Ity drilling in place, a single oper ation serves to drill through all the superposed thickness without stop ping the tool ; whereas, when the pieces are separate, as in the shop, as many separate drilling opera tions are required as there are pieces.
Each drilling-machine is com posed of two parts: First, a small hydraulic motor Jl, driven by wri ter pressure supplied from amain through flexible or jointed pipes.
The discharge water is led away through India-rubber tubing. The motors are Brotherhood's three-cylinder engines. Second, it drill-holder, consisting, of a small frame F of C-shape, in which are arranged the bearings of the driving-shaft A from the motor, and of the hollow drill-spindle D at right angles to it. On the motor-shaft A is keyed a bevel-wheel B, gearing with a bevel-pinion Pon the drill-spindle D. At one end of the drill-spindle is a socket S for holding, and the other end is threaded internally for receiving the setting-up screw T. which is turned by the hand-wheel either to give the feed while drilling or to withdraw the drill when the hole is finished. A longitudinal slot b for the key of the bevel-pinion P allows the drill-spindle to slide through the pinion while the latter is kept in place by an annular recess R. Beyond the hand-wheel W the screw 7' terminates in a point .I, which can be pressed against a cross-piece or frame, smelt as is used for drilling with a ratchet-brace. The
central part of the frame is bolted to the flange of the motor ..1/, and thus forms a long bearing for the shaft A; and small closed lubricators insure the bearing being properly oiled, in Whatever position the drill may be held. In the base 0 of the mut or are slotted holes for fixing it to the strut-titre., These machines are made of steel and phosphor bronze. The weight does not exceed 103 lbs. fur the 1 horse-power drill and 62 lbs. for the I horse-power drill. Trials made for a lengthened perhal have proved that, in the case of a large armer clad man-of-war, built on the cellular system. and consequently of very ettmplicated design, the number of holes drilled in place by these small hydraulic mac•tiines is at least 25 per cent greater than the number of similar holes that can be drilled in the stone time by stationary maehines itt the shops. and is at least six or seven times greater than the !mintier of similar holes that can be drilled in place by ratchet-braces. In the 1 horse-power machine the motor makes 90 revolutions per minute. It drills holes from It up to 2 in. diameter. The horse power machines make 130 revolutions per minute and drill holes up to 14 in. diameter.
Drill : see Coal-illining Machines, Grinding 31achines, Seeders and Drills, and Watches and Clocks.