There are three tool options to consider when drilling large-diameter holes in thick steel: twist drill bits, hole saws and annular cutters. 1. Twist drill bits. Especially in steel thicker than ...

Here's how the tunnel boring machine, or TBM, works: As the 200-ton TBM moves forward, a round cutter head studded with titanium teeth grinds into the tunnel face and splits large chunks off the rock.