Table showing Number of Drilling-Machines Broken, &c.
| 1866 | No. Machines Broken. | Cross Heads. | Cylinder Flanges. | Coupling Nuts. | Feed Springs. | Feed Palls. | Ratchet Covers. | Valve Stems. | New Packing. | Tapper Bars. | Screw Spindles. | Union Coupling Nuts. | Feed Nuts. | Shields. | Piston Heads. | |
| July | 21, | 32 | 5 | 2 | 4 | 3 | 2 | 2 | 1 | 10 | 7 | - | - | - | - | - |
| 31, | 67 | 7 | 2 | 1 | 10 | 4 | 5 | 2 | 18 | 14 | 2 | 3 | - | - | - | |
| Aug. | 7, | 75 | 4 | 1 | - | 18 | 15 | 8 | 4 | 39 | 6 | 4 | - | - | - | - |
| 14, | 76 | 6 | - | 5 | 25 | 17 | 11 | 3 | - | 10 | 1 | 6 | 1 | 1 | - | |
| 21, | 65 | 7 | 1 | 3 | 28 | 15 | 13 | 7 | - | 12 | - | 1 | 2 | - | - | |
| 31, | 102 | 1 | 1 | 9 | 64 | 7 | 18 | 2 | - | 10 | 2 | 4 | 5 | 1 | - | |
| Sept. | 7, | 65 | 1 | 1 | - | 27 | 4 | 24 | - | - | 5 | 2 | 1 | 1 | - | - |
| 14, | 60 | 2 | 5 | - | 23 | 2 | 12 | 2 | - | 10 | - | 3 | 2 | 1 | 1 | |
| 21, | 56 | 1 | 1 | 1 | 28 | 6 | 13 | - | - | 3 | - | 1 | 2 | 2 | - | |
| 30, | 56 | 3 | 2 | 1 | 31 | 3 | 16 | 2 | - | 4 | - | 1 | 9 | 1 | - | |
| Oct. | 7, | 54 | 7 | - | - | 39 | 2 | 7 | 1 | - | 9 | 3 | - | 1 | 2 | - |
| 14, | 53 | 5 | 1 | 2 | 28 | 5 | 10 | 1 | - | 9 | 1 | 4 | 6 | 2 | - | |
| 21, | 58 | 3 | - | - | 28 | 4 | 13 | - | - | 9 | 3 | - | 4 | 2 | - | |
| 31, | 77 | 7 | 1 | 2 | 63 | 4 | 11 | 2 | - | 12 | 1 | 2 | 6 | 2 | - | |
| Nov. | 7, | 38 | 2 | - | 2 | 19 | 3 | 13 | - | - | 8 | 2 | - | 3 | 4 | - |
| 14, | 40 | 1 | 1 | - | 17 | 2 | 9 | - | - | 8 | 3 | 2 | 4 | - | - | |
| 21, | 44 | - | 1 | - | 32 | 1 | 4 | - | - | 7 | - | 1 | 1 | 1 | - | |
| 31, | 66 | - | - | - | 34 | 2 | 11 | - | 13 | 8 | 1 | 1 | - | 1 | - | |
| 1,084 | 62 | 20 | 30 | 517 | 98 | 200 | 27 | 80 | 151 | 25 | 30 | 47 | 20 | 1 | ||
About forty of the Brooks, Burleigh and Gates machines have been used at the tunnel; of these eight or ten were originally vertical, and intended for use at the Central Shaft. At the commencement of their use, the machines were new and had their best wear in them; there were from twenty to twenty-four at the beginning. In a short time they began to break down, but by putting on a large repair force and converting the vertical machines into horizontal ones, a fair supply was kept up for from two to three months, at the end of which time the greatest machine progress was attained, viz., fifty-four feet and six inches, in September. After that the progress diminished very much, and in proportion to the giving out of the machines. It is the opinion of the engineer that if a constant supply of machines could have been furnished, that the progress would have reached a point much beyond that obtained by hand labor; but with the stoppage of the supply, the number of machines that could be kept in working order was daily reduced, and at last it fell down to two or three, and finally, at times, none were in condition to work. The frames were, however, kept in the tunnel to await the completion of the Burleigh machine, the reception of which was retarded till late in October; much beyond the time anticipated by the commissioners, although the work of their construction was carried on continuously night and day. They came at intervals of several weeks, two at a time; the first of which were put into the tunnel on the thirty-first day of October. Through the month of December, four of these machines were at work.
