Page:Miscellaneous Papers on Mechanical Subjects.djvu/146

 passed under a frame, in which works a sliding carriage driven by a crank; in this carriage is fixed the circular cutter at the required angle, and as the stone is carried along, the cutter is driven backwards and forwards across its face at right angles to the direction in which it moves, and chips off parallel breadths of stone at every cut.

The cutters can be used for planing from 300 to 400 square feet of freestone surfaces, and about 150 square feet of granite, without being ground.

39. Stone Polishing Machine.—The stone is polished by a flat circular disc of soft iron, which is made to revolve horizontally. The axis of a disc is fixed at the end of a heavy frame, which moves round a strong centre shaft in a radius of about 12 feet.

The polishing disc revolves at the rate of 180 revolutions per minute. It is driven by a strap, to which motion is given by a driving pulley, fixed on the centre shaft. The disc is guided, and its pressure regulated by hand. It will polish about 400 square feet of surface in a day of ten hours.

40. Brickmaking with Dry Clay.—A machine for making bricks from dry clay was in operation