Darwin’s Hand planes

Diversity in the natural world arises from genetic variation introduced to an organisms and selection via interaction with a fitness landscape. Characteristics that provide an important fitness advantage remain conserved while characteristics that are not under selective pressure tend to diverge. In addition, the fitness landscape may evolve in time changing what characteristics provide a fitness advantage. While evolution applies to biological species, studying how man-made objects disappear, persist, or emerge within the marketplace can provide some insight into how the fitness landscape, or simply the societal context, changes with time. In that light, I think the study of western versus Japanese woodworking hand planes provides an interesting perspective on societal context. 

Most tools for working wood involve thrusting hard bits of sharpened metal to sever or remove wood fibers to shape the wood into a desired shape. The metal bits are connected to easily shaped wood to make wielding the sharpened end easier. These tools include a hand saw – a thin metal plate with a set of even jagged teeth fastened to a wooden handle design to cut narrow slits in wood; a hand chisel – a thick metal bar attached to a wooden handle designed to cut deep furrows into wood; and an axe and adze – a thick block of metal sharpened at one end attached to a long wooden handle enabling the user to swing the block of metal with great force to cut wood in the same plane (axe) or perpendicular plane (adze) as the swinging action. As a successor to the adze but with more subtle action, a hand plane has a wide flat metal plate inserted through a wooden block designed to slice and flatten a wooden surface. Discovery of Viking and early Roman tools suggest that the emergence of trade by sea helped the exchange of ideas and homogenize the design of these woodworking tools. 

To counter outside influences, Japan isolated itself from the rest of the world for over 250 years by restricting trade and travel through punishment with death. Trade with the west started to resume upon arrival of Commodore Perry with a fleet of U.S. Navy warships in 1853 to now Tokyo harbor and subsequent trade treaties. Hand planes in the west and in Japan diverged over that period. 

By the mid-1800’s, hand planes in both regions consisted of a laminated plane blade married to a wooden body, but there were some differences. In particular, Japanese planes cut on the pull stroke while western planes were pushed to cut. Both plane blades are adjusted with a hammer and tapered in thickness but in different directions. Western plane blades had parallel sides but the thickness tapered such that the thickest part was at the cutting edge. This taper in blade thickness combined with a wooden wedge helps keep the plane blade in place during use. Japanese plane blades taper both in thickness and width with the narrowest thickness and width at the cutting edge. This blade design dispenses with the need for a wooden wedge to fix the blade location as the blade becomes tighter as it is tapped into place. The blade in western hand planes is inclined with a steeper angle of attack, typically 45 degrees, compared with a Japanese plane nominally at 38 degrees. While the difference in attack angle may seem subtle, it can impact the quality of the planed surface of the wood and also changes the resistance in how the plane moves across the surface. 

In the 1700’s, a second blade was attached to back of the cutting blade to put a bit of back pressure on the wood shaving as it was cut, called a chipbreaker or cap iron. Without a chipbreaker, wood grain that dives down into the board can split ahead of the cutting edge causing a divot in an otherwise smooth surface. This is called tear-out. The chipbreaker was introduced in Japan around 1900. Interestingly, what a chipbreaker does became a bit unclear due to collective loss of hand tool knowledge with increased reliance on machines. It is claimed that a cap iron reduces vibration of the cutting edge but that doesn’t jive with its’ use with thick laminated blades. A relatively recent video from Japan illustrates the chipbreaking action of this second blade. 

Both pre-industrial western and Japanese plane blades were a laminated construction that required hand crafting by a blacksmith. This laminated construction marries two different types of steel to take advantage of their strengths and compensate for weaknesses. In particular, the cutting edge consists of a high carbon steel layer married to a body of more malleable low carbon steel, like wrought iron. The high carbon steel layer can be hardened to take a very sharp edge but can become brittle and difficult to sharpen in the process. The malleable low carbon body of the blade reduces the fragility of the edge by providing support and reducing the amount of high carbon steel that needs to be removed to resharpen the blade. 

Divergence in hand plane design really started to accelerate in the mid-1800’s. In the west, the mass production phase of industrial revolution was taking place while the Edo period was coming to an end in Japan. Initiated by the US Naval visit, the end of the Edo period marked a transition. The highly skilled blacksmiths that once made swords turned to making woodworking tools, like chisels and plane blades. In the west, a hand-made laminated plane blade did not transition well to mass production and was replaced by a blade made of a single steel. A wooden plane body transitioned to a more complicated plane design of iron, which doesn’t warp with changing humidity.

Western hand planes made from cast iron emerged in the mid-1800’s, with one of the notable inventors of new designs being Leonard Bailey of Boston, Mass. In 1869, Bailey sold his patents for cast iron hand planes to Stanley Rule and Level Company. One of the key advantage of a metal hand plane over a wooden one is the lower learning curve for a novice. By 1900, Stanley had sold over 3 million hand planes. Mirroring hand woodworking tools in general, the quality and volume of iron hand planes produced peaked right before World War II. 

In recent years, specialized and boutique makers have resurrected making high quality woodworking tools in the west. In Japan, the quality of hand plane is directly related to the skill of the blacksmith in crafting the blade, which is recognized and supported as a traditional craft in Japan. Today, a Lie-Nielsen Number 4 and a kanna from Seisuke Mizuno, a 4th generation master blacksmith from Nagaoka City, illustrate high quality hand planes from the west and Japan, respectively. Both are fun to use.