The Japanese Gennou Hammer & Handle Part 22 – Tasting the Pudding

True perfection is unattainable, but if you chase perfection you will catch excellence!
Vince Lombardi

In previous articles in this series about a craftsman-made gennou hammer handle, we discussed how to design and make a handle to fit Beloved Customer’s body and way of working. This article assumes you’ve mostly completed your handle, attached the head, and are now ready to test it. So let’s get started.

Why Testing Matters

I don’t know about you, but after all the research, design and fabrication work we’ve invested in your gennou handle, I need to see how it performs and determine if its performance is superior to a Minion impaled on a stick. Being a Beloved Customer and therefore highly intelligent, you’ve asked yourself the following three indubitably perspicacious questions about testing.

What can I learn from testing?
Against what performance standards should I compare my most excellent new hammer handle (besides to a Minion on a stick)?
How should I conduct that evaluation?

To perfect your hammer, you will need the answers to these questions and more. You can get them over years of use, or get many of them now by testing it in a methodical manner and paying attention, but one way or another, you must get answers, bro.

Desired Testing Results

We can learn several things from testing our gennou with its new handle, but I encourage you to do your best to ascertain the following two things at minimum.

The first thing, of course, is whether or not the hammer with its new handle is comfortable and stable to use, and if possible, what needs to be improved to make it more stable and comfortable. This may entail many small details depending on your requirements and powers of perception.

Whether it’s comfortable in-use or not is subjective and entirely up to you, but you can probably identify problems easily through this testing process. Pain, soreness and blisters and the lack thereof are solid indicators (ツ).

Whether or not it’s stable in use is another important thing to determine early. Does it tend to track straight on the downstroke, or does it want to twist off your intended path of travel striking chisel handle or nail head erratically? When it hits the chisel or nail, does it convey its energy into the target smoothly, or does it wiggle like an eel on a hook on impact?

An unstable head and handle combination may perform well for one or two consecutive strikes, but because Murphy’s Law of Buttered Toast irrevocably dictates that small errors accumulate to maximize damage, an unstable head will often wiggle off-line enough for the third swing to hit weakly, even miss entirely, ruining your rhythm, damaging your confidence, and eliciting snide looks from resident bench cats. Oh, the shame…

A second thing you need to learn is whether or not the face of the hammer is striking the chisel/nail squarely and if the center of mass of the head is aligned with the vertical axis of the chisel handle or nail. Please make sure you understand the meaning of the previous sentence.

With this experience and the answers to these questions under your belt, you will be in a position to adjust the handle to perform its best for you and the way you work.

Testing Procedures

Out of an abundance of well-deserved humility combined with a strong desire to avoid looking even more the fool, your humble servant will refrain from suggesting any specific objective tests, or urge you to use quantifiable standards, or seek concrete empirical results because that would be too silly to even contemplate. Unless, of course, Beloved Customer will conduct these tests in your super-secret laboratory, possibly located at the heart of a dormant volcano on an uncharted South Pacific island, maybe covered by coconut palms with cold beer taps, probably surrounded by hundreds of horny bikini babes, likely frolicking in crystal surf. BTW, if you do have such a lab, please text me the address!

In this super-secret lab you will probably have access to equipment and software suited to more scientific, empirical, replicable methods of comparison, such as those developed for analyzing and improving the apparent performance, marketability and profitability of mass-produced sports equipment such as baseball bats, golf clubs, and green dildos (シ). Sadly, while your humble servant does not possess such equipment, most (but not all) humans own and operate one of the world’s most refined super-computers and sensor networks: our bodies and brains. I therefore propose you focus these formidable tools on this analysis. (brains and bodies, that is, not dildos).

Below are four absolutely subjective tests only you can perform, the results of which only you can evaluate.

Incorporating Test Results

To thwart the confusion promulgated by Murphy and his multitudinous malevolent minions, I strongly recommend you use the results of your analysis to guide you in making incremental improvements to your handle over time rather than large changes immediately, so to that end, please plan to remake your handle, once, twice or even thrice, improving it a little each time. Such is the true path of the craftsman.

Please update your handle drawing each time to record the improvements you’ve made and ensure no “increments” are misplaced.

In scobe veritas. (“In sawdust, truth”).

