In the previous post about designing a handle for your gennou hammer on paper we discussed the reasons for making a drawing and a few of the details. In this post we will begin by representing the head and its key lines in our drawing.
But first, a disclaimer. Some of our Gentle Readers will find the idea of making a drawing in preparation for making something as apparently simple as a handle from a single stick of wood nonsense. Indeed, I felt the same way once, but I was wrong. That is not, heaven forefend, to imply that our Gentle Readers could ever possibly be wrong in anything they undertake, or less than towering intellectual giants, only that the lowly gennou handle is not as simple as it appears.
You may recall your humble servant mentioned the two points listed below in a previous post. They remain valid principles that should guide your eye and hand when making a drawing. Or, if wood costs you nothing and your time is worth even less, feel free to ignore them.
The first point goes like this: “When making some things, past a certain point there is simply no room for either improvisation or trial & error without starting all over again.”
The second point is a little longer, but no less valid: “The principle of “less is more” absolutely applies, but achieving an elegant and functionally superior “Less” is neither accidental nor serendipitous, but can only be consistently realized through “More” thought, planning, and eyeball time, things difficult to do without a drawing.”
A Sample Drawing
The drawing below is an actual drawing your humble servant prepared for one of his gennou incorporating a 375gm (100monme) classical-style head by Kosaburo. Although it’s a simple drawing made entirely by hand, it includes all the critical details other than the species of wood and flow of the grain. Please notice that it consists of a top view, side view, end view (butt) and 2 sections, all combined in a one-sheet, compact drawing.
You will want to make a similar drawing incorporating all the lines shown but adapted to your gennou head, your body’s dimensions, and your preferences.
You can download this drawing in jpeg format by clicking the link below.
You can make your drawing on paper or wood, with wood being the more durable medium since ancient times because it does double duty as both parchment and drafting board, and can be erased entirely with a handplane. Moreover, the combined drawing and drafting board can be hung on a nail on the wall for future reference without fear of deterioration. But paper is easier to use.
Begin by making one horizontal parallel line across the sheet of paper. In the drawing above, this is the horizontal line touching the flat face of the hammer labeled “Striking Face.”
When orienting your head on the drawing, the flat striking face must face towards the bottom of the page. The head’s brand will be nearest the striking face and facing towards the right edge or butt of the handle.
Draw a vertical line, of course perpendicular to the Striking Face Line you just drew, and to the left of the page through the centerline of the gennou head. We will call this the “Vertical Centerline.”
Next, draw a horizontal line parallel with the Striking Face line, through the perfect center of the head’s eye (the mortise hole in the gennou head). To do this, you will need to first mark the center of the eye on the Vertical Centerline.
Begin by measuring the distance from the actual head’s striking face to the endwall of the eye closest to the striking face, and transfer this distance onto the Vertical Centerline starting from the Striking Face line using either a vernier caliper or a sharp compass.. Then measure the interior length of the eye, and add this distance to the measurement you just made. Now you have the location of both endwalls of the eye located on the drawing. Divide this line in half using your calipers or compass, and you now have located the center-point of the eye.
Be sure to precisely measure and mark these distances because if you get it wrong, problems will result.
Then draw a “Horizontal Centerline” through the center-point of the eye across the sheet, of course perfectly parallel with the Striking Face line.
Next draw two more horizontal lines from the top and bottom endwalls of the eye across the page. The width of these two lines is labeled “Eye” on the side-view drawing above.
Place the head on the drawing, with its flat face perfectly flush with the Striking Face line. You may want to lay/clamp a piece of wood along the Striking Face line make sure you get the head oriented properly centered on the vertical and horizontal centerlines you drew earlier. Then draw the outline of the head on the drawing.
Insert the wooden layout tenon you made previously into the eye, place the head back on the drawing as before, and transfer the layout tenon’s outline onto the drawing. If the eye is perfectly perpendicular to the head’s centerline then the layout tenon may not be necessary, but using the layout tenon helps to ensure the eye’s angle is accurately represented in the drawing to avoid unpleasant surprises.
Draw the Key Lines for theTop-view
Moving onto the Top View, make another horizontal line 5~6 inches above the Horizontal Centerline across the page. This line will be the centerline through the head and handle seen from above. Measure the width of the eye (the narrowest dimension), divide it in half, and transfer it to the drawing. Draw two horizontal lines from the location of the eye’s endwalls across the page. These lines are labeled “Eye” on the Top View.
Place the gennou head on the drawing and trace the outline of the striking face.
The head, it’s striking face and profile, the width, length and angle of the eye, the centerline of the handle in both side view and top view are all now accurately represented on the drawing.
In the next post in this series we will measure your body and add those details to the drawing. You don’t need a Savile Row tailor for this task, but if you have one just lounging around on your couch, hogging the remote control, drinking your beer and smoking your cigs, go ahead and put the bum to work! (ツ)
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, incompetent facebook or the owners of Tik Tok and so won’t sell, share, or profitably “misplace” your information. That would be criminal.
Previous Posts in The Japanese Gennou & Handle Series
This is the first of six posts in a sub-series describing why and how to make a full-scale drawing in preparation for making your gennou handle.
Please note that the principles described in these posts on Japanese gennou handles apply to all varieties of hammer and axe handles, and can be adapted to Western tools with great success.
Why Bother Making a Full-scale Drawing?
