Sharpening Part 20 – Flattening and Polishing the Ura

A mind needs books as a sword needs a whetstone, if it is to keep its edge.

George R.R. Martin

Now that we are geared-up and our sharpening stones are flat, let’s make our blade sharp. The first step in sharpening a new blade is truing the ura. So let’s get to it.

General

All standard chisel blades and plane blades, whether Japanese or Western, need to have a planar flat or ura that it will be in contact with the sharpening stones its full width, and ideally, full length. Perfection is not necessary, however, so don’t let yourself get obsessive. If the ura is arched (concave), for instance, so it is in contact with a flat sharpening stone near the neck of a chisel, or head of a plane blade, and the cutting edge, that may be workable, but it must be in complete contact right behind the cutting edge. I cannot stress this importance of this point too strongly.

Once the ura of your chisel is flat and true, you should not need to true it again unless the blade needs major repairs. Japanese plane blades, on the other hand, are a little more complicated because repeated sharpenings tend to gradually wear out the land right in front of the cutting edge, called the “ito ura,” and the bevel must be tapped-out to compensate, and the ura re-flattened. I won’t delve into the subject of “tapping out” the ura of plane blades in this post but will save it for future discussions about Japanese planes.

Evaluate the Ura

The first step in flattening or truing an ura is to evaluate its condition. Don’t start grinding away willy nilly without first checking it and making a plan. If you find you cannot stop yourself, don’t walk but run to the nearest pharmacy and buy a bucket of the medicine discussed in part 19 in this series about maintaining sharpening stones.

There are several ways to check the ura’s condition. A narrow straightedge works well in most cases. Place the edge on top of the full length of the shiny land at one side of the ura all the way to the cutting edge. Keep the straightedge touching the land; Don’t let it span the hollow- ground urasuki. Hold the straightedge and blade up to a strong light source and look for light passing between them. This technique is quick and dirty and will suffice in most cases, but does not tell you a lot about twist.

Use a straightedge to check the right and left lands for flatness. It doesn’t do any good to span the hollow-ground urasuki, so don’t bother. These photos are taken from above for clarity, but you want to hold the blade and straightedge together up to a strong light to observe any light showing between them that will indicate a gap. I am using a small square, but a simple small straightedge is more convenient. This takes a bit of coordination so be careful not to drop a chisel on your toe. I’ve done this once or twice before. Monkey-football.
This is a 30mm Sukemaru atsunomi, a famous brand and an excellent and powerful chisel hand-forged by Mr. Usui from Shirogami No.1 Steel. It’s in pretty good shape, but can benefit from a little truing as can most new chisels and plane blades.

Another method to check the ura for planar is to paint the shiny lands with dark marking pen ink or Dykem liquid, apply a bit of fine sharpening stone mud to a piece of flat glass, like the piece mentioned in Part 17, and rub the blade’s flat or ura over the glass. The high spots will become obvious. If the ura is banana shaped (convex), mark the high spot with your marking pen. More often than not, the ura of chisels will be generally flat, but the last 6mm or so of the cutting edge will be curved upwards towards the chisel’s face.

I learned two things from my examination of this Sukemaru brand atsunomi. First, there is a high spot (convex) at the skinny land on one side located approximately 1/2 to 5/8 the blades’s distance from the cutting edge. The land on the other side seems a little low. Hmm, curious. This is a bit unusual, but it happens when a blade warps during heat treat, which Shirogami steels tends to do frequently.

The second problem I observed was that the last 3~4mm of the land right behind the cutting edge curves downward away from the ura just a tiny bit, enough to cause problems.

I next need a plan to resolve these problems with a minimum of time and effort and without making things worse.

Make a Plan

The temptation to start grinding away immediately will be powerful. If it becomes too much, take a coffee cup or three of the medicine mentioned above and slather it on your head forcefully. Don’t hold back, for Pete’s sake, rub it in really good now. Some say my excessive use of this medicine is why I am as bald as an egg, but I prefer to believe it is caused by the light radiating from my gigantic brain (ツ). Thank goodness for my aluminum foil skull cap with its protruding copper wires!

