The Care and Feeding of the Wild Mortise Chisel – Part 2

By concentrating on precision, one arrives at technique, but by concentrating on technique one does not arrive at precision.

Bruno Walter

As mentioned in the previous post in this series, in Japan the mortise chisel is called the “Joiner’s Chisel,” because it is specifically designed for precisely and quickly cutting the many small mortises craftsmen in the joiners trade use in making doors, windows, shoji, screens, furniture and cabinetry.

Why must it cut mortises quickly? Simply because a few seconds of time wasted on each one of many mortises cut during the workday by an uncooperative chisel will quickly add up to hours of lost productivity.

Why must it cut mortises precisely? Simply because defects hidden inside mortises with poor internal tolerances tend to accumulate and too often turn what would otherwise be a well-made piece of furniture or joinery into a rickety old Chinese lawnchair.

In this post we will discuss what to look for in a mortise chisel, and how to correct some typical problems. Most of the concepts discussed in this post are applicable to oiirenomi and atsunomi used for cutting mortises as well, although such chisels lack the same shape advantages.

Klipstein’s Law of Thermodynamics

Just in case Gentle Reader didn’t notice, your humble servant has strong opinions about mortise chisels, partly because I was trained by no-nonsense professionals to cut hundreds of mortises in a single sitting, and partly because bitter experience has taught me the truth that sloppy mortises result in both sloppy products and crushing headaches. Nothing like a bunch of tiny errors when making a series of latticework doors to painfully confirm the validity of Klipstein’s Law of Thermodynamics: “Tolerances inevitably accumulate unidirectionally toward maximum difficulty to assemble.”

Because of this hard-earned experience we have given our blacksmiths specific dimensional tolerance criteria for the mortise chisels they make for us. I can’t always clearly hear what they are muttering in response to my pointed insistence, but it sounds something like “frikin prissy pink princess expects too much of a damned chisel.” Your most humble and obedient servant, however, is much too dignified and polite to respond in so many words, but at such times I think they are stubborn old farts that have never used a mortise chisel. In any case, those who use our mortise chisels benefit from the princess impulse in us.

What to Look For

Mortise chisels are used routinely by only the most skilled craftsmen. Despite their simple appearance, mortise chisels are required to cut to tighter tolerances than other type of chisel, but because they are handmade in the traditional manner without the use of CNC machinery, and because perfection is unattainable in mortal endeavors, they are seldom perfect when new, so Beloved Customer should plan on tuning your mortise chisels before doing serious high-volume work. Indeed, it has long been standard practice among Japanese joiners to modify their chisels and planes to their preferences, and correcting the dimensional imperfections of mortise chisels is at the top of the list, not because they tend to have more imperfections than other chisels, but because more precise work is expected of them.

If you recall some of the mortises you have cut before now you may have noticed that despite your best efforts and forehead-splitting concentration, the sides ended up out-of-square with the workpiece’s top surface, or the side walls were raggedly gouged, or even undercut. These defects are not unusual, and may be due to pernicious pixies, your technique, or perhaps a combination of both, but my money’s on the chisel being the culprit.

Please examine your mortise chisel. If it does not meet the ideal standards in the list below (and it won’t), you should make corrections. You’ll be glad you did. There is a link to a document below that illustrates the ideal mortise chisel as well as some typical problems that may prove useful.

  1. The plane formed by the flat lands surrounding the hollow-ground ura depression should be truly flat and without twist over its entire length from cutting edge to shoulder. 
  2. The blade’s width should be consistent over its entire length. Alternately, it is acceptable if the blade’s width becomes just slightly and gradually narrower moving from cutting edge to neck. But not too much. On the other hand, a blade that widens towards the neck is an abomination to be avoided like the spotty-bottom footpads at the California Franchise Tax Board.
  3. The blade’s sides should be flat, planar, free of twist, square to the ura, and square to the blade’s top face. Accordingly, a cross-section taken anywhere across the width of the blade should be rectangular anywhere along its length, with all corners 90°. Picky details, but they can make a big difference in the quality if the finished mortise.
  4. The top face (surface where the brand is stamped) need not be straight, but it must be square to the sides at all points along the blade’s length. 

