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North Adams, Massachusetts, February 26, 1872.
GENTLEMEN: In reply to your letter of the 20th instant, asking some particulars of our experience in the use of the Burleigh rock-drill, the machines we have been using are those known as the "tunnel-drill," having, in the terms of your inquiry, "their operating-end made as axial continuation of the piston-rods." We have some sixty of these machines in service, and they have given great satisfaction, working under an atmospheric pressure of from 55 to 60 pounds on the square inch, and making upward of 200 strokes per minute. We estimate the saving in expense, as compared with hand-drilling, at about 333 per cent., and in point of time there is a gain of fully 50 per cent.; in other words, effecting a saving of at least five years in the finishing of the Hoosac tunnel.
Messrs. CROSBY & GOULD, &c., &c.,
F. SHANLY & CO.
[From the London Morning Journal, November, 1871.]
SIR: Regarding the introduction of drilling-machinery into mines as a very important subject, and as I happen to be familiar with the results obtained from the working of the Burleigh drill, on Lake Superior-where, by the way, it is by no means common-perhaps you will allow me space for the accompanying remarks.
Doering's machine was tried in Tincroft and in Dolcoath mines, Cornwall, and thrown out, I believe, because it would not pay. I was never fortunate enough to learn the results obtained from working it; but it seems to me that somebody ought to have been sufficiently interested in this machine to find out what work it did, as well as what work it could do, and make it public. I saw a statement made that the machine drifted a given number of feet more in a month than six good miners could do; but, as its use has been discontinued, I infer that it cost more to break the ground than by hand-labor. I was underground in this country with Mr. Nobel, when he was making efforts to introduce nitro-glycerine; he, of course, was praising the compound, and remarking on the success attending his endeavors to get it into use; "but," said he, "I could not succeed in Cornwall-they are prejudiced there against everything new." I felt my "Cornish" get up, at the time, and was inclined to dispute the assertion made, but, on reflection, it seems to me that there is a deal of truth in what was said. I believe the putting in of the man-engine at Tresavean mine was due as much to the efforts of the Polytechnic Society as to those running the mine. One of the deepest and best-managed mines in the Camborne district was a long time seeing the propriety of using skips, and how many now stick to the kibble! Ten years ago the wheelbarrow was as common as the tram-wagon. I have yet to learn that it is gone out of fashion. It is only of late that any attention has been given to increasing the stamping duty in mines; and when Messrs. Harvey & Co. set up and tried the pneumatic stamps, in their very laudable efforts to reduce the cost of stamping, if I remember aright the tenor of the remarks made by the "astute" manager of a very rich tin mine was to the effect that "we will let somebody else try them, and in that way learn if they are a success."
There is a difference in starting a drilling-machine in a mine, with the authorities interested in, or indifferent to, its success; the men commonly regard an innovation with disfavor; and I would defy any inventor to succeed in working a machine by Cornish miners if they considered it was against their interest that it should succeed, unless he personally supervised it, or had a competent person in his interest to do so. Cornishmen are good miners, and good mine managers-they ought to be-but they are just as apt as others to conclude that what they do not know is not worth knowing.
I am not going to draw the inference from the foregoing that the Doesing machine did not get a fair show, nor would I for a moment suppose that the authorities in the mines where it was tried had prejudged it; even if they had, they would exert no undue influence against it. Still, if they were not in favor of it, I would certainly venture the opinion that the Doering machine did not do its very best. I am ready, however, to drop the Doering as a failure, and will try to tell you what I know of the Burleigh drill.
The first machine of the kind brought into the copper region of Lake Superior was tried at the Pewabic five years ago. The Red Jacket inine used one for a short time just afterward in sinking a perpendicular shaft from surface. The motive-power applied was steam in both instances. I cannot conceive that a hot-drilling machine could be a success. The next trial-and the first with air-compressors-was made at the Aztec mine, Ontonagon County; this was a disgraceful failure.
