... require different taper angles. When drilling with high impact hydraulic rock drills in medium-hard to hard and ... 12-degrees are normally used on modern drill rigs. For low impact rock drills and softer rock formations, a ... (mm):29,30,31,32,33,34,35,36,37,38,39,40,41 Integral Drill Steel is used ... drills, etc. It can reduces the expense of impact energy, improves the drilling speed and efficiency, also ...