The fundamental problem in rock working is the breakage of fragments out of the face of a solid rock wall rock. Mechanically. this can be done only by forcing a tool into the rock surface. after the manner of an indenter is commonly used in the testing of surface hardness. https://www.roneverhart.com/032-0092-Gauge-Air-Compressor-2-300-PSI-X-1-8-NPT-Gauge-Coleman-Powermate/