Grindstone

a well known instrument for sharpening tools. In use, a hone is laid on a bench and the tool is moved to and fro on its surface; the whetstone is held in the hand and drawn along the edge of the tool; the grindstone is larger and is mounted on an axle. It consists usually of a piece of fine sandstone shaped like a section cut from the end of a cylinder. The axle passing through the center rests on smooth wheels or well oiled bearings. It may be turned by hand or by a treadle, or caused to rotate by a belt. The grinder holds his tool against the rotating surface. Water is applied usually to the grinding surface, not only to carry away the loosened parts of the steel and the stone, but to prevent heating and gumming. A grindstone may be a few inches or it may be several feet in diameter. The larger the stone, the slower must be the rate of rotation. Owing to centrifugal force, a large grindstone will fly into pieces if turned too fast. Workmen in machine shops are killed not infrequently by such an accident. Artificial grindstones are made of powdered emery and cement. Such a stone is less liable to break under rapid motion. It is called more frequently an emery wheel. Suitable material for grindstones is found in England, Germany, Nova Scotia, Canada, and at Berea, Ohio. Valuable quarries have been opened in Colorado. Machinery is employed in shaping the stones into the cheese form required. See Emery