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"Quarry methods are determined largely by the attitude of cleavage. Thus, in the eastern part of the Lehigh-Northampton district, the flat cleavage planes make possible the use of channelling machines; not only is it easy to run the channeller on a track, but the blow is downward and assisted by gravity. In the Slatington region, however, where the cleavage dip is steeper, the channeller can only be used under somewhat unusual conditions,-for example, in freeing the lowest or "key" block; here instead much of the work can be done by drilling, because the drill can be more easily mounted so as to drive horizontally. Focht has pointed out that even the wire saw, which is a far more flexible cutting device than the channeller, is operated with more difficulty where the cleavage dips steeply. In general the quarry operations are complicated by steeper dips"
"Quarry methods are determined largely by the attitude of cleavage. Thus, in the eastern part of the Lehigh-Northampton district, the flat cleavage planes make possible the use of channelling machines; not only is it easy to run the channeller on a track, but the blow is downward and assisted by gravity. In the Slatington region, however, where the cleavage dip is steeper, the channeller can only be used under somewhat unusual conditions,-for example, in freeing the lowest or "key" block; here instead much of the work can be done by drilling, because the drill can be more easily mounted so as to drive horizontally. Focht has pointed out that even the wire saw, which is a far more flexible cutting device than the channeller, is operated with more difficulty where the cleavage dips steeply. In general the quarry operations are complicated by steeper dips"
Charles Behre 1933
Most of the following information is taken from Oliver Bowles' 1922 book, The Technology of Slate.
Patented July 6, 1926. the drawing below is from a patent application no. 1591377, for a broaching attachment for fluid actuated rock drills of the hammer type. It was applied for by Charles C. Hanson from Easton Pennsylvania.
Drilling and Broaching
"Drilling and broaching" is a general term used to describe a common method of creating a long narrow slot or "channel" into stone which would define an edge to a block once it was removed from the quarry wall. The approach required the drilling of a series of closely placed holes which were then joined together by breaking out the intervening material. Hand drilling, using a drill and hammer, was an early method of quarrying slate but the amount of labor involved in the process made it costly as methods of mechanical drilling became available. This early approach required two people. One person would hold the drill while the other would swing the sledge usually weighing about seven or eight pounds. These holes would take a fair amount of time to complete and would seldom be deeper than five feet.
Compressed air became the most common method of drilling and was used to create holes for setting powder to create floor breaks, or when splitting off a block from the wall of the quarry using a plug and feather method. Additionally, the drilling was used in combination with a broaching tool to break out blocks instead of blasting. A broaching tool had qualities about it that were similar to a jack hammer. Instead of rotating like a drill bit, the broaching tool was used to "smash out" the small sections of stone that remained between the drill holes.
One of the earliest advances in stone quarrying was the quarry bar, also known as the bar channeller which first appeared in slate quarries around 1887. This tool could be used for either plug and feather work or channelling and employed a drill and broach process to function. Fundamentally, a tool that could hold a drill in a specific location, and at virtually any angle without needing an excessive amount of human strength, this tool consisted of a bar about 12 feet long supported by four iron legs. Drills were mounted on this bar, and by moving the drills to different positions on the bar closely spaced holes were projected in line. After a hole was completed a plug was placed inside to prevent debris from falling in as the next hole was drilled. The spacing between the holes was then crushed with a blunt end flat bit or "broach" which breaks out the webbing between the holes. Broaching was ideal for stone that was too hard for regular channeling machines especially in other types of quarrying. While channeling was the preferred method for many slate quarries, broaching was used in quarries where the slate was brittle or "tender" or where the amount of shattering from channeling machines was excessive. The method was well adapted for the Pen Argyl beds, especially those above the Albion run.
By broaching out the intervening rock a channel was formed that would define the edge of a block. While the tool helped by eliminating the need to hold the drill, the process was so slow though that it was not widely used.
Track Channellers
About 10 years after the bar channeller, the track channeller was designed. This was the modern type of channeling machine, which traveled back and forth on a track and cut out a channel much more rapidly than the primitive bar machines. While designed to fundamentally do the same thing, hence the use of the word "channeller", the track channeller was a larger piece of equipment that required fewer steps to achieve the same goal. With the bar channeller, it required a two step process. First the holes were drilled one or two at a time, depending on the number of drills attached to the bar, with the second step requiring the process of broaching to follow. With the track channeller the two processes were combined, the system used a new Z shaped cutting tool for work in slate. Channelling machine were common in Pennsylvania slate quarries. The channeling machine was desirable because it reduced the amount of damage that the stone sustained when compared with blasting. In addition, the channeller produced a much smoother surface on the extracted material as well as providing much more regularly shaped blocks. The best condition for running a channeller though was a flat floor which was not always available in slate quarries based on the dip of the stone. Based on dip, much of the work had to be done on floors that inclined anywhere from 5 to 30 degrees. This slope ran in the direction of the channeller's tracks so in order to work on grade, one of the tracks on the channeller was provided with a rack that engaged gears similar to that found on a cog rail train. In cases where the grade was too steep for the gear system, a track parallel to the channeller was run that contained a second "balance" car. This car was cabled to the channeller and then weighted to counter the pull of the channeller.
Ordinarily in slate quarrying a channeling machine could be driven at full capacity, but in some slate beds the heavy blows by the channeller bars fractured the rock adjacent to the channel cut. The use of the channeller was affected by the cleavage dip in the slate and therefore was not universally use throughout the Slate Belt. The success of the channeller depended also upon the resilience or toughness of the rock. Quarrymen claimed that the slate in the Bangor beds was fractured over a much smaller area adjacent to the channeller than in the Pen Argyl beds, and that in the latter the slate of the Diamond run was more heavily shattered than that in the Albion run.