Any plan needs goals and objectives. In this case the goal is a perfectly planar ura, but if this goal is difficult to achieve quickly there is an objective you should plan to achieve immediately in any case, one that may make it possible to achieve the larger goal over multiple routine sharpening sessions without any special effort.

As I keep harping, to make a chisel or plane work well, you need a flat area right at the cutting edge. This is where the cutting occurs and the area I need to keep sharp, so I will make creating this flat area the first objective in my plan, and then determine the steps to achieve it. Make certain every step in your plan and every stroke on the stones gets you closer to this objective, not further away. This means working smart.

If the blade is arched (concave), touching at two points, one near the neck of the chisel blade, or head of the plane blade, and at the other at the cutting edge, and not in between, all is well. I recommend you leave a blade like this as-is because after a few sharpening sessions the ura will become flat and twist-free without any special effort, and the blade will become very sharp and be entirely functional.

If the blade is wavy (rare) or banana-shaped (convex), your plan needs to take those details into account.

I located the highest point of the bulging area at the ura and marked a line across it with my marking pen. I then measured halfway between this line and the cutting edge and made another line. This area we will call the “focus line.” It is here where I need to focus the most pressure when grinding down the ura, not the entire length of the blade.

The purpose of doing all this prissy planning and layout work is to protect the right and left side lands from being wasted unnecessarily. Newbies try to work the entire length of the blade, but this is illogical and ignores three points. The first point is that the majority of the metal I need to waste is usually located to the right and left of the land nearest the cutting edge, not the full length of the blade, so there is little benefit to grinding the entire ura. The second point is that the side lands are thin as a blade of grass and will abrade very quickly with almost no effort. Besides, without using large plates and stones, it is very difficult to work the blade’s full length accurately without wearing notches in the side lands anyway. The third point is it makes no sense to try to grind down the land nearest the neck since the plane of the ura hinges on this land. Best to leave it alone and focus my efforts where they will make a difference.

Plane blades don’t even have a land near the head, so the futility of working the entire ura on plane blades is even more obvious than for a chisel.

Work the Plan

The traditional Japanese tool used to flatten and/or correct ura is a smooth steel lapping plate called a kanaban, meaning “metal plate.” To use it, carborundum powder and water are placed on the plate, and the blade is lapped. This is not a difficult process at all, but there is a tendency for the blade’s perimeter to be ground more than the interior areas as the grit is forced in between the kanaban and the blade’s perimeter. To avoid this tendency, and to speed the process up, I prefer to use diamond plates instead of kanaban.

Whatever plan you developed, and whichever tool you selected for this job, the time has come to work the plan. Do you need more medicine? A bigger coffee cup?

First, color the ura’s perimeter lands with a marking pen or Dykem to help you see where the ura is being ground down. Don’t ever guess.

Place the most pressure on the focus line selected above. Move the blade back and forth (not side to side) onto and off of the diamond plate or kanaban with the cutting edge and the focus line always touching the diamond plate or kanaban. Don’t go past the high point for now. Be careful to not grind a notch into the narrow side lands where they meet the edge of the diamond plate or kanaban. Most people make this mistake at first.

Grind the ura down so the line at the highest point and the cutting edge is fairly flat.

Work the blade on and off the edge of the diamond plate using short strokes and without going much past the highest point marked earlier. This works because the right and left side lands are thin and can be abraded in just a few strokes. I have moved my fingers to reveal the lines, but in actuality my fingers will press down hard on the focus line while working the blade.
Using a stick to apply more pressure to the blade. I am holding the end of the stick and the chisel’s handle together in my right hand. This is simply illustrating a technique. This chisel did not actually require this sort of aggressive attention.
The same stick technique works even better for plane blades and makes it easier to apply pressure right behind the cutting edge. When doing this, however, be sure to work the blade both forward and backward while moving it right and left on and off the plate’s edge to avoid digging a trench in the narrow side lands.

Remember, the narrow lands at the sides of the hollow-ground urasuki will abrade down quickly. And the rest of the ura can be gradually flattened during subsequent sharpening sessions using regular sharpening stones. It doesn’t need to be made perfect immediately. What matters most is the steel on the land right at the cutting edge.