The Grip

As you are aware, for any testing other than drinking beer or women choosing wall paint color to be meaningful, some basic techniques must be established and followed to reduce variables to a manageable degree. How you hold the gennou handle to be tested is just such a basic technique.

The handle design presented in this series of scribbles is intended to work best when gripped in a particular way, so when performing the following tests, it’s important that you grip the hammer correctly thereby removing one huge, often-problematic variable.

Of course, I’m describing a particular grip here as being “correct,” but that’s just my well-informed opinion. In any case, I promise your hammer will work more efficiently if you abandon the so-called “hammer grip” (what I call the “Hobbit-killer” grip with the handle grasped in your fist) right away and switch to this more advanced grip.

I didn’t invent this grip, BTW, but observed and consulted with craftsman I respected in the USA and Japan who used it for many decades, all of whom are now working overtime in the big lumberyard in the sky. I later came to call it the “Sam Snead grip,” after the extremely successful pro-golfer of the same name who made it famous, and him rich, in tournaments and in dozens of books he wrote on the subject of using golf clubs skillfully.

We’ve talked about this grip in some detail in Part 13 of this series, but please review the photos below to confirm your understanding.

The first photo labeled “Bridging the Palm” shows how the hammer’s handle is NOT held in a fist, but is angled diagonally across the palm, supported on the first joint in the index finger, as well as the heel of the palm.

You can see how the index finger wraps around the handle while the thumb is pressed against the side so that the handle is strongly clamped between index finger and thumb, but can still pivot the handle if the operator so desires. This grip affords the joints of the forefinger and thumb, digits accustomed to fine motor control (unlike the fist), absolute control over three critical surfaces of the handle.

This grip also provides better control, more power, and greater reach without forcing the wrist to do the strange, unnatural contortions the Hobbit Killer grip does.

The Three Tests

Following are three tests to help you ascertain how well your new gennou and its handle suits your body and your work style.

Before attempting these tests, however, it is important to use your new handle for a time to establish a connection between it, your hand, and your eye (using the proper grip, of course).

Besides moral virtue and a sense of humor, you will need a few things.

A wood chisel suitable for cutting a mortise hole, around 24mm.
A piece of light-colored scrap wood for cutting a test mortise hole;
A stick of light-colored wood approximately the size and shape of the handle of the chisel you would normally use for cutting mortise holes:
An ink pad, wide-tip marking pen, or Dykem.
A lab assistant. I recommend a buxom, young lass with a cute giggle wearing a sexy lycra lab uniform (Warning: bad stuff may happen if you let She Who Must Be Obeyed meet, or even see, this assistant!)

So, now that we have our supercomputer and its sensor suite warmed up and focused, our tools laid out, and a bubbly lab assistant standing by, sound the trumpets and let the testing begin! We who are about to dye salute you!

Test No. 1: The Blind Retrieval Test

After you have used your gennou with its new handle for a few weeks such that your hand has become accustomed to it, please give your bench dogs a few treats, shoo away any arrogant bench cats, set it on your de-cluttered bench, step back a few steps, close your eyes and turn in-place once or twice like a ballerina with hairy legs. Now, have your lab assistant, perhaps a child, a friend, a neighbor, your girlfriend, or wife, or even a clever bench dog (but never your neighbor’s girlfriend’s wife’s cat!) change the gennou’s orientation on your benchtop by turning it over, switching it end for end a few times, spinning it, or whatever. Random orientation is what’s needed.

Next, with your eyes still closed, grab the gennou with your hammer hand in a correct grip ready to rock-n-roll. Notice how easy or difficult it is to grip the handle correctly, without fumbling and without opening your eyes. If it’s not easy to do, however, you need to know it now. It may be simply that you’re not accustomed to your hammer, or that the geometry or details are out-of-wack.

By “correctly” in the previous paragraph, I mean (1) the flat striking face of the head is facing away from you and toward the chisel or nail; (2) the handle and head are aligned straight in your hand, and not twisted, (3) the heel of your hand is pressing against the flat spot on the back edge of the handle adjacent the butt; (4) the distance from the center point of the face to the heel of your hand is located precisely the distance shown in your design drawing.

BTW, whether you picked up the habit from your daddy or some internet guru, choking-up on the grip is an inefficiency you should discard simply because it’s counterproductive and silly, like a powerful cane corso dog wearing flower brocade.

