Month: November 2021

Handsaws: Some Guidelines to Aid Precision

A famous wood block print by Katsushika Hokusai titled ” Mount Fuji Seen from the Mountains of Totomi,” one scene in thirty-six. With pre-big-bang Mount Fuji in the background, a group of four sawyers, and judging from the mother and baby in the foreground, probably including at least one family, are sawing boards from a huge timber on the very mountain where the tree was felled. Two men are sawing away with maeibiki ooga saws, one from above and another from below, while a third sharpens a saw underneath. OSHA approval was not obtained for this working arrangement, oh my! They probably slept in the rough shelter erected at the left. A brutal, if scenic, lifestyle with abundant, fragrant fresh air.

Perfection is a necessary goal, precisely because it is unattainable. If you don’t aim for perfection you cannot make anything great, and yet, true perfection is impossible.

Leonard, The Outfit

Cutting joints connecting one piece of wood to another, such as mortise and tenon joints, bridle joints, dovetails, etc. using only handtools is not difficult, but most people find, at least initially, that executing them to fit together tightly without slop or unsightly gaps can be challenging.

The ability to routinely and quickly cut tight, workman-like joints with a handsaw is a critical skill for the professional that specializes in making limited runs of custom furniture and casework because including exposed joints not only sets his products apart from mass-produced dreck, but the apparent precision of those joints is a direct, long-term reflection of his standards of quality. And while it may not be a critical skill for the amateur who produces high-quality woodwork, it is nonetheless extremely satisfying, especially if the cabinets, furniture or casework he makes will remain in his house or with family where any poorly-fitting joints will silently laugh at him with “open mouths,” as the Japanese saying goes, over many years. Your humble servant loathes and fears such mocking whispers!

So, how does one go about improving one’s skill with handsaws thereby avoiding the sidelong glances and silent, but nonetheless snide, remarks of gaping joints? In this article your most humble and obedient servant will be so bold as to provide some guidelines I have shared with friends and Beloved Customers over the years, but which I have never before compiled into a single document. Please let me know in the comments below if these techniques prove useful.

The Saw

Of course, hand-cut joinery is accomplished using handsaws, tools that vary widely in quality and performance, so it is appropriate to begin this discussion with an explanation of the features a high-performance handsaw should incorporate.

In your humble servant’s well-informed opinion, the handsaw is by far the most difficult woodworking tool for the blacksmith to produce. Sadly, there are few skilled blacksmiths producing handmade saws nowadays, and while new companies producing pimped-out high-priced backsaws targeting amateurs have sprouted up, many of those exhibit performance inconsistent with the high prices their manufacturers demand. Imagine that….

But never fear, for below is a list of key things Gentle Reader should look for in a high-performance, professional-grade handsaw to be used for precision joinery.

The Plate

Whether Western or Japanese, the “plate” of a saw (the piece of sheet steel that comprises the blade) is its most important component. It must be adequately hard to resist bending and buckling, and so the teeth cut into it can be made sharp and stay sharp a long time, but not so hard the blade will crack or the teeth break off. This is a delicate balance. Sadly, most manufacturers err on the side of softer and duller. Sigh…

The best handsaws are made from plain high-carbon steel with a fine crystalline grain structure. Thus it has always been, and for good reason. Sadly, high-quality steel of this sort is difficult to procure nowadays.

Most of the new American and European manufacturers of backsaws, as well as all the Japanese manufacturers of replaceable-blade handsaws, make their saw plates from pre-hardened, thickness-sanded steel purchased in sheets or rolls, metal never touched by a blacksmith. This is a cost-efficient material that eliminates the need for blacksmithing skills, but it has a few serious limitations that negatively impact a saw’s performance.

In the case of Japanese blades with the discolored, hardened teeth, after the plate has been stamped out with dies and a press, or cut to shape with a laser, the teeth are shaped by grinders, set is applied by machine, and the blade is passed quickly through an induction coil formed by two metal blocks charged with high voltage electricity, suddenly heating the teeth in a technique called “shock hardening.” The plate never slows down, and as the red-hot teeth exit the copper-alloy blocks charged by an induction coil, they pass through a coolant spray which instantly quenches them creating a hard, crystalline structure in the metal.

Most Western backsaws are made using similar materials and processes but without the induction hardening step.

210mm Dozuki saw hand-forged by Nakaya Takijiro, the ultimate handsaw for precision woodworking.

Taper Grinding

A high-performance saw’s plate will be taper-ground in at least one direction, with the plate made thinner at the back than at the teeth, providing extra clearance in the cut, increasing as the blade cuts deeper into the wood, reducing friction between wood and plate for a smoother cut with less effort, and reducing the risk of buckling.

Handmade Japanese handsaw blades are of course double-taper-ground, as once were all quality Western handsaws too, but sadly neither replaceable-blade Japanese handsaws nor modern Western backsaws are taper-ground to any degree. John Disston would puke.

Unfortunately, too many modern users of handsaws, lost in a Twitter world, have become entirely inured to terminal Chinese Logic, such that most are incapable of even considering qualities they can’t instantly infer (correctly or not) from a photograph on the internet. These confused souls deserve our pity.

Gentle Reader would be wise to place his priorities regarding performance above outward appearance, because a prettily-finished exotic hardwood handle, a beautifully sanded/polished finish on a sawplate, and even an eye-catching etched brand contribute neither diddly nor squat to a handsaw’s job of making precision cuts.

