The teeth of the MB471-316 machine, now under construction, are 85 rolling steel disc cutters meticulously arranged on a cutter face (also made of steel) that rotates up to seven times a minute. The cutters, each nearly two feet long, will be among the largest ever made for tunnel
digging. They spin freely to carve
concentric circles in the rock and produce more than 1,600 tons of
rubble an hour. The face of the drill contains a small door through which workers can crawl to replace the 15 or so cutters that wear out every day.