If the grip area of your handle is shaped as shown in the drawing with a flat back edge and sides perpendicular to it, a radiused front edge, and flared toward the butt, it should be easy to instantly grip the handle in precisely the proper place, with the intended striking face oriented properly, without opening your eyes and without any fumbling whatsoever.

If, on the other hand (the one with six fingers (ツ)), your hammer doesn’t leap into your hand in perfect alignment without argument or eyeball action, some adjustments to the handle are called for.

For example, a frequent cause of confusion between handle and hand is the leading edge of the grip being square instead of rounded. Or the sides and butt of the handle being angled wrong. These details can all be adjusted once you know they need to be adjusted

A gennou that naturally orients itself in your hand with the striking face in the right direction, the same distance from the striking face first time every time without your having to look at it, will provide you a tremendous advantage in speed, efficiency and confidence. It will become a good friend and companion.

BTW, just for gits and shiggles, try this test with any name-brand one-size-fits nobody nail bender you have laying around. The virtues of your new handle will become immediately apparent.

Test No. 2: The Blind Swing Test

This test will teach you something about handle length and other details.

Once again, perform this test after you have used the gennou with its new handle for some time and have become accustomed to it. A sexy lab assistant (one who doesn’t talk too much) in slinky woodworking togs is optional (ツ).

Grip the gennou properly in one hand and the stick shaped like your chisel handle in the other just as you would an actual chisel. But instead of placing the end of the stick against something as if you might cut it, please keep the stick in the air without butting it against anything. Now, with your eyes still closed, swing the gennou at the end of the stick of wood.

You should be able to strike the stick with the flat end of the gennou solidly and squarely on the first, or perhaps second try. Success in this test is common.

If your hammer misses the stick consistently, it may be because you aren’t yet accustomed to the handle, or it may be that you are choking-up up on the grip, or it may be you need to make it shorter or longer, or the grip shape needs to be adjusted. Or it may be that Murphy keeps distracting you by sending dickpics. It’s absolutely worth figuring out.

Once again, if you consistently miss the target, pay attention to why and where you are missing. Is the handle too long? Is it too short? Are you missing off to the side? Make notes recording the results and your observations on the design drawings to incorporate into your Mark II handle.

If accuracy can be improved by shortening the handle or modifying the grip, go ahead and make the necessary changes a little at a time. It’s easy to shorten the handle, but lengthening one requires an ACME Wood Stretcher Mark 2. I can lend you mine if you don’t have one (ツ)

Test No. 3: The Ink Test

Never fear: this test has nothing to do with gossip screeds or Rorschach drawings. It will help you determine if the handle of your gennou is the right length, if it is cocked at the most effective angle, and whether or not it should be canted to the left or right, and all without pulping an innocent tree.

This test works best if preformed after the Blind Retrieval Test and Blind Swing Test.

Begin by coloring the striking face of your gennou with an ink pad or by applying dark marking pen ink or Dykem to the gennou’s striking face (the flat face). Clean or sand the end of your chisel’s handle to produce a clean, white surface. Then cut a mortise using this gennou in the same posture you assume when cutting most of your mortises.

For instance, if you mostly cut mortises in wood located at a constant height on your workbench, such as drawers and furniture parts, you should employ that position. Or, if you tend to cut mortises in timbers while sitting on or straddling them using the venerable butt-clamp, please assume that position.

The impact with the chisel’s handle will wipe ink off the face of hammer and deposit it on the end of the chisel’s handle at the same time. This ink transfer will print the story you need to read. Check the ink on the gennou’s face and the end of the chisel every two strikes.

This is a time-tested technique professional golfers use to select/design golf clubs, BTW.

If the ink at the center of the striking face is scrubbed clean first, and the center of the chisel handle becomes inked first, then you have made your handle the right length with the head angled correctly. If not, you should make notes describing the results in the handle drawing you made earlier, and adjust the design of your next handle accordingly.

Again, you may find it enlightening to perform this same test with conventional hammer with a standard handle.

When your done testing, be sure to record your conclusions. Either erase and adjust the drawing, or trace over it to make and date a new drawing with your revised details. Tracing paper is our friend.

In either case, be sure to add a date and/or revision number to the drawing to ensure you don’t confuse it with older, superseded drawings. Don’t put this off but do it right away before you forget. This applies to all the tests described herein.

