requisite, they are mounted on wheels, and may be easily taken from place to place to saw up trees which could not conveniently be moved entire.
27. Planing Machines.—A numerous variety of planing machines are in common use. For flooring boards, Woodworth's machine is found
to answer very satisfactorily. In planing mills at Philadelphia, four of them were working in one room side by side; they have three cutters on each horizontal axis, having a radius of 6 inches, and making 4,000 revolutions per minute. The cutters are said to be capable of planing from 2,000 to 3,000 feet of work without being
sharpened with the oil-stone, and from 20,000 to 30,000 feet without being ground.
They plane boards 18 feet long, varying in width from 3 to 9 inches, at the rate of 50 feet per minute. At the same time that the face of the board is planed, it is tongued and grooved by cutters revolving with a radius of about 3 inches, on vertical axes on each side of the board.
The chips made by the four planing machines are driven through large pipes, and fall into a trough about 20 inches wide, running across the room immediately under the cutters. In this trough works an endless chain, on which are fixed
