30 CFR § 33.35 Methods of drilling; dust-collector unit.
(a)General. All drilling shall be done with conventional,
commercial drilling equipment pneumatic--percussion, hydraulic-rotary, and/or
electric-rotary types--in accordance with the applicant's specifications.
(b)Pneumatic-percussion drilling. A stoper-type drill with a
piston diameter of 2 1/2 to 3 inches shall be used for roof drilling, A
hand-held, sinker-type drill with a piston diameter of 2 1/2 to 3 inches
shall be used for down drilling and also for horizontal drilling, except that
the drill shall be supported mechanically. Compressed air for operating the
drill shall be supplied at a gage pressure of 85-95 pounds per square inch.
Drill bits shall be detachable, cross type with hard inserts, and shall be
sharp when starting to drill each set of 10 holes. In roof drilling, 1 1/4-
and 1 1/2-inch diameter drill bits shall be used; in horizontal and down
drilling, 1 3/4-inch diameter bits shall be used. The drill steel shall be
7/8-inch hexagonal and of hollow type to permit the introduction of
compressed air through the drill steel when necessary to clean a hole during
(c)Rotary drilling. A hydraulic-rotary drill with a rated
drilling speed of 18 feet per minute free lift, capable of rotating drill
steel at 900 revolutions per minute with 100 foot-pounds torque, and having
a feed force of 7,000 pounds, shall be used for roof drilling. An
electric-rotary drill, supported by a post mounting, with a rated drilling
speed of 30 inches per minute and powered by a 2.25 horsepower motor, shall
be used for horizontal drilling. For roof drilling, the bits shall be
hard-tipped, 1 3/8 and 1 1/2 inches outside diameter, and 1 1/4-inch
auger-type drill steel shall be used. For horizontal drilling, the bits
shall be hard-tipped, 2 inches outside diameter, and 1 3/4-inch auger-type
drill steel shall be used. Drill bits shall be sharp when starting to drill
each set of 10 holes.