Adjustments to Your Handle

You should use the results of these tests to make small, incremental adjustments to your handle, as you deem necessary, rather than big, drastic changes.

For instance, you may need to shorten the handle. This is easily done if your handle is a little long and you’ve made the neck as I recommended. Worst case, make notes, adjust the drawing and remake the handle with as few changes as possible to avoid confusing over-complication.

A common correction you may want to try is, after becoming accustomed to using the hammer, to reshape the grip area to distribute pressure more evenly over the hand, and to reduce stresses induced in skin, muscle, tendons and bones by easing edges and corners while maintaining control and indexing. Most importantly, you should shape the handle so it doesn’t twist in your hand stretching your skin in uncomfortable ways, a common cause of blisters, especially in plastic-handled one-size-fits-nobody hardware store hammers.

If I may share an example from my experience, every new hammer handle I make tends to produce a blister on the first joint of my right hand index finger. Obviously a lot of pressure focus on this location on my hand. So I know to smooth the transition from back edge to the side just where this joint bears to avoid blisters.

This modification creates an obvious dent in the smooth lines of my handles, but your humble servant is resigned to sacrificing beauty for performance when necessary. Just look at the sorry state of my career as a fashion supermodel if you doubt my dedication to performance.

Another less-common problem is the hammer’s face striking the chisel handle or nail head at an angle instead of being centered on, and at a 90˚ angle to, the long axis of the chisel handle. The ink test will reveal such impish behavior.

This tendency usually improves with practice, but you can adjust for it by making a new handle with the head skewed to the left or right as necessary.

As a way to determine how much skew is required, you can plane down the sides of your test handle, glue on slips of wood, shape them as you see fit, and test the results. Once you’ve determined how much total correction is necessary, you can remake your final working handle accordingly.

Once again, work patiently to achieve small, incremental improvements, and be sure to record the results on your drawings.

Don’t hesitate to methodically scrape, shave and experiment with this first handle.

The design of this handle, and the process your humble servant has described for making it, is suited not just for Japanese gennou hammers but for all short-handled hammers and axes. Give it a try and you’ll see what I mean.

In the next article of this series we’ll apply a protective, and maybe even tastefully elegant, finish. Please remind me to call Ramon and beg him cater the unveiling party! I simply love his cheesy shrimps on crackers, don’t you?

YMHOS

A list of our gennou heads: C&S Tools – Gennou Hammer Head Pricelists & Photos

If you have questions or would like to learn more about our tools, please use the questions form located immediately below. To see a list of our tools and their pricing, or to contact us, please click the “Pricelist” link here or at the top of this page.

Please share your insights and comments with all Gentle Readers in the form located further below labeled “Leave a Reply.”

We see data miners and their bilious bots as dastardly sneak thieves and so promise to never share, sell or profitably “misplace” your information for any reason. If I lie may the heads of all my hammers fly away to Valinor!

Brother Saint Martin and the Three Trolls by *John Bauer*. Supernatural creatures are everywhere, if you have eyes to see.

Previous Posts in The Japanese Gennou & Handle Series

The Japanese Gennou Hammer & Handle Part 21 – Installing the Head

No one should be ashamed to admit he is wrong, which is but saying, in other words, that he is wiser today than he was yesterday.

Alexander Pope

In the previous article in this series we finished fitting and shaping the handle of our gennou hammer in accordance with our design document. Some refinements may be pending the results of testing, but in any case the time has come to attach the head.

This is an important task, perhaps not as easy as it sounds, because this is a craftsman’s handle, made with love and skill, not a mass-produced cockroach killer ground out by barefoot Bangladeshi farmers and secured with crude wedges. It’s not a typical tool of the sort sold at Home Despot designed to fail quickly and be tossed into a landfill soonest. And because the head is not secured with barbaric wedges but relies entirely on the extremely tight fit between the eye of the steel head and the tenon Beloved Customer cut on the end of the handle, some careful, but nonetheless violent action is required to successful connect head and handle. The purpose of the article, therefore, is to help you install it carefully with all due violence.

Installing the Head

Beloved Customer can install the head either before or after sanding and finishing the handle, but in this example we’ll attach the head before testing and finishing the handle. This approach will be most efficient if you decide to adjust or rework the handle after performing the tests I recommend in the next article.

