Tools and Machinery of the Granite Industry, Part III

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

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The first practical hand-held pneumatic hammer (weighing about fifteen pounds) was designed and patented (1885, no. 323,053) by James S. McCoy of Brooklyn, New York, (Figure 41) based on a smaller dental tool designed by Samuel W. Dennis and patented by him in 1878 (no. 205,169). The hammer operated on 40 psi compressed air that was alternately directed to the back and front of a piston by a transverse annular value and achieved several thousand strokes per minute. The pneumatic hammer piston impacted a removable tool (or bit) that was held in a spring-retracted tool holder. The pneumatic hammer produced an almost continuous sequence of impacts, allowing a rapid removal of a large quantity of granite during roughing out and producing a very smooth granite surface during finishing. McCoy patented a number of improvements as he experimented with different designs-testimony to the difficulty in designing a really practical pneumatic hammer.

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The big breakthrough in pneumatic hammers was the valve-less design, which was first patented by Herman Kotten of New York City in 1898 (patent no. 605,486) but probably invented earlier around 1883 by Thomas Dallett of Philadelphia, Pennsylvania, who never patented his designs. Dallett protected his market by continuous design improvements and by a solid reputation for high quality. Later patents by Samuel Oldham of Philadelphia, Pennsylvania (1898, no. 609,162,), and William Holden of Barre, Vermont (1902, no. 711,859), claimed various improvements. The valve-less pneumatic hammer design resulted in a highly reliable tool with only one moving part-the piston (Figure 42). An elaborate, and usually patented, system of ducts and ports in both the piston and the cylinder wall was employed to alternately direct the compressed air to the front and back of the piston. As it moved, the piston itself opened and closed the input and exhaust air ports to drive the piston back and forth; the movement of the piston itself acted as a valve. The front of the piston narrowed into a neck-like hammer, which extended into an airtight bushing. The front of the bushing accepted the tool shank, which was struck by the piston hammer from two to four thousand times per minute. The manufactures of pneumatic hammers made many claims-longest wearing, smoothest running, quickest action, least friction, most sparing use of compressed air, and best control of the force of the hammer blow. Each of the major manufacturers (Dallett, Kotten, Oldham, and Trow & Holden) seemed to have had its loyal following of users. In the early 1900s, these small pneumatic hammers cost about $200 each.

Usually, the stonecutter had three sizes of pneumatic hammers: large (1-inch-diameter piston) for initial roughing out, large raised letters, and heavy carving; medium (¾-inch-diameter piston); and small (½-inch-diameter piston) for fine work such as sunk letters and tracing and for carving and finish work (Figures 43 and 44). The pneumatic hammer had many different tool bits that performed functions similar to the hand tools. In fact, some manufacturers offered a detachable striking cap that fitted over the shank of a pneumatic hammer tool bit so that it could be struck with a hand hammer. The point bit was used to rough out stone and knock off high places. The ripper bit was used for fast removal of stone in hard-to-reach places. The cape chisel bit was used for crisping lines, joining corners, detailing, or splitting. The four-point tooth chisel bit was used for fast, aggressive roughing out and the nine-point tooth chisel bit was used after the four-point to make a more uniform surface. The double-blade chisel bit might be used after the four- or nine-point tooth chisel to smooth the surface and take off high points. The three-blade bush chisel bit, smoother than the double blade, leaves an axed or brushed surface. The bush chisel bit, a finishing tool, was used to close the grain. The criss-cross chisel bit might have been used after the nine-point or three-blade chisel and leaves a unique cross-hatched finish. The cup chisel bit, a bushing tool, closed the surface and leaves a unique texture (Figure 45).

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Tools and Machinery of the Granite Industry, Part III

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

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