Hammer Tensioning

Hammer tensioning is an ancient technique whereby the sawsmith or saw sharpener rests the plate on an anvil and taps the plate with his hammer creating small dents in specific areas. Each tiny dent deforms the metal making the plate slightly thinner at the point of impact while at the same time displacing a corresponding amount of metal away from the point of impact. Being constrained from expanding as much as it wants to by surrounding metal, the accumulated strain of many dents creates internal stresses that tend to make the saw wider and longer. Taken too far, these stresses will make the sawplate buckle or oilcan, but if done just right, for all practical purposes the sawplate will remain flat and stable.

Why bother with all this noisy hammer tapping? Clearly Gentle Reader is exceptionally perceptive to pose this question, and accordingly your humble servant quivers with joy at the prospect of clarifying an elegant and ancient mystery, one that is still employed to good effect in high-quality modern circular saw blades as I learned during recent meetings in Nagoya with three of Japan’s largest circular saw blade manufacturers.

So here’s the reason: As a sawblade heats up due to friction in the cut, the metal of course expands, but not uniformly over the blade’s entire surface. This differential heating and resulting differential expansion causes a sawplate that has not been hammer tensioned to temporarily warp, increasing friction in the cut even further, and making the cut wander thereby ruining the precision of the cut, and in the worst case, causing the saw to buckle. The residual stresses produced in a saw’s plate through proper hammer tensioning counteract and cancel out stresses produced in the sawblade through friction heat thereby preventing the plate from buckling, excessively warping, or oil-canning, with the result that the saw will cut straighter and cleaner with less effort even as it heats up.

I don’t know who invented this subtle technique far back in the mists of time, or where, but it is genius-level craftsmanship.

The better-quality Japanese replaceable-blade handsaw makers have taken a page from the circular sawblade manufactures and run their sawblades through a pair of opposed steel rollers which induce stresses in the steel similar to hammer-tensioning by hand. I may be wrong, but I am unaware of any modern Western backsaw makers that either hammer-tension or roller-tension their sawplates, but instead rely solely on the stiffness of the applied back to prevent buckling. Once again, JD would weep.

Another benefit of hammer-tensioning, and one Gentle Reader can ascertain easily by examining a saw blade in person (but without the back installed) is that the internal stresses resulting from hammer-tensioning make the sawblade much stiffer than it would normally be without adding metal or weight. Simply remove the back and handle and hold the sawblade out level supported on only one end. A hammer-tensioned blade will sag significantly less than one that has not been hammer-tensioned.

Another easy test for hammer tensioning applicable to panel handsaws is that of bending the sawplate and tapping it with a fingertip producing a musical note that can be varied by changing the degree of bend in the sawplate. In fact, believe it or not, the handsaw was once a popular musical instrument in some quarters in the USA, with all the major saw manufacturers producing specialty musical saws (sans teeth).

In summary, a properly hammer-tensioned saw will be stiffer, will cut straighter, can be made thinner and lighter, and will require less force to operate for the amount of sawdust generated.

The hand-cut and hand-filed teeth of a 210mm Dozuki saw by Nakaya Takijro. The small dings visible near the chin of the blade are the marks left by hammer tensioning.

Teeth

Tooth types and preferences in handsaws vary so widely that little can be said that applies to all. However, Gentle Reader should consider the following when evaluating a handsaw to be used to cut precision joints.

First, assuming the teeth are the desired shape and size and progression, they should be uniformly and extremely sharp, indeed, sharp enough to cut you if touched carelessly. If you place the palm of your hand gently on the line of teeth, you should feel the little buggers trying to grab your skin. Not just one or two of the vicious little teeth should frantically try to eat you, but all of them in contact with your hand should seem eager to nibble because each tooth is either a frightfully-sharp, pointy little knife, in the case of crosscut saws, or a razor-sharp little chisel, in the case of rip teeth. And of course, a well-made and sharp saw is always eager to cut anything and everything it can get its teeth into. Just ask it.

Unfortunately, the teeth of most of the new crop of Western saws made nowadays are, in my experience, poorly sharpened and in need of TLC before they are useable. I say this as someone that prefers Western handsaws for some tasks, sharpens his own saws by hand, has purchased, collected and tested both new and antique Western handsaws over the years, and continues to use the better of them regularly.

In the case of most woodworking tasks, sawteeth need to have some degree of set to make the sawkerf wider than the thickness of the plate to reduce friction, binding, and buckling. Indeed, to compensate for a missing taper-grind and hammer tensioning, most modern Western saws are made with excessive amounts of set. This matters because all the extra wood the sawblade must cut to accommodate this extra set is wasted effort turned into sawdust that does nothing to improve speed or accuracy. Therefore, a good handsaw will have no more set than absolutely necessary to get the job done.

This means, of course, that one needs different saws with different set and different tooth styles for different types of cuts in different types of wood. It makes a difference.

On the other hand, if Gentle Reader uses handsaws solely to burn calories, the aforementioned points should all be studiously ignored. (ツ)。

The teeth of a 210mm Hozohiki rip saw hand-forged by Nakaya Takijiro. The hand-filed steel back finished in traditional burnt silk is also visible at the top of the photo. These teeth are specifically designed to meet the demands of professional Japanese luthiers working in exotic hardwoods.

If Gentle Reader is in need of a high-quality hand-forged saw, you may want to consider those made to C&S Tools’s specifications by one of Japan’s last remaining master sawsmiths, Nakaya Takijiro. You can see some of his products at this link.

A 210mm Hozihiki rip saw hand-forged by Nakaya Takijiro from White Label steel No.2. This saw, and especially its teeth, are specifically designed for cutting precision knock-down joints in the hard, exotic woods, such as ebony and rosewood, that Japanese luthiers use to make shamisen, harps, lutes and other traditional musical instruments.

