The heavier types of these machines are usually provided with back gearing similar to that employed in engine lathes. The power feed is obtained by suitable spindles and trains of gearing which drive the rack and sleeve by using a pinion, as in the hand feed machine.

The essential differences between this machine and the smaller type are: (a) its heavy rigid frame and moving parts; (b) its range of spindle speed changes made possible by the cones and back gears; (c) its spindle feed by power gearing instead of a hand lever; (d) its greater spindle driving power gained largely by use made of the back gears; and (e) its sub-base for holding the heavier work.

While the machine shown in Fig. 175 is belt driven, as relates to its stepped cone pulleys, the work spindle S is gear driven and gear fed. The trains of gearing, which rotate the spindle and which provide for feeding it downward, are, as in all modern geared machines, so covered as not to be plainly visible. The back gears are engaged at all times, but are brought into active driving service by operating a clutch B through use of the clutch lever C. The smaller spindle A passes downward through a cone of gears located in the gear box G to a train of gearing which is mounted upon the head bracket. The head bracket carries not only the work spindle sleeve and feed rack, but, besides these, has mounted on its frame the power and the hand feed mechanisms. The hand feed is operated by rotating the hand wheel H. The power feed is controlled by the clutch lever L. The changes of feed from fine to coarse are made by means of a slip key actuating the cone feed gears through the shaft E and the smaller hand wheel F.

Fig. 175. Standard Power Feed Driller Courtesy of Reed-Prentice Company, Worcester, Massachusetts.

Multiple Spindles

Drilling machinery, both horizontal and vertical, is sometimes provided with more than one spindle. In the smaller drillers of the vertical type, the spindles are fixed in their relative positions, and are not intended to be operated simultaneously, the work passing from one spindle to another. The true multi-spindle driller, Fig. 176, is for the purpose of drilling several holes at one time and in any relative position within the limits of adjustment of the machine.

Fig. 176. Typical Multi-Spindle Driller.