Make no mistake, this is a tall order in a hand-forged tool that has never seen a milling machine, planer, or CNC grinder. Few handmade mortise chisels can meet these standards when new, but these details can make all the difference.

Let’s begin the examination part of this job. You will need a 6~12″ straightedge, a small precision square like the Matsui Precision products we carry, and a vernier caliper.

Record Your Observations

Too often the number of dimensional irregularities that require attention are complicated enough to create confusion. This can result in even experienced people making one irregularity worse, or even generating new problems, while attempting to resolve the initial irregularity, like inadvertently creating more knots while trying to untangle a snarled mess of string.

To avoid confusion, I recommend  you make a simple orthogonal hand sketch of your chisel to record irregularities. This sketch should show at least four views of the blade including left and right sides, its face (opposite the hollow-ground ura), and an end view looking towards the cutting edge’s bevel. You may also need to make a few cross-section sketches

Record the results of your examination as annotations and red lines on these sketches to help you plan and execute the work of correcting any problems you may find. There are always a few, and you will need to keep track of each one, and its relationship with the others.

Examine and True the Ura

The first step is to check the ura, the polished lands (flat surfaces) surrounding the hollow-ground depression on the chisel’s back. These must be flat and in the same plane (coplanar). This detail is very important.

A straightedge is good enough for a quick examination, but a more reliable method is to use a granite surface plate. A less expensive and handier option is a simple piece of ⅜” or thicker float glass. 

To use a glass surface plate, apply marking pen ink or Dykem to the ura’s lands. Smear a tiny amount of finishing stone mud around on the glass plate. With the entire blade resting on the plate, and finger pressure straight down in the middle of the blade’s face, move it in a oval pattern through the sharpening stone mud. The ink or Dykem at the high spots will be rubbed off, but will remain at the low spots. This will show you where and how much material must be removed to flatten the ura’s lands

Then, true the ura using a diamond plate, diamond stone, sharpening stones, and/or the glass surface plate. This step is not so important in the case of other types of chisels, but a mortise chisel must have a reasonably flat ura. Without a planar ura, the rest of your examination may be inaccurate. The article at this LINK contains a more detailed discussion with pretty pictures.

Do this work carefully. If you heavy-handedly remove too much steel, the useful life of the chisel may be dramatically reduced. This is a one-time operation in the life of most chisels.

Examine the Blade’s Width and Taper

Next, check the width of your mortise chisel measured across the ura using a vernier caliper or micrometer or other reliable gauge. Relative width is what you need to check, not absolute inches or millimeters, unless you expect your chisel to cut precisely-dimensioned mortises, something that is seldom necessary in the real world.

Measure the blade’s width at five or six locations along the cutting edge, in the middle, and near the neck before it narrows. Make a sketch of the blade and annotate these dimensions on it

Use the glass surface plate at this time to check the sides for flatness. The black oxide surface skin will be worn away by the sharpening stone mud marking the high points, but don’t let the change in cosmetic appearance bother you.

Ideally, the blade will be the same width its full length. However, it is usually acceptable if the blade is slightly wider at the cutting edge than near the shoulder. But if it is wider at the shoulder than the cutting end, it will bind in the cut, tend to split the mortise, and the finished mortise will be skiwampus. This must be remedied by grinding the blade on diamond plates and polishing on sharpening stones.

But don’t do anything yet since there are more details you need to examine first. Just make a note on your little sketch.

Examine the Blade’s Sides

Straight Sides

Use a good straight-edge to check both sides of the blade’s sides. They must be straight. If they curve in or out it will be difficult to convince it to cut a clean straight mortise. If the blade is banana-shaped, it can’t cut a straight mortise anymore than a politician can tell the truth while his heart beats (it’s rumored that many have hearts).