The greatest fun in working wood as a hobby for your humble servant is watching an object evolve in my hands, sometimes magically becoming better than what I had imagined it would be. Many Gentle Readers have the same experience.
My day job in Japan’s construction industry is not so fancy free: I spend too many hours each day planning, discussing, reviewing/marking-up, and writing about complicated drawings, so drafting a drawing to make something from just a single stick of wood feels kinda silly on the one hand and too much like real work on the other. But despite these conflicting emotions, please understand I am dead serious about the importance of a drawing, and you should be too.
So why am I recommending you make a drawing? There are 3 reasons:
Record of Ergonomic Parameters
A gennou design must begin with the fixed parameters of your gennou head, but there are several ergonomic measurements from your own body you will need to incorporate into your handle design and meld with the specific details of the head you select. This isn’t difficult to do, but because every head, every body, and therefore every handle is different, and because there are a surprising number of details that must be combined, it can be difficult to get everything right without a drawing, especially the first few times.
Develop an Elegant Minimalistic Design
The second reason for making a drawing before you make sawdust is that the gennou I am teaching you how to make is in every way a minimalistic object comprised of only two simple components the details of which require thoughtful planning to get right.
Allow me to share a couple of points about minimalism I learned from observing the successes and failures of world-class architects and designers in New York, San Francisco, London, Hong Kong and Tokyo: When making some things, past a certain point there is simply no room for either improvisation or trial & error without starting all over again. Assuming one is not so fatuous or deluded as to accept a monkey’s scribbling as high-art, you can imagine the resulting potential for wasted time and money and brain cells.
The famous architect Frank Loyd Wright once said: “An architect’s most useful tools are an eraser at the drafting board, and a wrecking bar at the site.” Which of these tools used with skill do you think is the most cost and time effective?
Here is wisdom: The principle of “less is more” absolutely applies, but what most people not involved professionally in the design and fabrication of expensive minimalistic physical objects do not realize is that achieving an elegant and functionally superior “Less” is neither accidental nor serendipitous, but can only be consistently achieved through “ More” thought, planning, and eyeball time, something difficult to do without a drawing.
How does this apply to making a simple gennou handle, you ask? Excellent question; You really are paying attention, I see. Once you have cut or shaved away too much wood (even a single shaving can easily be too much), there can be no more thinking, planning or eyeball time without starting over, wasting much of your valuable time and wood. Best to avoid that nonsense if possible, don’t you agree?
Take a Mulligan
The third reason for making a drawing is related to the first and based on the unfortunate likelihood that your first attempt is unlikely to produce ideal results. But don’t be discouraged because your second attempt will be much better. If you begin with a drawing, by the third attempt you will have figured out precisely what works best for you, knowledge that will serve you well your entire life. I promise.
In order to accomplish the goal of the perfect handle in just two or three iterations you will need to record the measurements, assumptions and changes you made each time so you can effectively fine tune them without having to start from scratch each time. A drawing is the best tool for this purpose.
A drawing will also help you eliminate repeated errros. A drawing will also help you eliminate repeated errros.
What to Include in the Drawing
I recommend you make a full-scale drawing of the handle viewed from the side, the top (back) edge, and the butt for a total of 3 viewpoints on a single piece of paper. You should also make cross sections at several locations at the handle inside the side view.
It is also useful include general dimensions, such as overall length, width at the eye and width at the butt to help you select a suitable piece of wood.
Developing Drawing Skills
Many have no experience making drawings. That’s perfectly OK. The only way to become competent at making simple drawings using orthographic projection is to do it.
The basic idea of orthographic projection is to represent a 3-D object in 2-D drawings, usually a side view(s), top/bottom view, and end view(s), but for the purpose of drawing a simple gennou handle without power windows and tuned exhaust, a side view, top view, end view and a few simple sections are plenty.
The drawing below is one I made for one of my gennou showing just top and side views. As you can tell, it starts with the head. Sorry, no sections. I will provide more drawings beginning with the next post.
If you are serious about making quality objects in wood long-term, the ability to make a simple drawing is a skill you should develop. The drawing doesn’t need to be pretty, it doesn’t even need to be detailed if you are making it for your own use, but it should represent and record things like dimensions, straight line/curves, and the locations of features.
“Why can’t I just do it in my head?” you ask? Of course that is an option; There are times when we all shape wood as we imagine it, the instant we imagine it.
But a drawing lets you combine and adjust details, wait some time to grow “fresh eyes,” and examine the product. A drawing makes it easy to make fine adjustments to a minimalist object. It lets you share the design with others and get their opinion. It lets you record your successful designs for future use. It is a powerful tool, one that will improve your woodworking skills.
And with practice, the act of making drawings refines your eye and your imagination, improving not only your design ability on-paper, but your ability to create an object in your head and examine it from different angles. Just ask any second-year architecture student.
Tools for Drawing
I will go into more details about drafting tools every woodworker should own and become proficient with in a future post, but in preparation for producing the drawing we will begin in the next post, and assuming you will make the drawing on paper instead of a board, you should gather the following minimal tools:
Drawing board: A plain wooden board with four straight sides and square corners at least a little bigger than the finished gennou. Any smooth, flat board will suffice;
Paper: Better quality drafting paper, vellum, or mylar is best, but any smooth, white paper will suffice;
Masking tape: To secure paper to board (drafting tape will damage the drawing least);
Straightedge: 12″ or longer (must be truly straight);
Mechanical pencil with lead;
Eraser: A good quality one that won’t leave smudges;
Square: A clean framing square without burred edges will suffice;
Drafting Triangle: A 45° plastic or steel drafting triangle, with minimum 8″ legs (cheap is OK);
Compass: With pencil;
Divider: With sharp points;
Vernier caliper (not mandatory but helpful);
Eraser shield (not mandatory but helpful).