The high spot on the land near the top of the photo has been relieved after a few passes on the #400 diamond plate. The side lands are in fair condition, and the land behind the cutting edge (itoura) needs just a little more work.
After a few more passes on the diamond plate, the ura is in good shape. Note the land at the photo’s bottom is not in full contact, but the opposite side is. This is will not impact the blade’s performance, and will work itself out during future sharpening sessions without special attention.
Flattening my stones before using them. Notice I am using two 1,000 grit stones to save time and stones. Don’t neglect flattening your stones, whether you use waterstones, novaculite stones, coticule, or even sandpaper.
Working the ura on the flat 1000 grit waterstone. Did I mention it is flat? Notice that I am working on and off the stone, not side to side, to save the right and left lands. Some but not all strokes are full length. The goal is simply to remove the deep scratches left by the diamond plate.
The ura after polishing on the flat 1000 grit waterstone. At this point the ura is in good shape. Notice how the land at the photo’s left is wider that elsewhere. This increase in width developed because this location was the high spot on this convex ura. Notice how the land on the left side is not even touching the plane in one area. What you should take away from this photo is the realization that if I had focused my efforts on this high location first and ignored the downward curvature of the land nearest the cutting edge, I would have wasted a lot more time and valuable metal only to shorten the useful life of this excellent chisel. Do you see the benefit of carefully checking the ura’s condition, making a plan with clear goals and objectives, and then working the plan? Did the medicine work? Next, we’ll work on the bevel, make a tiny burr, polish it off by making a few strokes alternating from bevel to ura, and be ready for the finishing stone.
Working the bevel on the flat 1,000 grit waterstone. Notice the mud piling up in front of the blade indicating the extreme cutting edge is in contact with the stone. I am applying pressure only on the push stroke to prevent the stone from rocking and developing a “bulging bevel,” A honing jig is not necessary.
The bevel after working on the 1,000 grit waterstone. No jigs were used. No “tricks” involving rulers were used. A silly, inefficient “micro-bevel” was neither wanted nor needed. The bevel is perfectly flat. Flattening the ura and polishing both ura and bevel to this level took less than ten minutes. When the purchaser of this blade eventually dulls the edge, he should not need to spend more than 2~3 minutes to sharpen this blade once his gear is ready, assuming he is able to sharpen freehand.

Polish a blade’s ura up to the level of your finest finishing stone once, and don’t touch it with rougher stones again unless it is absolutely necessary, or further gradual flattening is required. This means that in normal sharpening sessions you must remove all the damage at the cutting edge by abrading the bevel with the rougher stones, and only when the bevel is ready for the finish stone, do you work on the flat or ura, alternating from bevel to flat/ura until all defects, burrs, and even visible scratches are polished away.

If you condition the flat (ura) side of the blade correctly, and keep it polished, you should not need to work it on anything but your finish stone until it is time to tap out and grind the ura or back in the case of plane blades. Therefore, the bevel side of the blade is where we spend most of our time and effort.

Now that the ura is in good shape, we will look at sharpening the other side of the wedge, the blade’s bevel, in the next post in the series.

