Perhaps you have an internal metronome. If not, it may help to take advantage of an extremely ancient tool called the “work song,” later called the “sea shanty.” These were songs sung by men and women working in groups to coordinate their physical labor and make it more effective, whether planting rice seedlings in flooded fields, pushing wagons over mountains, dragging logs through forests, or pulling ship anchors up from the depths. If the song is in your head instead of just your ear you can easily adjust the song’s rhythm to match the natural frequency of your body and your tools.

I hum a work song when I do repetitive chisel work. I suppose two of my favorites are “What will we do with drunken sailor,” and “Roll the Old Chariot Along.” There are also lots of old plantation and work gang songs that work well. Two modern tunes I sometimes hum are “Señorita” and “Poker Face,” depending on my mood. Here is another, more unusual version by an entertaining German polka band.

Just so there’s no confusion, unlike Miss Germanotta, I don’t wear a sequin bikini and white Gestapo hat when I hum Poker Face while sawing wood or chopping scarf joints. No doubt I would look fetching in such an outfit, but I have found some of my chisels to be quite sensitive in matters of decorum. Don’t hate me because I’m beautiful.

Summary

The main points I wanted to make in this article can be summarized as follows:

  1. Whether you realize it or not, your chisel, hammer, and body have a natural frequency that you can either work with to your advantage, or fight against;
  2. Using the principles listed in earlier posts in this series you can develop a chisel/hammer combination that balances well with your body, adjusting your natural frequency to improve your productivity and precision;
  3. Develop a rhythm when doing repetitive work that compliments your natural frequency and that helps you maintain both focus and a steady wood-eating pace. Work songs really help. A sequin bikini and Ray Bans are optional.

Well that’s enough German polka music and doggie apparel for now. In the final article in this series we will examine some health matters related to hammers. Y’all come back now, y’hear.

The traditional Japanese roof structure. Notice that no members are subject to tension forces, only compression and bending. Notice also that the bottom of the central beam is finished with just an adze in the classical “naguri” style.

YMHOS

Other Posts in this Series “Hammers to Use With Our Chisels”

Part 1 – Hammer Varieties

Part 2 – Hammer Faces

Part 3 – Hammer Weight

Part 4 – The Chisel Cha-Cha

Part 5 – Rhythm & Song

Part 6 – Hammers & Health

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.” We aren’t evil Google or incompetent facebook and so won’t sell, share, or conveniently and profitably “misplace” your information.

Hammers to Use With Chisels Part 4 – The Chisel Cha-Cha

Stan Laurel

You can lead a horse to water, but a pencil must be led.

Stan Laurel

In previous articles in this series about hammers to use with our chisels, we discussed the varieties of suitable hammers, the appropriate faces on those hammers, and recommended some weight ranges. In this article we will examine some important hammer and chisel techniques you should consider that will make your chisel work more efficient and help your chisels last longer.

Your Most Humble and Obedient Servant hard at work. A dab of skin lotion might be nice.

The Chisel Wiggle

Something to keep in mind about our chisels when beating on them is that their cutting edges are intentionally and carefully hand-forged and heat treated by experienced blacksmiths (none with less than 40 years independent experience) to be especially hard to meet the demands of professional craftsmen who demand the extra sharpness and cutting longevity hard, fine-grained steel makes possible. They are not the sharpened Chinese screwdrivers sold by the big corporations that amateurs are accustomed to using nowadays.

To maximize the advantage such excellent steel affords, our Beloved Customers must avoid driving the chisel so deeply into the wood when cutting mortises, for example, that the extreme cutting edge binds in the wood forcing the user to wiggle the chisel forward and backward to loosen and extract it from the cut. I call this movement the “chisel wiggle.” I know this is contrary to what many woodworking gurus teach, but it is careless in the case of our professional-grade tools because binding the blade in the wood this way creates what we call a “high pressure cut” placing a tremendous amount of clamping force on the thin, extreme cutting edge. Doing the “chisel wiggle” in this high-pressure situation will damage the cutting edge dulling it quickly. If you doubt this, please dig out your hand-dandy loupe and do a before-after comparison.

