Discoveries and inventions of the nineteenth century (1905)
Routledge, Robert · London : G. Routledge and Sons · leaf 408
presently be mentioned. The crown 3- thus set with the boring gems is attached to the end of a steel tube, Idv which it is made to rotatewith a speed of about 250 revolutions per minute while pressed against therock to be bored. Water is forced through the steel tul)c, and passing outbetween the… … ROCK BORING. 361 which the crown is forced forward depends, of course, on the nature of therock to be cut, and varies from 400 lbs. to 800 lbs. In this way the hardestrocks are quickly penetrated—sometimes, for example, at the rate of 4 in.per minute, compact limestone at 3 in., emery at 2 in., and…
Inventions
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