If the blade’s sides are not straight, they must be corrected by carefully grinding and polishing them. But hold your horses there Hoss, don’t do anything drastic yet, just make a note on your little drawing: there’s still more to check first.

Flat Sides

Next check the sides of the blade across their width. They must be either flat (best) or hollow ground (acceptable). If they bulge outwards the blade will bind and can never cut a clean precise mortise, so corrections are absolutely necessary. 

Mark any irregularities on your sketch.

Right Angled Sides

The sides of the blade should be at right angles (90°) to the ura lands. If not, the chisel will skew left or right during each cut, a common problem with most chisels. Gentle Reader has no doubt experienced this.

Slightly less than 90˚ may be acceptable (but less than ideal) if both sides are the same angle. If, however, one side is 90˚, for instance, and the opposite side measures 80˚, well that is not good and may require correction.

For now, just mark any irregularities on your sketch.

Examine the Blade’s Face

Next, examine the chisel’s face (the surface with the brand). 

This surface need not be straight along its length. It doesn’t even need to be flat across its width, but can even be be hollow or bulging to a minor degree without causing trouble. But you do need to pay attention to two key details. 

First, if it is hollow or bulging, the curvature of the bulge or hollow across the blade’s width must be uniform. If not, you should grind it flat. 

The second thing to check for is that a line between and touching the corners where the surface of the face meets the blade’s sides must be parallel with the ura. In other words, if you draw a line 90˚ across the width of the face, that line should be parallel with the ura. If it isn’t corrections are necessary.

Why does the relationship of these two surfaces with each other matter? Two reasons. First, if they are not properly aligned, and assuming the ura is flat, it means the blade is thicker in cross-section at either the right side or left side. There is a strong tendency for the bevel and to become skewed during sharpening, with the result that the cutting edge is not square to the center line of the blade’s long axis.

Of course a skewed cutting edge will push the blade to the right or left in the cut, and cannot cut a flat bottom, a serious defect in advanced mortise and tenon work. This deformity can be compensated for with careful attention during sharpening, but you should not have to work so hard. Better to correct the problem now and get it over with once and for all, I promise.

The second and most important reason is that the skewed bevel will cause the blade to dive to the right or left when cutting a mortise ruining precision and gouging the mortise’s walls. This is different from the problem noted in the previous paragraph, although it may seem to be the same. It’s a serious defect in a mortise chisel, one that causes the most self-doubt among craftsmen.

Even the very best blacksmiths frequently fail to give this surface proper attention You are hereby warned: Do not underestimate the importance your chisel’s face.

Examine the Blade’s Corners

Finally, examine the two lines formed by the 90° intersection of the sides and the ura. Are they clean and sharp, or are they ragged, radiused or chamfered? These corner edges serve an important function in dimensioning and shaving the mortise’s side walls. They must be clean and almost acute enough to cut your fingers, but please don’t.

If they are not right, you can correct this now or a little bit at a time during subsequent sharpening sessions. The important thing is to be aware of any defects so you can make corrections, so make a note on your little sketch.

The Plan

You should now have a sketch describing those areas that need to be corrected. Use it to make a plan. A rough sketch showing how a mortise should should be and common problems is linked to below.

Beloved Customer should keep two important factors in mind in mind when planning and executing corrections to mortise chisels.

First, you should strive to achieve the corrections with the minimum expenditure of time, effort and stone/diamond plate, and while wasting the minimum amount of steel. I am not saying work hard or work fast, but rather to work efficiently.

Second, you should work carefully to avoid creating new problems while attempting to fix existing ones. This is why you need a plan, one that will vary a little with each chisel, to guide you in working efficiently and carefully. Remember, double work takes more than twice the effort, and often wastes lots of expensive steel.

I suggest you write your plan down.

