Sashimono

“Sashimono” is a technique for assembling furniture and other wooden items without nails, using both simple and highly complex wood joints. Mortises or grooves called ‘hozo’ are carved into the wood in order to join two boards in a blind joint that’s not visible from the surface. Furniture makers are known as sashimono-shi (指し物師)

The term “Sashimono” derives from the traditional practice of using a woodwork ruler called a “monosashi” to carefully measure timber materials.

Edo Sashimono

“Edo Sashimono” refers to the wood joinery that evolved through the 17th to 19th centuries. The technique was introduced in cabinetwork for Samurai families and wealthy merchants. The joints of Edo Sashimono are made so they’re barely seen from the outside. Although delicate in appearance, the joinery is strong and lasts generations. Edo Sashimono is designated by the Japanese Government as a Traditional Craft of Japan.

Tools

The tools commonly used by Japanese carpenters are divided into a few basic families.

Japanese saw (鋸, nokogiri), which cuts on the pull stroke, rather than the otherwise globally prevalent push stroke. This allows the blades to be quite thin in comparison to the Western saw. There are two main kinds of cutting teeth on Japanese saws: crosscut (横挽き, yokobiki) and rip (縦挽き, tatebiki). The rip and crosscut are combined in one blade, known as a ryoba (両刃, lit. ’dual edge’). The rip and crosscut patterns are also made in single-edged saws, kataha nokogiri (片刃), both with stiffening back pieces and without. The stiff-backed saws, known as douzuki (胴付き, lit. ’attached trunk’) are typically used in cutting fine joinery. There are many other types of Japanese saws as well: osae-biki (押さえ引き鋸, lit. ’press-cut saw’), used for flush-cutting pegs to a surface without marring the surface. The saw teeth have no set to one or both sides to accomplish this feat. There is the azebiki (畔挽き, lit. ’ridge saw’), which has cutting both rip and crosscut teeth, and is short and rounded in profile. It is used for sawing in confined areas and starting cuts in the middle of surfaces. There are many other types and sub-types of saw. Most saws sold in the West are mass-produced items with induction-hardened teeth and relatively cheap replaceable blades. The handmade forged saws are very laborious to make and involve more manufacturing steps in the forging to complete than planes or chisels.

Japanese plane (鉋, kanna), is most commonly a wooden block, or dai (台) containing a laminated blade, sub-blade, and securing pin. In the Japanese plane, the blade is fixed in position primarily by the plane’s abutments that are cut in the sides of the dai. This is similar to a still manufactured type of European wooden plane, in which the blade is fixed in place by tapping down upon a wooden wedge. Unlike a western plane, the support bed for the blade is not a flat surface in a Japanese plane – rather it is convex. The blade itself is tapered in thickness so as to wedge tightly into the dai when tapped down into place. The blade is also tapered in width to allow its projection to be adjusted by tapping it from side to side, so that a uniform shaving thickness can be attained. Japanese planes are generally operated by pulling rather than pushing, and work can be done in the seated position or using the whole body for more power. Considered part of the kanna family, the yarigana is an archaic type of Japanese plane resembling a spear. The yarigana is a single piece of steel with one end being used as a handle and the other forged into a leaf shaped blade. The carpenter holds the yarigana with two hands, perpendicular to his arms, and pulls towards his body producing a concave gouge in the timber. The yarigana was in universal use prior to the introduction of the block-mounted wood plane to Japan, and is today typically reserved for use on large circular columns or in cases where a more rustic appearance is desired in the final element.

Japanese chisel (鑿, nomi). There are bench chisels, paring chisels, striking chisels, heavy timber chisels and slicks, and myriad others for specialized applications. Like the planes, the blades are of laminated hard steel/soft steel construction. Bevel angle varies from 20˚ to 35˚ typically, with mortising and heavy chisels featuring steep angles, and paring chisels having shallower angles. It is common in Japan to work with softwoods, so many chisels are made with that in mind, and require the bevels be steepened if employed for harder woods.

Japanese gimlet (錐, kiri). The kiri is used for boring circular holes in a timber, often as the first stage in the hollowing out of a mortise. Though seemingly simple to use, the kiri is commonly considered one of the most difficult tools to master.

Inkpot (墨壺, sumitsubo). The sumitsubo is used for marking long straight lines onto various surfaces. A thread (tsuboito) is tied to a rounded piece of wood with a needle fixed at the end (karuko). The other end of the thread is passed through the small opening at the end of the sumitsubo (itoguchi), through the depression containing ink (ike) and wound around a spool (itomaki-guruma). The ink is stored in the ike soaked in silk wadding. Silk threads are used as tsuboito. To draw a line, the sumitsubo is held in the left hand and the karuko’s needle is fixed onto the surface determining the position of one end of the thread. The sumitsubo is gradually moved away from the karuko until the required length of the thread is unreeled at which point the rotation of the spool is stopped using the thumb. With the index finger the thread is pressed down at the required end point of the line. Using the right hand, the thread is pulled upwards into tension and then suddenly released, consequently hitting the surface and leaving a straight line of ink onto any surface, regardless of any surface irregularities.

Japanese axe and adze (ono (斧) and chōna (釿)).

Japanese hammer (玄能, Genno or Gennoh). There are several types of carpentry hammers. Some hammers are used for chisel work, some for positioning hand plane blades, some for hammering and pulling nails, and others for tapping out laminated hardened steel from base of plane blades and chisels.

Tools for measuring and marking include the bamboo pen (墨さし, Sumisashi), carpenter’s square (差し金, Sashigane), marking knife (切り出し, Kiridashi), the traditional single and multi-blade marking gauges (罫引, Kebiki and Kinshiro), among others.

Blades. Though a carpenter will typically fashion handles and woodblocks and set and sharpen their blades themselves, the blades themselves are forged by steel smiths and provided unmounted to the carpenter. Japanese steel has long enjoyed a high level of refinement, without which the fine surfaces and detail for which Japanese woodwork is renowned would not be possible. The blades used in the Japanese chisel and the Japanese plane shares similar constructive principles to the Japanese sword. A thin piece of extremely hard blade metal called ha-gane (鋼, lit. ’edge metal’) is forge-welded to a softer piece of metal called ji-gane (地金, lit. ’base metal’). The function of the softer base metal is to absorb shock, and to protect the more brittle ha-gane from breaking. This technology allows for the use of steels in the hagane which are harder than in use in Western chisels, typically Rockwell 62 and up, and also allows for the honing of a much finer edge than is typically known in carpentry outside Japan. When sharpening a blade, a Japanese carpenter will typically use three or more whetstones of varying coarseness, progressing from the roughest stone to the finest.

The traditional Japanese vice was a wedge of wood tied to a post with a coil of rope. The wood was inserted under the wedge and the wedge hammered down.

Vices of any sort are used far less in traditional Japanese carpentry than would be the case for equivalent tasks in the traditional crafts of the West. Many tasks in Japanese carpentry associated with building, involve very large pieces of timber, and in general, the weight of the timber and of the carpenter are used to stabilize the piece on which the carpenter is working. For this reason the carpenter’s horses used in Japan are much lower than their Western counterparts, and carpenters must always position themselves over their work. Much of the work on smaller pieces of material can be done in the seated position, and relies on the fact that the saws and planes both cut on the pull stroke, enabling stabilisation of the work using the body or shooting board.