The Gennou Head
In this series we’ve looked at a lot of gennou heads of many different varieties and weights made by different blacksmiths. Now that we have are on the brink of making a design drawing, however, the time for talking is over. If you don’t have a good gennou head in-hand, please get one. The design of your handle simply cannot begin without it.
In the next installment in this story of love and longing we will begin our drawing. Please sharpen your pencils and get your eraser ready.
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, incompetent facebook, or troublesome Twitter and so won’t sell, share, or profitably “misplace” your information. May all my toes turn green and go squishy if I lie.
Previous Posts in The Japanese Gennou & Handle Series
In the previous post in this series about the Japanese gennou hammer we looked at an old-fashioned laminated gennou with some simple surface decoration and discussed its construction and benefits.
In this post we will take a gander at some other styles of expensive heads with decoration for the sake of being decorative.
Decorative Gennou Heads
For a higher price, more decorative gennou can be had. Some of these have various surface textures and finishes applied, while others have designs etched into their surfaces, with the more expensive varieties even have designs of dragons, tigers, zodiac and religious figures deeply hand-engraved into their surfaces.
One of my favorite gennou is an 80monme square head with the figure of a monkey acid-etched on one side and some Chinese characters on the other referring to the patron god of those born in the Year of the Monkey, which I am. Sorry, I don’t have the hammer with me here in Tokyo, so no pictures. It was a gift from my Japanese Mother-in-Law (RIP) and so I value it highly although I don’t use it anymore.
She had it blessed by a Shinto Priest at the same time he came to perform the annual blessing of their book-binding factory, so I consider it more of a good-luck charm than a working tool. It has not aged gracefully.
BTW, it’s not at all unusual for carpenters, construction companies and factories to have Shinto Priests perform similar ceremonies at least once a year to purify their tools and equipment and to bless their workplaces for safety purposes. Both of the large construction companies I worked for in Japan had Shinto “Kamidana” shrines in their offices and smaller ones installed at their major jobsites to encourage deities and spirits to protect the jobsite, people and tools, an drive off malevolent spirits that might cause harm.
Construction companies in Japan are especially old-fashioned this way. One large construction company I worked for in Japan was established 147 years ago. Just a youngster by Japanese standards. Perhaps the oldest construction company in Japan is Kongo Gumi Co., Ltd. established in the year 578. Other large and old Japanese construction companies include Kajima Corporation, established in 1840, Shimizu Corporation, established in 1804, and Takenaka Corporation, established in 1610. Long memories and deep traditions.
Of course, decorating a gennou head adds nothing to its functionality while significantly increasing cost, so highly-decorated heads are probably more suitable for ceremonial purposes, for displaying in a collection, or as gifts rather than practical tools. In fact, the older generation of Japanese craftsmen I learned from, now all either in their late 80’s and retired, or passed on to the big lumberyard in the sky, considered such decorated tools frippery beneath the dignity of a respectable “shokunin” (a wabi sabi sorta thing) and would mercilessly rib someone who brought a gaudy tool to the jobsite or workshop.
If you are considering purchasing a decorative gennou head, one factor you should seriously consider is the appearance of the head after many years of use. After all, a quality gennou head should be a lifetime investment and an heirloom tool. It may look as beautiful as Raquel in her fur bikini when new but will it look better than my scratched and rusty etched zodiac monkey head after 20 years of use?
Some heads pictured in this article show a pattern-welded structure known as “Damascus” in the West, or “Suminagashi,” meaning “ flowing ink” in Japan. This structure is not the famous Damascus steel developed in the Levant centuries ago and made famous by sword blacksmiths. It is simply a mix of at least two different types of steel, one of which resists oxidation/discoloration when exposed to an acid wash, creating the difference in color. Theoretically, this construction neither improves nor harms the performance of the steel so long as the deferential hardening process is handled properly, but personally, while it looks fun, I distrust this material for gennou heads and blades that must do real work.
Other heads have received fancy decorative surface treatments that neither harm nor improve a hammer’s performance. However, being decorative, one should consider the durability of such treatments. Chrome, nickel or copper plating, for instance, will not remain unchanged long in the case of a hammer used frequently on the jobsite or if laid on the concrete floor of a workshop frequently. Color case hardening, pickled finishes, paint, and even most bluing will look nasty and may rust before too long.
Perhaps the most durable surface is the black oxide that forms naturally on the steel surface during the heat-treatment process because it is reasonably rust resistant and naturally harder than the steel/iron it covers. It’s my favorite, but for some reason doesn’t seem to attract the ladies. Bummer. Decisions, decisions…
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, incompetent facebook, or a driver for Speaker of the US House of Representatives and so won’t sell, share, or profitably “misplace” your information. May the bird of paradis fly up my nose if I lie.
Previous Posts in The Japanese Gennou & Handle Series
In the previous post in this series we talked about the difference between mass-produced and hand-forged gennou heads. In this post we will take a look at a more antique style of gennou head.