Using a Handsaw to Make Precision Cuts

The overarching guiding principles in using handsaws to make precision cuts are the following:

  1. The Saw: Use a high-quality saw with the features described above. If you don’t yet own such a saw or can’t afford one, and even if you do, educate yourself in blade sharpening, applying set, and in the techniques of straightening sawplates so your saw will achieve its maximum potential performance;
  2. Layout: Layout the cut so there is no confusion about where it starts, where it continues, where it ends, and the angle of the cut. Whenever possible mark cuts in such as way that the sawblade can positively index itself. Marking knives and marking gauges with sharp cutters can produce such layout lines better than pencils and pens. If there is any chance of confusion, include marks in your layout indicating, for example, the side of the line to cut to and where to stop;
  3. Arrangement: Arrange, support and align the workpiece, your body, and your eye to produce only straight cuts with every single stroke. This point is relevant to item 4 below;
  4. Make of Thyself a Machine: More details below;
  5. Attention: Pay attention to make every single stroke accurate;
  6. Stop & Correct: The instant a stroke goes astray or the cut wanders even a little, stop sawing, figure out why, and make corrections, dammit. Not ten strokes or even two strokes later, but instantly. This requires concentration and iron-handed control of your inner honey badger.

Layout

Spend the time to do layout and marking properly, because confusion and uncertainty during the cut will result in reduced mental focus, and often, poor precision. A solid, well thought-out plan combined with a sharp marking knife, a sharp marking gauge, and an accurate, hardened steel square help to make good lines yielding good cuts.

Arrangement

In order to achieve No.4 in the list above, “Make of Thyself a Machine,” you should spend the time and develop the habit of securing the workpiece at a height and angle that will aid the imperfect human body to make perfect cuts. In my case, this means checking the angle of the dangle and using a vise, C-clamp or a butt-clamp to hold the wood down. It also means stopping work to rearrange the workpiece when necessary. I recommend you try various methods to find which one works best for you when making each type of cut.

In most cases, I like to make gravity my friend by positioning and securing the workpiece so the plane of the cut is vertical. My workbench is level, so a square usually suffices to confirm alignment, but a small spirit level is sometimes helpful too.

For example, when cutting the tails of dovetail joints, I secure the board in a leg vise, and tilt it so the cuts for half the tails are plumb. When done making those cuts, I next rearrange the board in the vise so the opposite sides of the tails are in the vertical plane, and cut them. Perhaps this is overkill, but it is a habit that helps me to consistently make precise cuts with less damage to brain and eye.

The body must be aligned with the cut to avoid stresses and strains from misaligning “The Machine.” A comfortable position is therefore necessary.

If at all possible the eyeball must be positioned so it can see both sides of the cut to not only guide the cut, but quickly detect a wandering cut, because we all tend to get lazy partway through a cut and stop looking, allowing our inner-honey badger to run amok with predictable results.

3 sawyers sawing lumber from a timber, one on top, one from below, and another carrying a saw, probably one he has freshly sharpened. At the right, a carpenter with pipe and tobacco pouch hanging from his waist sash (obi) is using square, sumitsubo, and sumisashi ink pen to do layout on the end of another timber. The mother hens at OSHA would simply be clucking with disapproval if they saw this scene in the flesh.

Make of Thyself a Machine

The title of this section is not intended to suggest Gentle Reader should surgically install bionic parts or change their racial and gender pronouns listed in social media to “Synthetic Person.” (シ) No indeed, nothing so “progressive” is necessary (BTW, what is the politically-correct pronoun for a cyborg: Clank or clunk?). Rather, this phrase refers to a combination of techniques that will help even non-cyborgs overcome the erratic tendencies of flesh, sinew and bone in order to produce more consistent, precise results with a handsaw.

To make a straight cut, the sawblade must travel within a single vertical plane during both the cutting and return strokes. While obvious, this is where nearly all people screw up, always when learning how to use a saw, and in most cases, forever. But we can do better.

If Gentle Reader will pay close attention when making a cut with a handsaw, you will notice that the hand, and consequently the saw handle, tend to move in an arc right and left in a horizontal plane as seen from above. This movement is a result of naturally flexible linkage between hand, arm and shoulder that transmits the force generated by the muscles to the tool handle. We must control the limits of this “flexibility” if we are to make a straight cut. We can do this by making of ourselves a “machine.” It’s almost as easy as the “tricky part” of the Big Fig Newton dance.

How to do this? Let’s take it step by step. First, grip the saw firmly but not too firmly. The old swordmaster’s instructions apply: Hold the handle like a small bird: Too loose and it will fly away; Too tight and the little bird will be crushed. This grip is important because if you hold either sword or saw too tightly, your muscles and tendons will lock up and you will be unable to form the consistent machine necessary to accurately control the tool’s movement.

The second point to understand about grip is that, while all of the fingers of the hand may touch the saw’s handle, apply your gripping force through the index finger and thumb only (in the case of straight-handled Japanese saws), such that the saw can almost freely pivot around a line drawn between these two fingers and through the handle.

Next, with the workpiece arranged securely, assume a relaxed stance facing the layout line you will be cutting to on the workpiece. Then, with saw held in the relaxed swordsman’s grip you intend to use during the cut, hang it loosely down alongside your leg. Stand back from the line and adjust your stance so the plate of the hanging saw is in the same plane as the the intended cut line. This next part is important: Don’t move your hands, arms, shoulders or hips to align the sawblade with the plane of the cut, but rather move your feet. This is approximately the ideal angle between your body and the intended cut.

Next, without changing position, center your dominant eye on this plane.

