Stephens' " Climax" the construction of this drill (shown in Fig. 15), one of the principal feat ures is the reversible tappet-valve V, which is a flat plate rocking on a center pin, and actuated by a spher teal boss on the piston-rod, midway between the two pistons. The valve contains a pair of admission-ports .1, and a pair of recesses or cxhaust-ports B, which control two corresponding pairs of ports in the valve chest face, communicating with the ends of the cylinder and with the atmosphere. On the back of the valve is another pair of recesses or exhaust-ports, corresponding with those on the face, so that when worn the valve can be reversed back and face and upside down ; it is then practically as good as a new valve ;ma new tappet.
A second feature is the twisting or rotating device on the rifled spindle in the back end of the cylinder, which consists of a crown ratchet-clutch whereby the use of pawls is dispensed with. The strain which would come upon a single pawl and tooth for rotating the drill, or upon a pair, is here distributed equally over 15 catches, which all act at the same time, the sliding half of the clutch being, all in One piece, and pressed forward against the rotating half by a single spring. This arrangement admits of the clutch
from 1 in. to V in. larger in diameter than a ratchet wheel in the same eylinder-c•over, liecanse no since is required for pawls and springs outside the circumfer ence of the I.:n(11cl. Thr strain, therefore, besides being distributed over a much larger number of teeth, is also removed to in greater distance from the center. An other feature is the insertion of loose adjusting liners L in the cradle C, which are so arranged that any movement of the cylinder in the cradle can be readily adjusted in a few minutes by these loose liners; and provision is made for them in the construction of the cradle. The feed is given by a screw worked by hand. A 3-in, drill unmounted weighs about 240 lb., and a 31:in. about 280 lb.