... rock formations, a wide taper angle is normally used. Taper angles of 11 and 12-degrees are normally ... angle of seven degrees is used. A 7-degree angle can also be used if bit spinning is a ... ,37,38,39,40,41 Integral Drill Steel is used by a hand held drill machine in Underground mining and ... the drilling speed and efficiency, also it can be used for drilling bore hole diameter from 30mm to 41mm usually ...