YMHOS

Links to Other Posts in the “Sharpening” Series

Sharpening Japanese Woodworking Tools Part 1

Sharpening Part 2 – The Journey

Sharpening Part 3 – Philosophy

Sharpening Part 4 – ‘Nando and the Sword Sharpener

Sharpening Part 5 – The Sharp Edge

Sharpening Part 6 – The Mystery of Steel

Sharpening Part 7 – The Alchemy of Hard Steel 鋼

Sharpening Part 8 – Soft Iron 地金

Sharpening Part 9 – Hard Steel & Soft Iron 鍛接

Sharpening Part 10 – The Ura 浦

Sharpening Part 11 – Supernatural Bevel Angles

Sharpening Part 12 – Skewampus Blades, Curved Cutting Edges, and Monkeyshines

Sharpening Part 13 – Nitty Gritty

Sharpening Part 14 – Natural Sharpening Stones

Sharpening Part 15 – The Most Important Stone

Sharpening Part 16 – Pixie Dust

Sharpening Part 17 – Gear

Sharpening Part 18 – The Nagura Stone

Sharpening Part 19 – Maintaining Sharpening Stones

Sharpening Part 20 – Flattening and Polishing the Ura

Sharpening Part 21 – The Bulging Bevel

Sharpening Part 22 – The Double-bevel Blues

Sharpening Part 23 – Stance & Grip

Sharpening Part 24 – Sharpening Direction

Sharpening Part 25 – Short Strokes

Sharpening Part 26 – The Taming of the Skew

Sharpening Part 27 – The Entire Face

Sharpening Part 28 – The Minuscule Burr

Sharpening Part 29 – An Example

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Setting Up Japanese Chisels

This post contains information for the Beloved Customers of C&S Tools to reference when setting up their new chisels. While you don’t have to perform this process before giving your chisels a ride around the block, these setup procedures are essential to ensure your chisel’s handles will endure hundreds of thousands of hammer blows and provide trouble-free service for many decades. Please, don’t put it off too long.

Which Chisels Require Setup?

There are several general categories and many types of Japanese chisels. I will delve into this subject in great detail in future posts, but the two general classifications are Tatakinomi (叩鑿)meaning “striking chisel,” which are designed to be motivated with a steel hammer to cut larger quantities of wood, and Tsukinomi (突き鑿), which translates directly to “thrusting chisel,” the equivalent of “paring chisel” in the Western tradition, and are designed to be pushed by hand for paring operations. The setup measures described herein are not entirely irrelevant, but are normally unnecessary for tsukinomi.

Tatakinomi, including oirenomi (bench chisels), atsunomi (oirenomi on steroids), and mukomachinomi (mortise chisels) are the focus of this post.

Steel hammers are not gentle, so takinomi always have steel hoops or crowns on the end to reinforce the handle and prevent them from cracking and splitting. This crown, as well as the ferrule installed at the blade end of the handle (kuchigane) can be highly stressed in use and failure can occur with unpleasant results. In this post I will explain how to setup your tatakinomi to ensure they are happy and provide you excellent service for many decades of hard use.

Why Should I Setup My Chisels?

C&S chisels are professional-grade tools each hand-forged by a single blacksmith in the traditional manner from plain, pure, high-carbon steel designated Shirogami No.1 produced by Hitachi Metals in their Yasuki plant. They are not mass-produced consumer-grade tools and will serve you best if you treat them in a professional manner.

Japanese tatakinomi chisels are designed and manufactured assuming the end user will perform some setup work before using them. Performing setup will probably help your chisels perform a little better and will absolutely ensure the handles last longer. And by avoiding the deformation and damage that typically develops without proper setup, you will preserve your reputation as a professional woodworker in the eyes of other professionals.

The chisel shown in the photographs in this post is a variety of tatakinomi called an Atsunomi, written 厚鑿 in Chinese characters and which translates to “thick chisel.” Not a romantic name, but certainly accurate at least in comparison to the smaller, more common oirenomi. It is intended for heavier work such as timber framing. I chose it for this blog post because it is easier to photograph.

This chisel was forged by a famous Japanese blacksmith named Shimamura Kosaburo (RIP) who used the brand Kiyotada, meaning “pure and faithful.” During his lifetime Mr. Shimamura was lauded by experts in the fields of blacksmithing and metallurgy as the finest chisel blacksmith in Japan.

Kiyotada Brand Atsunomi Chisel

Unlike western chisels, Japanese tatakinomi chisels are designed to be struck with a steel hammer. These impact forces tend to cause the handle to mushroom and even split, but the crown (hoop) contains and compresses the wood fibers preventing this damage. Even then, however, the force of impact does crush and break fibers at the handle’s end so that after decades of use the handle will gradually become shorter.

For the crown to continue to protect the handle properly, it must be able to travel down the handle in tiny increments without gouging and splitting the handle. Also, your hammer may occasionally strike a bit off-center mushrooming the end of the metal crown over time and preventing it from traveling down the handle. If this deformation becomes too great, the mushroomed crown will dig into the handle damaging it. The crown must therefore be chamfered to prevent deformation and to allow this travel to occur without gouging the handle

The truncated metal cone or ferrule that fits between the handle and blade is called the kuchigane (口金), which translates to “mouth metal.” It serves to keep the hammer impulse forces from splitting the handle, but if it does not fit tightly, or if it digs into the handle, it can weaken it, so the wide end of the kuchigane must be deburred and chamfered. In some cases, the handle may need to be shaved to properly accept the kuchigane. The following pictures show what these measures will help avoid.