I also recommend you keep the following points in-mind when considering your plan and its execution.

  1. As mentioned above, the first step is to true the ura so it is planar. It need not be perfect at first; Close is good.
  2. After the ura is more-or less planar, grind the right and left side, whichever is in better shape, straight along its length, flat (or sightly hollow) across its width, and perpendicular to the planar ura using diamond plates. Electrical grinders and sanders can be used, but there is a real risk of ruining the temper if you allow the steel to get hotter than is comfortable to touch, so great caution is necessary. This means working slow and using lots of water.
  3. When one side is done, grind the opposite side straight along its length, flat (or sightly hollow) across its width, and perpendicular to the planar ura using diamond plates (if necessary). It will be at the same angle with the respect to the ura as the opposite side, of course. Here is where more caution is necessary: pay close attention when grinding this side to make it parallel with the opposite side. Worst case, the blade width measured across the ura can be slightly wider at the cutting edge than the neck, but uniform width is best. On the other hand, a blade narrower at the cutting edge than near the shoulders is useless for cutting mortises and must be corrected.
  4. Finally, grind the face of the blade (the upper surface with the brand) so that any point along its length is parallel with the ura. It need not be straight or even perfectly flat over its entire length, just parallel with the ura to guide the chisel straight in the cut.

At the conclusion of the steps described in this article, your mortise chisel should now have an ura with all the lands surrounding the hollow-ground swamp forming a single flat plane. You should also have a nice little sketch describing all your chisel’s imperfections and a plan for making corrections.

In the next article in our joyous journey ass over teakettle down this rabbit hole of obscure woodworking tools, I will describe my observations about a particular mortise chisel, the plan for adjusting that chisel, and show the execution of that plan. Indeed, I have a box of chisels that are simply wiggling and squeeking with frantic anticipation to be first!

YMHOS

P.S.: After many months, we now have mortise chisels in-stock again. They won’t last long. Prices and availability can be checked at this LINK

A formal procession of frogs mocking the feudal lords of medieval Japan. I bet you haven’t seen many frogs walking around with swords. Such work was a rare opportunity for artists and the common people to mock the rich and powerful nobles that ruled the many little nations of the Japanese islands at the time with a steel and despotic fist.

If you have questions or would like to learn more about our tools, please click the see 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 in 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 mortise chisels all turn to glass.


Other Articles in “The Care and Feeding of the Wild Mortise Chisel” Series

Japanese Handsaws: The Twins

Communism is the opiate of intellectuals [with] no cure except as a guillotine might be called a cure for dandruff.

Clare Boothe Luce

his article is a show-and-tell about a matched set of custom-forged handsaws which have been your most humble and obedient servant’s trustworthy companions in the noble profession of making sawdust for many years.

The Twins

The archaeological record suggests that, at least in areas of the world where rusty remains have been excavated, the standard metal handsaw in ancient times had rip teeth only. As evidenced by the superior mental powers Gentle Reader exhibits, Woodworkers have historically been extremely intelligent people, so no doubt many sawyers, carpenters and joiners back in the mists of time independently discovered that filing (or stoning) their sawteeth to an acute bevel angle and alternating the direction of the bevel made the saw cut much faster and with less effort across the grain (i.e. crosscutting).

With this discovery, the crosscut saw was born, and thenceforth has been a worthy servant to its masters and a good companion to its elder sister the rip saw.

In modern times with the proliferation of inexpensive (and dangerous) circular saws, rip handsaws have become as rare as selfless tax collectors, but the combination of a rip saw for making cuts parallel with the direction of wood, and a crosscut saw for making cuts perpendicular to the grain of the wood has been common-sense among those who value accuracy and efficiency at least since the proliferation of carbon steel saws.

Some decades ago while working as a carpenter, your humble servant realized he needed a set of larger rip and crosscut saws for fabricating joints in timbers. The search resulted in the purchase of several saws, but the set described in this article are the two I have come to rely upon for such tasks most.