In addition, the time lost extracting the chisel and the resulting interruption in the workflow caused by repositioning one’s hands, and perhaps even setting aside the hammer (egads!) while doing the chisel wiggle, makes it impossible to maintain an efficient cutting rhythm. If you doubt this, we double-dog dare you to do timed comparative tests. The difference in efficiency will become instantly clear.

People accustomed to using Western chisels with their softer, more plastic blades made from high-alloy high-scrap metal content steel with higgledy piggledy crystalline structure are actively taught to use the chisel like a crowbar to lever waste out of cuts. This is another type of “high-pressure cut” that damages the tool’s cutting edge at the microscopic level.

The sharpened screwdrivers sold as chisels in the West nowadays are relatively soft, can’t be made that sharp to begin with, and they dull significantly during the first few hammer strikes anyway, so most people can’t detect the edge degradation the chisel wiggle and prying create. Those who are satisfied with sharpened screwdrivers don’t buy our chisels so I have no advice for those poor benighted souls, only prayers: Namu Amida Butsu. But it is of little matter: they seldom have the sharpening and tool skills required to tell the difference anyway. Horse, meet water; Ah… not thirsty I see.

The Chisel Cha-Cha

Now that we have explained what not to do, let us examine what we should do instead.

Here is wisdom: A more efficient, more craftsman-like way to remove waste when cutting a joint is to stop striking the chisel with hammer during each cut just before the chisel binds, or just before waste clogs the joint, and then, without changing your grip on its handle or losing a beat in your cutting rhythm, flick your wrist forwards or backwards so the chisel blade flips the waste out of the joint you are cutting. And Voila! No time lost extracting a stuck blade or setting down and picking up your hammer; and no repositioning your grip on the chisel. And the cutting continues uninterrupted.

Its very much a crisp dance step performed by hammer and chisel with a rhythm something like: “chop, chop, flick, (reposition chisel for next cut)… chop, chop, flick, (reposition chisel for next cut) … chop chop flick.” With each “flick” bits of cleanly cut wood fly out of the joint. But please use your hands, not your feet.

Next let’s examine the nexus between hammer weight and avoiding the dreaded chisel wiggle.

The Dance of the Hammer and the Chisel

Cha Cha

As mentioned above, the way to avoid the chisel wiggle and instead dance the more efficient chisel cha-cha is to avoid banging the chisel into the cut too deeply/tightly. You need to stop hammering just before the blade binds in the cut, precisely and unconsciously controlling the depth to which your hammer drives your chisel, stopping just before the blade binds. Easy to say but difficult to accomplish if the hammer is too heavy. On the other hand, too light a hammer is also inefficient. Therefore, there is no one-size-fits-all-situations hammer weight.

A well-balanced, stable hammer with a handle that fits your hand/arm, and of a controllable weight makes it easier to develop and maintain this precise, unconscious control. Lots of factors are involved but the weight of the hammer/chisel combination is the most important one of the bunch.

How to determine the best weight? It changes with the work and tool and material and the nut holding the hammer so trial and error is the only practical solution. But generally, a hammer that feels a bit on the light side is best. And a good handle makes a world of difference. More on that in future posts, so stay tuned.

Summary

The following summarizes the points you should take away from this series of articles so far.

  1. Select a hammer weight that balances well with the width and weight of the chisel, the hardness of the wood you are cutting, your body, and the type of cuts you are making.
  2. The hammer should not be so heavy that you cannot precisely control the chisel’s depth of cut while maintaining an efficient cutting rhythm close to the natural frequency of the hand/arm/hammer assembly;
  3. Don’t drive the chisel so deeply into the wood that it binds forcing you to wiggle the chisel, or heaven forfend, set down your hammer to extract it;
  4. Use your sharp chisel for cutting wood, not prying out waste like a screwdriver. Instead, remove waste from the joint you are cutting by flicking your wrist without stopping, disrupting your cutting rhythm, or setting down your hammer.