Split Handle
Mushroomed Crown and Handle Crack

Tools and Materials Needed for Performing Setup

  • Masking tape
  • Fine point marking pen or ball pen
  • Sharp knife for cutting wood
  • Sharp knife or deburring tool for deburring and chamfering mild steel (an inexpensive kiridashi kogatana with an edge sharpened to 45 degrees shaves metal faster and cleaner than a file)
  • Rat-tail file or chainsaw file (can also be used for deburring)
  • Flat mill file
  • Pliers
  • Block of hardwood for driving off crowns
  • Wet/Dry sandpaper (220, 320, 600 grit)
  • Satin varnish or polyurethane and thinner
  • Gas stove or propane torch (optional; outdoors use)
  • Silk cloth (optional)

Disassembly

Mark Orientation of Handle to Blade

Step 1: Safety first. You will need all your fingers for this process, so tape some cardboard around the cutting edge to ensure they remain attached to your hands.

Step 2: Mark the blade’s orientation on handle. Place a mark or arrow on the end of the handle in line with the flat of the blade to help you reassemble the handle in the same orientation. If you are setting-up multiple chisels at the same time, write the blade width on the handle’s end to avoid confusion later.

Step 3: Separate the blade from handle. If the process of removing the crown did not loosen the blade, hold the blade in one hand and strike the kuchigane against the corner of a wooden workbench or block of wood. The best locations to strike the kuchigane are at points in line with the corners of the square tang, as seen in the photos of the bare tange below. Notice how the tang’s flats are aligned with the top and bottom of the blade.

Strike each corner twice, then shift the point of impact 90° and repeat. The goal is to gradually rattle the handle off, so don’t be shy. If the blade and handle still refuse to separate, expand the kuchigane and shrink the wood using a heat gun or by placing the kuchigane nearly (but not quite) touching a hot incandescent light for a few hours. Do not place the chisel in an oven!

Rap the Kuchigane to Separate

Step 4: Remove the crown (hoop). Grip a block of hardwood tight against the handle, with one end butting up against the crown. Strike the opposite end with a hammer. Work the block around the crown and repeat until the crown comes off.

Remove the Crown

Step 5: Disassemble the handle and kuchigane. If you are setting-up multiple chisels at the same time be sure to keep each chisel’s components separate and mark them.

The Chisel’s Component Parts

True the Tang and Shoulder

Step 6: The tang and neck/shoulder should meet at a clean 90° angle (although a slight filet is acceptable), and the shoulder should be clean and flat. If necessary, true it up carefully with a flat file. At the same time, flatten and smooth the shoulder, but be careful to only true the shoulder and not file gouges into it. Also use the file to remove burrs and gross irregularities on the tang as necessary.

The tang before cleanup
The tang after cleanup

As you can see in the photo above, the tang does not need to be perfect, just free of big irregularities and burrs that might cause the fit between handle and tang to lossen after hard pounding,

When you are done, there should not be a pronounced gap between the shoulder and kuchigane when the chisel is assembled.

Prepare the Kuchigane (Ferrule)

Step 7: Check the blade end of the handle with the kuchigane in place. If it is a sloppy fit, adjust the handle using knives, files, and sandpaper as necessary.

Step 8: Flatten each end of the kuchigane with a flat file. Be sure the ends are in planes perpendicular to the kuchigane’s centerline

Kuchigane before chamfering

Step 9: Chamfer the inside of the kuchigane’s wide end (not narrow end) with a knife or round file. Shave or file a a 45° chamfer 1/2 to 2/3 the thickness of the kuchigane’s wall on the inside corner of the kuchigane’s wide end. An inexpensive kiridashi kogatana knife or deburring tool with a blade angle of around 40 degrees will easily shave the mild steel used for crowns and kuchigane and works quicker and cleaner than a file.