A Laminated Gennou Head
Prior to the advent of cheap imported steel from Europe, gennou had bodies forged of soft low/no-carbon steel with wafers of hard, high-carbon steel forge welded to each face. The shiny strips called “ Hachimaki” meaning “ headband,” polished onto the sides of the ends of genno heads sold nowadays are vestiges of this old-timey method.
The photos above are of a laminated gennou head hand-forged by Kosaburo which came to me long ago as payment for a debt. Laminated gennou heads made this way are still available today at exorbitant prices. I understand Hiroki occasionally makes a few.
Some believe the combination of hard face and soft body produces a softer impact and less vibration making the gennou less tiring to use. Others prefer the slightly different sound a laminated gennou head makes. I have used this laminated Kosaburo head for many years, and while I am very fond of it, I cannot detect any advantage to its laminated construction.
While laminated gennou are much more expensive, the blackmsiths I have spoken with have told me that they are significantly easier to make than one-piece high-carbon steel gennou since they do not require the more difficult differential hardening process. And they all agree that laminated construction provides no practical advantage to the end user. A practical curio in other words.
If you are just getting started in woodworking, or are on a tight budget, a quality mass-produced genno head will do the job if you clean up the eye and replace the handle with one that fits your body.
Better yet, buy a hand-forged head by Hiroki or Kosaburo and make your own handle in the best craftsman tradition.
However, if you have the budget and enjoy collecting traditional tools, then by all means try a laminated gennou head. They are not easy to find nowadays.
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 shorts if I lie.
The gentle reader will never, never know what a consummate ass he can become until he goes abroad. I speak now, of course, in the supposition that the gentle reader has not been abroad, and therefore is not already a consummate ass. If the case be otherwise, I beg his pardon and extend to him the cordial hand of fellowship and call him brother. I shall always delight to meet an ass after my own heart when I have finished my travels.
Mark Twain, The Innocents Abroad
In the previous post in this series we discussed the various styles of gennou heads you might consider when planning a custom-made gennou that fits your body perfectly, as well as the range of weights for each application.
While one has few options besides either using a mass-produced head or making one yourself nowadays, in Japan there are still a few blacksmiths that specialize in hand-forging high-quality gennou hammer heads. In this post we will compare mass-produced heads and hand-forged heads to help you make an informed decision.
Comparing Mass-produced Heads to High-quality Hand-forged Heads
When selecting a gennou head you have the choice of a mass-produced gennou (usually with a handle attached) or a handmade gennou head without a handle, if you can find one. Lets examine the differences.
Mass-produced genno are readily available, relatively inexpensive and for the most part, entirely useable. However, as with any product, it is wise to inspect a gennou carefully before purchasing it, as discussed in a previous post in this series, or to at least buy from a retailer with a solid return policy. When purchasing any gennou, check to make sure the eye is centered in the head and not skewed.
The practical advantages of a hand-forged gennou hammer head over a mass-produced factory head are as follows:
Proper differential hardness;
Precise eye placement;
Uniform interior dimensions of the eye, resulting in time saved and aggravation avoided;
Faces are square with the long axis of the head;
Unique appearance and pride of ownership.
Let’s examine these five points in more detail next.
Most Gentle Readers will have never given this matter any thought, but the quality of the heat treatment matters… a lot. This is a chemical/crystalline property impossible to confirm long-distance, so we must rely on the manufacturer, be it factory or blacksmith, to get right. Therefore, the manufacturer’s QC reputation as well as the retailer’s guarantee also matters.
A good head will be hard at the faces, becoming gradually softer towards the the eye, certainly softer than a file, to make the head “tougher,” using the materials engineering term, and to reduce resonant harmonic vibrations. If you have used hammers with uniformly hard heads and integral steel handles you have felt this tiring vibration before.
The faces must be hard, around 50~55Rc, to prevent deformation, but not so hard the hammer will chip or crack. You may think that wooden chisel handles could not deform a steel hammer face, but if the striking faces are not properly hardened, they will mushroom sure as eggses is eggses, something your humble servant learned when he made a gennou head for himself from octagonal bar stock back when dinosaurs roamed the earth.
It’s interesting to note that the handle I made so long ago was straight, unlike the handles your humble servant currently advocates, and that lower 1/3rd of the face mushroomed, while the upper 2/3rds did not deform at all. Curious…. This was the first time I really noticed that the head of hammer with a straight handle attached perpendicular to the head’s centerline tends to hit the chisel/nail cocked and not in-line with the long axis of the chisel/nail. I also realized that the direction of flow of this steel indicated a lot of energy was being wasted by my straight handle. I hope you can see why the solution the anaya carpenters of Japan developed so long ago resonated with me so strongly.
But what happens if the heat treatment results in a head that is too hard? In this case, while the head and faces may not deform, the face may chip and the entire head may fracture, sometimes even causing embarrassing leakage of sticky red stuff.
A word to the wise: always use properly heat-treated hammers and wear safety glasses when pounding nails, mixing acid, or writing your name on your forehead in pen after losing a tequila shot contest.
Precision of the Eye
Gentle Readers may think it passing strange that your most humble and obedient servant is seemingly fixated on the precision of something as boring as the hole in a hammer’s head. Rest assured, this concern is not a fever dream resulting from an obsessive/compulsive over-analysis of negative space, but was born of bitter experience. My new therapist concurs.