Then, being careful to avoid hitting anything (especially stray bench dogs or kitties), gently but freely swing the saw forward and back 90˚inside this same plane. If your hand or your saw touches your leg, or your elbow hits your side, then adjust your stance so they don’t. The saw must swing freely with the sawblade in the same plane as the cut, with your shoulder joint, elbow, wrist and eye all centered in the same vertical plane.

Next, swing the saw up into the cutting position, and move it back and forth as if cutting wood. Your grip should still be loose (remember the little bird), and the saw should continue to move in an invisible plane centered through your shoulder, elbow, wrist, sawblade, and the layout line. Now pay close attention to the movement of your hand as it goes forward and back. Is it still traveling a little right and left in a horizontal arc? It probably is, my cyborg friend.

Now, while maintaining the stance established earlier, step forward enough to actually make a test cut. Start with a few itsy bitsy teeny weeny little cuts in a test piece to establish a stable beginning for the kerf. Then begin cutting in earnest, but while doing so, pay attention to the movement of your hand. Is it still scribing right and left horizontal arcs in the air? If it is, then on the cutting stroke, in the case of a Japanese pull saw, or the return stroke in the case of a Western push saw, reposition your stance so the inside of your elbow lightly brushes your side. Then adjust your head and eye to match. This contact between elbow and side is an important target point that will help position one end of each stroke, essentially creating rails for the machine to operate within. Remember the feeling of this contact.

When you make the cut, you will notice the sawblade is still scribing small arcs right or left. This fine movement persists because the wrist joint is too stiff preventing it from rotating slightly to keep the sawblade moving in a straight line, with the result that the saw’s handle is either rotating too much or too little, too soon or too late, causing the sawblade to deviate from the plane of the cut. It is impossible to reduce this out-of-plane deviation to zero, but you can cancel out most of it by maintaining your swordsman’s grip, loosening your wrist and actively rotating it in anticipation of this right-left arc. Yes, you can do it.

Your shoulder, elbow, flexible wrist and hand, supported by the rest of your stone-stable body, and watched over by your unrelenting Sauron-like eye, now form a machine with invisible rails that will move the saw in a vertical plane almost perfectly aligned in the plane of the line to be cut (perfection is unattainable and unnecessary).

One last point. It is essential to realize that the saw cuts because it is sharp and wants to make sawdust, not because of thy mighty arm, Oh Lord Cyborg. This is another phrase worthy of a forehead tattoo if you have any room left (ツ)。When we actively apply much force to a saw, especially if the teeth are dull, it will resist our boorish behavior, stumble over the woodgrain, clog with the sawdust, and almost always wander out of the plane we want to cut in. To avoid giving offense, please ensure your saw has a true plate and sharp teeth, do your layout, make the machine, start the cut, then get out of the saw’s way, dammit, and patiently and carefully watch it make sawdust. Don’t be too proud, Lord Cyborg, because, after all, you are the weak link.

Making the machine takes practice and time, but once you have figured it out, and know how it should feel, you will develop muscle memory. It’s like driving a car: Every modern car is different, but every modern car is the same.

BTW, there are various saw jigs one can make and use to enhance one’s cybernetic capabilities which we will consider in future articles.

Pay Attention

Until the necessary muscle memory has permeated all the way to your bones, don’t forget to pay attention to every single stroke you make with your saw. This is exactly the opposite of human nature that wants to keep on cutting like a honey badger going after a ground squirrel sandwich until the cut is finished. But when training oneself to make highly precise sawcuts, it is best to concentrate on each stroke, making sure it doesn’t wander. After all, it is the accumulation of many accurate small cuts that results in an accurate final cut. Likewise, it only takes a few inaccurate cuts to result in a sloppy final cut, so please pay attention.

Once you have become the machine and developed the necessary muscle memory the process will go very quickly indeed. Sadly, this fine muscle memory is not a permanent thing, but once learned it can be quickly remembered.

Stop & Correct

While sawing away, if you notice your cuts are going astray, stop and figure out why. Is your position good? Is your eyeball where it should be? Is the sawblade aligned with the plane of the cut? Is tension released from your wrist? Is your elbow brushing the same place on your side with each stroke? Is the machine operating faithfully or are the invisible rails bent? Are the teeth dull? Are you applying too much pressure? If things aren’t right, stop the cut, figure out why, and make corrections NOW. Don’t wait.

This self-control is possibly the most difficult task in making accurate cuts with a handsaw, but also the most critical to gaining skill. Failure to do it will result in either learning bad habits, or in delays in correcting the ones you already have. BTW, everyone has bad habits they need to work on, including YMHOS.

The Essential Oilpot

Unlike quadruple-distilled, aged in ancient bog-oak unicorn wewe, wood is not a friction-less material. To make things worse, a saw kerf usually becomes “hairy” with loose wood fibers increasing friction in unpredictable ways. And the cherry on top is sap and resin residue found in all wood and which increases friction further.

This friction not only heats the sawblade, possibly warping it and wasting our energy and time, but it makes it more difficult to control the sawblade in the cut, often making our precision suck big donkey donuts. How to counteract this friction? The classical Japanese solution is the Oilpot.

This tool has long had counterparts throughout the world, and it’s as valuable now as it was six thousand years ago. If you want to use handsaws with high precision, you need to make yourself one. You will be impressed with the difference. Nuff said.

The Two-handed Pistol Grip

When I was a young carpenter working commercial construction, I had a foreman named (I kid thee not) Jack Frost who was offended that God did not give him a tail, especially when working on high scaffolding. Gentle Reader may agree that a fifth appendage could often be handy, despite the fashion compromises it would “entail.” However, consistent with human physical limitations, the fact remains that most joinery saws are operated using either one hand or two, but not by tails.

