Tools and Machinery of the Granite Industry, Part III

Chronicle of the Early American Industries Association, Inc., The, Dec 2006 by Wood, Paul

Initially, gang saws used hand-shoveled, sand abrasive. The introduction of abrasive elevators and cleaners for gang saws greatly increased the sawing rate. There were a dozen patents issued in the 1880s for abrasive (sand and water) feed mechanisms for stone sawing just to inventors in the Rutland, Vermont, area. At this time there were three Rutland manufacturers of gang saws (Lincoln Iron Works, Mansfield & Stimson Foundry, and F. R. Patch Manufacturing Co.) that were supplying the local marble industry. The water and sand (or chilled metal shot) abrasive mixture was lifted and mixed by means of a force pump. The pump used in abrasive feeds was a difficult problem due to the rapid wear out of the pump caused by the highly destructive nature of the abrasive being pumped. The common piston-type pump was not viable due to the need for constant repair and replacement of parts. Diaphragm pumps, the same design as previously described for quarry pumping, and centrifugal pumps were able to pump abrasives with very little wear and were used for most abrasive pumping applications. An abrasive distributor was introduced to feed abrasive to multiple gang saws so that one man could tend a dozen saws instead of just two.

Sand was adequate for soft stones such as marble, but for granite the use of chilled metal shot was required. In the mid 1870s, Struthers & Sons of Philadelphia was manufacturing 1/40-to-inch to 1/50-inch chilled iron shot for gang saws under a Tilghman patent. Chilling, the rapid cooling of the iron shot, hardened it and lengthened its abrasive life. Large granite blocks could now be sawn at the rate of three to four inches per hour and small blocks at twelve to fourteen inches per hour. (Using sand, the rate was about one inch per hour.) Three pounds of shot were consumed for every square foot of stone sawed. About 1885, John Harrison of Canada started his experiments with iron and steel shot abrasives. He later moved to England to be close to the sources of iron and began large-scale manufacture of abrasive shot widely used in the granite industry.

In the late 1940s and early 1950s, the wire saw replaced the gang saw for granite sawing (Figure 9). The wire cut faster, produced a narrower kerf- thus wasting less stone-and was quieter in operation. The wire saw might use a loop of single strand, multiple strand, twisted ribbon, or embedded diamond wire, but usually a two-strand twisted wire having a cross-section width of a quarter inch and a reverse twist every twenty-five to fifty feet was used (Figure 10). The wire loop moved at sixty miles per hour and a suspended weight of five to six hundred pounds maintained a constant tension in the loop. An automated down feed mechanism forced the wire down onto the stone and accelerated the cut. A flow of tungsten carbide abrasive was maintained into the cut by an abrasive pump. Joseph and John Dessureau of Barre, Vermont, one of the principal manufacturers of wire saws, were issued three patents for wire sawing: (1) improvements in automatic down feed for wire saws (1954, no. 2,674,238); (2) a wire design which claimed to have a longer life, to cut at substantially the same rate over its lifetime, to be easier to twist, to retain its twisted shape, and to retain adequate tensile strength (1958, no. 2,856,914); and (3) a machine to twist sawing wire so that it would be straight, free from torsion and have a tight uniform pitch. It also described a new method of producing twist reversals (1965, no. 3,225,798).