Loading often occurs on coated abrasive paper and fuzzy grain appears on a surface of wood sanded with coated abrasive paper, while no loading occurs on equisetum (scouring rush; horse-tail) which gives wood great gloss. The purpose of this study was to reveal these characteristics of polishing wood with equisetum, a natural abrasive meterial, compared with sanding wood with coated abrasive paper.
A work specimen was quarter-sawn Japanese cypress (Chamaecyparis obtusa Endl.) and abrasive tools were equisetum (Equisetum hiemale L. var. japonicum Milde.) and coated abrasive paper (silicon carbide 2C, 240 and 600 grit). A quantitative analysis by means of TAPPI standard method T 15 m-58 indicated that an entire stem of equisetum contains about 20% of ash. An observation through a scanning electron microscope showed that lots of removed chips were stored in grooves running on both sides of the warty processes while chips firmly overlapped one another among grits on coated abrasive paper and loading occurred there and that the chips removed with equisetum were thinner than those removed with coated abrasive paper. Since the heights of tips of grits on coated abrasive paper are approximately represented by a normal distribution, deep scratches appear on the surface of wood sanded, which may be responsible for fuzzy grain. On the other hand, no scratch is left on the surface of wood polished with equisetum probably because the heights of grits of warty processes are about equal and their tops approximately semi-spherical. The measurements with simulated single cutting edges (semi-spherical tips with radii of curvature of 0.4 and 1.2mm for equisetum and a quadrangular pyramidal tip with an apical angle of 80 degrees for grit) indicated that the ratio of vertical cutting force to horizontal one was significantly greater for the model of equisetum than for that of grit; equisetum required more vertical force than coated abrasive paper to abrade at an equal indentation. These experimental evidences suggest that the warty processes of equisetum might act on a surface of wood like a calender in the paper-making process. It is concluded that a unique structure of equisetum gives a surface of wood great gloss while coated abrasive paper causes rather fuzzy grain on wood.