The Central Mining Company next procured a Burleigh, about two years ago, to
work in an incline shaft which they have been sinking for several years. The said shaft is being sunk in the country 14 by 8 feet, at an angle of 300 from horizontal;, this machine is still at work. In last year's report of the mine the mining captain stated that by the use of the drill they had increased the rate of sinking 50 per cent. This was the first machine of the kind I saw at work; and it very forcibly struck me that the machine could drill more ground in an hour than three of the best miners could in a day. After that at the Central mine had been working some months the Copper Falls Company decided on trying one on what they term the Ashbed, a lode of amygdaloidal character, varying in width from 7 to 10 feet, and dipping at an angle of 26 from horizontal. The lode is known here as a "stamps lode;" the proportion of copper contained therein is about 1 per cent. of mineral, or per cent. of ingotcopper. The copper varies in size from the finest particles to pieces of 1 pound weight; rarely larger. The lode forms an integral part of the formation; the over and underlying belts of trap protrude irregularly into it, consequently there is no regular or defined foot or hanging wall. Another feature is the almost entire absence of "slips," or "breast-heads." The ground cannot be called hard, but is "short" to "break," requiring more than ordinary care in planning holes. Four good men can drive from 18 to 23 feet per month in an ordinary-sized level; the same number can stope from 10 to 12 fathoms in the same time. For the past two years, instead of letting the stope to the miner per fathom, he has been paid so much per foot to drill holes, under the direction of a competent person. A more trying place for a drilling-machine cannot be found, the inclination of the lode being a serious disadvantage in carrying a wide breast on a level. After getting fairly under way, it was found that three men and one boy in a shift, or six men and two boys with the machine, could drift from 40 to 44 feet per month, carrying a breast 18 by 8 feet; this was doing the work of 16 men, but at no reduction of cost. It was then decided to try what could be effected by stoping; and after a carriage was constructed for the purpose, work was commenced. The carriage and machine weigh about 14 tons. To move them up over the foot-wall a pair of common blocks and a small crab-winch are used. The mode of working is to set the carriage in the level, and commence cutting in for a stope, which is carried toward the bottom of the level over the stope worked out, lower the carriage down, and commence another. In working this way less drilling is performed with the machine, because more time is occupied in moving it; but it pays best. Early this summer three drills were started, two No. 1 compressors supplying motive-power; these last cannot be relied on to do good duty without hinderances; very commonly the pressure of air being insufficient to work with. To obviate this, a No. 3 compressor has been set up and was started two weeks ago. This gives ample air to run three, or even four drills, going from 60 to 70 revolutions per minute. The gauge shows a pressure of from 45 to 55 pounds per inch, varying, of course, with the number of drills running at the time. Since starting this an increase of duty has been effected, as well as a material saving in fuel.
I have been fortunate enough to obtain the results of last month's running with the three drills now in use; these figures may be taken as the result of running three machines, with two No. 1 compressors supplying air:
No. 1 machine is the improved tunnel-drill; No. 2, the small machine, as constructed five years ago; No. 3 is same as No. 1, but was worked irregularly, frequent stoppages being necessary to blast. The timing an average day's work with No. 1 machine before and after starting the new compressor gave the following figures, (time is given in minutes.) Men leave the "dry" at 7 o'clock; quit work at 6 o'clock:
The diameter of holes varies from 2 inches to 24 inches, none less than 2 inches. The heaviest day's work, or rather the heaviest shift's work, performed so far has been the drilling of 13 holes, or 64 feet of ground. Some shifts, when the machine is employed in drilling "dry holes" in the back, only about half that amount of work is performed. Copper commonly offers a serious impediment to the drill; but for this it would be easy to drill 60 feet per shift on an average. In the day's work given above one hole required 67 minutes of drilling-time to sink it 5.5 feet deep, when, but for the presence of copper, the same work could have been done in 22 minutes. The rock broken in the mine last month was at the fourth level, by hand-drilling exclusively, at the fifth level by Nos. 1 and 2 machines, at the sixth level by No. 3 machine and hand-labor combined. The rock from each level is carefully reckoned; that from fourth level amounted to 1,035 tons, from fifth level 1,941 tons. This is sufficient to show comparisons regarding cost, which, at fourth level, was as follows: Drilling holes, 3,035.7 feet, at 26 cents..... Man in charge..
Supply-Candles, 16 pounds, at 20 cents
Powder, 46 kegs, at $4
Fuse, 2,850 feet, at $10
Powder-cans, three, at 50 cents.
Cost of breaking 1,035 tons of rock, at $1.035 per ton
The cost of running Nos. 1 and 2 machines at fifth level was as follows:
There is nothing charged for repairs, which for the month were trifling, and could be. covered for a cent per ton. This answers the question whether the Burleigh drill will pay or not; and I have no hesitation in saying that better figures than these can be attained. These two machines broke, with twelve men and three boys, as much rock as could be obtained from thirty good miners. Better work can be done in a shaft where the ground is moderately hard, because a great deal more working time can be got out of the machine. Very much depends on the facilities for handling the machine; and it will require thought, experience, and time to decide what appliances are best. The mechanic puts into the miner's hands a machine that will drill 2-inch or 3-inch holes in diameter, from 40 to 60 feet in the shift, and he ought surely to have brains enough to handle that power to the best advantage. There surely can be no reason why a charge of powder in a machine-drilled hole cannot break the same amount of rock as if exploded in a hole drilled by hand-labor. Going back to the time when the United mines, Gwennap, were at work, I remember that over £100 per fathom was paid to sixteen men for cross-cutting toward the "hot lode," when, but for the excessive heat, £10 would have been a good price. What would have been the value of cold-compressed air and the Burleigh drill there? How many deep and hot engineshafts are now being sunk, where the rate of sinking is nearer 6 feet than 12 feet per month, and where the sinking could be doubled, or even quadrupled, by using a drilling-machine?
