Tools and Machinery of the Granite Industry, Part III

Later, circa 1890, pneumatic surfacing machines were introduced that used a single, powerful pneumatic hammer either attached to the end of a sliding horizontal bar-bartype- or mounted on a trolley that moved along a fixed horizontal bar-crane-type-(Figure 23). (The pneumatic hammer will be described later in "Roughing Out and Cutting.") The horizontal bar was supported by a vertical post which was mounted on a cart with wheels. The bar could be raised or lowered by a hand-cranked winch and could rotate around the post in a horizontal plane, allowing the operator to position the tool anywhere inside a circle up to twenty feet in diameter. Thus, the pneumatic surfacer could handle very large surfaces, larger than could be produced by the gang saw. Pneumatic surfacers cost about $3,500 each and were simpler and more reliable than the McDonald surfacing machine. James S. McCoy's American Pneumatic Tool Co. was one of the early manufacturers and supplied the Charles H. More & Co. of Barre and Montpelier, Vermont, with two of the first pneumatic surfacers. These were used on granite for the Iowa State Soldier's Monument, the largest monument of its type in 1894. The pneumatic surfacer used a four-point tooth chisel bit for the initial surfacing (Figure 24) and a nine-point tooth chisel bit or a bush chisel bit for the final surfacing (Figure 25). The surfacing machine bush chisel bit could have from four to ten blades-or cuts-of decreasing thickness; the more numerous and thinner the cuts the smoother the resulting surface. The bush chisel bit produced the following hammered surfaces: four-cut-suitable for steps, approaches, and upper building stories; six-cut-suitable for commercial and public buildings; eight-cut-suitable for memorials, mausoleums, building entrances, landscape art; and ten-cut-a velvety smooth surface suitable for monuments and statuary.

The surfacer's pneumatic tool required seventy-five psi compressed air and could surface about sixty square feet in nine hours, which was equivalent to a saving of eighteen dollars per day, or fifty-four hundred per year, over manual surfacing. It was said this machine replaced twelve men with hand bush hammers. A gang-sawed surface could not be used as an exposed surface since it was scored with blade marks and therefore had to be smoothed with the pneumatic surfacing machine. Since pneumatic surfacers were prodigious generators of airborne granite dust, they were later supplied with water to wet the stone and keep down airborne dust. Often during warmer weather, they were moved outside to alleviate the dust problem. By the late 1930s, most pneumatic surfacing machines were equipped with surfacer dust collectors which removed the dust by suction (Figures 26 and 27). The dust collector suction nozzle was positioned near to and moved with the pneumatic tool bit so as to suck up the highest percentage of produced dust. The nozzle was connected to a chip trap and suction fan via a flexible duct, allowing free movement of the surfacer bar and pneumatic tool.