In this case, I use the word “finish” to mean to apply a chemical “finish material” to the wood, not to “complete” the work or “conclude” the job. This difference in definition matters to me because confusion regarding the dual, even treble meaning of the word “finish” has caused problems for me in the past. So there you are.

Preparing the Tenon

First, remove any tape remaining on the tenon and, if necessary, use a solvent such as lacquer thinner to remove any adhesive residue. DO NOT USE soap, water, or any water-based chemical as this will make the tenon swell! After cleaning there should be no finish material, wax, oil or unicorn wee wee left on the tenon.

Depending on the relative humidity the handle is acclimated to, it may be advisable to make an effort to shrink the tenon a bit by placing the handle in a low-humidity environment for a time. Please do NOT microwave your handle, cook it in your oven, or heat it in your toaster, not even with cheese and Tabasco Sauce.

There are several ways to remove moisture from the tenon in order to shrink its width and thickness a bit without ruining the handle or burning down your workshop. Perhaps the safest way is to store it for a time in a tightly-sealed plastic container with packages of silica desiccant. Other ways include placing it in a warm spot close to an operating gas furnace, or indirectly exposing it to an electric room heater for a day or so.

If you use any method that involves heat, make sure you are nearby to monitor progress and deal with scorching and fires.

Orienting the Tenon

You’ve already shaped the handle, and shaved and lightly chamfered the tenon so it should partially fit into the head’s eye almost as deep as the chamfer, but should go no further using only hand pressure.

Please keep in mind during this process that it’s extremely important to get the tenon started in the eye straight, and to keep it straight, without allowing it to become cocked.

It’s also important to install the head in the correct orientation. This usually means it’s flat striking face is oriented towards chisel or nail, and with the brand oriented towards the handle’s butt.

Some people like to orient the head’s brand so it faces up (away from the butt) when using the hammer. I can understand this compulsion, and while it makes no difference in performance one way or the other, you should be aware that it’s seen as bass-ackwards among professionals in Japan.

Starting the Tenon

Of course, in accordance with your humble servant’s advice in previous articles, you’ve already created an elegant dome on your hammer’s butt to prevent these taps and strikes from damaging the handle.

I like to place the head on a working surface such as a benchtop or a softwood board like pine or cedar resting on the floor/ground cushioned by a piece of leather or rubber to prevent slipping.

Insert the tenon into the eye, and, after sighting the handle and head from multiple directions to check alignment, when you are absolutely certain the tenon is poised to go into the eye straight, tap the handle’s butt with a flat-faced hammer, genno (not a domed-face hammer) or mallet. After a few taps, stop tapping, check your progress, and make sure the tenon is going in straight and not cocked.

Although the tenon should not have entered the eye more than a millimeter or two, it should be an extremely tight fit, with each tap making barely any progress.

I can’t describe the sensation in writing, but if the fit is too tight at this point in the process, you may need to scrape or sand the tenon a little.

Driving the Tenon Home

This is where the “violent” part of the job I mentioned above begins.

With the tenon properly aligned and started in the eye, stand up, hold the hammer in a fist with the head hanging straight down, and strike the butt of the handle with your hammer or mallet paying attention to its progress into the eye with each strike and the friction created. Gradually adjust the impact force of your strikes accordingly. Don’t be surprised if it takes literally dozens of extremely hard strikes to install the handle completely. If the tenon just slips in, however, we have a problem, Houston.

If you find that the fit is too loose, however, don’t despair, simply shim it with quality paper as described in the last section of the previous article. Remember, most people find it difficult to get the tenon/eye fit right the first time. Such adjustments to a new handle are nothing to brag about, but neither are they something to be ashamed of. It’s more the rule than the exception until experience is gained.

Some people like to make their tenon extra-long so it projects out of the eye 6-12mm or so. Nothing wrong with this approach, but it looks silly to me in the case of a new handle. Once again, beauty is in the eye of the bean holder.

I was taught that the ideal is for the tenon of a new handle to remain recessed inside the eye a few millimeters. The purpose for this goes back to one of the reasons for the gennou handle design described in this series of articles, namely, that the handle does not have a tumorous swelling below the head but the neck is approximately the same dimensions as the eye for a portion of its length to permit the user to tap the handle further into the eye should it loosen. By leaving the end of the tenon short of the end of the eye in the case of a new handle, one provides visual evidence that (1) the handle is tightly fitted and; (2) that plenty of tenon length is available for making such adjustments.

