Commercial experiment had better results than that of bench test. Soft sponge back-lining carpet with symmetrical bubble hole density and high elasticity carpet was produced.

The paper introduced the successful application of high bench caving method of using deep hole roller rock bit into the practice of solving the complex goaf area, a stuff problem of this kind.

The bench test of three-cone bits and analysis of their bottom hole patterns are the simplest and useful means of checking and improving their design.