A stopped hole drilled into a board works well to secure parts when deburring and chamfering them. Vise grips also work well for securing crowns if you pad the jaws to keep them from gouging the parts, but tend to deform kuchigane

Just be careful not to cut yourself. They may be beautiful and very useful, but many chisels and knives are cold vampiric geniuses (genii?) that fear neither sunshine nor spaghetti sauce and want to cut you, so beware! Hold parts in a way the blades absolutely can’t bite you no matter how hard they try. A severed tendon can be a tragic life-changing injury.

Kuchigane after chamfering

Step 10: If you decide to refinish the kuchigane, remove the existing chemical bluing with sandpaper at this time.

Prepare the Crown (Hoop)

The Crown Before Deburring and Chamfering

Step 11: Chamfer both inside corners (top and bottom edges) 45° with a knife or a rat tail file. This step is very important.

The crown after chamfering. This step is critical.

Step 12: Deburr and clean up the crown’s inside surface. However, be careful to not remove too much metal or the crown may fit too loosely.

Deburred, Chamfered, Filed and Sanded Crown

Step 13: Lightly file and sand the crown’s exterior surfaces to remove major irregularities. There is little point in trying to make these surfaces perfectly smooth since they will get banged up by hammers.

Prepare the Handle

Step 14: Check the Depth of the Tang Hole. If this hole is too shallow, the pointy end of the tang will bottom-out and can cause the handle to split. Measure it with piece of wire or a stick. If it is not deeper than the length of the tang, drill the hole just a tad deeper.

Step 15: Check/Adjust Blade Alignment. With the kuchigane removed, insert the tang into the handle correctly oriented, and sight down the handle. If the handle and blade do not line up properly, you may need to correct the misalignment.

To do so, first try fitting the blade to the handle in a different orientation (90˚). If this does not improve things, make thin slips of wood the width of the tang’s flat and fit one into the hole before inserting the blade. Slips made of cardstock, manila folder, or cotton typewriter paper work well too. If you feel a lot of resistance when inserting the tang, attach the kuchigane to prevent splitting.

Thinner or thicker slips can be inserted if more correction is necessary, but there is a point where too many slips will make it impossible to insert the tang without splitting the handle. In this worse case scenario, shave the hole a bit wider with a chisel or other slender piece of steel sharpened as a scraper to permit adequate shimming. Be careful to remove the absolute minimum amount of wood.

Step 16: Check/Adjust Crown Fit. It is acceptable for the crown to leave a shallow ring depression in the handle, but if the crown digs deeply into the handle, shave or sand the handle to ensure the crown will not gouge it.

The Handle’s Coned End Before Fitting

Step 17: Prep the Shoulder. Most chisels have a shoulder turned into the handle where the kuchigane terminates, making for a smooth, attractive transition between kuchigane and handle. This is most pronounced in chisels made in Western Japan. However, if the kuchigane butts tight up against this shoulder, over time the force of the hammer can drive the kuchigane into this shoulder damaging the handle.

Relieving this shoulder with scallops will provide some room for smooth movement of the kuchigane over time. To do this, first mark a line around the handle where the kuchigane ends. Then remove the kuchigane.

Step 18: Wrap a piece of paper or light cardboard 3/16″ to 1/4” above this line, secure it with tape, and using it as a guide, mark another line around the handle with a fine-point marking pen, ball pen, or knife. Remove the kuchigane and paper.

Step 19: Mark the Handle: Use a pen, pencil or marking pen to mark the cone at diagonals across the tang hole and extend these marks to the line you made in the previous step. This will leave four lines 90° apart. Now make similar marks at the flats of the tang and extend the lines. There should now be eight lines separated by 45°.

Step 20: Cut the Scallops: Wrap masking tape around the cone as shown in the picture below to protect the cone from cuts which might weaken it. With a very sharp knife, make four cuts in small increments centered on one of the lines and forming a concave scallop between the two adjacent lines. Repeat for the other four lines. These curved scallops should transition smoothly into the wooden cone, but should not cut into it. This may not be as easy to accomplish as it seems. If done properly, the scallops should appear very uniform and attractive. Finally, shave off the ridge between the scallops creating a total of sixteen scallops at 22.5°.

