Abstract
Until the beginning of the Meiji Era (1868 –1912)， Japanese smoothing planes had long employed a single cutting iron. Under the influence of Western planes with their double irons， however， a double cutting irons became standard. Double cutting irons are designed to prevent torn grain. To a craftsman， however， the smoothness and gloss of the finished surface are the major considerations. Using Sugi (Japanese cryptomeria)， Hinoki (Japanese cypress) and Yellow ceder， we conducted finishing work with a smoothing plane using irons angled at about 40°. We changed the mouth openning distance fron 0.1 to 0.4mm，and measured and compared the surface smoothness of wood treated with single and double cutting irons. Even with a single cutting
iron， at cutting depths of about 50μm， no torn grain appeared. As the mouth opening became wider， the single cutting iron produced increasingly rougher surfaces.
Using the double cutting iron with narrower mouth openings， which allow back iron to be utilized， the surface was rougher than that profuced by a single cutting iron with a narrow mouth opening. In a comparison of the single cutting iron with a narrow mouth opening and the double cutting iron with a wide mouth opening， no differences in surface roughness were seen. In terms of type of wood treated， Sugi(Japanese Cryptomeria) yielded a fuzzier and rougher surface than either Yellow ceder or Hinoki (Japanese cypress).