Of all handtools, the hammer is one of the simplest. But is also the one that moves the fastest and is most influenced by dynamic physics. Things like concentricity, center of gravity, and moment of inertia make a difference to an object moving this quickly, then suddenly slowed by an impact with a chisel or nail, and then returned to battery for another blow faster than you can say ouch. Negative spaces like holes influence the physics, and therefore the stability, of hammer heads. Don’t make me inflict you with differential equations, just take my word the hole needs to be centered, not skewed, and of uniform size or the hammer will be skittish.
Another advantage of a well-made gennou head is that its eye will have uniform interior dimensions. We talked about this in an earlier post. In summary, all four walls will be straight, clean, flat, free of wind, parallel and square to each other. This matters because a sloppy eye will not apply uniform pressure on the handle’s tenon, ensuring it will come loose sooner than later. In addition, this uneven pressure may also induce unwanted vibrations in the handle.
If a gennou head has a sloppy eye, it needs to be trued, a task that is difficult to accomplish using files. Depending on the degree of error, correcting the inside walls of that tiny hole in a steel head with tiny files can be frustrating work and may even help your therapist buy that new bimini top he wants for his fishing boat. You see, most people make the problems worse the first time they try to correct them. If you count your time worth anything, the extra cost of a precision eye is money well spent, and certainly cheaper than a new bimini top.
Precision of the Face
Let’s move on to item 4 “Faces are square with the long axis of the head.” The striking faces of mass-produced hammer heads are often not square with the head’s axis, resulting most obviously in bent nails, but the less obvious consequence is that energy we intended to transmit directly to the chisel and into the workpiece ends up being wasted as heat and violent movement of the chisel out of alignment. It also wastes time and undermines the user’s confidence, once again providing a windfall to head doctors everywhere.
A hammer made using a good head and a handle made to fit both that head and your body will perform better than any tool you have experienced before. You won’t need to look when you pick it up to tell which face (or claw/vs face) is oriented towards the nail/chisel because your fingers will know instantly. The handle will fit your hand perfectly without slipping or causing blisters or needing to be “choked-up on.” You will be able to sense beforehand exactly where the center of the hammer’s face will strike, and will be able to hit the target dead-center and squarely even with your eyes closed.
The hammer that is stable during the swing and makes a solid impact exactly where you aimed it without producing strange vibrations or wasting energy will help you make every strike with confidence and greater control, and will make your woodworking more enjoyable and profitable. Not insignificant benefits.
Appearance and Pride of Ownership
And finally, let’s examine the more ephemeral item 5: “Unique appearance and pride of ownership.” I have mentioned it elsewhere before, but it is a fact that, no matter how much they may deny it, humans are competitive beasties in all endeavors.
As a day job your humble servant manages construction projects in Japan and spends a lot of time inspecting jobsites, meeting with construction companies and speaking with craftsmen. Indeed, there was a time when I was labor instead of management on construction jobsites, so I have enough experience to know that while professional woodworkers may not care about hair fashion or fine Italian footwear during the workday, they are conscious of their personal performance, and the performance of their tools, in comparison to those of their peers. It’s a guy thing, something women think they understand because they have similar tendencies in other areas, but rarely do. This performance is difficult to ascertain unless one is working side by side with one’s peers, so it is human nature to make indirect judgements about performance by observing the quality and condition of a fellow worker’s tools.
Of course, one casually notices the brand of chisel or plane a fellow craftsman is using. Next, if it can be done without being rude (sometimes a difficult thing to accomplish), one examines the fellow workman’s tool’s cutting edge and its sharpness because this tells much about his character and skill (chisels are terrible gossips, you see). Such a close examination may not be possible, but one can usually examine the finish left by his plane and crispness and precision of his chisel cuts.
But more than plane or chisel, the tool that is always visible to others during the workday is the craftsman’s hammer comprised of the head forged by the blacksmith, and the handle made by the craftsman himself. The quality of this combination tells Japanese craftsmen much about the man that owns and uses the tool. A hand-forged head by Kosaburo or Hiroki with a graceful, professional-grade handle made by the owner, even if it is dinged through years of hard use, will be noticed by those with eyes to see for decades, even generations.
Among the Japanese professional woodworkers your humble servant knows well, most of whom ceased getting older long ago, a highly-decorated expensive head is thought to be a gaudy, obvious plea for attention, and in poor taste, like wearing a purple sequined silk suit and Jimmy Choo 8″ gold lame stilettos to the hardware store (best saved for the New Years party, you sexy beast). A plain head by Hiroki or Kosaburo, on the other hand, is understated tasteful evidence of a serious craftsman that appreciates tradition and places quality first. Very much a wabi sabi kinda thing.
And finally, a quality hand-forged head is a lifetime tool, one that won’t wear out or break. The handle may be damaged and wear out over time and need to be replaced, but such wear and tear is unavoidable if the tool is actually used, like a good pair of workboots. But the handle made for a quality head will last longer and be much much easier and quicker to replace. To the professional focused on turning his time into money, this is not an insignificant consideration.
A mass-produced factory head, by comparison, simply won’t work as well. It is of course neither high-quality, unique, nor a lifetime heirloom tool. It isn’t pleasing to the owner’s eye nor impressive to his fellow workers. It is a consumable, expedient tool, the sort of thing a craftsman does not want himself to become.
