Tools and Machinery of the Granite Industry, Part III

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

The gang saw was the first stop for stone from the quarry (Figure 6). The objective of sawing is to cut the quarry saw block into slabs ranging from a few inches to a foot or more in thickness. A typical saw block was 10 feet by 5 feet by 5 feet. In 1909, the Woodbury Granite Co. at Hardwick, Vermont, had two gang saws-one accommodating a maximum stone size of 10 feet by 8 feet by 6 feet and the other a maximum stone size of 16 feet by 6 feet by 7 feet. The hard way (one of the 5-foot by 10-foot faces) was marked at the quarry so the stone could be oriented in the saw such that the cuts were made along the plane of the hard way. Hence, the faces of the slabs produced by the saw were along the hard way plane and would become the faces of monuments. The close grain of the hard way results in the most beautiful finished surface-polished or hammered. The gang saw consisted of a reciprocating frame with multiple cutting blades driven by a crank and pitman rod. The pitman rod was a long wooden shaft that transmitted poser from the crank to the blade frame (Figure 6). The name was derived from the pitman that powered the timbercutting down stroke of a pit saw. The main framework was initially wood and later iron. The saw used six or so steel blades 16 inches high and 16 feet long. The saw blade cutting edges had 2-inch-wide by 4-inch-deep rectangular notches spaced about 6 inches apart (Figure 7). Gang saw blades evolved from smooth-edged to notched and finally to brazed-on diamond segments. The gang saw was a noisy machine-making dragging and screeching sounds that could be heard a mile or more from the shed. They usually ran twenty-four hours a day with two-man crews.

The saw blades were tightened in the blade frame with wedges at the blade ends. Proper tension would be indicated by the ring of the blade when struck by the wooden handle of a shovel. Following cut marks made by the foreman on the saw block, blade spacing was set by placing wooden gauges between the blades. For example, eight blades spaced eight inches apart could yield seven 8-inch thick, 10-foot by 5-foot slabs from a 10-foot by 5-foot by 5-foot saw block. The saw block was positioned under the blades on a saw car that was secured by wooden blocks during sawing (Figure 8). The saw car tracks, which ran under each saw, were typically forty-five-pound rails laid seven to eight feet wide. In 1857, Andrews Merriman of Chicago, Illinois, patented (no. 24,478) a gang saw feed mechanism with four motor-driven dogged screws which forced the saw frame onto the stone through rigid hanging rods connected to the four corners of the frame. This greatly increased the sawing rate. The saw used abrasive steel shot stored in a tank above the saw. The abrasive was mixed with water and poured down onto the saw blades. The shot eventually fell into a pit under the saw and was recycled back up to the tank. If the blades started steaming, more shot was required. After sawing was complete, each slab was separated, chained, laid down and acid washed to prevent rust staining from the iron shot. Normally, the slab front and back was hammered or polished prior to splitting into dimension pieces. Since the gang saw produced a very rough surface with saw marks, a hammered surface was applied by a surfacing machine prior to polishing. After sawing and polishing or hammering, defects were often discovered that were not apparent on the exterior surface of the quarry saw block. For monumental work, this often resulted in the rejection of one or more slabs. The manufacturer and quarry owner usually came to a financial agreement-typically sharing in the loss.