There is nothing to stop you from using your hammer and chisel as a graceful but oh so violent dance team, so enjoy!

In the next installment in this tale of bold hammers and graceful chisels we will examine in more detail the rhythmical motions involved in doing chisel-work efficiently and the role of the hammer in that dance. No champagne or pretty girls but there just might be a song or two.

YMHOS

Other Posts in this Series “Hammers to Use With Our Chisels”

Part 1 – Hammer Varieties

Part 2 – Hammer Faces

Part 3 – Hammer Weight

Part 4 – The Chisel Cha-Cha

Part 5 – Rhythm & Song

Part 6 – Hammers & Health

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.” We aren’t evil Google or incompetent facebook and so won’t sell, share, or profitably “misplace” your information.

Hammers to Use With Chisels Part 1 – Hammer Varieties

Yet such is oft the course of deeds that move the wheels of the world: small hands do them because they must, while the eyes of the great are elsewhere.

Elrond
A modern-style 750gm gennou head hand-forged by Kosaburo, hung with a black persimmon handle. I purchased this high-quality head over 33 years ago. An heirloom tool and a good buddy.

This is the first article in a six-part series that condenses the advice we have given to our Beloved Customers over the years regarding the hammers they should use with our chisels. While some of this information is relevant to our warranty, all of it is relevant to how well our chisels will perform and the pleasure our Beloved Customers will enjoy using them.

In this first part we will focus on the varieties of hammers we recommend. Subsequent articles in this series will focus on appropriate hammer weights and faces, how to use a chisel efficiently, the “chisel cha-cha,” the importance of rhythm, as well as a discussion about health and hammers. There may even be a song or two to hum along with. Helluvalot better than a performance of Cats, and cheaper too.

In the future we will present several different series, one with more details about hammer heads, and another explaining why and describing how to make a handle for a Japanese gennou hammer (or any hammer for that matter), with scaled reference drawings. We will of course provide the entire contents of these articles in a single wiggling bundle to our Beloved Customers that purchase one of our gennou heads. Yes, there are more perks to being a Beloved Customer than simple toe-curling joy (ツ)。It’s a cunning plan, you see.

Hammer Materials

30mm Atsunomi by Kiyotada

We sell tatakinomi chisels such as oiirenomi, mukomachinomi (mortise chisels), or atsunomi all designed to be motivated by the most efficient method available, namely a steel hammer swung by human hand and arm. I won’t debate the pros/cons of steel hammers versus wooden mallets versus plastic mallets versus brass hammers versus unobtanium-platinum alloy hammers in this post because the physics are as obvious as a lemur in a lingerie shop (they’re a bit hairy, they jump and climb all over the displays and bras don’t quite fit them right) beyond noting that a hardened steel hammer imparts more energy to a chisel in a more easily focused and controllable manner than any other type of beater considering the economics of both initial cost and repair/replacement cost. Some may disagree; A mind is a terrible thing to taste.

The advantages of the steel hammer are quite obvious, even without doing energy calculations, but are there any disadvantages? Mochiron (Japanese for “of course”).

Steel hammers can concentrate so much energy on a tool handle so efficiently and so quickly that they may eventually destroy the handles of the sharpened screwdrivers sold as chisels nowadays in Western countries due to a faulty design detail. It’s this silly design flaw most modern Western chisels share that motivates people to use softer, fatter, energy wasting mallets made of wood, plastic or rawhide. So sad. 

An obvious solution is to use a steel hammer of a reasonable weight along with intelligent technique to effectively keep the energy imparted to the chisel within acceptable limits. But this may not be enough if the chisel design is weak.

