Compressed Air Work And Diving 1909

ROCK DRILLS. 105 I he drills are fixecl to the tripod by a universal joint clamp, or similar arrangement, permitting it to be set in any clesirecl direction without altering the position of the tripod. I he actual drill cylinder is fixecl in a cradle in which it slides when the drill is being fed forward. On the legs of the tripod are three weights which vary from T45 to 45° Ibs. the set of three. The smaller sizes with cylinders 2 in. and 2^- in. diameter are known as “baby” drills, and are worked by one man. All sizes above this require two men, a driller and a helper. I he driller stands by the bit and keeps a.11 eye on it to see that it is going straight. He generally holds a spanner in his hand to hit the drill it it sticks in the rock. I he helper stands behind the drill with his right foot 011 one of the weights fasteneel to the legs in order to help to steady it, and feeds forward the drill as clirectecl by the driller. 1 hese larger drills are known in the States by the name of “ Giant,” but it is a term not used over here. Another arrangement is a tunnel column which has a screw jack at one end by which it can be fixecl either vertically or horizontally or, in faet, in any direction in which a hold can be obtained, in a tunnel heading, or between the floor and ceiling of a compartment in a shielcl. I he drill is fastened to a cross arm which is in its tum clamped to the column. 1 wo drills are frequently fastened to one column. Sometimes small hand drills, similar in appearance and principle to a pneumatic hammer, are used. These are useful for putting in a small hole in a boulder or large piece of rock too big to go into the waggons or skips.