A TWIST drill should not always be regarded as something fit only, for producing holes of approximate accuracy. With close attention to the rules govering this kind of tool it is possible to turn out work with finished holes which are straight, smooth and to size: three most essential conditions. In many cases, it is true, the work demands the use of a reamer, but it is equally true that reamers are frequently used because the possibilities . of drills have not been fully explored. A brief description of some of this exploratory work can refer only to the smaller sizes of drills; generally understood to mean all those below a quarter of an inch. Drills above this size are usually handled in a manner quite different from the others.
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