Fig. 76.
Auger bits are usually supplied in sets of thirteen, in sizes varying from one-fourth of an inch to one inch, by sixteenths.
The size of hole that an auger bit will bore can be told by looking at the number on the tang or shank. If a single number, it is the numerator of a fraction whose denominator is sixteen, the fraction referring to the diameter of the hole which the bit will bore.
Exercise care in laying down a bit; it is easily dulled. Do not use a good auger bit where there is any danger of its striking nails or other metal.
Auger bits are easily sharpened, a small file being used, but they are more easily spoiled by improper filing, and no student should attempt to sharpen one without having personal direction from his instructor.
39. The Drill Bit; The Gimlet Bit.
—The drill bit, [Fig. 77], is quite hard and may be used for boring in metal as well as wood. It is easily broken and especial care must be taken to hold the brace firmly. Do not try to change the direction of the boring by inclining the brace after the bit has started into the wood.
Fig. 77.
