The Steel tooth bits have their cutting structure machined out of the special steel cone forging, this type of bits are basically used for drilling soft to medium hard strata. The profile , size , number of the cutting teeth and leg off-set varies from one bit to another depending upon the strata condition for which it is designed . The teeth's of each cone are inter fitting with adjacent cones this provides for a mechanical cutting, gouging and scraping action during drilling . A layer of hard-facing tungsten carbide is applied to the teeth and the gage of the cone to improve it's abrasive resistance and elongate the bit life in the toughest drilling condition. Steel tooth Bits are of basically three types:- Soft Formation Bit - These are bit designed for drilling soft strata having less comprehensive strength and high drill ability generally includes clay, shale, etc .In such bits the teethes 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 special hard-facing is applied on the complete tooth to elongate 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 teeth's are closely placed, and of lesser height 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 and crush cutting and only slight twisting action during drilling. The flanks of the teeth, the gage 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 maximum 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 gage and shirttail portion of the leg to elongate the life of the bit in the toughest drilling condition.
