A long solid rod, some thirty feet long, three
inches in diameter, and called the "stem," is screwed on the drill.
This stem weighs almost a ton, and its weight is the hammer relied on
for driving the drill through dirt and rock. Next come the "jars," two
long loose links of hardened iron playing along each other about a
foot.
The object of the jars is to raise the drill with a shock, so as to
detach it when so tightly fixed that a steady pull would break the
machinery. The upper part of the two jars is solidly welded to another
long rod called the sinker bar, to the upper end of which, in turn, is
attached the rope leading up to the derrick pulley, and thence to a
stationary steam engine. In boring, the stem and drill are raised a
foot or two, dropped, then raised with a shock by the jars, and the
operation repeated.
If I may hazard a further illustration of the internal boring
machinery of the well, let the reader link loosely together the thumbs
and forefingers of his two hands, then bring his forearms into a
straight line. Conceiving this line to be a perpendicular one, the
point of one elbow would represent the drill blade, the adjacent
forearm and hand the stem, the linked finger the jars, and the other
hand and forearm the sinker bar, with the derrick cord attached at a
point represented by the second elbow. By remembering the immense and
concentrated weight of the upright drill and stem, the tremendous
force of even a short fall may be conceived.
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