Several devices have
been applied to rock drills for reaming the hole by machinery while
drilling; that is, efforts have been made to combine the drill and the
reamer. Such efforts have met with only partial success. The perfect
alignment of the reamer is so important that where power is used this
point is apt to be neglected. It is also a well known fact that the
process of reaming by hand is not a difficult or a slow one. The
drilling of the hole requires the greatest amount of work. After this
has been done it is a simple matter to cut the V-shaped grooves. The
reamer should be applied at the center, that is, the grooves should be
cut on the axis or full diameter of the hole. The gauge of the reamer
should be at least 11/2 diameters. Great care should be taken that the
reamer does not twist, as the break may be thereby deflected; and the
reaming must be done also to the full depth of the hole.
The hole is now ready for charging. The powder should be a low
explosive, like black or Judson powder or other explosives which act
slowly.
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