The discussion above is relevant to all saw grips, but is focused mostly on the single-handed grip. However, just to be thorough, your humble servant would like to describe another style of grip used by some Japanese craftsmen, one your humble servant calls the “Two-handed Pistol Grip.” As the name suggest, instead of gripping the saw in one hand off to the side of the body, the saw’s handle is gripped first by the dominant hand in a pistol grip with the index finger extended along the handle’s side. The index finger of the off-hand is then extended alongside the grip parallel to and opposite that of the dominant hand, and the remaining fingers wrapped over those of the dominant hand.

The sawblade is then operated inside a plane going through the chest and centered on the user’s nose, often quite effectively counteracting the right-left arc tendency. The “swordsman’s grip” is essential to using this technique effectively.

This technique is not good for powerful cuts, but works well for shallow, precise cuts.

I apologize that, despite popular demand, this article lacks clean diagrams and pretty pictures of your humble servant exhibiting these techniques while wearing his sexy blue sequin bikini and famous aluminum-foil alien mind-ray dispersal cap (with curly copper wires and red fringe). But, as the saying goes, “Life is a bowl of cherries, mostly pits.”

Until we meet again, I have the singular honor to remain

YMHOS

Another construction jobsite non-compliant with OSHA rules.

If you have questions or would like to learn more about our tools, please click the “Pricelist” link here or at the top of the page and use the “Contact Us” form located immediately below.

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Japanese Handplanes: The Kiwaganna Skewed Rabbet Plane

I made myself a snowball
As perfect as could be.
I thought I’d keep it as a pet
And let it sleep with me.
I made it some pajamas
And a pillow for its head.
Then last night it ran away,
But first it wet the bed.

Shel Silverstein

In this article your humble servant will introduce a Japanese plane called the Kiwaganna, meaning “skewed rabbet plane.”

This is an important handplane in common use in Japan, and one we sell, although it’s not well known in the West. So for the benefit our Beloved Customers, I will explain of some of the solutions learned over the years from senior Japanese craftsmen, and acquired during many decades of brutal study at the University of Stoopid, School of Hard Knocks (Lower Outhouse Campus), which may prove useful.

What is the Kiwaganna Handplane?

The Japanese Kiwaganna is written 際鉋 in Chinese characters, and pronounced kee/wha/gah/nah. “Kiwa” means “edge” or “verge,” and “ganna” means handplane.

While the design of the Japanese version is unique, as far as your humble servant is aware many other versions exist around the globe. The Japanese version has a wooden body, a laminated blade, and is significantly lighter in weight and smaller in volume than its counterparts. It is a superior tool, IMHO, but it can be quirky.

This plane can handle a number of tasks, but it specializes in planing a straight-sided groove or rabbet right up to an edge or line with a clean 90˚ inside corner. A common application is planing the tongue around the perimeter of a board to make the bottom of a drawer, or a panel in frame and panel construction. In construction work it is frequently used to pare and clean tenons in timbers, especially those cut with circular saws which tend to leave a step, and to fit finish woodwork, among many other tasks.

Craftsmen who use kiwaganna typically own a two-piece set comprised of a right-hand and left-hand version to deal with tight access and changing grain direction. But the right-hand version is the most popular by far.

This plane is of course used by joiners, cabinetmakers, sashimonoshi and furniture makers, but you would be surprised at how popular it is with carpenters and timber framers for cleaning the 90˚ inside corners of joints such as tenons.

In general, a skewed blade in a rabbet plane provides two benefits. The first is that the reaction forces pushing back on the blade include a vector that tends to push the plane towards the line, edge, inside corner or verge being planed to, making the plane more stable in the cut, an important factor where precision is necessary.

The second and most important benefit of the skewed blade, however, is the smoother cut and reduced tearout it makes possible, especially important when planing cross-grain.

Another benefit the skewed blade provides in the case of the Japanese kiwaganna is the point of the skewed blade penetrating the body of the plane and ending flush with the side of the body, making possible a zero-clearance cut to a line without the extra weight and cost of complicated mechanisms and reinforcing plates. It’s a deceptively simple but clever design.

Points to Keep In Mind

While a simple tool, the kiwaganna often proves frustrating to first-timers. Indeed, your humble servant struggled with kiwaganna for far too long before he figured them out. To avoid similar damage to brain and ego, Beloved Customers that wish to become proficient in using this elegant tool will find it useful to understand the following nine points.

1. First, a brief inspection of the body and the cuts made to receive the blade will make it clear that kiwaganna dai (body) are more fragile than that of regular hiraganna planes, so when adjusting the blade, please use a wooden, plastic or rawhide mallet, not a steel hammer.

2. When removing the blade, strike the dai at the same angle as the blade is inlet into the dai to reduce unnecessary stresses. This means you will hit the top corner of the dai on the side opposite where the blade’s point exits. Clip off and round over this corner of the dai with a knife or chisel to prevent your mallet from chipping the dai. Striking the opposite corner can have bad results.


3. The first step in truing/adjusting the blade of a kiwaganna plane is to sharpen and polish the blade and uragane (chipbreaker) well, make sure they fit each other tightly without a gap near the cutting edge, and check that there is adequate and uniform clearance at the mouth so that shavings flow smoothly without clogging. The skewed nature of the blade and chipbreaker make this difficult to judge, so exercise caution. In many cases, the plane will work just fine, and maybe even better, without its uragane. The uragane has a bevel ground into its pointy corner. Make sure this is not touching the dai when inserted properly. Keep in mind that you will need to periodically grind this bevel down after sharpening the blade every few times or it will touch the dai creating a restriction where shavings will become jammed. When you sharpen the blade, you will also need to resharpen the uragane too to ensure they match each other tightly. Not every time, but once in a while. A lot of people fail to maintain the uragane and then suffer emotional anguish when their plane mysteriously stops working. Mystery solved.

