Engineering reminiscences contributed to "Power" and "American machinist"

by Charles T. Porter

We never ran over the stone with the points but once. They made everything before them fly. On the other hand, the droves merely dusted the surface, to take out the marks of the tooth-chisels. All surplus force in the blow was received on the 6-inch cross-bar. The tools stood motionless unless pushed back by the stone, when they received a sufficient portion of the blow to drive them forward to their position.

The feed motion was powerful, being imparted by a worm engaging in a worm-wheel 24 inches in diameter, while the run back was swift, quite 100 feet in a minute.

The sides of the steel tool-holders, rubbing against each other, became after a while badly abraded. I was obliged to plane them off and dovetail thin strips of hardened steel into them. These prevented any further trouble. The sides of the end tool-holders, however, which rubbed against the cast-iron side-bars, I observed, were polished without sensible wear.

This was a very important observation. These surfaces all rubbed together dry. The pressure was only the side thrust, which was very trifling. Under these conditions the molecules of the same material interlocked, while those of the different materials did not. These two materials were, however, extremely different in their constituent features. Perhaps this point of freedom of some different materials from interlocking was still better illustrated by the set-screws, where this difference of molecular structure did not exist in the same degree. These were made of Ulster iron, a superior quality of American iron then largely used in New York City for bolts. They were ⁵⁄₈-inch screws, and were also used dry, no oil being allowed anywhere over the stones. Each tool-holder contained three of these set-screws. The outside ones were tightened and loosened sixty times every day. The middle ones, where only the points were used, were tightened and loosened twenty times every day and at other times stood loose in their threads. The tool-holders being massive, and the blows of the hammers also coming on the leather cushion, there was no vibration. At the end of the two years’ running the outer bolts were all perfect fits. The middle ones were loose, but still held the tools perfectly.

The rollers on which the hammers ran were hardened and turned on hardened shafts. The hammers themselves had chilled faces, and their surfaces running on the rollers were also chilled. The surfaces of the tool-holders and of the bar on which these rocked were provided with hardened strips to the extent that they came in contact with each other. The cams and rollers and their pins were also hardened.

When built this machine was found to require only a single alteration. I had welded the cams onto the shaft, the welds being guaranteed by the smith to be perfectly sound. No appearance of unsoundness could be detected when the shaft was finished, but after running a week or two the cams became loose. This also gave me a useful lesson. I was obliged to send to England for blocks of steel, which were bored, finished and keyed on the shaft in the manner [shown], and the working surfaces of the cams were hardened. This required the substitution of new hammers, because the cams could not be threaded through the old ones. The hubs of these cams were 6 inches long, covering the shaft.

Our company, being satisfied from its design that the machine when finished would prove a success, rented from Mr. Astor a large lot on the south side of Fourteenth Street, west of Ninth Avenue, extending through to Thirteenth Street, and erected and equipped a building and established a stone-yard, where the machine ran successfully for two seasons, principally employed in facing ashlar, as the flat-faced stones of buildings are termed. It turned out with ease 600 square feet of finished surface per day, which was the work of thirty men, and it never broke a stone, however thin.

For facing in the machine the stones were set on bars 2 inches thick and 4 inches high, cast on the surface of sliding tables. These were both longitudinal and cross bars, and were provided with holes ³⁄₄ inch in diameter and about 3 inches apart. There were two tables, each 16 feet in length.

Several pieces of ashlar were set upon each table and held by dogs and wedges on these bars. They were wedged up very easily by skilled workmen, so that they would finish at the same level. At one side of the ways on which the tables moved, near each end, was placed a swing-crane, which was double- and triple-geared, so that by means of it any stone that the machine was adapted to cut could be lifted by two men. The operations of cutting the stones on one table and removing the stones and setting others on the other table went on simultaneously, so that the cutting was never interrupted, except to change the tools and the tables. This last was done as follows: Each table, when the work on it was completed, was run rapidly backward or forward to attach it to the other table. It was then connected with this by a couple of hooks, and, the motion being reversed, pulled it into place under the tools, and in doing this took its own place under a crane, so that the work of removing the finished stones and setting rough ones went on continuously at one end or the other of the ways.

In addition to the machine I designed the building and the whole plant and the plan of its operation, which moved like clockwork. I made every drawing myself. The cranes I obtained in Rochester, N. Y., of a pattern which the builders made for railroads for handling heavy freight.