Accordingly, a tenon projecting a long way out of the eye indicates to the knowledgeable observer that either the handle is either old and has been adjusted many times, or the tenon fit was sloppy from the beginning. In my humble opinion, a tenon of a new handle projecting from the eye a significant distance looks odd, but in practice, it doesn’t make much difference. The choice is yours.

In the next article in this series of articles about danger and violence, we’ll test you’re new handle. How exciting!

YMHOS

If you have questions or would like to learn more about our tools, please use the questions form located immediately below, or email us at Covingtonandsons@gmail.com. To see a list of our tools and their pricing, or to contact us, please click the “Pricelist” link here or at the top of this page.

Please share your insights and comments with all Gentle Readers in the form located further below labeled “Leave a Reply.”

We see data miners and their bilious bots as dastardly sneak thieves and so promise to never share, sell or profitably “misplace” your information for any reason. If I lie may all my hammers swim away from me!

Title: Cormorant. This ink drawing was made by Japan’s most famous swordsman, Miyamoto Musashi (c. 1583 – 13 June 1645). This style of art (suibokuga) is not well-known outside Asian countries, but despite the few materials used (paper, ink stick, inkstone, brush and water), it’s an extremely difficult art to master. Why? There’s no pencil layout to follow, so the artist must have the drawing planned down to the last stroke in his mind’s eye. Each stroke must be made precisely but without hesitation or mulligans. The ink is black, so color gradations can only be achieved by altering the speed of the brush and the ever-changing water/ink balance contained in the brush. High-speed, high-precision, powerful lines, no wasted strokes. Very much the work of a swordsman.

A list of our gennou heads: C&S Tools – Gennou Hammer Head Pricelists & Photos

Previous Posts in The Japanese Gennou Hammer & Handle Series

The Japanese Gennou Hammer & Handle Part 20 – Making Sawdust

Woodworking minus patience equals firewood.

– Author Unknown

In the previous article in this series, we selected and prepared the wood for our gennou handle and layed-it out in accordance with our design drawings.

The next step in the process is to gather our tools and begin the fun work of making sawdust. Yeeehaaaa!

Tools

I prefer to use the following tools when making a gennou handle. You will need to have similar tools on hand for layout and fabrication, but the specific choice is entirely yours.

Divider with sharp points (transferring dimensions and tenon layout);
Sharp pencil (making pencil marks (ツ);
Small try square (laying-out and checking tenon);
Marking gauges (Titemark and kama kebiki. Marking tenon and centerlines) ;
Marking knife (layout);
Hozohiki rip saw and/or dozuki crosscut saw for cutting the tenon (in hardwood, a sharp hozohiki rip saw frequently makes both rip cuts and crosscuts cleaner and more precisely than a crosscut dozuki saw);
A fine saw such as a fret saw or coping saw for making curved cuts;
Auriou cabinet rasp (Lie-Nielson) (optional);
Boggs-pattern flat-sole and curved-sole spokeshaves (Lie-Nielson. Optional but very handy and pleasant to use if you can tolerate A2 steel);
Sandpaper;
A board to support the handle-in-progess. I suggest dimensions of 300-400mm long x 50-60mm wide x 40-50mm thick, with a “V” groove cut full-length and a cross-stop inlet about 2/3 its length. The handle will rest, more-or-less securely in this groove, and be restrained at one end by the stop when using spokeshaves and rasps. This support board can be clamped in a vise, or clamped to a workbench with a C clamp. I also find it most efficient to place this board on my benchtop with the gennou handle resting in the v-groove with one end touching my chest, perhaps cushioned by a rag, and use rasps and spokeshaves pulled towards me to shape the wood.

Safety

I dislike safety nannies and never want to become one. But Gentle Readers of this humble website include everything from venerable old-timers to fresh newbies, so it would be unkind of me to write for the benefit of only accomplished woodworkers while ignoring the new guys. And since the operations described herein include sharp tools, and potentially harmful substances, please plan to work safely. The following webpages may help.

In addition, before you start making (and sucking into your pretty pink lungs) the millions of the tiny airborne wood particles that comprise sawdust, please check that the species is not dangerous in general, and that you do not have allergies in particular. The website at the link below might be useful.

Wood Allergies and Toxicity

The Tenon and the Unblinking Eye

Let’s start by cutting the tenon and fitting it to the gennou head’s eye.

