An instrument employed for shaving wood and other substances to a true plane or smooth surface, of which there are a great variety; they are usually divided into two principal kinds, namely, bench-planes and moulding-planes; of the former, the principal are the long, jack, trying, and smoothing-planes: each of these is again distinguished into double or single iron, according as the cutting part is formed. The single iron is an iron blade, the lower end of which is steel; and the cutting-edge is formed by grinding it to a single acute angle, as represented by the piece marked d in the following cut; its operation ispartly of a cutting and partly of a scraping nature. In planing some kinds of wood great inconvenience was found from this form by its frequently tearing up the surface instead of smoothing it; a partial remedy for this defect was, in consequence, introduced about thirty years ago, by which another plane-iron, called a "top-iron," represented at e, was added to the under one by means of a strong connecting screw, which causes the edge to press closely upon the lower one.
The cutting-edge of d, which projects a little beyond e, is, therefore, the same as before; but it is prevented from entering so deeply into the wood, or rather, the shaving which has been abraded from the wood receives a new direction by the abrupt interposition of the top iron e, and prevents the surface of the wood from being torn. This improvement is so decided as to cause almost an entire disuse of single iron planes. The remedy, however, is incomplete, especially for the planing of very hard woods; for which purpose, in particular, Mr Williamson, of Kennington, has found it advantageous to modify the single iron d, by making it of greater thickness, and giving it a bevel on both the top and bottom sides, at an angle similar to that shown on the under side of d. By this altered form of edge, it will be evident that it partakes more of the scraping action; yet it is found to obviate more effectually the defects of former constructions. The edge is stronger and more durable; it gives a beautiful smooth surface almost without the aid of the scraper; and, from its utility to workmen, entitles the inventor to the reward (of ten guineas) given to him for it by the Society of Arts. It is peculiarly valuable in planing hard woods across the grain; as in preparing box for the use of engravers.