Both saws were hand-forged 70~80 years ago in Sanjo, Japan by a saw blacksmith named Azuma with the brand-name of Nakaya Choujiro (中屋長次郎), a venerable name in Eastern Japan. The grandson of this blacksmith is still producing saws in Sanjo today, including the Seijiro brand ryouba saws we carry. Nowadays nearly all of his production has shifted to short saws used by luthiers.

I found these saws in a tool store in Tokyo which is now defunct due to the owner’s inconvenient relocation to the big lumberyard in the sky. At the time of purchase, the store owner informed me they were originally commissioned by and custom forged for a Miyadaiku (temple carpenter) in Arakawa Ward of Tokyo, but sadly he had moved on to sorting boards in heaven without picking up these sawblades, leaving them sad and lonely in a cabinet hidden behind buckets of paint and roofing materials.

I get misty remembering their joy at being rescued after languishing so many years in darkness…

The Bukkiri Gagari Rip Saw

The saw in the photograph above and at the top of this article is a large kataba (single-blade) rip saw with aggressive, progressive-configured teeth called a “bukkiri gagari.”

“Bukkiri gagari” is a name used for large rip saws with this style of handle. The word “gagari“ refers to a large rip saw. The word “ bukkiri” probably means “chopped” or “cut down,” referring to the shortened tang.

The pointed tang, typical of handsaws intended to be fitted with a straight in-line handle, was bobbed at the time the saw was forged, evidence that it is not a conversion, but was intended to be a bukkiri gagari when just a twinkle in Grandfather Choujiro’s eye.

The large brownish-orange discoloration seen on the blade is neither corrosion nor a shadow due to poor lighting, but a remnant of the heat-treating process common to saws forged in Eastern Japan, more evidence of quality handwork.

The blade’s length measured from tip to the beginning of the tang is 425mm (16-5/8″). The cutting edge (teeth) measures 330mm (13″), making it a 1-shaku 1-sun blade a slightly unusual length. The blade’s overall length measured from the tip of the exposed tang to the tip of the blade is 625mm (24-5/8″). It measures 130mm (5-1/8″) at the widest point at the tip of the blade. The back of the blade has a slight curvature away from the cutting edge as is standard for larger rip saws forged in Eastern Japan.

A closeup of the tang of the bukkiri gagari member of the team. Sorry for the poor focus, but the hand-carved signature of Nakaya Choujirou (中屋長次郎) is plain to see. Some people prefer to jamb the handle on permanently, while I prefer the options a wedged handle provides. The wedge can be inserted from front or back, top or bottom, changing the angle of the handle and its distance from the cutting edge. The forge-welded connection between iron tang and steel handle is more visible in this photo. This detail is coveted by aficionados of Japanese saws as witness of quality handwork.

I made the handle from Japanese White Oak stained mahogany. It measures L270mm x w38mm x t30 (10-5/8″ x 1-1/2″ x 1-3/16″).

No doubt Gentle Reader is familiar with the more common Japanese handsaws with straight, softwood handles. This style of handle attached to the tang at an angle is called a “shumoku tsuka” 撞木柄 (shoe/moh/ku/tsu/kah). A shumoku is a wooden mallet used to strike bells in the Buddhist religion. I don’t know why this word is used for a saw handle; No one I have asked has been able to provide useful insight.

The shumoku handle can be attached to most any Japanese sawblade with a straight tang. It has several advantages. First, compared to the standard long handle attached in-line with the tang, it makes the saw much shorter in length and therefore handier for working in tight spots. This is especially useful when making vertical cuts from below for joints in the ends of large timbers resting on sawhorses or during erection where a long handle would get in the way.

The second advantage of the shumoku handle is the fact that, when combined with the stiffer blades of large rip saws, the user is better able to bring the stronger muscles of legs, back and both shoulders into play for more powerful cuts, an ergonomic principle similar to the thumbhole handle once common in Western handsaws.

