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 do it before giving your chisels a ride around the block, performing these setup procedure is 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.
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 growth hormones), and mukomachinomi (m0rtise 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 Shirogami steel. 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.
Does Chisel Setup Help?
Unlike western chisels, Japanese tatakinomi chisels are designed to be struck with a steel hammer. These impact forces tend to make the handle mushroom and 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 and weakening it. The crown must therefore be chamfered to prevent deformation and to allow this travel to occur without gouging and splitting 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 hardware.” 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.
Tools and Materials
- 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
- 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)
Step 1: Safety first. You will need all your fingers for this process. Tape some cardboard around the cutting edge so they remain attached to your hands.
Step 2: 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.
Step 3: 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 4: 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!
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.
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.
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
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.
Step 10: If you decide to refinish the kuchigane, remove the existing chemical bluing with sandpaper at this time.
Prepare the Crown (Hoop)
Step 11: Chamfer both inside corners (top and bottom edges) 45° with a knife or a rat tail file. This step is very important.
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.
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.
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 sharpen the blade before final assembly.
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, and now is a good time too.
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. It only needs to be driven down 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.
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 make the wood softer and easier to deform. The problem with this technique is 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.
Use the Right Hammer
When cutting wood, 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, will 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 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 80~60 monme (300gm/11 oz to 236gm/ 8.3 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.
But we will dive head-first down that rabbit hole in future posts.
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, and paint overspray. Convenient though it may be store chisels in an exposed rack or bare on a shelf, unless you use chisels stored this way nearly everyday and clean and oil them frequently, such storage methods 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.
PS: If you have questions, please use the form below. Your information will remain confidential (we’re not evil Google or incompetent facebook).
© 2019 Stanley Covington All Rights Reserved