The Burleigh Machine.
Has a solid piston (so called,) which has a hole in its back end to allow the feed-screw to pass in without touching; the drill is secured to this piston. On the back end of the piston is a section of a ball used as a cam, which works the valve and the feed-motion. The valve is rotated by a rod lying on the band of the cylinder; upon this rod are two cams which perforate the band of the cylinder. The action of the piston brings the ball on its end in contact with these cams, rocking them up and down; the rod to which they are secured being connected with the valve, imparts to that its motion. This machine is fed altogether on ways, or a bed-piece, upon which is the feed-screw; the feed-nut is upon the end of the cylinder-band. To this feed-nut is attached a feed-ratchet, which is held between two collars, allowing it to turn round. Upon the cylinder-band is a lever, one end of which passes through the band; upon the other end is a pall. The motion of the piston raises the lever up, pressing the end containing the pall against the ratchet which turns the nut on the feed-screw, thus moving the machine forward. The rotating ratchet is in the band of the cylinder and has a spline in it, and a pall on its outside. The piston having a spiral groove is turned by this ratchet as it moves down. On the return of the piston, the pall drops into the ratchet and then the piston is turned. The piston is not encumbered with any machinery, and moves alone; its area of air is greater on the forward than on the backward stroke; the alternation of the valve admits the air. The machine, like the one last described, contains eighty pieces; it has the same number of screws and pins, and weighs 372 pounds including the ways or bed-piece; without the ways its weight is 212 pounds. Its number of strokes is about 300 per minute, and its blow somewhat lighter than that of the other. This machine is not entirely automatic; the feed-motion not working regular; when it does not, it is fed by hand, which is a simple process.
These machines stand the work much better than those first made at Fitchburg. Their average time in the tunnel without repairs in the interval, is about five days; they have needed repairs in two days; one remained at work fourteen days. They accomplish double the work without repairs that those do which were made after the previous pattern. There is a further advantage in using the Burleigh machines; their breaking, when it occurs, is not very serious, the injured parts consisting mainly of cams, can generally be replaced at the tunnel; whereas for the repairs on the Brooks, Burleigh and Gates machine, the dependence to a very great extent has been upon the machine shop at Fitchburg.
The piston-head of this machine has a diameter of 425/100 inches. The diameter of the piston-rod is at the large end, 3 inches, at the small end, 275/100 inches.
So the number of inches of air area, is 820/800 when the drill is propelled upon the rock, and 77/100 when returning from it.
A full complement of men to work the machines first used, would be, perhaps, thirteen. Mr. Gates, who superintended their operation in the first instance, began with fourteen, but they were reduced to thirteen. The Burleigh machine practically requires feeding, and a full set at work would probably demand fifteen men for their successful operation.
The value of these machines has not yet been ascertained. The Committee are of opinion that when a full complement shall have been obtained, so that the workmen can have at all times a full supply upon the frames, that greater progress can be obtained by them than by hand drilling; and after a few months operation, the cost of using them, in comparison with hand labor, can be fairly tested. But as the Brooks, Burleigh and Gates machine has been abandoned, no useful results would be obtained by comparing the expenses within the tunnel during the months of July, August and September, with three corresponding months when hand drilling was carried on, and no satisfactory comparison can be made between the working of the Burleigh machine and hand drilling, until a sufficient number of machines has been introduced into the tunnel to keep the men fully employed. It is to be hoped that machines sufficient to make the test may be soon obtained, and that this desirable information may be made known.