The stance this handle makes possible also provides more leverage (greater moment couple) when cutting in tight situations and at unusual angles than a longer, straight handle can. This last factor makes the bukkiri gagari saw most valuable IMHO.

The Crosscut Saw

Notice the curvature to the back which is the approximate inverse of the curvature of its twin the bukkiri gagari saw shown above. Subtly beautiful.

The crosscut member of this dynamic duo is also a kataba 片刃(single-edge) saw with a custom-made but more ordinary straight handle.

It’s overall length is 845mm (33-1/4″), with 420mm (16-9/16″) of that being the blade extending past the handle. The blade is 125mm (4-15/16″) wide at the tip.

The cutting edge portion of the blade matches its companion at 330mm (13″), so it too is a “Juissun” saw, meaning 11 sun.

It too has a beautiful curvature to its back which in this case is directed towards the cutting edge instead, giving it a diligent posture. As is the case with all matched sets forged by the same blacksmith, the curvature of the back of each saw is the inverse of its partner so that they nest neatly against each other lovey dovey. Although it has little if any practical purpose, Japanese shokunin are unreasonably fond of this cosmetic detail, as am I.

Of course, the handle is approximately the same length as the the blade (not including the tang), and oval in cross section measuring 30 x 35mm x 425mm (1-3/16″ X 1-3/16″ X 16-3/4″). We will discuss how to make this type of handle in a future article.

I made this handle long ago from a piece of scrap Akita Sugi cedar (cryptomeria) , wrapped it tightly with copper wire at the mouth end to reinforce against splitting, applied a dab of solder to lock the wire in-place, and finished it by rubbing the wood with a tool called an “uzukuri” made from skinny plant roots to partially remove the softer summer wood leaving an excellent, textured surface that won’t slip no mater how wet with sweat it becomes. I love Akita Sugi

Gentler Reader (may the hair on your toes ever grow long!) may be wondering why one would use a short, sideways handle for a rip saw but a long straight handle for a crosscut saw. An excellent question indeed and further evidence of your superior intelligence!

Some crosscuts in timber work benefit from a longer reach. But more importantly, while the longer handle provides less power than the shumoku handle, it provides more control, essential for precise crosscuts. The way it was explained to me is that the large bukkiri gagari rip saw is used up close to the face and “guided by the nose,” while the large crosscut saw is guided from further away by the eye. Give it a try and you’ll see what I mean.

Although I haven’t used these saws professionaly for far too long, I had the teeth sharpened and plate tuned a few years ago by a famous blacksmith and saw sharpener named Nakaya Takijiro located in Kawagoe.

In one or two of the photos you may detect the little marks his tapping tapping tapping hammer left on the blade when he trued and corrected it. No, he didn’t straighten it, but he induced internal stresses to relieve some oil canning that had existed from Choujiro’s forge. He also made other subtle stress adjustments with his little hammer that made the saw track straighter and smoother with less friction as it heats up. What a difference it made! He is literally a genius with a sawblade.

The blacksmith’s hand-cut signature on the crosscut saw: “Nakaya Choujiro.” The blade was shaped and tapered in thickness by hand using a “sen” scraper, as evidenced by the visible marks. Close observation reveals that the soft tang is not electronically welded to the blade as has become SOP post-WWII, but is forged welded, a technique lovers of hand-forged saw greatly appreciate. Sadly, most of the surface corrosion occurred before your humble servant rescued these excellent saws.

I don’t use these saws much anymore, but I enjoy taking them out of their protective wrappings once or twice a year to clean and oil them, catch up on news, and sing a song of sawdust together. They love to sing.

I hope you found this little show-and-tell amusing. I have other unusual saws I will introduce in future.

Until then, I have the honor to remain,

YMHOS

If you have questions or would like to learn more about our tools, please click the see 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 the teeth on my saws all snap off.