Compressed air brought a granite revolution

He hand-held pneumatic carving tool is arguably the single most important tool ever invented for working granite. It was introduced into the Barre granite industry in the early 1890s. From Barre, the tool spread to other Vermont granite centers, as well as to Aberdeen, Scotland.

The first practical large-scale use of pneumatic stone working tools in America was at the Hoosac Tunnel in Northwestern Massachusetts. A ponderous boring machine with a 25-foot diameter cutting head and a smaller steam-powered drill had been tried but both failed. The boring machine got stuck after progressing only 12 feet. The steam drill was quick to overheat and its exhaust nearly asphyxiated the operators.

Drilling of the tunnel continued, but at an impossibly slow pace, with hand drills and black powder.

In the winter of 1862-63, civil engineer Charles Storrow went to Europe to view the use of pneumatic drills and nitroglycerine in the construction of the Mount Cenis Tunnel between France and Italy. On his return, he recommended use of these technologies for the Hoosac Tunnel.

In 1863, civil engineer Thomas Doane began the implementation of Storrow's recommendations by damming the Deerfield River to provide a 16-foot head of water to power turbines connected directly to air compressors that Doane had designed. Next, Charles Burleigh of Fitchburg, Mass., designed a lighter and more efficient version of the Mount Cenis Tunnel pneumatic drill. With Doane's air compressors and Burleigh's pneumatic drills, progress improved immediately.

The successful use of air compressors and pneumatic drills at the Hoosac Tunnel led eventually to their application to quarrying granite. Large deep-hole drills mounted on tripods or channel bars and hand-held pneumatic jackhammers and plug drills transformed granite quarrying from small manual production to an industrial scale.

However, the key to harnessing compressed air for stone cutting and carving in the finishing shed was the invention of a lightweight tool of five pounds or less that could be hand-held and guided to produce fine work.

The first patent (1885) for a hand-held pneumatic carving tool (weighing about 15 pounds) was issued to James McCoy of Brooklyn, N.Y., and based on a smaller dental drilling and tamping tool. McCoy's tool operated on 40 psi compressed air.

The pneumatic tool produced an almost continuous sequence of impacts, allowing a rapid removal of large quantities of granite during roughing out and producing a very smooth 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 carving tool.

The air compressor evolved along with the pneumatic tool – first being powered by water turbine and then successively by steam turbine and electric motor. By the early 1900s, large two-stage electric-powered compressors were available, producing 100 psi air in amounts adequate for large finishing operations. Often, small companies purchased compressed air from nearby large companies with an excess supply.

The big breakthrough in pneumatic hammers was the valve-less design, first patented by Herman Kotten of New York City in 1898, but probably invented in the 1880s by Thomas Dallett of Philadelphia, who never patented his designs. Dallett protected his designs and his market by continuous improvements and by a solid reputation for high quality. Later patents by Samuel Oldham of Philadelphia in 1898, and William Holden of Barre in 1902 claimed various additional improvements. With the Holden patent, Trow & Holden Co. became a manufacturer hand-held valve-less pneumatic tools in Barre.

The valve-less design resulted in a small and highly-reliable tool with only one moving part – the piston. An elaborate 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. The piston itself acted as a valve, opening and closing the input and exhaust air ports to drive the piston back and forth. The front of the piston narrowed into a neck-like hammer which extended into an airtight bushing. The front of the bushing accepted the bit shank which was struck by the piston hammer from 2,000 to 4,000 times per minute.

The manufacturers 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. These small pneumatic tools were highly productive but expensive – about $200 each in the early 1900s or about one quarter of the typical stone worker's annual wage.

Usually, the stonecutter works with three sizes of pneumatic tool: large for initial roughing out, cutting large raised letters and heavy carving; medium; and small for fine work such as sunk letters and tracing, and for carving and finish work. Some bits designed for the pneumatic tool, most performing functions similar to hand tools, include: point to rough out stone and knock off high places; ripper for fast removal of stone in hard-to-reach places; cape chisel for crisping lines, joining corners, detailing, and splitting; 4-point tooth chisel for fast, aggressive roughing out; 9-point tooth chisel to make a more uniform surface; and bush chisel for finishing to close the grain.

Makers of hand-held pneumatic tools also manufactured pneumatic surfacing machines that used larger and more powerful valved pneumatic hammers. These heavy tools were mounted on a 10-foot long horizontal bar that was in turn supported by a vertical post. Two types of surfacing machine were available – the sliding bar type where the tool was fixed at the end of a horizontally-movable bar and the crane type where the bar remained fixed horizontally and the tool moved along the bar on a trolley. In both the types, the bar could swing a full circle around the post and could be raised and lowered. The pneumatic tool could, under operator control, reach any point on a planar surface within a 20-foot diameter circle. The adjustable height allowed the surfacer to cut a flat surface on a block of various heights. For very large slabs, a surfacer with a wheeled base would be moved right onto the slab.

At 75 psi, the pneumatic surfacing machine could surface about 60 square feet in nine hours – equivalent to 12 men with hand bush hammers. Although the machine cost $3,500, at $2.50 per day for a stoneworker it saved the plant owner about $5,000 the first year (including the cost of the machine) over manual surfacing. The pneumatic surfacer was less expensive, simpler and more reliable than the McDonald mechanical surfacer and, soon after its introduction in the mid-1890s, the mechanical surfacer became a relic. As early as 1894, Charles H. More Co. of Montpelier had purchased two surfacing machines from James McCoy's American Pneumatic Tool Co.

The surfacing machine tool bits were similar to hand surfacing tools but heavier duty. They included the four point, the nine point, the cross chisel, and the bush hammer. The primary task of the surfacing machine was to smooth sawed surfaces either to a finish or in preparation for polishing. As the number of blades in the bush hammer bit increased, the smoothness of the surface increased. Four-blade surfaces were appropriate for steps, approaches and upper building stories; six-cut surfaces for lower building stories; eight-cut for memorials, mausoleums, building entrances and landscape art; and the "velvety smooth" 10-cut for monuments and statuary.

After World War II, the pneumatic surfacing machine was obsolete, replaced by the wire saw that produced a smoother surface and by the grinding-polishing machine that could work directly on a wire-sawed surface without any intermediate smoothing by a surfacer.

About 1940, Granite City Tool Co. of Barre became sole agent for Dallett pneumatic tools. The Reed Roller Bit Co. purchased Dallett Co. in 1950 and, not wanting to retain the stone industry part of the business, sold the Dallett designs, dies, and name for stone-working tools to Granite City Tool Co. and Trow & Holden Co.

For the next 20 years, Trow & Holden manufactured a "Dallett-style" tool with the Granite City Tool name on it and Barre became the principal supplier of pneumatic tools to the granite industry. There was a melding of the Trow & Holden designs and Dallett designs to produce the new Barre "Dallett-style" tool.
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