MACHINE Toots. In all large stone-yards machines are used to prepare the stone. There is great variety in their form; but since the surface never takes its name from the tool which forms it, it will be neither necessary nor profitable to attempt a description of individual machines. They include stone-saws, stone-cutters, stone planers, stone-grinders, and stone-polishers.
The saws may be either drag, circular, or band saws; and the cutting may be done by sand and water fed into the kerf, or by carbons or black diamonds. Several saws are often mounted side by side and operated by the same power.
The term "stone-cutter" is usually applied to the machine which attacks the rough stone and reduces the inequalities somewhat. After this treatment the stone goes in succession to the stone-planer, stone-grinder, and stone-polisher.
Those stones which are homogeneous, strong and tough, and comparatively free from grit or hard spots, can be worked by ma chines which resemble those used for iron; but the harder, more brittle stones require a mode of attack more nearly resembling that employed in dressing stone by hand. Stone-cutters and stone
planers employing both forms of attack are made.
Stone-grinders and stone-polishers differ only in the degree of fineness of the surface produced. They are sometimes called rubbing machines. Fssentially they consist of a large iron plate revolving in a horizontal plane, the stone being laid upon it and braced to prevent its sliding. The abradant is sand, which is abundantly supplied to the surface of the revolving disk. A small stream of water works the sand under the stone and also carries away the debris.