4. The right and left side edges of the blade must fit the retention grooves tightly where they exit the top surface of the dai. If the fit is too loose, the blade will be difficult to keep in alignment, but if the fit is too tight the blade may crack the dai during seasonal shrinkage. Older dai are usually safe, but a plane shipped from a wet Tokyo summer to a hellishly dry Arizona may experience problems. This article provides more details about fitting the body to the blade.

If it becomes necessary to shave the grooves, work very slowly and carefully. Color the blade’s side edges with pencil lead or marking pen ink. Insert it into the grooves and note the high colored areas. Shave these down just a tiny tiny bit with a very sharp chisel, then insert the blade and check. Repeat as necessary. Don’t create a big gap between the walls of the groove and the sides of the blade (versus face and underside of the blade which must be tightly pinched in the grooves), just make sure the blade is not wedged tightly between the grooves.

5. Check that the “ear” of the blade (the chamfered corner at the cutting edge opposite the pointy corner) is ground back enough so it does not terminate inside the groove, because if it does, shavings will become jammed. Don’t forget that, with each sharpening, the blade will become a little wider and this chamfer a little smaller. If it becomes too small, shavings will become jammed between the blade and retention groove, so please grind this chamfer back after every few sharpenings.

6. Here is wisdom: Contact between the back of the blade and the block should not be too high-pressure, otherwise the area on the sole behind the mouth may be pushed out making the plane misbehave, an extremely common problem with this plane. You want uniform pressure where possible to ensure the blade is stable, but remember that it is the grooves pinching the blade that keep it in place, not pressure on its back.

7. With the blade fitted to the grooves and most of the pressure relieved from its back, insert the blade. Check that it projects evenly from the mouth its full width. This is very important. If it projects further on one side than the other, resharpen/reshape the cutting edge so it projects perfectly uniformly. This uneven projection is almost always the result of the user unintentionally and gradually changing the angle of the skew over multiple sharpening sessions. Besides projecting uniformly from the mouth (when the sole is at the mouth is perfectly flat), the point of the blade must penetrate the dai (body) and be flush with the outside surface of the sidewall. Failure to get these two subtle details right is the most common cause of failure to perform in the Kiwaganna plane.


8. The mouth opening, in other words the gap between the blade and the sole of the dai where it exits the dai, must be narrow, and even in width, but not closed or skewed, otherwise shavings will jamb in the mouth, another common problem with kiwaganna. If the mouth is not even, use an adjustable steel protractor to match the angle of the blade measured from the side of the dai where the point of the blade exits. Remove the blade and mark the mouth with a sharp marking knife so the mouth is exactly the same angle as the blade. When doing this layout, be extremely careful to make the mouth opening of uniform width to match the cutting edge, but keep the mouth as narrow as possible. Use a sharp chisel to cut to this line making the mouth perfectly uniform. Insert a thin knife blade (or sharpened utility knife blade) into the mouth to shave and clean it after chiseling.


9. There is nothing wrong with leaving the sole perfectly flat instead of having the hollowed-out areas typically added to standard hiraganna planes. Just make sure it is truly perfectly flat. I have no problem with using sandpaper on float glass to true the sole of a kiwaganna, but a card scraper is a better tool for the job.

Juggling Blades

Although we addressed them above, let’s review the two critical factors you must juggle to keep a kiwaganna working well. I’m repeating these points not because I doubt Beloved Customer’s intelligence, but only because repetition improves understanding.

First, maintain the angle of the blade’s skew so that it projects a uniform distance from the mouth (with the mouth/sole flat and true). To do this you must pay more attention when sharpening the blade than is normally necessary. If you get this wrong, nothing will go right.

Second, as mentioned above, to cut into the corner of the rabbet cleanly, the point of the sharpened blade must penetrate the sidewall of the dai and be perfectly flush with the sidewall but without projecting out past the sidewall when the blade is projecting the right amount from the mouth and uniformly across its width. If the skew of the blade is wrong, or the dai is warped or worn, this point will end up being either recessed inside the sidewall or projecting outside it. It needs to be flush with the sidewall. If it is not, you may need to either shave material from the side of the plane (not recommended) or grind down the side edge of the blade near the point, a drastic measure. This is seldom necessary, and when it is, the reason is almost always a badly warped dai.

As you can see, this is a juggling act, but so long as you focus on these two points, and maintain the proper skew angle, all the blades will remain spinning in the air as you grin from ear to ear.

YMHOS

If you have questions or would like to learn more about our tools, please click the “Pricelist” link here or at the top of the page and use the “Contact Us” form located immediately below.

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The Varieties of Japanese Chisels Part 17 – The Sokozarai Chisel

底さらえ鑿の一分五厘 : 日々の製作と研ぎの記録 ～木工 藤原次朗のブログ～

Quality is not an act, it is a habit.

Aristotle, 384–322 BC

In this article your humble servant will introduce a standard woodworking tool which I believe to be unique to Japan, although I have no doubt individual craftsmen around the world have produced versions of it for their own use for hundreds, maybe thousands, of years.

I will explain the jobs this tool is used for, how it is used, how to fettle it, and how to sharpen it. I will also share some first-hand business insight regarding why Japanese women make this tool essential to the joiner in both performing traditional joinery in Japan, as well as the sometimes challenging task of getting paid for his work.

Mr. Spock will also make a brief contribution to the discussion.

Definition & Pronunciation

The Sokozarai Nomi (pronounced Soh/koh/zah/rahi noh/me and written 底浚い鑿 ) translates to “bottom-cleaning chisel.”