Ooh ooh! I got’n idea. Why not design and manufacture a chisel that a steel hammer won’t destroy as a matter of course? Wow! Such an innovation would be right up there with the rumors I’ve heard of buggies that move without horses. Imagine that…

Fortunately, the tataki nomi chisels we sell are professional tools designed to be struck by steel hammers so they need not be coddled. They have a mild steel kuchigane (coned ferrule) fitted where the handle meets the blade, and a mild-steel hoop, or crown seated at the butt end of the handle. When properly fitted to a dense, straight-grained Japanese oak handle, this steel furniture does a great job of protecting the handle from splitting or breaking.

However, along with the handle, these parts do need to be setup properly to ensure they continue to protect the handle for a long time. We have provided clear instructions for how to perform this setup job here.

So, please use a hardened steel hammer with our chisels.

But there is more to hammers than just materials, so let’s continue onto the next subject.

Japanese Hammer Types

A Kosaburo head with a brand-new nuclear-flash colored Osage Orange handle

The traditional hammer used in Eastern Japan for striking chisels and general carpentry work is called a “gennou” pronounced “ghen-noh.”

Janus Coin

The gennou common to Eastern Japan is a simple symmetrical cylinder of one sort or another with a flat face on one end and a domed face on the other, often called the “ryoguchi gennou,” or the “Janus Hammer” by those with a classical education. No claws, no pointy tail. The flat face is used for striking chisels and pounding nails. The domed face is used for something called “kigoroshi” and for the last stroke when setting nails. It’s a handy tool and more stable in the swing than a claw hammer. It’s a matter of physics.

Japanese carpenters use a specialized nail bar for pulling nails effectively increasing the lifespan of their hammer handles, so claws are not necessary.

3 gennou heads. The far left head is a simple economy head. The center head is a higher-grade head slightly flared towards the ends. The far right head is an entirely hand-forged classical “swollen eye” tool by Kosaburo.

The Yamakichi style gennou head (see photo below) is another variety popular primarily in Western Japan. The tail is not pointy but rather a small square face that is useful for starting small nails and for “ tapping out” plane blades. The face typically has a slight curvature which is helpful for setting nails, but not enough to damage a chisel. The moment of inertia is less than the symmetrical gennou head so it is not as stable in the swing, but it is still a fine head.

A “Yamakichi” style head by Hiroki with a mellowed Osage Orange handle

The pictures below are of a gennou head called “Funate,” which translates to “boat hand.” I have heard it originated with ship carpenters, but am uncertain. The tail end is a small square as you can see from the photo, and is handy for setting nails. It makes a great finish hammer, but as a hammer for striking gennou it never appealed to me. But there are plenty of craftsmen that love this hammer.

a Funate gennou with a bubinga handle

Any of these hammers will do the job: it’s all personal preference.

Western Hammer Types

The purpose of this article is is not to suggest that our Beloved Customers must use a Japanese hammer when beating on our chisels. In fact, nearly any variety of quality steel hammer can be easily modified to do the job satisfactorily, including claw hammers, engineer’s hammers, or even ball peen hammers, so it isn’t necessary to buy a special hammer.

Please note that the closer the hammer’s center of mass is aligned with the center of the striking face, and the higher the hammer’s moment of inertia, the better. A cylindrical head is the closest to ideal from a physics viewpoint.

We’ll talk about the governing physics of hammers in future posts for those Gentle Readers that enjoy math.

In the next post in this series we will examine the type of face a hammer used to strike our chisels should have. Please come back and bring your lingerie-loving lemur friends. A Brazilian body wax is not required.

YMHOS

Other Posts in this Series “Hammers to Use With Our Chisels”

Part 1 – Hammer Varieties

Part 2 – Hammer Faces

Part 3 – Hammer Weight

Part 4 – The Chisel Cha-Cha

Part 5 – Rhythm & Song

Part 6 – Hammers & Health

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.” We aren’t evil Google or incompetent facebook and so won’t sell, share, or profitably “misplace” your information.