Finish the Handle

Some people prefer a handle without any finish, while others like a shiny finish.

Hand sweat tends to react with the tannic acid in Japanese White Oak handles turning them a dirty-looking grey. Japanese Red Oak, as in the handle in the pictures above, does not discolor as much.

Whether you refinish the handle, leave it as-is, or sand it bare is your choice. It makes no difference to the chisel’s performance.

Step 21: Sand the Handle. So at this point, you can either (1) Not sand the handle (unless it is damaged), and varnish the scallops and any areas shaved at the crown end of the handle to match the existing handle finish; (2) Sand off the existing finish entirely to bare wood; or (3) Refinish the entire handle.

Step 22: Apply a Finish: This step is applicable if you decide to apply a finish to the handle. Sweat may cause Japanese White Oak, a wood commonly used for chisel handles, to discolor, so a light finish (not a thick glossy finish) is appropriate in my opinion. The following is the method I recommend. First, sand off any remaining finish on the handle. Apply a coat of satin varnish or polyurethane diluted 100% with thinner. Allow as much of this mixture to soak into the wood’s fibers as possible. Rub the wet varnish mixture forcibly into the wood using wet-or-dry sandpaper. Thinned varnish will penetrate further into the wood than straight varnish, and the pressure of sanding will force it deeper into the fibers than just capillary action. In addition, sanding will create a wood/varnish slurry filling the grain.

Allow this mixture of varnish and wood dust to dry without wiping it off. It will look terrible, but never fear. Repeat these steps for a second coat and allow to dry. Apply a third coat, sand lightly, and then wipe off the varnish slurry with a cloth.

When dry, the result will be a non-slip surface free of lathe marks that does not appear to have any finish, but that will protect the wood from sweat and moisture. If a little bit of visible surface finish is desired, a final single coat of thinned varnish can be applied. To ensure the previously cut scallops remain nice and crisp, do not sand them.

Warning: Do not apply finish to the crown end of the handle because the finish will make the wood fibers too stiff to deform properly. If you want to go the extra mile, a bit of melted paraffin wax or beeswax allowed to soak into the end of the handle will protect it from water and make it more resilient over time than just bare wood.

Finish the Kuchigane and Crown

This is an optional cosmetic step, but will make your chisel more attractive. There are several ways of surface finishing the metal of the kuchigane and crown:

Heat Bluing: Simply heat the kuchigane and crown on a stove until it is blue-black. Not very durable.

Oil Black: Coat the metal with motor oil and heat it until the oil is burnt off. This method makes a lot of stinky smoke, so don’t do it indoors. Fairly durable.

Gun Blue (chemical bluing): Brownells’ cold blue formula works well. Birchwood Casey also makes a convenient chemical bluing product. Looks nice, but not very durable.

Rust Blue or Rust Black: These are classic, beautiful gun metal finishes that are much more durable than chemical or heat bluing. However, the process requires dangerous chemicals and time. A description of the process is not possible here. Extremely durable.

Burnt Silk Finish: This is my favorite finishing method because it is quick and easy and looks good. Simply heat the metal parts over a flame, and using pliers so you don’t burn yourself of course, wipe the metal in a wad of scrap silk. An old silk necktie works fine. The silk protein will char, coating the metal with a carbon finish with an interesting texture. Wipe the metal quickly but thoroughly to prevent globs of melted silk from sticking to the metal. Don’t do this inside the house because the smoke will set off the smoke alarm and the stink will endure for weeks. SWMBO will not be pleased.

Reassemble the Chisel

If this is a new chisel, it may be convenient to true the blade’s ura and sharpen it before final assembly. These tasks are a little easier with the handle removed.

Step 23: Install the Crown. To begin assembly, hold the handle in the air by one hand and drive on the crown using a mallet, not a steel hammer. You should always remove your wrist watch before wacking chisels if you want it to keep working. A word to the wise.

There is a specialty tool for this job, essentially a steel cone that fits over the crown, which you strike with a hammer. If you enjoy spending money on heavy tools that take up space and are seldom-used, then you gotta have one. But a wooden mallet works just as well and can do many more tasks.