It is a simple tool consisting of a differentially-hardened steel shaft, with a small, short, sharp foot formed at the end, attached via a tang to a wooden handle, and secured by a conical ferrule.

The Sokozarai chisel is one of three specialized chisels used specifically for joinery work. Cabinetmakers and furniture makers use it too. Two other specialty joiner chisels are the “Mori Nomi,” which translates to “harpoon chisel,” and “Kama nomi,” which translates to “sickle chisel.” Perhaps we will discuss these in a future article.

A larger version of the sokozarai chisel is used for cleaning the bottom of the larger mortises commonly cut in timber frames.

The Role of the Sokozarai Chisel

The sokozarai chisel is used for two purposes. The first is loosening and removing chips from inside mortises. One simply hooks the offending waste with the chisel’s toe and flips it out. 

The second role of the sokozarai chisel is to flatten and even plane mortise bottoms. When set up correctly, it will cut shavings from the bottom of mortises cut in softwood planing them flat and clean.

Indeed, in advanced joinery work, a skillful joiner will plan and execute his joints such that the material left remaining at the bottom of a mortise cut into a stile intended to receive the tenon from a rail is less than 1mm thick, thin enough to allow light to pass through. The ability to routinely cut joints like this, without cutting all the way through, is a mandatory skill of the professional joiner.

I suspect that about now Gentle Reader is forming his elegant eyebrow into an artistic and skeptical arc as he ponders why one would go to the trouble of making clean and pretty the bottom of a hole upon which no one will ever gaze, leaving a paper-thin wall of uniform thickness at the bottom admitting light into a space no one will ever see. Can there possibly be method to this madness? Welcome to traditional Japanese joinery.

Consider that a rough, bumpy floor in a mortise prevents the tenon from seating the last few millimeters, but by planing it flat with a sokozarai chisel, those last few millimeters can be converted to useful space to house maximum-length tenons ensuring maximum resistance to withdrawal and bending forces resulting in strong, slender but durable joinery without adding extra weight. This is a big deal in the case of the slim, flexible frame members found in operable traditional Japanese joinery such as shoji, itado and tsuitate screens, joinery that must satisfy the severe eye and meet the high standards of fit and finish expected by many Japanese women, the most unforgiving consumers in the world.

I don’t know when this detail entered common use, but as Gentle Reader is no doubt aware, the older and more common type of mortise and tenon joint found in joinery worldwide is the through single or double tenon with the tenon’s end exposed at the rail where it is often wedged, a technique that is undoubtedly stronger.

On the other hand, the fully-housed tenon made easier to fabricate using the sokozarai chisel has two advantages over its older, less-refined brother the through-wedged tenon. First, it simply looks better and more elegant when new, and is therefore better able to survive the strict final inspection by the lady of the house thereby more reliably earning the reward of final payment. Hallelujah, pass the bottle brother!

Second, it simply looks better to the eye and feels better in the hand as time goes by because, as the stile shrinks during drier months, the once flush end of the through-tenon won’t project past the surface of the stile creating an unslightly, uncomfortable bump, and during the wetter months it won’t recede back into the mortise leaving an indentation in the stile and an uneven appearance.

These details are not based on esoteric imaginings about quality, but are make or break business decisions essential to avoiding complaints from the same unforgiving Japanese women. And of course, in a country where advertising and representations are routinely and intentionally false (sad but true), word of mouth among sharp-eyed quick-tongued women is critical to a craftsman’s success. Please note that I say this as someone who has has been married to a Japanese woman for 43 years, has lived and worked in Japan for over 30 years, and during those 30 years has had plenty of direct commercial experience working with Japanese women as both customers and team members.

Next time we are sharing a cup of hot cocoa around the evening fire, remind me to tell you the story about two stressful days spent inspecting Thassos marble slabs for a new building’s lobby walls in the company of three Japanese women: an Architect, a Quantity Surveyor, and a Project Manager. All the story lacks is a Rabbi and a Priest to make a rib-splitting joke (ツ)。

A 4.5mm differentially-hardened sokozarai chisel with red oak handle

Using the Sokozarai Chisel

To use the Sokozarai chisel, and assuming you are right-handed, hold the handle in a fist in your right hand with the blade projecting from the bottom of the fist. Lay the back of the fingers of your left hand on top of and crosswise to the long direction of the mortise. Insert the blade of the chisel into the previously cut mortise hole and press the back of the blade’s neck (opposite the cutting edge of the foot) against the outside edge of your forefinger. Then pinch the blade’s neck between your thumb and forefinger. This is the grip.

To remove loose waste, insert the sokozarai chisel into the mortise hole and move it around gathering chips on the chisel’s toe. Then pull the chisel up and out of the mortise quickly to pop chips out.

To cut loose chips still attached in the mortise hole, press the chisel’s foot to the bottom, move it forward until it snags on irregularities, then rotate the handle towards your body using the forefinger of your left hand as a fulcrum to lever waste out.

To shave the bottom, simply move both hands forward with the bottom of the foot parallel with the intended bottom of the mortise. Developing a sense of the chisel’s action will take practice. Shining a flashlight into the mortise frequently at first will help develop these senses.

To check the depth of the mortise, a specialist kamakebiki, essentially a small router plane, is ideal. But you can make a simple depth gauge by sharpening the edges of the head of a nail or drywall screw, driving or screwing it into a small block of wood, then cutting off and filing the point to avoid ouchies. Using this, you will be able to detect bumps and irregularities remaining on the bottom. Indeed, it too can be used to shave the bottom, but it won’t clean all the way into corners unless you grind the head square or rectangular.

