The sheet of
stone which we wish to shear from place has a bed running horizontally
at a depth of say 10 ft. One face is in front and a natural seam
divides the bed at each end at the walls of the quarry. We now have a
block of stone, say 50 ft. long, with all its faces free except
one--that opposite and corresponding with the bench. One or more of
the specially formed holes are put in at such depth and distance from
each other and from the bench as may be regulated by the thickness,
strength and character of the rock. No man is so good a judge of this
as the quarry foreman who has used and studied the effect of this
system in his quarry. Great care should be taken to drill the holes
round and in a straight line. In sandstone of medium hardness these
holes may be situated 10, 12 or 15 ft. apart. If the bed is a tight
one the hole should be run entirely through the sheet and to the bed;
but with an open free bed holes of less depth will suffice.
[Illustration: Fig. 8, 9]
The reamer should now be used and driven by hand.
Pages:
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57