A high-quality head combined with a handle that fits your body will accomplish more work more precisely with less mental concentration and physical effort. It will become a lifetime friend and a source of satisfaction boosting your confidence. It will be relatively easy to make replacement handles for during your lifetime, and those handles will stay tighter longer. It will tell those who see it that you are serious, no-nonsense craftsman who understands true quality and prefers understated elegance.
If you take pride in your tools, appreciate heirloom value, don’t want to waste time reworking sow’s ears into silk purses, and are not inclined to invite psychiatrists to rummage around in your head, then a hand-forged gennou head is worth owning, in the opinion of your most humble and obedient servant.
In the next post in this swashbuckling adventure on the high seas we will try to dispel some rumors about laminated gennou heads.
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.
In the previous post in this series about Japanese hammers we examined a feature found in all modern hammer heads: the essential, unblinking unseeing eye. In this post we will touch on the style of heads recommend for using with Japanese chisels. We discussed this subject in this postas well.
Gennou Head Shapes
The most common head shapes commonly available in Japan nowadays are: ryoguchi, daruma, funate, yamakichi and various hybrids thereof.
Ryouguch is the most common style of head, at least in Eastern Japan. It has two faces: A flat one for striking chisels and nails, and a slightly domed opposing face for kigoroshi and setting nails below the surface of boards.
While a simple design, this style of head has a relatively high moment of inertia, making it is more stable than other styles and therefore less likely to twist out of alignment during the swing, or twitch upon impact, a positive thing if you are a card-carrying member of NBA (Nail Benders Anonymous). (ツ)
Face designs in this style vary widely including round, oval, square, rectangular (usually with corners removed for a more octagonal shape) true octagonal, and the “Ichimonji” style with roundish sides and a flat top and bottom. We prefer the rectangular shape with cut corners best, but one style is no better than another. We don’t recommend, however, faces with 90 degree corners as the corners are counter-productive during kigoroshi operations and are structurally weaker.
If you are worried about pulling nails, we encourage you to use a nail bar to reduce the number of broken hammer handles wandering the world sad and lonely as a cloud.
Named for a famous buddhist priest of oval stature who lost both arms and legs through excessive meditation in his quest for “satori,” an intensely spiritual obsession that no doubt consumes the attention of some of our more enlightened Beloved Customers, the daruma (pronounced dah/rhu/mah) style gennou head is a stubbier version of the ryouguchi gennou, always with a round face.
This style of head is more popular outside of Japan than it is domestically, for reasons your most humble and obedient servant fails to understand. From a physics viewpoint, at a given weight it is less stable than any other style of gennou, but because it has a bigger face, and is intended to be used at constantly differing angles such that stability is not so much a virtue, it is preferred by carvers. Joiners like it too for cutting repetitive mortise and tenon joints, but it is not favored by most trades and may invite remarks at jobsites from other workers about the owner being unable to find his derriere with both hands and a GPS. That said, your humble servant frequently uses daruma heads for cutting precise mortise joints. Wait a minute…. where did I set down that darn GPS tracker….?
An 80monme/ 300gm/ 11oz daruma head with an rock maple handle.
The funate gennou is closer in appearance to Western hammers with a skinnier neck behind the striking face, but without the split-tail “piano chisel” a foreman from my misspent youth named Jack Frost called the claw on his 28oz waffle-face framing hammer. It is more commonly seen in the Western Japan than Eastern Japan where I learned Japanese woodworking.
This gennou is useful for finish work involving nails and for tapping-out plane blades, but less useful for wacking chisels.
Yamakichi was the name of a gennou blacksmith working in Fukuoka on Kyushu Island that originated this style of head and gave it his name. “Yama” 山 means “mountain” and “kichi” 吉 means “luck” or “lucky.” Kosaburo introduced this style to Tokyo in response to customer demand and with Yamakichi’s permission, we are told, improving the design somewhat.
This style is a heavy-duty stubbier version of the funate with a slightly domed face and a kinda sorta pointy tail, perhaps better suited to driving/setting nails than the ryouguchi head, but certainly better for striking chisels than the funate style.
Better with nails than the ryouguchi style, this head makes an excellent all-round hammer for working in the field, and can even handle tapping-out and kigoroshi tasks.
The design has a unique and interesting appearance which reminds this humble scribbler of a 1956 Ford F100 truck in that, while neither sleek nor smooth, it has a sculptural quality not seen in the other styles that “grows on you.” It feels good in the hand.
There are other in-between head shapes, but these are the four basic styles generally available for woodworking today.
The subject of gennou head weight was examined at some length in a previous post.
Regardless of the type of gennou head you select, weight is a critical factor that will depend on what you plan to hit, your height above the thing you are hitting, how hard you need to hit it, and how precisely you need to hit it. Your own practical experience is the best basis for selecting the genno weight for a particular job, but some guidelines can be suggested.
To begin, the traditional measure used for gennou in Japan is the “monme,” with 100 monme equaling 375 grams or 13.2 ounces (1 ounce = 28.35 grams).
The standard middle-of-the-road weight for genno used by carpenters in Japan is 100monme (375grams/ 13.2 ounces). The most common hammer used for finish carpentry in the United States weighs 16oz = 120monme, a size commonly available in gennou too. So if you are going to buy your first gennou, and you intend to use it for general finish carpentry or furniture making, a 100 or 120 monme genno is a good place to start.
For finer work, an 50-80 monme (11-7 oz) to gennou is a good choice. If you intend to make furniture or joinery, one in this weight range is a must-have.
