Augers. Fig. 110 shows a double-twist spur auger, a form generally used by carpenters. They are made in sizes varying from 1/2" to 4" (in diameter), but are not much used below 1". The spur A, Fig. 111, is in the form of a tapered screw, which, besides centering the auger in its motion, draws or "feeds" it into the work. The two nibs B, B score the work, and the lips C, C cut and remove the shavings, which are carried to the surface by the screw-like action of the body of the tool.

Fig. 110

Fig. 111

Fig. 112 shows part of a single-twist auger which, as will be seen, has but a single nib B, and a single cutting lip C.

The cuttings are thrown into the center of the hole, and deFig. 112 livered easily by this auger, and, in this respect, it is superior to the double-twist, which crowds the cuttings to the outside of the hole, where they are likely to become jammed between the tool and the work. This characteristic of the single-twist auger particularly adapts it to the boring of deep holes. "Ship augers" are of this kind, and have handles like the one shown by Fig. 113. This form of handle has the advantage of allowing the use of both hands, without the interruption experienced in using the one illustrated by Fig. no. Augers are seldom required by the bench-worker, but are presented here because of their relation to other boring tools.

Fig. 113