Once the crown is flush with the handle, angle the handle and strike the crown with your mallet driving it further onto the handle. You only need to be drive it down far enough so the top of the crown is below the end of the handle by 1/16”. More is wasteful. Then use a steel hammer to lightly mushroom over the corners of the handle securing the crown in place. Do not soak the handle in water, for Pete’s sake!

Soaking the handle in water prior to fitting the crown is a method preferred by handlemakers and wholesalers that fit hundreds of crowns a day. They will soak 50 handles at a time in a shallow pan of water to soften the ends making it easier to mushroom. Convenient for them, but bad for the chisel because the water will also cause the wood to swell, and when it later dries and shrinks, the crown may become loose over time. Your handle deserves better.

Step 24: Install the Kuchgigane. Fit the kuchigane to the handle lightly and insert the blade’s tang oriented according to the marks you made previously. Tap the end of the handle to lightly seat the blade, but allow enough room so the kuchigane can be rotated by hand. Rotate the kuchigane to minimize any gaps between it and blade’s shoulder. If you see any big gaps, lightly file the kuchigane to match the blade’s shoulder. If any part of the handle projects past the kuchigane’s mouth, carefully shave it off with a sharp knife.

Step 25: Seat the Blade. Finish seating the blade by holding the chisel in your hand in the air and striking the end squarely with a steel hammer until it seats tightly.

Voila!

Use the Right Hammer

When cutting wood with a tatakinomi, please use a hammer with a flat face, such as a Japanese gennou, to strike your chisel. A hammer with a domed or convex face, as are almost all hammers sold outside Japan nowadays, may damage the chisel’s handle after enough strikes. Ergonomics aside, a ball peen hammer or claw hammer with its face ground flat will work just as well as a Japanese hardware-store gennou.

And while we are on the subject of hammer faces, I recommend you smooth and even polish your hammer face so it will strike cleaner and reduce the wear on your chisel handles, counterintuitive as that may seem. Slipping will not be a problem, trust me.

I encourage you select a hammer weight that balances well with the weight and blade width of your chisel, the type of wood and type of cutting you plan to do, and your body and style of work. This decision will make a difference in the precision and speed of your work, the energy you expend, and the stress on your joints.

375gm (13.2 ounces) is a standard medium weight for gennou hammers in Japan, perfect for driving nails, general carpentry work, and motivating atsunomi. However, many find a lighter-weight head, perhaps in the neighborhood of 60~80 monme ( 236gm (8.3 oz) to 300gm (11 oz)), works better with smaller chisels, such as oirenomi, for furniture and joinery work.

I also encourage you to make a handle for your hammer that suits your body and style of work.

This post is already too long so I won’t go into details, but suffice it to say that commercial hammer handles are a one-size-fits-nobody design that confuses the hand, is un-aerodynamic (I bet you never thought about air-drag in relation to hammer handles), transmits excess vibration to your joints, and ignores obvious ergonomics causing the head to impact the chisel off-center and out-of-kilter. There is a better way, and you will love the results.

We will dive head-first down that rabbit hole, screaming like a banshee on fire, in future posts. So y’all come back now y’hear.

Kosaburo Gennou Head and Black Persimmon Handle

Rust Prevention & Storage

If set up properly, a quality set of Japanese chisels will endure decades of hard daily use with no maintenance beyond oiling and sharpening.

You should store your chisels where they will be protected from weather, water, sudden temperature changes, dust, fly-specs, spilled beer, and paint overspray. Convenient though it may be store chisels in an exposed rack or bare on a shelf, unless your workshop is a temperature and humidity controlled cleanroom, or you use chisels stored this way nearly everyday and clean and oil them frequently, such storage methods are guaranteed to reduce their useful lifespan and will waste your sharpening efforts and sharpening stones sure as eggses is eggses.

I recommend you make a wooden chisel box with a lid to store your chisels. I am preparing an article on how to design and make a chisel box, and will post it on the blog when it is ready.

After every use, oil the blade to prevent rust. An aburatsubo or oilpot is a critical accessory for chisels, and is easily made. You can find details here.

YMHOS

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