For advanced work, make a slightly undersized test stub tenon with shoulders from hardwood the depth of the finished mortise, and anoint the end with cheap dark lipstick or Vaseline with black oil pigment mixed in. High spots remaining at the bottom of the mortise will be highlighted. With practice, you won’t need this test tenon, but you will still definitely need a sokozarai that is sharp enough to plane the bottom.

Next, let’s consider how to prepare a new sokozarai chisel.

Fettling the Sokozarai Chisel

Unlike most other Japanese chisels, the Sokozari chisel is not laminated construction, but is formed of one piece of differentially-hardened high-carbon steel. Differentially-hardened in this case means that the foot and lower 1/4 of the leg’s length are hardest, becoming progressively softer going up the leg until it is dead soft at the tang. This means the cutting blade, (what your humble servant calls the “foot”) of this chisel will become sharp and stay sharp, but the neck is left softer so it will not snap off, and can even be bent a little to adjust the angle of the foot if necessary.

Low-quality sokozarai have both soft shafts and feet.

Flatten and Polish the Foot’s Bottom

The bottom of the foot needs to be flat and polished, but because of this surface’s narrow width and short length, it can be challenging to accomplish without rounding it over or skewing it.

It often helps to grind a hollow into the foot’s bottom the thickness of a nat’s eyebrow to help speed up the flattening and polishing process. If you use a grinder, be very careful to avoid overheating. It should take no more than one or two brief touches to the wheel.

When flattening and polishing the foot’s bottom surface on diamond plates and stones, it also helps to make a guide block. Cut a slot in the side of a small block of hardwood to house the bent shaft with the bottom of the foot located flush with the block’s bottom surface. Lock the shaft into the guide block with a wedge or a clamp to stabilize it. 

The jig in the photos above was made by a Most Beloved Customer who does exceptional high-quality joinery work.

An alternate sharpening jig can made by cutting a crosswise groove, similar to the one shown in the photo below, into the top surface of a stick of scrap wood, perhaps 50mm wide, 200mm long and 20mm thick. The bottom surface of the foot should be almost, but not quite flush with the stick’s edge, projecting the thickness of a piece of paper. Secure this jig to your workbench with a clamp or in a vise, press down on the blade with one hand, and move a sharpening stone along the side of the jig over the foot.

This guide block rides directly on the stone as you flatten and polish the foot’s bottom. Don’t let the foot’s bottom get skewed or rounded over. Work slowly and check constantly. This is a one-time operation.

Once the bottom is flat and polished, you should only need to polish the bottom of the foot on your finishing stone.

Adjust and Polish the Cutting Edge’s Bevel

The bottom of the foot is now flat and pretty, but the angle of the cutting edge is usually still far too steep, and the bevel’s surface is rough. This must be corrected.

Modify the cutting edge’s angle by grinding the bevel on a diamond plate. The final angle you chose for the cutting edge will depend on your preferences and the wood you will be cutting. Steeper angles are more durable. Shallower angles cut better, but dull quicker. 20~24 degrees is usually OK. When I was a young man, I knew professionals who took the bevel angle down to 15 degrees. 

You may want to make another narrower guide-block clamping 90 degrees across the the shaft to help hold/stabilize the blade during this operation. When you have adjusted the angle to where you want it to be, then polish it on your sharpening stones. Be careful to avoid skewing it or rounding it over. You want sharp, clean corners.

To routinely sharpen/polish the bevel, hold the chisel in one hand with the bevel face-down on the long side of your sharpening stone. While stabilizing the blade and applying pressure on the bottom of the foot with a fingertip, move the sokozarai chisel back and forth in small strokes being careful to avoid rocking it and rounding it over.

Adjust the Foot’s Length

This step is unnecessary for most applications, but I will touch on it just to be thorough.

The length of the foot is fine as-is for most furniture mortises, but for very tiny mortises as in screens, light fixtures, and small casework, the foot may need to be made shorter. It is not unusual for a tategushi or sashimonoshi to own multiple sokozarai nomi with feet and shafts of different widths and lengths and bevel angles to clean the mortises he makes the most.

Please note that the mortise holes for kumiko members installed in shoji screen and most other types of latticework are shallow and do not require the strength of long tenons, so the mortises are usually cut using mori nomi (harpoon chisels) with a hook on the end to pull out waste quickly, and the bottoms are left rougher.

Conclusion

Beloved Customers that have purchased our chisels, and diligent Gentle Readers that have read this blog, are aware that your humble servant insists our chisels not be used to scrape or lever waste out of joints. The reasons for this are my desire for Beloved Customer’s most excellent chisels to remain as sharp as possible as long as possible, and to avoid chipping the cutting edge. They are, after all, refined cutting tools with sensitive feelings, neither thuggish prybars nor pot-metal screwdrivers.

The Sokozarai chisel was invented specifically as a partner to chisels used for cutting the clean mortises essential to Japanese joinery, and to protect the super-sharp cutting edges of those chisels from damage resulting from barbaric treatment. I encourage you to level-up your joinery skills by procuring and using one. You will be glad you did.

And so I wave farewell until the evening we share a cup of hot cocoa around the irori fire. In the meantime, I am humbly grateful for the honor to remain,

YMHOS

Adieu for now, Gentle Reader!

If you have questions or would like to learn more about our tools, please click the “Pricelist” link here or at the top of the page and use the “Contact Us” form located immediately below.

Please share your insights and comments with everyone by using the form located further below labeled “Leave a Reply.” We aren’t evil Google, fascist facebook, or thuggish Twitter and so won’t sell, share, or profitably “misplace” your information. If I lie may my sokozarai chisels get athletes feet!