You’ve already layed-out the tenon, so next use a fine precision rip saw like a 210mm hozohiki to cut the four cheeks being extremely careful, like a big-eyed kitten stalking a grasshopper, to stop short of the layout line. Be careful to work very precisely with your saw to not cut too deeply as any excess meat removed from the tenon, or sawcuts left in the tenon, will fatally weaken it. I’m not kidding!

I humbly confess to making this mistake more than once, ruining all my work to that point and wasting some nice wood. Indeed, it may be best to cut the shoulders shallow and trim with a chisel, once again being careful to not cut too deeply. Ruthless, merciless, unrelenting control of your coke-snorting inner-badger is critical!

At this point, the handle is a chunky, graceless block with square edges, flat surfaces and a stubby tenon sticking out at one end. That’s alright. There’s no need to contour the handle yet.

Cut itsy-bitsy teeny-weeny chamfers on the end of the tenon to help guide it into the eye without cocking and binding. A big chamfer will benefit nothing and look ghastly.

Mark the reference face annotation on the corresponding tenon cheek because you don’t want to mistakenly force the tenon in bassackwards.

Test fit the tenon into the eye a few millimeters but without driving it all the way on. It should not start by hand pressure.

Although you shouldn’t have yet tried a full-length, full-power test fit, when you are satisfied that the tenon will fit into the eye of your gennou head without the tight fit shaving off much wood, and marked the reference faces, then tape the tenon with masking tape so you don’t accidentally knick or shave it. Don’t ask me why I know this risk exists.

With the tenon close to completion, let’s next shape the curved front, back and side surfaces to fit.

The Back and Front Edges

The tools you use don’t matter so long as when this step is complete the back edge is perpendicular to the reference face, the opposing side face, and is consistent with the layout lines.

Cut the back and front edges (surfaces parallel with the long axis of your gennou head) to your design profile using saws, rasps, knives and/or spokeshaves. The two guiding details in this process are the butt and the tenon, with the tenon being most important. These two surfaces should be shaped to smoothly connect the butt with the tenon, not the other way around.

However, leave the corners of the neck and handle area square for now to help guide you in shaping the critical back and side surfaces because, if you start rounding and smoothing edges and corners now, it often happens that the geometry which aligns the hammer’s face with chisel and nail will be compromised.

I recommend you cut outside the layout lines plus a millimeter or two because accidentally cutting deeper than your layout lines will not only disrupt the even flow of the design but may damage the structural integrity of this elegant, minimalist tool.

Do not shave the handle’s sides flush with the tenon yet, but leave them just a hair proud.

When done with the this, lightly remark the centerline and extended the eye’s lines.

The Sides

At this point in the process the right and left sides should still be flat and parallel, perpendicular at any point with the back surface, and have neat, square corners.

Use the paper/cardboard profile pattern from your design drawing to mark the handle’s layout on the back and front edges.

Just as with the back and front edges, cut the side surfaces using saws, rasps, knives and/or spokeshaves.

Although some prefer handles with a broken dogleg shape, I recommend you make the transition from tenon to butt gradual and smooth.

As you approach the final dimensions, be careful to avoid tearout or gouging in the neck area since removing these irregularities may require you to reduce thickness too much.

Do not cut or shave the sides flush with the tenon’s cheeks yet, but leave them just a hair proud.

Smoothing and Rounding

I find it most effective at this point to shape the back edge (opposite the flat striking surface of the head) flat with slighty relieved corners, not rounded-over corners. You can always change it later.

Some people like to make the back edge of the handle oval or egg-shaped, but I recommend you leave it flat at first and then adjust it to fit your hand as you use the gennou.

At this point your industrial-designer sensibilities will scream at you in a voice like a nazgul commanding you to round the the back surface entirely or to make it oval or egg-shaped, but while such surfaces might look better hanging on a peg in a hardware store, or in pictures in a magazine, or as an image on you facebook or Instagram page, and may even feel better when used to kill cockroaches, I promise you it is counterproductive when doing serious work.

Why? Because, despite what you may think, a flatter back surface does not bite into the hand in-use, but because of the greater surface area in contact with the hand it provides, it actually reduces the pressure of impact reaction forces on the hand reducing fatigue and bruising. More importantly, it helps with quickly and unconsciously indexing the striking face of the head correctly.

