ABSTRACT
Manufacturers' recommended bit loadings for the rockbit go as high as four tons per inch of diameter so, for a six inch rockbit, a loading of twenty-four tons of drill collars should be used. The choice of bits is, or has been, so vast that it became imcomprehensible to all but a few. Both approaches have their snags, especially fast rotation, which will "scrub" our bits out. The finger bit has been with us a long time, especially in augers and is excellent in the more consolidated of the softer formations. The rockbit has been around for over seventy- five years and in that time has undergone considerable changes. Whilst there are probably two or three grades of soft bit, we will generalise a little, which should be sufficient for our purpose here: this also applies to medium and hard bits.
