The chisel is a very useful tool in it’s own right. For anyone wishing to purchase their first Japanese woodworking tool, a good place to begin is the (not so) humble chisel. Practically all aspects of the Japanese chisel encompass the renowned qualities of Japanese woodworking tools. The combination of extremely hard high carbon steel, forged to a softer wrought iron backing for support is legendary.
The main type of chisel available is the Oire Nomi (Nomi is Japanese for chisel).
To the western eye the Oire Nomi somewhat resembles a butt chisel having a shorter blade than a normal European bevel edge chisel. The Oire Nomi is the most common chisel used by Japanese furniture makers, cabinetmakers and woodworkers in general. The Oire Nomi is controllable and responsive, much suited to fine or close work.
Manufacturing, parts & assembly
The similarity between western and Japanese chisels stems from their intended purpose; both do virtually the same job. However, the manufacturing methods, parts and assembly are entirely different. The first thing to note is that the Japanese chisel is a collection of four separate parts.
Unlike its western counterpart which generally consists of only two, the blade and the handle, a Nomi consists of a blade, a tapered ferrule, a handle and a steel hoop. The blade has a tang, which fits into a hole in the handle; the ferrule fits around the tapered end of the handle forming a socket. This method of attaching a chisel handle makes it doubly secure.
Striking the chisel has the effect of forcing the end of the handle deeper into the taper, thereby causing it to grip the tang ever tighter. It is worth inspecting the area just above the ferrule occasionally. If the wood of the handle is riding on the rim of the ferrule, then maybe pare a little away to give clearance. However, this will probably only require attention after years of use.
After fitting the handle, the maker grinds the junction between the ferrule and blade’s bolster until it is smooth and free of any burrs. In fact, he often does the job so well it is sometimes impossible to see the join. When visible it resembles a hairline crack, customers occasionally return these as defective. There is nothing at all wrong with the chisel, except perhaps the maker did too good a job on all the others. Indeed after long usage or sometimes just a change in humidity, the join may well re-appear.
At the top of the handle sits a steel hoop. Most Japanese chisels these days arrive with the hoop ready seated and the very top of the chisel mushroomed into a slight dome shape. In the past, fitting the hoop was the responsibility of the purchaser. The hoop protects the top of the handle from the blows of a steel hammer.
After years of using a large wooden mallet on one’s best chisels, striking them with a metal hammer might seem like sacrilege to say the least. However, the hoop, when properly fitted, protects the handle.
There is a significant advantage in using a hammer with a small head rather than a thundering great mallet, especially if working in close. It does seem to give a lot more control and feedback.
Does your hoop need fitting?
Should you find the hoop requires fitting, remove it from the handle and gently pare or sand a little of the wood away. It is easy to see where attention is required if, when testing for fit, rotating the hoop leaves a rub mark. Stop when the hoop slips on tightly with just about 1.5mm of the handle protruding. Then gently tap the end of the handle with a hammer so that it mushrooms over keeping the hoop permanently in place. Some advocate tapping the side of the handle with a hammer, crushing the fibres to reduce the diameter sufficiently to get the hoop into the right position. A bit of judicious whittling is easier and just as effective. Some types of Japanese chisel do not have a hoop. This indicates that they are for paring by hand and not struck with a hammer or mallet.
That is about all there is, apart of course from giving some love and attention to the blade itself…
The main thing is to use the tool
The man who forged it put a great deal of pride into his work. It would be unfair to the maker not to use the fruits of his labours as fully as possible. Once the few steps described above are complete, there is an immense amount of pleasure gained from using a quality tool. The procedure doesn’t take long and only needs doing once. Perhaps it’s because these chisels are amongst the few virtually hand made tools available nowadays rather than mass-produced that gives them some of their mystique.
Japanese steel hardens to a much higher degree. The blades of western woodworking tools are most commonly made of either O-1 or A-2 tool steel. The former preferred for edge quality, the latter for edge retention. Japanese chisels and plane blades are for the most part made of different tool steels. Japanese tools are either of White Paper steel (Shirogami) or Blue Paper steel (Aogami). The colours referring to the paper used to wrap the steel by the manufacturer, Hitachi Yasugi.
Over 1,500 years ago Japanese smiths perfected a method of smelting steel that had a high degree of purity. Using charcoal as a fuel rather than coke, they smelted iron sands obtained from the bed of the Hino River. The result, known as Tamahagane steel, was used to produce the legendary Samurai swords, famed for their incredible sharpness.
To the naked eye, White Paper steel and Blue Paper steel look identical; the difference lies in their composition.
White Paper steel begins with JIS SK steel which after undergoing several purification processes becomes White Paper steel #2. This pure form of high carbon steel contains 1.05-1.15% carbon, with very low levels of sulphur and phosphorus. Further processing of White Paper steel #2 and adding more carbon produces White Paper steel #1. The additional carbon increases hardness, but decreases toughness. Taking White Paper steel #2 and adding tungsten and chromium as alloying agents, results in Blue Paper steel #2. A further addition of more carbon, tungsten, and chromium creates Blue Paper steel #1, with an increase in hardness but again a decrease in toughness.
Finally, if you then take Blue Paper steel #1, add more carbon, more tungsten plus molybdenum and vanadium, you get Super Blue steel, which has even more abrasion resistance. A fine balancing act, additional amounts of carbon in the steel decrease the toughness but increase the potential hardness.
Alloying it with other elements increases abrasion resistance, but of course, as sharpening is an abrasive process these steels are harder work to bring to a good edge. White paper steel (Shirogami) is one of the purest steels available anywhere in the world. Similar to crucible steel it is extremely fine grained and once forged and heat treated, displays phenomenal sharpening and edge holding characteristics. Blue Paper Steel (Aogami) slightly alloyed carbon steel is tougher and more resistant to wear. To put things into context, compared with their western equivalents, white and blue paper #2 steels contain more carbon than either O-1 (0.9%) or A-2 (1.0%). Just as O-1 is easier to sharpen but A-2 holds an edge longer, white and blue paper steels are similar except the Japanese steels will harden to a much higher degree.
It’s not just about the steel
The steel used to make a tool isn’t the whole story; a further factor lies in the skill of the blacksmith. Although White paper steel is cheaper than Blue, it requires greater precision to produce a quality tool. The temperature range necessary to correctly anneal, harden and temper White Paper steel is much narrower. When purchasing any tool, the decision needs to take into account its intended use. The type of timber worked and whether it is for fine finishing work or coarser roughing out. The essential differences between White and Blue Paper steels are hard to discern. In practice, quality Japanese tools have outstanding performance.