DRILLS DRIVEN BY Hand POU'er Drill (Fig. M.—This consists of a strong cast iron cylinder, shown in Fig. 16, in which works a steel rod R in place of a piston-rod, carrying the drilling tool at its outer extremity by means of a suitable clip. Across the cylinder at about midway in its length is fixed a shaft, carrying two fly-wheels W, with handles. and two hardened steel cams C, each of which has 3 points, thereby producing 3 blows at each revolution. As the cams revolve they alternately lift and release a steel cross-head 11, which is fixed by a collar on the working-rod R, and projects on each side of the cylin der, and is surmounted by a strong volute spring in closed in the cylinder. The spring is compressed by the lifting of the cross-head, and its recoil on release produces the blow, which is delivered dead on the stone without shock to the men. The spring ordinarily sup plied for a drill to be worked by two men is compressed to 200 lbs., ant produces with the momentum of the working-rod and drill a blow of about 300 lbs. The rotation of the drill is provided for by a ratchet-wheel with oblique teeth fixed on the working-rod, into which engages a long oblique spring-blade or feather-pawl P, fixed in the thickness of the cylinder, whereby a partial turn is produced in the backward stroke ; while in the forward stroke the rod goes free, without any impedi ment to the blow. The automatic feed is effected by
the tail end of the working-rod, which projects through the back cylinder-cover, and is tapered off in a cone at its extremity. As the work progresses, this cone grad ually conies within the cover, and permits the inward movement of a small radial lever L, to which is jointed a pawl that works into a ratchet-wheel nut running on the feed-screw. In the backward stroke of the work ing-rod its thicker part below the cone pushes the lever outward, whereby the pawl is thrust into the ratchet, thus giving it a turn on the screw and feeding the machine forward. This feed adapts itself exactly to the rate of penetration. It can be thrown out of gear when desired. The length of the stroke is 3i in., and the weight of the machine is 300 lbs.