For cutting deep mortises in heavy timbers with large chisels, as in timber framing or boat work, a 200monme (26oz) hammer is frequently used, but 250 (33oz) and even 300monme (40oz) heads are available. I own and use them when necessary. Some factors to consider when selecting a heavy gennou are that with greater weight comes greater impact force, and greater penetration, but heavier gennou are more tiring to swing and harder to control precisely.
Other factors to consider are the width of the chisel blade being used, since a wider blade requires more force to cut to a given depth, and the hardness/toughness of the wood being cut. Only experience can tell Gentle Reader what weight will work best in a given situation. Just be aware that, unlike bobby socks and government health care, there is no such thing as one-size-fits-all.
We hope this article has answered some of Gentle Reader’s questions on the subject of selecting a gennou head. If you have additional questions or need clarification, please use the “Leave a Reply” form below.
In the next post in this metaphysical adventure series we will discuss the differences between mass-produced and hand-forged gennou heads. We will look at woods suitable for making handles, and gennou design in much greater detail in future posts, promise.
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 by using 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.
Tempo is all, perfection unattainable, as at the top of the swing… …there’s a hesitation, a little nod to the gods that he is fallible. That perfection is unattainable.
“The Golf Swing” by Roy McAvoy
The Japanese gennou is outwardly the simplest of hammers comprised of just a differentially-hardened steel head attached to a wooden handle without wedges, pins, epoxy or rubber. But as simple as it is, there are several factors that drive this tool’s performance. One critical factor is its “eye.”
The Unblinking Eye
Since ancient times, hammer handles have ended in a “tenon” designed to fit inside a rectangular through-mortise hole in the hammer’s head called the “eye,” in English, and “hitsu” in Japanese. In Western hammers and the majority of Japanese hammers the interior walls of the eye are angled so that a wedge driven into the end of the handle will splay the tenon keeping it from slipping out of the eye. This connection works as well as can be expected, if the eye is deep and tolerances are acceptable, but Japanese gennou heads are compact and their eyes are not deep, so a better solution is called for.
The downside to securing the head with a wedged tenon is that the wedge will frequently cause the handle to split weakening it considerably. Also, a wedged connection seldom has uniform contact and pressure inside the eye and may therefore loosen as the wood wears from impact forces. In addition, uneven pressure between tenon and eye may induce unpleasant vibrations in the handle, a phenomenon you have not doubt experienced without realizing it, like an itch on the back of the neck felt long after the mosquito’s theft.
A tight, high-friction, uniform-pressure fit between the eye’s walls and the tenon keeps the quality Japanese gennou head in place and working efficiently. Straight, parallel, square, clean walls are therefore critical.
Inexpensive mass-produced gennou and hammers typically have eyes with poor tolerances hidden by the handle tenon and sometimes concealed under resin caps. The heads and handles of such hammers and gennou seldom remain securely attached if used heavily long-term. Experienced Japanese professionals, therefore, have traditionally preferred to buy just the head without a handle so they can inspect the quality of the eye before laying down any money, and then make the handle themselves. This is consistent with the frugal craftsman ideology once common throughout the civilized world wherein the craftsman would make as many of his own tools as possible, often in imitation of his master’s tools and using metal components forged by the local blacksmith, all to be completed by the conclusion of his apprenticeship and graduation to “journeyman.”
This explains the demand in Japan for high-quality relatively expensive heads such as those hand-forged by Kosaburo or Hiroki. Not only are they properly shaped and consistently heat treated, but they have precisely dimensioned eyes that will not only hold onto the tenon a long time and reduce unwanted vibrations, but will save the owner a ton of effort both truing the eye and replacing failed handles later. And since the gennou is an heirloom tool, the extra cost of such a head is not wasted.
Since so much relies on the connection between the handle’s tenon and unseeing eye, let’s examine it and correct any deficiencies revealed.
Examining the Eye
The first step in inspecting a gennou head is to check the eye because if this is wrong, then the head will not only be difficult to make a handle for, but it will be unstable during the swing and skittish on impact, intolerable failings in a tool we need to use with speed and precision unconsciously.
Just sight down the length of the head’s body with the eye in view. The eye should be of uniform width over its entire length, and the sides parallel, of course. It should also be centered in the body and not skewed. The narrow end surfaces of the eye should also be straight and square to the sides. Mass-produced gennou heads typically fail this examination to some degree, and even some expensive handmade heads will too, sorry to say. Be sure to inspect both the top and bottom surfaces of the head.
Next you need to inspect inside the eye. Use a flashlight to check the interior walls are straight, parallel, square, free of twist, and without significant bumps, bulges or gouges. You may need to make a tiny square from wood or metal to perform these checks. There are special machinists squares and depth gauges that are ideal for this purpose. An accurate vernier caliper will prove useful.
Ofttimes the eye’s walls are intentionally sloped inwards from both ends so the center of the eye is narrower than either opening. This geometry is intended to compress the tenon as it is driven through the constriction locking the tenon into the eye. The crushed tenon is then supposed to expand afterwards, essentially relying on kigoroshi to bind the tenon in the eye. This geometry does work, kinda sorta, if a wedge is driven into a sawkerf cut into the tenon. Gennou heads with this style of eye are much easier to produce and are intended for mass-production beaters. Such head/handle combinations may exhibit strange harmonic vibration, which you may or may not be able to detect, and since pressure on the wooden tenon is not uniform, swelling/shrinking of the tenon with seasonal humidity changes will always cause the head to loosen over time.
