. Bulletin of the Department of Agriculture. Agriculture; Agriculture. PHYSICAL PROPERTIES OF ROAD-BUILDING ROCK. MfH t>6//7/ So/c/ensd onc-fourth-inch pipe, while the drill is held in its lower end by means of a headless set screw instead of the usual drift hole. In this way water may be carried in a very simple and convenient manner to the inside of the revolving drill. This method of supplying water to the drill has proved simpler and more satisfactory than the scheme described in Bulletin 44, in which the water is introduced at the side through a stationary brass ring. The Tobin br
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. PHYSICAL PROPERTIES OF ROAD-BUILDING ROCK. MfH t>6//7/ So/c/ensd onc-fourth-inch pipe, while the drill is held in its lower end by means of a headless set screw instead of the usual drift hole. In this way water may be carried in a very simple and convenient manner to the inside of the revolving drill. This method of supplying water to the drill has proved simpler and more satisfactory than the scheme described in Bulletin 44, in which the water is introduced at the side through a stationary brass ring. The Tobin bronze drill crown C, carrying the diamond points, is soldered to the lower end of the steel core tube A as shown in the cut. The crown should measure about one- eighth of an inch thick across its lower face, should be about three-sixteenths of an inch thick, and show a slight taper in its outer side, to allow clearance when cut- ting. Eight or ten holes are drilled in the lower face of the crown, of such size that the diamonds will wedge firmly into them, until nearly flush with the surface. Black diamonds or carbons. The diamonds used in the drills and saws should be dense, reg- ular in shape, and should range in size from one-sixteenth of an inch to three thirty-seconds of an inch in diameter. No flat, scaly, or porous diamonds should be used. Diamonds suitable for this work will usually weigh about one-tenth of a carat ( gram) each. Diamond saw. A cut of the diamond saw is shown at A, figure 4. The saw proper is made of Russia iron and consists of a flat disk 8 inches in diameter and inch thick. It is made as follows: The saw is firmly clamped between two circular wooden blocks 7J inches in diameter, leaving one-eighth of an inch projecting all. 0/am g, cardon po//7fc Fig. 3.—Diamond core drill. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustration
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