PLANING MACHINERY. The first at-; tempt to economise labour by means of plan ing machinery was made by General Bentham, who obtained a patent in 1791 for a contriv ance by which large Planes, Vide.enough to take the whole width of a plunk st one and supplied with apparatus for directing their course, regulating the depth to which they could cut, and, generally speaking, for superseding the necessity of skill and judg ment on the part of the operator, might be worked either by mechanical power or by manual labour. The improved principle, now generally adopted, was introduced in Bramah's patent of 1802. In a beautiful machine which he constructed for the Woolwich Arsenal, the wood is placed upon a carriage, and drawn by hydraulic power under the lower surface of a rapidly revolving disk or mill, to the faro of which a series of planes or cutting instruments are attached, which, acting upon the wood i* quick succession, brine it to a very smooth and even surface.
Immense saving of labour, accompanied with a corresponding improvement in accuracy has been effected by the application of planing machinery to the levelling of iron and other metals, in lieu of the cold chisel and the file, worked by hand. In some instances this has been done on the principle of Bramah's ma chine above referred to; but ]more generally the planing of iron is effected by a stationary cutter, the iron being brought under it by a rectilinear motion. For this purpose it is not usual to employ wide cutting instruments, as for wood ; but a narrow tool, cutting a mere line of the surface at once, is brought into contact uith all parts of the surface to be lev elled in succession.