I am not writing in the interest of the manufacturer, who, by the way, could improve the machines by putting in better material, but simply as one who firmly believes that machinery will, in less than ten years, very generally supersede hand-labor in mines.
KEWEENAW COUNTY, Michigan, October 9.
To these statements I add the following, from a paper read before the American Society of Civil Engineers, on the Nesquehoning tunnel, in Pennsylvania, in the construction of which the Burleigh drill was employed. The paper contains valuable statistics of its economy:
Nesquehoning tunnel, in Carbon County, Pennsylvania, is a work of the Lehigh Coal and Navigation Company. It pierces Locust Mountain, and will connect their railroad in Nesquehoning Valley with their extensive coal operations in the valley of Panther Creek. At present this coal finds its way to market by that interesting system of inclined planes and gravity-roads known as the "Switch-backs of Mauch Chunk," which has commanded the admiration of travelers for more than forty years, not only on account of the beautiful scenery which the route displays, but also from its early and admirable adaptation to the purpose for which it was designed. It has, however, become worked up to its capacity, and in arranging to extend their coal-mining operations, the company have wisely determined to avail themselves of the locomotive, which has had its practical development since they were the pioneers in railway enterprise. It passes through the base of the mountain at an elevation of some 15 feet above the water on either side, and 554 feet below the crest, and cuts the strata at right angles, where they have a south dip of about 450. Its length is 3,800 feet, of which 1,300 feet are through the coal-measures, with all their various strata of coal, coal-shale, sandstone, and conglomerate; 1,200 feet through the conglomerate formation, with its occasional strata of coal-slates and sandstone; 1,000 feet through the red shale, with occasional strata of sandstone, and 300 feet at the north end through the débris, and soft and decomposed red shale which is found overlying the red shale formation. It has encountered in its progress as hard and as soft material as is often met with in tunneling.
After mature investigation it was determined to use the Burleigh drills, driven by compressed air. With the advantage of the experience at Mont Cenis and Hoosac before us, we should, and it is believed we have, obtained better results, as to cost and progress, than attended either of those works in their early stages, and I may here state that I believe no other known process is capable of penetrating this conglomerate formation with that economy and rapidity which are necessary to meet the present demands of capital. This whole work has been done with 6 of the "two-drill" compressors, made at Fitchburgh, Massachusetts, and with sixteen-drill engines, and we have averaged as much as one-half of the drill-engines constantly in operation, and sometimes two-thirds.
The explosive used was gunpowder, ignited by the electic spark; but the requireinents of ventilation and the hardness of the rock demanded powder of the highest Government standard. Some doubts which existed as to the economy in the use of the more powerful explosives, when the cost of drilling was reduced by machinery, and their greater danger, with the existing knowledge of workmen of their use, caused them to be rejected, and the result, in the freedom from serious accident, has been satisfactory, as we have not, thus far, lost a life from premature explosions.
American steel has been used. Several of our own makers produce a better and cheaper article for the purpose than can be obtained from abroad, and the best we have had is from the William Batcher Steel-Works at Philadelphia.
The headings are driven at the bottom, 8 feet high by 16 feet wide, and where arching is required, the full width for a double track is taken out, that the tunnel may hereafter be enlarged without disturbing the arches. At this date both headings are in the red shale and about 500 feet apart; they will be joined in August, and, until the tunnel is finished, full details of the work cannot be given; but the accompanying statement of Thomas C. Steele, chief assistant engineer, of the operations at the south end, up to June 1, may be of some interest.
The heading to which the tabular statement refers has been twelve months in the conglomerate, and two months in the red shale; the progress in the conglomerate has been about 100 feet per full month's work, and in the red shale 160 feet. The holes drilled per cubic yard of rock removed have been in the conglomerate about 11 feet, and in the red shale about 63 feet. The powder used per cubic yard has been in the conglomerate about 6 pounds, and in the red shale about 3 pounds, though a bad lot of powder ran the consumption in the conglomerate up to 7 pounds for two months. The operation in the enlargement to which the statement refers has been eight months in the coal-measures, and two months in the conglomerate; its average monthly progress has been 166 feet; its average holes drilled per cubic yard of rock removed, 3 feet; and its average powder used 26 pounds per cubic yard.
In this enlargement a portion of hand-drilling is included, which extended over the operations of one month, and it increased both the holes drilled and the powder consumed, showing that men do not use better judgment in directing hand than machine drilling. Statement of the workings of the south end of Nesquehoning tunnel.