Soft Formation Bit – These are bit designed for drilling soft strata having less comprehensive strength and high drilling ability generally includes clay, shale, etc .In such bits the tooth points are widely spaced and are of greater length to allow maximum penetration into the formation, resulting in removal of large chips. These bits are generally run with lesser weight on bit and higher rotation speed. Maximum cone off-set (usually 5 degree) is maintained for such bit; this results in maximum scraping – twisting action on hole bottom during drilling. A considerable amount of special hard-facing alloy is applied on the complete tooth to enhance the bit life.
Medium Formation Bit – These are bit designed for drilling medium formation with higher comprehensive strength such as hard limestone, dolomite and hard shale. In such bits the tooth points are closely placed, and are of lesser height as a result the number of teeth’s are increased. During drilling the weight on bit is required to be more with lesser rotation speed. Moderate cone off-set (usually 3 degree) is maintained which results in chip & crush cutting and only slight twisting action during drilling. The flanks of the teeth’s the gauge and the leg shirttail are hard-faced for abrasion resistance.
Hard Formation Bit – These are bit designed for drilling hard and abrasive formation such as limestone, dolomite, sandstone, and graphite. In such bit the teeth’s are relatively shallow and the number of teeth is more so that individual tooth load is not too great. The cone off – set is generally nil to give the cone a true rotation resulting in less gouging and scraping action and more of chipping and crushing action. A good amount of hard-face and/or Tungsten Carbide Insert are provided in the cone gauge and shirttail portion of the leg to elongate the life of the bit in toughest drilling conditions