THE DIAMOND DRILL.

New Zealand Tablet, Volume III, Issue 145, 11 February 1876, Page 8

THE DIAMOND DRILL.

One of the most remarkable mechanical processes, recently introduced, is the diamond drill for boring— in principle quite distinct trom any other system of holing rock, and works by rotation without striking a blow. Its action, in fact, is rather that of abrading than cutting, and its effect is produced by 1 the sheer difference in hardness between the diamond and the rock it is operating upon whatever sort the latter may be. So great, in fact, is the difference^ that there is really no comparison between the hardness of the diamond and that of ordinary rock ; and if a diamond were to be kept rotating against a sandstone it would cut a hole say a mile deep, before becoming seriously worn. The diamonds employed for this purpose are not, however, valuable gems, but carbonate, a substance that till lately had no commercial value, and was first introduced for the purpose of cutting other diamonds. It comes from Hra/.il in considerable quantities, and its appearance is much like that oi a piece of coal, or dull jet, and, though just the reverse in this respect to the diamond gem, the two are chemically identical in composition. One is presumed to be perfectly, and the other imperfectly crystallized— ie being this very imperfect crystallization, probably, that gives to carbonate its peculiar value for this purpose. The operation, in this system of rock drilling, is quite simple. The stones are set in a ring ma d e of steel; they are fastened in by making holes as nearly as possible the size of the stones to be set, and then burying them, leaving projecting only the amount necessary to allow the water and debris of the cuttinoto pass ; the metal is then drawn around the stone, so as to closo it on every side, and give as large a bearing surface as possible to resist the tendency to be forced out.