Engineering Wonders of the World
Volume III

ARTESIAN WELLS, AND HOW THEY ARE BORED. 339 A CALYX DRILL. shot, poured down of the general struggle to find a substitute have emerged two successes— the calyx drill and the shot drill. In the calyx drill a crown of steel with large saw - like teeth is rotated upon the rock. It resists the turning effort, applied at the top of the rods, for part of a turn ; then it slips suddenly under the torsion strain of the rods. This rapid jumping action is very effective in cutting the rock, and gives good cores. The calyx drill cannot, however, penetrate really hard rock. For this work the shot drill proved its superior fitness The shot boring head is a cylinder of steel slotted upwards in the end at several points. Small chilled steel the hollow rods with the water, get in below the end of the boring cu * fa .... crown by way of the slots and are rolled between the steel head and the rock. The curious rolling action breaks up the rock, and the débris is washed up. Progress is as rapid as with the diamond, and the cost of the chilled shot is only a small fraction of that of a single diamond. That such work can be done by small chilled shot may seem curious, but is explicable by a sort of mathematical reasoning. In mathe- Its Principle. matic8 a P°int hath n0 magni“ tude. When a perfectly hard sphere rests upon a perfectly hard plane sur- face the two bodies make contact at a mathe- matical point. Now, since a point has no area, the pressure at the point of contact must be infinite. Even the weight of a little chilled shot jV7 diameter is something, and since the shot rests on a point of no area, the pressure must be infinite. In shot drill- ing we do not get mathematical points of contact, nor infinitely hard surfaces, but we are able to place a heavy pressure on the small shot which roll between the end of the crown and the rock. This pressure is far beyond what the rock can withstand, and so the latter is crushed by the shot and the particles de- tached and washed away The next little shot rolls over the clean path and crushes the surface again ; and so the work goes rapidly forward. The removal of the core is effected by pouring some Detaching r & Cores. grit down the tubes to wedge the core against the walls of the tube, and A GROUP OF WELL-SINKING TOOLS, ETC. A, butt-jointed pipes, with tapered collar; B, a “ crow’s-foot; C and D, latch tools for getting hold of broken rods and pipes; E, a shot drill, showing slot by which the steel shot gets under the bottom of the drill; F, circular chisel for rock work.