The planing machine consists of an upright frame, in which revolves a vertical shaft, carrying three horizontal arms. At the extremities of these arms are fixed circular cutters, inclined outwards about 45° from the perpendicular, or about the angle at which the workman would hold his chisel. They are about 10 inches in diameter, and ¾ inch thick, made of steel, and bevilled on both sides, leaving a sharp edge. They are fitted upon axes, and are at liberty to revolve loosely in their bearings as their edges strike the stone.
The cutters are carried round by the shaft at the rate of about eighty revolutions per minute when planing freestone, and sixty when planing granite.
The stone is moved forward on a bed to which it is keyed; the cutters strike its surface obliquely as they are carried round on the revolving arms, turning at the same time on their own axes, and chipping and breaking off the projecting portions of the stone at every cut.
The machine planed the face of a stone slab 4 feet long and 2 feet wide, in seven minutes.
Another modification of this machine, which is not so economical, is employed when it is necessary that the face of the stone be left in lines as it came from the tool.
The stone is keyed on a travelling bed, and