With the back edge where it needs to be, next round the front edge into the design profile. I prefer this surface to be more-or-less a perfect radius at any point in the handle area, but some guys feel an egg-shaped cross-section fits their fingers better. Six of one half-dozen of the other.

In any case, this surface must smoothly morph into a flat surface with slightly radiused corners in the neck area, and finally with no radius as it approaches the tenon. Yes, you read correctly: no radius.

I usually round-over the flat on the back edge right where my index finger wraps around to the side just a little to avoid developing a blister. But keep in mind that the only way to tell what small details works best for you is trial and error.

Doming the Butt

A Hiroki head (bright finish) with a handle of ushikoroshi wood. Notice the domed butt.

The butt should be flat with sharp edges at this point in the process.

You may find a domed butt strange, but it has both practical and aesthetic purposes.

Let’s consider the structural, practical purpose first. If the wood is adequately hard, and the tenon is not too skinny, you will need to pound on the butt like a son-of-a-gun dozens of times to get the tenon into the eye. That’s as it should be. Don’t start yet, but when the time comes you must be careful with the accuracy of your hammer strikes to avoid damaging the butt or breaking the tenon.

If the butt is flat with crisp edges, unless you have perfect aim with every swing, your hammer might chip or even split it. A domed butt, by comparison, directs impact forces of your hammer away from the edges of the butt and into the neck to help to prevent chipping. Likewise, a domed butt will also reduce damage to the handle over many years of hard service.

Moving on to aesthetics, a domed surface is more organic and, to my beauty-deprived sensibilities, more elegant than a flat one because straight lines seldom exist in nature, are boring to the eye, and are seldom aesthetically pleasing

A warning. Everyone has different opinions about what pleases the eye, as you know. Beauty is in the eye of the bean holder, or something like that, so I entirely understand if you dismiss the aesthetic reasons I’ve suggested. But please don’t ignore the practical, structural reasons if you want to avoid wasting your time and wood.

Assuming the butt is flat and its surface is more or less perpendicular to handle’s centerline, use a marking gauge set at ¼” to scribe a shallow line on the butt’s face (the part the will be domed), and around the butt’s sides (the handle’s sides and front and back edges). These lines will be the limit of the chamfer between the grip and the butt.

Next, mark a cross on the butt using the front and back edge’s centerline, and a perpendicular line parallel to the back edge. This cross will be useful in maintaining the centerline while profiling the butt.

Use a knife, chamfer plane, block plane, files or other tools to make a 45˚ chamfer up to the lines just scratched.

Next facet the butt using planes or a sharp kiridashi kogatana knife and remove all tearout and filemarks Try to keep it symmetrical if you can.

The butt can be left faceted (my preference) or smoothed using sandpaper later. That decision must be made before finishing the handles, but need not be made now.

Why might one elect to leave the butt faceted instead of smoothing and polishing it? I’ve done it both ways, and if I’m in a hurry, I sand it smooth and get it over. But all commercial products nowadays are smooth and symmetrical, but a factory cannot facet a curved surface easily. A faceted butt sets my hammers apart from all commercial products while giving them the craftsman’s signature.

Fixing a Loose Head

So here’s the “I toljaso” in advance.

If you were not as careful and clever as big-eyed kitten stalking a grasshopper when fitting the tenon, you may find it becomes loose and the head begins to wiggle with the passing of a few seasons. A Sergent Elias moment!

I won’t say it out loud, but just between you, me and CCP, you can remedy a loose head by removing it and shimming the eye with quality high-rag-content typing paper. Don’t have any typewriter paper left in your bat cave? It may be your not using your IBM Selectric much nowadays. Are there alternatives?

Don’t tell the Secret Service I said so, but nothing works better for shimming a tenon than a strip cut from a dollar bill. Crane Stationary makes the best paper in the world, and by no coincidence, also makes the paper used in US currency.

In the next few articles in this series we will attach the gennou head to the handle, apply a London Finish, and sample its performance. Yummy!

Until then, I have the honor to remain,

YMHOS

Lena Dances With the Knight by John Bauer 1915

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Month: March 2026

The Japanese Gennou Hammer & Handle Part 22 – Tasting the Pudding

Why Testing Matters

Desired Testing Results

Testing Procedures

Incorporating Test Results

The Grip