If a gennou head is secured to the handle with wedges, it may be because the eye is sloppily made, or just because that is what amateurs are accustomed to seeing, but a quality gennou head fitted to a proper handle does not need wedges to secure it no matter what Fat Max says.
Correcting the Eye
As the erstwhile golf poet Tin Cup taught the World: “Perfection is Unattainable,” so I don’t encourage anyone to go OCD over the hole in a hammer head, but if you are patient, you can use small files to true the unseeing eye to the best of your patience and ability. This may be a tedious job because only small files can be used, and that within a narrow space both difficult to see into and with little room to develop leverage.
Please be careful when filing to avoid making things worse. Remember, flat, parallel walls free of twist with clean sharp corners are the goal. Once you have trued one poor quality eye you will understand the value of a high-quality premium gennou, which has nothing to do with finish or decoration.
If your gennou head has a constricted eye, please file all four walls straight.
Whatever you do, don’t leave the walls curved outwards so that the eye is wider at any point inside than at its openings, because the handle can never be properly fitted to such an eye and will always work loose.
Make a Layout Tenon
Once the eye of your gennou is true, cut and plane a piece of softwood that perfectly slip-fits into and through the eye with 3 or 4 inches protruding out both sides. Draw lines on the stick where it projects from both ends of the eye. We will call this stick the “layout tenon.” Save it to use later in the handle-making process.
In the next post in this series on making a handle for the Japanese gennou hammer we will look at selecting a gennou head.
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.
The handle that is the focus of this series of posts is an interpretation of the gennou handle developed over several centuries by the anaya carpenters of Japan. In this post I would like to touch on some of their history and the ergonomic factors that drove their subtle innovations.
The word Anaya (穴屋) translates to “hole maker,” a type of carpenter that was common in Japan before the general availability of portable electrical mortisers. These craftsmen had their own guilds in major urban areas and specialized in cutting mortises in beams and columns for wooden structures. They didn’t do layout. They didn’t dimension timbers. They didn’t saw tenons. They didn’t do assembly or erection. Their only tools were the chisels and hammers they used from sunrise to sunset to cut mortises as quickly and accurately as they could.
Anaya did piecework, meaning they were paid according to the number of mortises they completed each day, not by the job or an hourly rate. Each individual Anaya was in direct competition with his fellows for speed and efficiency, so they were serious about the performance of their tools.
Consistent with the Japanese obsession with constantly making minor improvements to their tools, Anaya were forever asking blacksmiths to make them custom chisels and hammer heads reflecting their latest opinions. There are records of more than one chisel blacksmith, including the famous Chiyozuru Korehide, refusing to make chisels for Anaya because of their persistent, obsessive demands.
The gentleman that taught me how to make gennou handles 30 something years ago is now in his late 90’s. He was a young man back when the anaya trade in Tokyo was still burgeoning, and he learned from the best in the business.
Following are four ergonomic principles related to hammers in general and gennou in particular you should keep in mind when planning your handle. These principles are applicable to not just Japanese gennou, but to all varieties of hammers swung with a single hand. You need to understand them before you design your gennou handle.
Handle Length: Every person’s combination of bones, tendons, muscles and work habits is different. Therefore one size of handle does not fit all; There is a handle length that best fits your body, the way you work, and the type of work you do.
The Grip: For the reasons stated in No.1 above, one grip style does not fit all; There is a handle shape with dimensions that best fits your body, the way you work, and the type of work you do.
The Knuckles: The human body operates a hammer or gennou most effectively when the plane of the head’s striking face at the instant of impact is oriented in line with the surface of the finger knuckles, particularly the pinkie finger, of the hand holding the hammer.
Head Angle: When swinging a hammer, the hand naturally moves ahead of the hammer’s striking face. Therefore, instead of being in line with the arc of the swing, the head’s centerline will typically end up cocked out and away from the arc of the swing, assuming the handle is straight and hung (installed) with its centerline perpendicular to the head’s centerline. As a result:
The hammer’s face is unlikely to strike the nail or chisel squarely;
The center of mass of the head will most likely not be in alignment with the intended axis of travel of the nail or chisel on impact;
The nail or chisel will therefore be kicked out of the desired axis of travel;
Precision will suffer, and;
Time and energy will be wasted.
Before you design your handle, I highly recommend you thoroughly understand these four essential principles. If you doubt their validity, investigate them yourself. Google will not suffice. There are a couple of tests described in future posts in this series you can perform to verify them. In the meantime, here is a homework assignment: Figure out a way to determine if your hammer’s face is striking the handle of your chisel squarely, or if it is cocked. Let me know your conclusions in the comments below.
The positive impact of incorporating these ergonomic principles into your handle design, as well as the negative impacts of ignoring them, can make a big difference in your performance and work efficiency. In future posts we will show you how to deal with these ergonomic factors to design and make a gennou handle perfectly suited to your body and the way you work.
But before our tumble ass-over-teakettle down this particular rabbit hole loses every semblance of dignity, in the next post in this series we need to examine a critical but oft-ignored part of any hammer : The Unblinking Eye.
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. Promise.
The difference between something good and something great is attention to detail.
Charles R. Swindoll
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.
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.
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.
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.
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.
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.
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
It’s hubris to think that the way we see things is everything there is.
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
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.
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.
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.
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