National Geographic : 1918 Nov
Photograph from U.S.Bureau of Mines UNDERCUTTING A BREAST OP COAL WITH A COMPRESSED-AIRPUNCHER There are many types of cutting machines for overcoming the wasteful methods of "shooting from the solid" orblasting the coal loose without cutting around it first. Some are driven by compressed air, some by electricity, some by steam generated on top oftheground. One cave-cutter is not unlike a mowing machine. A cutter-bar reaches out from the driving mechanism and has, insteadofpitman-operated sickles, anendless chain revolving around sprocket wheels. On this chain coal knives or picks are fastened, and as they travelalong they cut away the coal. When acut, such as the one being made in the illustration, is finished from one side of the chamber to the other, holes aredrilled and light blasts put in. When fired, these blasts cause a great block of coal to break loose and fall to the floor, where it isbroken up and loaded into cars.