Blasting
Blasting was the most common method of removing material in the early period of slate quarrying where holes were drilled and black powder was used. By the 1920's though this method was greatly discouraged since it damaged much of the surrounding slate resulting in a higher rate of material loss. For an industry where loss rates were between 65% and 80%, methods for removal that contributed to this loss were not ideal. In addition to impact damage to the slate, the blasting process often resulted in mill blocks that had sharp angular points which were not ideally shaped for easy cutting and were therefore removed resulting in additional loss.
With the development of channeling machines, the use of blasting was limited to smaller charges most often used for loosening large blocks from the walls of the quarry. For this application, holes would be drilled and powder was then inserted and fired to create a fracture along the grain or "sculp". (to better understand this process see Cracking a Block) Blasting was also used to create floor breaks if nature did not provide one instead. In situations where a quarry's floor paralleled the slatey cleavage, horizontal drill holes were projected at the floor of the bench to parallel the slatey cleavage. By means of small charges of black blasting powder a fracture was made separating the mass from the quarry floor. The process of making floor breaks was locally termed "split-hole" blasting.
Image Source: Pennsylvania Geologic Society
A drill and bar broaching system
A Sullivan VX channeler being used in the Excelsior Slate Quarry in Pen Argyl some time around 1905.
Image Source: Pennsylvania Geologic Society
A wire saw in operation. The wire is seen entering the cut about half way up the nearest standard (support pole).
The Wire Saw
While the channeller had been a significant contribution to the quarrying process, reducing the amount of damage to stone as it was quarried, the Bureau of Mines introduced the wire saw to slate quarries in 1926. Up to that point, the wire saw had been used in marble quarries both in America and abroad and one of the possible reasons that it had not been used in the slate quarries was based on a point that Oliver Bowles made when talking about the channeler.
"Many slate quarries are run by primitive methods, and strong objection is made to the introduction of any new devices. In many organizations no one has ever seen a channeling machine in operation, and this lack of familiarity with it has discouraged its introduction. "
"Many slate quarries are run by primitive methods, and strong objection is made to the introduction of any new devices. In many organizations no one has ever seen a channeling machine in operation, and this lack of familiarity with it has discouraged its introduction. "
The wire saw usually consisted of a three-strand endless wire rope about one-fourth inch in diameter. The wire passed around a driving wheel and was carried on pulleys from the driving wheel all the way to the location in the rock where a cut was needed. An abrasive was fed to the rope at the point where it entered the rock. To prevent too rapid abrasion of the wire, a length of wire rope, sometimes exceeding a mile, was used. In Behre's book claims about the wire saw at that time stated that the amount of stone breakage was reduced nine fold from the cutting done by the channeler and that the total amount of slate that could be cut with the wire saw was four to five times greater than what could be cut in the same amount of time with the channeler. Added to that was the fact that the cost per foot of operating the wire saw was one third that of the channeller.
In the image of the American Bangor quarry to the top left, the two highlighted areas in the image show the remains of two separate holes approximately 5 feet deep which were drilled into the stone to allow the wire saw standards to be sunk down for cutting. The surface of the wall between these two sections of holes is where the wire would have run for cutting. In addition to these holes, the saw frame is still present.
The lower image shows a modern wire saw which is still being used in quarries all over the world. The older saws ran with similar types of equipment. Notice the wire running off the right edge of the image.
The More Things Change, the More they Stay the Same.
While progress was made in the methods of extracting slate, success was slow to come. As with much of workings of the slate industry, many of the quarrymen themselves were set in their ways and were resistant to changes, even when proven successful. In 1915, the author J. S. Grasty, of the University of Virginia wrote the following statement about the relationship between quarrymen and geologists in an article titled The Failure of Slate Enterprises written for Stone Magazine which sums up this notion.
"In reference to the value of the cooperation between the quarrymen and the geologist, D. C. Davies, in his “Slate and Slate Quarrying” says: “The present race of Quarry managers will not deem it a personal allusion when I say that in time past there has not only been an indifference to the acquisition of the simplest elementary scientific knowledge on the part of former managers and, indeed, proprietors also, but a large amount of hostility to the intrusion of science into their so-called practical domain. There has been a good deal of open sneering at scientists, theorists and all of the members of the Geological Society put together. It is beginning to be understood however that It requires one set of gifts to catch the hare and another set of gifts to cook it well, and the luckiest man is he who possesses the two kind of qualifications.” it is just this very field by the way that applied geology undertakes to cover. 3
And Still there were the Men
"When a block of the desired size was broken loose, it was raised by means of heavy bars with curved ends. Several men used the bars simultaneously as levers, and thus gradually raised the block from the floor. Freeing the rock was sometimes slow and difficult, not only because of weight but because of many interlocking corners that had actually to be broken. The most effective work resulted when the strength of all the men was applied to their bars at the exact same time. To obtain such unanimity the foreman frequently lead in a sing-song rhyme like those sung on ships when raising sails, the men joined and kept perfect time with their crowbars. When the block was raised enough a fragment of rock or a wedge would be dropped in the crack, the bars were then placed in more advantageous positions, and the process continued until the hoist chain could be passed under the block." 2
Where vertical breaks were made by blasting, block raising was more difficult than where channeling machines were used, since the channel cut provided space for lateral movement and relieved the block from much of the interlocking which otherwise hindered free movement.
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