Planes came into use in Japan much later than in Europe, sometime around the year 1500. Until that time, surfaces were smoothed with the so-called spear planes, called yari ganna. The spear planes, with their short, slightly curved blades at the end of a long handle, were drawn two-handed over the wood. They left behind a smooth, but slightly wavy or grooved surface. The models for wooden planes with a fixed iron probably came from China or Korea. With these tools, achieving a truly flat surface first became possible. Planes with a chipbreaker on the iron first appeared at the end of the 1900s. This feature perhaps was borrowed from Western tools at that time.
With its basic, rectangular form, the traditional Japanese plane is representative of a lot of the aesthetic that informs traditional Japanese design. But despite its almost primitive simplicity, the high performance and efficiency of the tools is surprising. It consists of basically two parts, sometimes four: the low wooden plane body, or stock, the very thick, slightly wedge-shaped iron, and sometimes a chip breaker and a retaining pin. There is no front knob, and no metal striking button. They have no grip, or tote, and there is no fine adjustment using a threaded shaft. Their handling and most importantly learning to set the iron using light taps with a hammer requires some time and practice to learn well enough to get good results. The planes are mostly designed for, and work best on various kinds of softwoods. Because of their minimal height and low center of gravity, the planes ride well on wood and tend to wobble less than their Western relatives. You work much closer to the wood with the Japanese planes than with the Western styles.
In Japan, plane bodies were traditionally made using the wood of the Kashi tree, a kind of evergreen white oak. Because of its high hardness, there is very little wear on the sole of plane. Kashi wood is very strong and resists splitting, and so there are seldom problems with cracks or splinters in the body. Finally, the relatively light color of the wood makes sense, as it is easy to check the position of the dark plane iron because of the contrast between the two. So use a blank in Kashi wood, or a well seasoned blank from a species with similar properties, such as red beech, hornbeam, or fine grained maple.
The wood must be chosen with special care. It should be straight-grained and tension-free, and should have been allowed to season at least two years. The "left" side, the side toward the center of the tree, is used for the sole of the plane, and the "right" side faces upward. It is possible that as the wood dries over the years, the sole of the plane can become slightly hollowed. The grain should run parallel to the sole of the plane or slant slightly down toward the iron. Such a grain orientation allows the plane to glide over the wood more smoothly, and wear on the sole is reduced. The two ends of the plane body, or dai, are named "atama" for the front, or toe, and "shiri" for the back, or heel.
Note: these directions were documented in the Inomoto workshop in Sanjo, Japan, which specializes in the production of smoothing planes. Mr. Inomoto also provided the directions for the individual steps based on his own methods for building traditional plane bodies.
Have a look at this video of our customer BergWerk how he made a DAI.
For fine adjustments when fitting the iron to its bed, you pass the the iron over an oil-soaked pad. It is then tapped into place with a hammer, and then knocked back out. The oil will have marked the spots where there is good contact with the plane body, and where you might need to remove a little material. The bed for the plane has to be cut slightly convex. This kind of fine adjustment, removing tiny shavings of material at a time, can need to be repeated dozens of times. So take the time to do it right and cut a perfectly-fitted bed to hold the iron properly.
To reduce friction, the soles of traditional Japanese planes are planed slightly concave. On most smoothing planes, the sole contacts the wood at the toe of the plane and just in front of the mouth. In those areas, a strip of wood about 1 - 1.5 cm is left in place and the rest of the sole is planed or scraped away slightly, to about the thickness of a piece of paper. This is easiest to do with a traditional plane, called "dai-naoshi-ganna" (literally, a plane to tune plane stocks”). With these planes, the iron is set at almost a right angle to the sole, similar to our toothing or scraper planes.
The width of the plane’s mouth depends on its use. If the plane will be used as a smoothing plane, the slot between the iron and the front of the mouth should be kept as narrow as possible. When making a plane, start out with a slot of about a half a millimeter. You can always make it wider if you find you need too. On planes like this one, with a chipbreaker fitted, the angle on the face of the throat away from the iron is about 80 degrees.