Introduction
|
Courtesy of the
University of Montana Mansfield Library Archives. |
Percussive or hammer drilling is most often used to drill rock. In ForestService
trail work, gasoline-powered hammer drilling is common. Hand drilling
is sometimes necessary however, because machines cannot be used. This
manual describes elementary tools and techniques for hand drilling rock.
Although hand drilling is slow work, it is a safe and simple way to
prepare rocks for breaking with explosives, wedge and feather sets or
expansion chemicals, or to accept anchor bolts. The driller drives the
steel by methodical hammering and turning. When the hammer strikes the
head of the steel, the bit is forced against the rock. After each blow
of the hammer, the driller turns the steel slightly and strikes it again.
With each blow the bit chips small amounts of rock that collect in the
hole as "drilling dust." The driller removes the dust by adding
water to the hole, which creates a mud that sticks to the sides of the
steel. To clear the mud, the driller removes the steel and raps it against
the rock. The procedure is continued until the hole is deep enough;
longer steel is substituted as the hole lengthens.
The steel is manipulated with one hand while the other hand hammers
(single jacking), or the steel is manipulated by two hands while another
person hammers (double jacking). This manual describes correct techniques,
discusses proper tool maintenance, and includes sources of tools and
a bibliography.
Although hand drilling is not commonly used in the Forest Service,
it can effectively remove rock from trails and does observe the Chief's
directive to resurrect, develop, and utilize primitive skills in wilderness
management. Hand drilling skills have been all but forgotten; we hope
to preserve them with this manual.
No cost comparisons have been made between hand drilling and gasoline-powered
drilling. Initial tool costs are much less for hand drilling, however,
and the techniques can be learned by unskilled or low salary employees.
Since gasoline-powered drills are prohibited in wilderness, hand drilling
allows wilderness managers to maintain trails without violating wilderness
guidelines.
Hand drilling is an effective method for
maintaining forest trails.
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