Chisel Type – Chisel type insert’s have opposing flats and a broad elongated crest, like the teeth of a steel tooth bit. These inserts are used for drilling soft to medium formation.
Conical Type – Conical type insert’s are cone shaped and have lesser protrusion, they have good resistance to breakage and are generally used for drilling medium to hard formation.
Spherical Type – Spherical type insert’s have a very small protrusion and are hemispherical shaped, they are used for drilling hardest formation.
TCI Bits are of basically three types:-
Soft Formation Bit – These are bit’s designed for drilling soft strata. Generally Chisel & Conical Type inserts of greater height and less numbers are used to form the cutting structure. Maximum cone off-set (usually 5 degree) is maintained for such bit this results in maximum scraping – twisting action on hole bottom during drilling.
Medium Formation Bit – These bits are designed for a wide field of application and are suitable for drilling medium to hard strata, most of the Inserts are conical and spherical for such bits. Moderate cone off-set (usually 3 degree) is maintained which results in chip & crush cutting and only slight twisting action during drilling.
Hard Formation Bit – These bits are designed to drill the hardest and the most difficult to drill strata, the bit is designed to carry the maximum number of spherical inserts. Adequate protection is provided to the shirttail portion for bearing protection. The cone off-set is generally nil to give the cone a true rotation resulting in less gauging and scraping action and more of chipping and crushing action.